This is a Geant4 [1] [2] [3] simulation of the Upstream Target Room (UTR) at the High Intensity γ-ray Source (HIγS) facility [4], located at the Duke Free Electron Laser Laboratory (DFELL) of the Triangle University Nuclear Laboratory (TUNL) at Duke University, Durham, NC, USA.
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2.1 Geometry
2.3 Event Generation
2.4 Physics
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3.1 Dependencies
3.2 Compilation
This section is an overview or checklist for a user who wants to implement his own geometry and do simulations.
See section 3 Installation
See section 4 Usage and Visualization
- Create a new campaign in
DetectorConstruction/and/or a new directory inDetectorConstruction/Campaign_YEAR. - Implement a geometry in a
DetectorConstruction.hhandDetectorConstruction.ccfile in this directory and maybe some auxiliary files following the conventions (see section 2.1 Geometry). - Configure
utrto use the new geometry using the cmake build option (see sections 2.1 Geometry or 3.3 Build configuration)
- In
DetectorConstruction.cc, set volumes as sensitive detectors. There is the choice between 3 different detector types that record different information about particles (see section 2.2 Sensitive Detectors). - Using cmake build options, set the quantities that should be written to the output file (see section 2.2 Sensitive Detectors and 3.3 Build configuration).
Configure utr to use either the G4GeneralParticleSource, the AngularDistributionGenerator or the AngularCorrelationGenerator using the CMake build option (see sections 2.3 Event Generation and 3.3 Build configuration)
Using cmake build variables, activate or deactivate physics modules, or implement a custom physics list and include it in src/Physics.cpp (see section 2.4 Physics and 3.3 Build configuration)
In src/utr.cc, set the random number seed explicitly to get deterministic results. It is not clear whether this works in multithreaded mode. See section 2.5 Random Number Engine
Create a macro file that contains instructions for the primary generator (see section 2.3 Event Generation).
Do not simulate more than 2^32 ~ 2 billion particles using /run/beamOn, since this causes an overflow in the random number seed, giving you in principle the same results over and over again. Execute the same simulation multiple times instead.
Consider creating a macro like the example loop.mac in macros/examples to loop over variables in your macro file.
(See section 4 Usage and Visualization)
See section 5 Output Processing. For some tasks, for example the extraction of full-energy peak efficiencies, complete toolchains already exist which probably need only minimal adaptions.
See section 6. The utr Wrapper. The utr wrapper utrwrapper.py was introduced to simplify, automate and systematize the workflow of conducting simulations with utr once the detector construction is implemented and uses extended macro files to achieve this goal.
Using utrwrapper.py with an extended macro file ideally allows to combine steps 1.8 (Set up a macro file) to 1.10 (Analyze the output) into creating one file and executing one simple command.
In Geant4, all geometry is implemented in a class which is derived from G4VUserDetectorConstruction. In utr, the user-implemented geometry can be found in files called DetectorConstruction.hh or DetectorConstruction.cc. Since the setup at HIGS is subject to many changes in between, and also during experiments, many different geometry implementations exist.
Since the 2018 campaign, we encourage to stick to the following directory structure and naming convention for the geometry files:
utr/
include/utr.cc # main()
include/ # user actions and auxiliary permanent geometry
src/ # user actions and auxiliary permanent geometry
DetectorConstruction/
Campaign_YEAR/
include/ # auxiliary campaign- and run-specific geometry
Setup_RUNS.hh
src/ # auxiliary campaign- and run-specific geometry
Setup_RUNS.cc
TARGETS_RUNS/
DetectorConstruction.hh
DetectorConstruction.cc
As in reality, a geometry file only holds for a certain number of runs, which are part of a campaign. Therefore, unique DetectorConstruction.cc files can be found at the run-level. In principle, one could put all the geometry into this file, and before the 2018 campaign, it was done like that because the file was growing and growing. In the meantime, UG has tried to learn from his mistakes: The DetectorConstruction.cc files should be as short as possible, delegating all the low-level construction jobs to auxiliary classes (please see 2.1.1 Note on auxiliary files). The auxiliary classes can be placed into different directories, depending on their nature:
Geometry which is expected to be permanent (for example detectors, or furniture), even between different campaigns, should be placed in the utr/include and utr/src directories.
More volatile geometry should be placed in the corresponding campaign, i.e. utr/DetectorConstruction/Campaign_YEAR/include and utr/DetectorConstruction/Campaign_YEAR/src.
Sometimes, the difference may not be so clear, and at the moment the sorting is probably not consistent, but our team is still tidying up the 2018 campaign. Everything before 2018 does not follow these conventions, but has been sorted according to the directory structure above anyway to ensure backward compatibility.
At the moment, detailed implementations of the geometry of the 2016/2017 campaign and parts of the 2018 campaign exist. They include geometry close to the beamline in the collimator room and the UTR including, of course, the experimental setups (γ³ setup [5], second setup and recently also an ionization chamber for photofission experiments). Less detailed geometries exist for selected experiments in older campaigns. The geometries for the 2013 and 2014/2015 campaign are based on the geometry from 2016/2017, the geometry for the 2012 campaign is based on the geometry from 2018.
An implementation of the Darmstadt High-Intensity Photon Setup (DHIPS) [6] is under construction at the moment. Its geometry will be organized similar to the HIγS geometry from 2018.
By default, utr will use the geometry in DetectorConstruction/Campaign_2018/64Ni_271_279. Existing geometries can be switched very quickly using cmake build variables. For example, to use the geometry in utr/DetectorConstruction/Campaign_YEAR/TARGETS_RUNS, set the corresponding CMake variables and re-build the code (see also 3 Installation):
$ cmake -S . -B build -DCAMPAIGN="Campaign_YEAR" -DDETECTOR_CONSTRUCTION="TARGETS_RUNS"Several pre-defined classes exist to simplify the geometry construction which are explained in the following.
In order to prevent the geometry files from growing too large, it is very helpful to divide the setup into logical parts and implement them im separate auxiliary classes. This also makes it easy to switch parts of the geometry on and off without having to comment hundreds of lines.
A common practice is to create LogicalVolume objects (pointers) in the auxiliary files that contain several parts, import their mother volume into DetectorConstruction.cc, and place it:
// Auxiliary.hh
...
class Auxiliary{
...
Auxiliary();
G4LogicalVolume* Auxiliary_Logical;
G4LogicalVolume* Get_Logical(){ return Auxiliary_Logical };
...
};
...
// Auxiliary.cc
...
Auxiliary::Auxiliary(){
...
Auxiliary_Logical = new G4LogicalVolume(...);
...
}
...
// DetectorConstruction.cc
...
Auxiliary_Logical aux;
G4LogicalVolume* aux_log = aux.Get_Logical();
new G4PVPlacement(rot, pos, aux_log, "aux", ... );
...
However, this caused some problems in the case of utr.
For example, the floor and the walls are clearly a logical unit that can be implemented in a separate file. Since the floor and the walls are as long and wide as the whole setup, the mother volume of this auxiliary class would unnecessarily overlap with everything.
Here, instead, we chose to pass the global mother volume to the auxiliary classes and let them make the placements in a Construct(G4ThreeVector global_coordinates) method.
// Auxiliary.hh
...
class Auxiliary{
...
Auxiliary(G4LogicalVolume* World_Log){World_Logical = World_Log};
Construct(G4ThreeVector global_coordinates);
G4LogicalVolume* World_Logical;
...
}
...
// Auxiliary.cc
...
Auxiliary::Construct(G4ThreeVector global_coordinates){
...
new G4PVPlacement(rot, global_coordinates + pos, Aux_Logical, "aux", World_Logical, ...);
...
}
...
// DetectorConstruction.cc
...
Auxiliary_Logical aux(World_Logical);
aux.Construct(global_coordinates);
...
By passing the global coordinates to the auxiliary file, the placements there can still be done in a local coordinate system. These examples are only to illustrate the differences, have a look at the geometry from the 2018 campaign for more details.
This positioning scheme prevents overlaps of mother volumes. However, the order of placements is still important! The last element placed will be at the top of the hierarchy. For example, if there is a target mounted inside the beam pipe (i.e. the volume of the pipe completely covers the target), the following would be the correct order of placements:
// DetectorConstruction.cc
beamPipe.Construct(global_coordinates_beamPipe);
target.Construct(global_coordinates_target);
The alternative order
// DetectorConstruction.cc
target.Construct(global_coordinates_target);
beamPipe.Construct(global_coordinates_beamPipe);
would place the beam pipe on top of the target, and therefore ignore the target when tracking particles. Note that this problem would also occur if we used the other placement scheme.
A disadvantage of this placement scheme is that the volume hierarchy is very flat, because everything is placed inside the global mother volume. This makes it harder, to find a specific volume in the UI mode and easier to have name clashes. Nevertheless, we think that the advantages are more important.
Since the 2018/2019 campaigns (for older geometries, see the next section, 2.1.3 Detectors before 2018 campaign), the detector placement is done by an auxiliary class, in complete analogy to the procedure described in 2.1.1 Note on auxiliary files). All parts of the detectors are placed inside the global world volume to minimize the risk of overlaps.
To simplify the placement of a detector, their Construct() method takes four additional mandatory arguments, which are the angles θ and φ in spherical coordinates, a radial distance rt to the point indicated by global_coordinates, and an intrinsic rotation angle intrinsic_rotation with respect to the main axis. For many of the detectors, the main axis is equal to the cylindrical symmetry axis. However, there are some detectors which break the continuous rotational symmetry around the main axis, for example the clover detectors. This is why the README refers to the 'main axis', whose meaning should be intuitive even for non-cylindrically symmetric detectors. If placed with the Construct() method, the main axis of the detector crystal will be parallel to the unit vector in spherical coordinates defined by θ and φ, and it will face a target at the point global_coordinates. To be precise, rt defines the distance from global_coordinates to the center of the detector face. Furthermore, the detector will be rotated by an angle of the magnitude intrinsic_angle around its main axis.
Assuming that a detector of the class Detector should be placed in the world logical volume World_Logical at angles theta and phi, with the distance distance_from_center to the point global_coordinates, the most general procedure for the placement is:
// This line is always necessary
Detector detector_instance(World_Logical, detector_name);
// The following two lines are only necessary if such a collection of detector properties exists
Detector_Collection collection_instance;
detector_instance.setProperties(instance.DetectorXY)
// Code similar to the following 3 lines can be used to add shielding to the detector which
// will be placed automatically. By convention, shielding which is added first will be placed closest to
// the detector. The set of parameters of the methods may depend on the detector type.
detector_instance.Add_Wrap("G4_Pb", 1.*mm)
detector_instance.AddFilter("G4_Cu", 1.*mm, 45.*mm)
detector_instance.AddFilter("G4_Pb", 2.*mm, 45.*mm)
// This line is always necessary
detector_instance.Construct(global_coordinates, theta, phi, distance_from_center, intrinsic_rotation);
In the following, the mandatory lines in the code example will be described first. After that comes a description of the placement of filters, and in the end the concept of detector collections will be explained.
In order to place a detector, an object of the corresponding detector class must be created, which takes its world volume as a first argument in the constructor. The second argument of the constructor in the code example is the name of the detector object, which should be unique in the whole detector geometry. It will be appended as a prefix to all solid/logical/physical volumes of the object to be able to identify them unambiguously. Furthermore, it will be the name of the logical volume of the detector crystal, which must be passed to the SetSensitiveDetector() method in order to make it a sensitive detector (see also 2.2 Sensitive Detectors). In the case of a clover detector, which consists of several disconnected crystals, a suffix will be added to detector_name to be able to identify the single crystals (see below). By deriving most of the existing detectors from the abstract base class Detector, it is ensured that all detectors provide the same Construct() function and methods to add filters and wraps (see below). An alternative version of the Construct() function exists which does not need the intrinsic rotation angle.
In addition, most of the implemented detectors have a method to automatize the placement of shielding on the face of the detector (filters) and around the front part of the detector (wraps). They are called Add_Filter() and Add_Wrap() and must be called before the Construct() method is invoked, because they append new entries to an internal list of filters and wraps which will be iterated through during construction. The position of the detector as defined by the variables θ, φ and rt will not be changed by the addition of filters and wraps. If multiple calls of Add_XY() are made, the corresponding filters (wraps) will be stacked on top (wrapped around) the previously constructed objects automatically. The first filter or wrap place by the Add_XY() method will be in direct contact with the detector surface if no filter cases are used. Filter cases are white plastic cases which were designed by B. Löher and J. Isaak and manufactured by the TUNL workshop at some point during the 2015/2016 campaign to simplify the placement of filters. They consist of a plastic case with an inner thread that contains a set of filters. A ring can be screwed into the thread to keep the filters in place. Some Construct() methods provide flags to enable the construction of such a filter case with or without the aforementioned ring (At some point, it was found that the screwing and unscrewing of the rings is tedious, so they are not used frequently anymore. Since using the ring or avoiding it changes the distance of the filters slightly, this options also exists in the simulation code).
The utr code includes implementations of several different detectors. Most of the detectors are implemented by reading off the dimensions from some data sheet. Usually, these data sheets, for example the ones from the ORTEC company, only include the front part of the detector around the crystal. However, all detectors have an additional case for the electronics/photomultipliers/preamplifiers, and most HPGe detectors, in particular, have a dewar vessel for liquid nitrogen cooling. To get a better feeling for the dimensions of the setup and for aesthetic reasons, the dimensions of these parts have been measured or estimated by the the authors. Usually, the dimensions that can be measured without taking a detector apart are known well (for example the length of the dewar vessel), while the inner structure is poorly known (for example the wall thickness of the cases, or the composition of the electronics). Therefore, they have mostly been constructed as empty shells (mostly made of aluminium). The hope is that they represent a zero-order approximation to the actual composition of the detector parts. If desired, only the parts that are actually taken from data sheets can be constructed by setting the corresponding flags. For example, only by calling the HPGe_Coaxial::useDewar() method before invoking HPGe_Coaxial::Construct() the dewar vessels of the coaxial HPGe detectors will be constructed.
Depending on the topology of the detector, general classes exist in some cases to avoid copying and pasting. For example, all coaxial HPGe detectors contain essentially the same components, but with different dimensions. Therefore, a general HPGe_Coaxial class, structures to associate meaningful names with the dimensions HPGe_Coaxial_Properties and a dictionary of dimensions, called HPGe_Collection, have been implemented to avoid very repetitive class definitions for each detector. In between the creation of an object of a general class and the actual construction, the particular properties have to be initialized using the setProperties() method. Without this, the detector construction will fail or produce nonsense values. Below is a list of real detectors that can be built with the existing code, ordered by the style of implementation. If not mentioned otherwise, the detectors are derived from the Detector class.
Coaxial HPGe detectors: An abstract class HPGe_Coaxial exists, which implements the main parts of a coaxial detector (crystal, mount cup, end cap, cold finger, dewar). The particular dimensions of the parts for each detector are stored in a data structure called HPGe_Coaxial_Properties. The dimensions of each of the following detectors and a short description can be found in an additional header file, src/HPGe_Collection.hh:
- Duke 55% HPGe (Ortec serial number 4-TN21638A)
- Duke 55% HPGe (Ortec serial number 4-TN31524A)
- Duke 60% HPGe (Ortec serial number 36-TN21033A)
- Duke 60% HPGe (Ortec serial number 36-TN30986A)
- Duke 60% HPGe (Ortec serial number 36-TN31061A)
- Duke 60% HPGe (Ortec serial number 36-TN40663A)
- Duke 120% HPGe "Zero degree detector" (Ortec serial number 33-P40383A)
- TUD 80% HPGe (Canberra serial number 90006)
- TUD 100% HPGe (Canberra serial number 73760)
- TUD 100% HPGe (Canberra serial number 72902)
- TUD 100% segmented HPGe (Canberra serial number 72930)
- Cologne 100% HPGe (Ortec serial number 73954)
- Stuttgart 86% HPGe (Canberra serial number 37-N31120A)
- ANL 100% HPGe (Ortec serial number 42-TP41203A)
- ANL 100% HPGe (Ortec serial number 43-TP31670A)
Clover HPGe detectors: An abstract class HPGe_Clover exists, which implements a standard Eurisys/Canberra clover detector (four germanium crystals, aluminium cases and a dewar). The particular dimensions of the parts for each detector are stored in a data structure called HPGe_Clover_Properties. A suffix _crystalI, where I is either 1,2,3, or four will be appended to the argument detector_name of the constructor to be able to unambiguously identify the four crystals when defining them as sensitive detectors (see also 2.2 Sensitive Detectors). The dimensions of each of the following detectors and a short description can be found in an additional header file, src/HPGe_Collection.hh:
- Yale Clover HPGe (Eurisys serial number OC107395)
3"x3" LaBr detectors: These detectors are based on a 3"x3" cerium-doped lanthanum-bromide crystal (the material is manufactured by the company Saint Gobain and it is called "BrillanCe 380") and belong to TU Darmstadt. They are implemented in a class called LaBr_3x3. All of the four existing detectors are approximately equal.
1.5"x1.5" LaBr detectors: These detectors are based on a 1.5"x1.5" cerium-doped lanthanum-bromide crystal (the material is manufactured by the company Saint Gobain and it is called "BrillanCe 380") and belong to the university of Cologne. At the moment, they are not used by any geometry of utr. They were originally intended to be used at forward angles in the γ3 setup. All of the four existing detectors are approximately equal. They are not yet derived from the Detector class.
Ionization chambers: Different types of ionization chambers for use in photofission experiments are implemented in the subdirectories of the 2018/2019 campaign. Due to their fundamentally different detection principle, the ionization chambers are not derived from the Detector class.
Blowfish array: The dimension of the Blowfish array of neutron detectors, which is available at HIγS, were imported from the repository https://github.com/ryan-duve/blowfishGDHfridge. The classes Blowfish_Frame and Blowfish_ArmSegment implement the holding structure and the detectors, and can be constructed by calling their respective Construct() methods. Since they were found to be much too large for the utr, they are not used in any geometry at the moment. Due to their origin from another project, these detectors are not derived from the Detector class.
Deprecated! Only valid for geometries before 2018 campaign
Classes for several different detectors exist. In all of those, a G4LogicalVolume that contains all the parts of a detector is implemented which is returned by the class' Get_Logical() method. Furthermore, each detector class can return its mother volume's length and radius.
To place a detector DetectorXY in the geometry, create an instance of the detector class in DetectorConstruction.cc, get the logical volume and place it in the geometry (using Get_Length() and Get_Radius() if necessary):
DetectorXY* detectorXY_Instance = new DetectorXY("DetectorXY_Name");
G4LogicalVolume* DetectorXY_Logical = detectorXY_Instance->Get_Logical();
new G4PVPlacement( ... )
The name "DetectorXY_Name" is the name of the logical volume of the detector crystal which can be used to register it as a sensitive detector.
At the moment, the following detectors are implemented:
- Cologne LaBr, Saint Gobain BrilLanCe 380 1.5x1.5"
- Darmstadt LaBr, Saint Gobain BrilLanCe 380, 3x3"
When looking at the code, even at the latest campaign, you may notice that parts of the code are redundant (for example several DetectorConstruction/Campaign_2018_2019/src/Table2_XY.cc files which contain almost the same information except for little changes).
This is because we have learned, that, in the UTR, anything can change at any. We are using different detectors every time, which have to be moved/shielded/exchanged between runs, shielding on the tables is reinforced or removed, new things are very often custom-made and don't have simple shapes, ... The code somehow reflects this volatility of the setup, therefore it must include some more copy & paste and less abstract programming than other simulations with a well-defined setup.
Deprecated! Only valid for geometries before 2018 campaign
For maximum flexibility, the shielding of the setup can be constructed brick by brick. To avoid the G4Solid->G4LogicalVolume->G4PhysicalVolume procedure each time one would like to place a standardized brick, a lot of them are predefined as classes in Bricks.hh.
Once instantiated in DetectorConstruction.cc, bricks can be placed inside the G4LogicalVolume which was defined to be their mother volume via their constructor. To place a brick, use the Put(x, y, z, angle_x, angle_y, angle_z) method in which the coordinates and rotation angles around the coordinate axes can be specified.
Bricks are assumed to be cuboid objects, i.e. they can have 3 different side lengths. In Bricks.hh, the convention is that the long side points in z-direction, the medium side in x-direction and the short side in y-direction, if they can be distinguished. The respective lengths can be accessed via the member variables L, M and S.
Deprecated! Only valid for geometries before 2018 campaign
Similar to bricks, filters and filter cases in front of detectors are implemented in Filters.hh and can be placed using their Put() methods.
The intent of this was to give the user an overview which filters are really there at the UTR. Sometimes, the documentation of experiments only mentions "thin", "medium" and "thick" filters, but no actual dimensions. Providing fixed filter types hopefully helps with such issues.
Deprecated! Only valid for geometries before 2018 campaign
Complicated targets can be implemented in Targets.hh. The placement in DetectorConstruction.cc works analog to the placement of detectors. Relevant properties of the targets can be made accessible by implementing Get() methods.
Information about the simulated particles is recorded by instances of the G4VSensitiveDetector class. Any unique logical volume can be declared a sensitive detector.
Unique means volumes with a unique logical volume name. This precaution is here because all bricks and filters of the same type from the previous sections have the same logical volume names. Making one of those a sensitive detector might yield unexpected results.
Any time a particle produces a hit inside a G4VSensitiveDetector object, its ProcessHits routine will access information of the hit. This way, live information about a particle can be accessed. Note that a "hit" in the GEANT4 sense does not necessarily imply an interaction with the sensitive detector. Any volume crossing is also a hit. Therefore, also non-interacting geantinos can generate hits, making them a nice tool to explore the geometry, measure solid-angle coverage etc. After a complete event, a collection of all hits inside a given volume will be accessible via its HitsCollection. This way, cumulative information like the energy deposition inside the volume can be accessed.
Three types of sensitive detectors are implemented at the moment:
- EnergyDepositionSD Records the total energy deposition by any particle per single event inside the sensitive detector.
- ParticleSD Records the first hit of any particle inside the sensitive detector.
- SecondarySD Records the first hit of any secondary particle inside the sensitive detector.
No matter which type of sensitive detector is chosen, the simulation output will be a ROOT tree with a user-defined subset (see section 2.6 Output File Format) of the following 10 branches:
- event
Number of the event to which the particle belongs. This number is the same for all secondary particles and their corresponding primary particle. It is also the same if
G4ParticleGun->GeneratePrimaryVertext()is called multiple times in a single event. The latter point makes this variable especially useful in case of theAngularCorrelationGenerator(see 2.3.3 AngularCorrelationGenerator). - ekin Kinetic energy (in MeV) of the particle at the time of its first hit of the sensitive detector.
- edep Total energy deposition (in MeV) of the event (EnergyDepositionSD) OR energy deposition of the first hit of the sensitive detector (ParticleSD, SecondarySD)
- particle Type of the particle whose first hit of the sensitive detector it was (ParticleSD, SecondarySD) OR type of the very first particle in this event that hit the sensitive detector (EnergyDepositionSD). The type of the particle is encoded in the Monte Carlo Particle Numbering Scheme.
- volume User-defined identifier of the sensitive detector that recorded this set of data.
- x/y/z Coordinates (in mm) of the first hit of the sensitive detector by a particle (ParticleSD, SecondarySD) OR coordinates of the first hit by the first particle in this event that hit the sensitive detector (EnergyDepositionSD)
- vx/vy/vz Momentum (in MeV/c) of the particle at the position of the first hit of the sensitive detector (ParticleSD, SecondarySD) OR momentum of the first particle hitting the sensitive detector in this event at the position of its first hit (EnergyDepositionSD).
The meaning of the columns sometimes changes with the choice of the sensitive detector.
To make a volume whose logical volume name is "Logic_Name" a sensitive detector of type XYSD, add the following lines in DetectorConstruction::ConstructSDandField(){}
XYSD *xySD = new XYSD("SD_Name", "SD_HitsCollection_Name");
G4SDManager::GetSDMpointer()->AddNewDetector(xySD);
xySD->SetDetectorID(volume); // volume is the detector ID which will be displayed in the ROOT output file
SetSensitiveDetector("Logic_Name", xySD, true);
The following example illustrates how the different sensitive detectors work.
In the figure, a photon (orange, sinusoidal line) and several electrons (blue arrow) are shown which are part of a single event. Each hit in the sensitive detector (black circle) has a label that contains the particle number and the number of the hit. The history of the event is as follows:
The primary particle 1 (a photon with an energy of 2.5 MeV) enters the sensitive detector at (0,3). It is Compton-scattered at (2,5) and transfers 1.0 MeV to an electron (particle 2). The electron slowly loses its kinetic energy again in scattering processes at (4,8), (6,9) and (7,8) inside the sensitive detector which do not create new secondary particles. In the meantime, particle 1 travels to (6,1) and creates an e-/e+ pair with its remaining 1.5 MeV. Each lepton (3 and 4) gets an initial energy of (1.500 - 1.022)/2 = 0.239 MeV. Lepton 3 loses its kinetic energy inside the sensitive detector, Lepton 4 leaves the sensitive detector.
The following information would be recorded if the volume was a ...
- ... ParticleSD
| ekin | edep | particle | volume | x | y | vx | vy |
|---|---|---|---|---|---|---|---|
| 2.5 | 0. | 22 | 0 | 0 | 3 | 2 | 2 |
| 1.0 | 0. | 11 | 0 | 2 | 5 | 2 | 3 |
| 0.239 | 0. | 11 | 0 | 6 | 1 | 3 | 3 |
| 0.239 | 0. | 11 | 0 | 6 | 1 | -3 | -3 |
- ... SecondarySD
| ekin | edep | particle | volume | x | y | vx | vy |
|---|---|---|---|---|---|---|---|
| 1.0 | 0. | 11 | 0 | 2 | 5 | 2 | 3 |
| 0.239 | 0. | 11 | 0 | 6 | 1 | 3 | 3 |
| 0.239 | 0. | 11 | 0 | 6 | 1 | -3 | -3 |
- ... EnergyDepositionSD
| ekin | edep | particle | volume | x | y | vx | vy |
|---|---|---|---|---|---|---|---|
| 2.5 | 1.989 | 22 | 0 | 0 | 3 | 2 | 2 |
For simplicity, the momentum vector is given as the vector of the depicted arrow/wave. The real values would be
vx_real = 1/sqrt(vx^2 + vy^2)*cos(arctan(y/x))*ekin/c
vy_real = 1/sqrt(vx^2 + vy^2)*sin(arctan(y/x))*ekin/c
Event generation is done by classes derived from the G4VUserPrimaryGeneratorAction. In the following, the three existing event generators are described.
By default, utr uses the Geant4 standard G4GeneralParticleSource. To use the AngularDistributionGenerator or the AngularCorrelationGenerator of utr, which implement angular distributions and correlations (not exclusively, but mainly for Nuclear Resonance Fluorescence (NRF) applications at the moment), set the corresponding GENERATOR_XY option when building the source code (see also 3.3 Build configuration):
$ cmake -S . -B build -DGENERATOR_ANGDIST=ON -DGENERATOR_ANGCORR=OFFAll the event generators have macro commands defined that simplify their control. Sample macro files can be found in the macros/examples directory. As a rule of thumb, a user should use ...
- ...
G4GeneralParticleSourceif the source is sufficiently simple to be controlled via the macro commands of Geant4. For an overview, see the webpage given below. An typical application would be the simulation of a point-like radioactive source or a beam with an intensity distribution that depends on the energy of the particles and the spatial coordinates. - ...
AngularDistributionGenerator, if monoenergetic particles should be emitted from a set of user-defined volumes with a user-defined angular distribution, that has an arbitrary dependence on the solid angle. A typical application would be the simulation of gamma-rays that are emitted by a target that was excited with a (polarized) beam of particles. - ...
AngularCorrelationGenerator, if user-defined volumes and angular distributions are used, and, in addition, several monoenergetic particles should be correlated. This means that the emission angles and the polarization plane of the n-th particle depend on the emission angles and polarization of the (n-1)-th particle. Typical applications would be the simulation of beta-plus decay where ultimately two correlated photons from the annihilation of the positron are emitted, simulations of particle cascades from an excited nucleus that has been excited via a beam or decays via exotic double-gamma or double-beta decays.
The event generators are listed by complexity above. If in doubt which event generator to use, it is strongly recommended to take the most simple one that can do a given task, because especially the distribution- and correlation generators create a lot of overhead due to their Monte-Carlo sampling and heavy usage of trigonometric functions.
This event generator uses the G4GeneralParticleSource (GPS) whose parameters can be controlled by a macro file. For further information, see the GPS documentation.
The macros source.mac and beam.mac in the macros/examples directory model an isotropic point-source and a circular beam using the G4GeneralParticleSource. Many more examples can be found in the manual of Geant4.
The AngularDistributionGenerator generates monoenergetic particles that originate in a set of G4PhysicalVolumes of the DetectorConstruction and have a certain angular distribution.
The physical volumes (the "sources") and angular distribution can have arbitrary shapes. Starting positions and momentum directions are created using a Monte-Carlo method ('rejection sampling'), which is explained shortly in the following: Given a(n)
- Cuboid in 3 dimensions ("container volume") that completely contains the source volume
- Angular distribution W(θ, φ)
AngularDistributionGenerator generates
- Uniform random positions
(source_x + random_x, source_y + random_y, source_z + random_z), |random_I| <= 0.5*sourceDI, I in {x, y, z} - Random tuples
(random_θ, random_φ)with a distribution such that they represent uniformly distributed random directional vectors in spherical coordinates - Uniform random numbers
random_W, so that |random_W| <= MAX_W
until
- The position
(random_x, random_y, random_z)is inside one of the source physical volumes random_W <= W(random_θ, random_φ)
If both conditions are fulfilled, a particle is emitted from (random_x, random_y, random_z) in the direction (θ, φ).
The process of finding a starting point is depicted in 2 dimensions in the figure below. The yellow source volume consists of two disconnected parts. It is placed inside a dashed box which is the container volume. Random points inside the container volume are either black or red, depending on whether they are inside or outside the source volumes. Only from the black points, particles are emitted (in random directions).
Finding the correct dimensions of the container box might need visualization. Try placing a G4Box with the desired dimensions at the desired position in the geometry and see whether it encloses the source volume completely and as close as possible.
The process of finding a starting vector is shown in one dimension (W is only dependent on θ) in in the figure below. First, a random value random_θ for θ with a uniform random distribution on a sphere is sampled. Note that this is not the same as a uniform distribution of values between 0 and π for θ. Then, a uniform random number between 0 and an upper limit MAX_W is drawn. If the value MAX_W is lower than W(random_θ) (black points), then a particle will be emitted at that angle.
Clearly, the algorithm works well if
- the cuboid approximates the shape of the sources well and wraps it tightly
- the angular distribution varies smoothly in the
(θ, φ)plane andMAX_Wis very close to the actual maximum value ofW
The maximum number of randomly sampled points is hard-coded in AngularDistributionGenerator.cc and AngularCorrelationGenerator.cc where it says:
MAX_TRIES_POSITION = 1e4
MAX_TRIES_MOMENTUM = 1e4
The event generators can do a self-check before the actual simulation in which they creates MAX_TRIES_XY points and evaluate how many of them were valid or not (N_NotValid). From this, the probability p=(N_NotValid/MAX_TRIES_XY)^MAX_TRIES_XY of never hitting one of the source volumes / angular distributions in MAX_TRIES_XY attempts can be estimated. In the case of the position generator, an individual check is done for each source volume. If p * N >~ 1, where N is the number of particles to be simulated, the algorithm will very probably fail once in a while so try increasing MAX_TRIES_XY or optimizing the dimension of the container volume or MAX_W. A typical output of the self-check for the position generator looks like:
G4WT0 > ========================================================================
G4WT0 > Checking Monte-Carlo position generator with 100 3D points ...
G4WT0 > Check finished. Of 100 random 3D points, 82 were inside volume 'Se82_Target' ( 82 % )
G4WT0 > Probability of failure: pow( 0.18, 100 ) = 3.36706e-73 %
G4WT0 > ========================================================================
Both the momentum and position generator will also check whether the given limits MAX_W and SOURCE_DI are large enough. For the position generator, it is clear why this needs to be checked.
For the momentum generator, the check is necessary because the value of MAX_W that was introduced above has been arbitrarily set to 3 in AngularDistributionGenerator.hh and AngularCorrelationGenerator, which should be a sensible choice for most angular distributions. However, it may be that W(θ, φ) > 3 for some distribution.
Too small values of MAX_W and SOURCE_DI can also be detected by the self-check with a Monte-Carlo method. For each of the MAX_TRIES_MOMENTUM (MAX_TRIES_POSITION) tries, utr will also check whether
- the inequality
W_max <= W(random_θ, random_φ)holds. - the randomly sampled points
(+- 0.5*SOURCE_DX, random_y, random_z),(random_x, +- 0.5*SOURCE_DY, random_z),(random_x, random_y, +- 0.5*SOURCE_DY)are still inside the source volume.
If yes, this could be a hint that the value of MAX_W or SOURCE_DI is too low and should be increased.
The corresponding messages would look like
G4WT0 > In 5624 out of 10000 cases (56.24 % )
W(random_theta, random_phi) == MAX_W == 1 was valid.
This may mean that MAX_W is set too low and
the angular distribution is truncated.
and
G4WT0 > In 3277 out of 10000 cases (32.77 % ) the randomly sampled point (sourceX +- sourceDX, sourceY + randomY, sourceZ + randomZ) was still inside the source volume. This may mean that the x range does not encompass the whole source volume.
If everything is okay, it will display
G4WT0 > MAX_W == 3 seems to be high enough.
and
G4WT0 > X range 0 +- 25 seems to be large enough.
However, 'large enough' may still mean 'too large'. The user is encouraged to try to optimize the parameters SOURCE_DI and MAX_W, to meliorate the disadvantages of the rejection sampling algorithm. Be aware that the position and momentum sampling have to do expensive calls of trigonometric functions for each random position/momentum vector, i.e. number of tries should be kept as low as possible.
To change parameters of the AngularDistributionGenerator, an AngularDistributionMessenger has been implemented that makes the following macro commands available:
/ang/particle NAMESet the particle type by name. See the GEANT4 documentation for a list of possible particles./ang/energy ENERGY UNITSet the kinetic energy of the particle/ang/nstates NSTATESDefine the number of states for the angular distribution (see below)/ang/stateN VALUEDefine state number N (where N is in {1, 2, 3, 4})/ang/deltaN1N2 VALUEDefine the multipole mixing ratio for the transition between states N1 and N2/ang/sourceX VALUE UNITAlong withsourceYandsourceZ, defines the position of the container box/ang/sourceDX VALUE UNITAlong withsourceDYandsourceDZ, defines the dimensions of the container box./ang/sourcePV VALUEEnter the name of a physical volume that should act as a source. To add more physical volumes, call/ang/sourcePVmultiple times with different arguments (about using multiple sources, see also the caveat at the end of this section)./ang/polarized VALUEDetermine whether the excitation (i.e. the first transition in the cascade) is caused by a polarized photon (default value). To simulate unpolarized photons, the angular distributions for the two possible polarizations are added up in the code. This is done by choosing different parities for the first excited state in the cascade. This means that both distributions (for example 0+ → 1+ → 0+ and 0+ → 1- → 0+) need to be implemented. The user needs to give only one of the two possible cascades as a macro command.
The container volume's inside will be the interval [X - DX/2, X + DX/2], [Y - DY/2, Y + DY/2] and [Z - DZ/2, Z + DZ/2].
The identifiers of the angular distribution are given to the simulation as an array of numbers states = {state1, state2, ...} whose length NSTATES can to be specified by the user.
For "real" NRF angular distributions, this array of numbers will be the spins of the excited states in a cascade, with the parity indicated by the sign of the numbers.
Due to parity symmetry, an inversion of all the parities in a cascade will result in the same angular distribution. For example, the transition 0+ -> 1- -> 0+ has the same angular distribution as 0- -> 1+ -> 0-. This is indicated by the notation "+-" and "-+" in the list below (the example is listed as "0± -> 1∓ -> 0±").
It was chosen to represent the parity of a state as the sign of the spin quantum number. Unfortunately, this makes it impossible to represent 0- states, because the number "-0" is the same as "+0". Therefore, the value "-0.1" represents a 0- state.
A list of all implemented angular distributions can be found at the bottom of the angdist.mac sample macro in macros/examples for AngularDistributionGenerator.
The macro file angdist.mac in the macros/examples directory shows a commented example of the usage of AngularDistributionGenerator.
When using multiple sources, be aware that AngularDistributionGenerator samples the points with a uniform random distribution inside the container volume. How many particles are emitted from a certain part of the source will only depend on its volume.
This is not always desirable. Imagine the following example: The goal is to simulate a beam on two disconnected targets. The first target has twice the volume of the second target, but the second target has a four times larger density. That means, the reaction would occur approximately twice as often in the second target than in the first. Implementing the targets like this in AngularDistributionGenerator would not give realistic results because of the weighting by volume. In a case like this, one would rather simulate the individual parts of the target and compute a weighted sum of the results.
The AngularCorrelationGenerator generates monoenergetic particles that originate in a set of G4PhysicalVolumes of the DetectorConstruction, have a user-defined angular distribution and are correlated. The last point is what distinguishes it from the AngularDistributionGenerator: In a single event (G4Event), this generator launches several particles from the same origin by multiple calls of G4ParticleGun::GeneratePrimaryVertex(), for which the angular distribution and polarization depends on the previously emitted particle. In other words, the particles will be part of a cascade of transitions (of a nucleus) which has an arbitrary number of steps.
Since the particles belong to the same events, they can be easily picked out by the event number in the ROOT output file see 2.6 Output File Format.
This is accomplished by rotating the angular distribution of the follow-up particle by the Euler angles α, β and γ which define the emission direction and polarization of the previous particle.
The reference emission direction is (0, 0, 1), i.e. the z-axis, and the reference polarization axis is the x-axis (1, 0, 0). The rotations with the Euler angles are executed in the extrinsic reference frame (i.e. the original coordinate system) in the order z-x-z, i.e. a rotation around the z-axis, followed by a rotation around the x-axis and again around the z-axis as they are defined above.
In the following, the rotation matrices around the x- and z-axis are called M_x(ω) and M_z(ω), where ω is the rotation angle around the corresponding axis. The first particle is assumed to be emitted in a direction v1 with its polarization axis p1.
It is now the task to find the emission direction v2 and polarization p2 of the second particle, whose emission is subject to the angular distribution W2(θ, φ) in the laboratory frame. To get the emission direction with respect to the first particle which defines the quantization axes, the three Euler angles are determined which yield v1 and p1 if applied to the reference vectors:
p1 = M_z(α) M_x(β) M_z(γ) (1, 0, 0)
v1 = M_z(α) M_x(β) M_z(γ) (0, 0, 1) = M_z(α) M_x(β) (0, 0, 1)
The second equation can be simplified, because a rotation about the z-axis leaves the vector (0, 0, 1) unchanged.
For the known normalized vectors v1 and p1, this results in a set of equations for the Euler angles α, β and γ.
At the moment, in the case of polarization, the ultrarelativistic approximation that p1 . v1 == 0 (scalar product) is taken. This means that the polarization can only be perpendicular to the propagation direction. This approximation is valid for highly-energetic or massless particles. It allows for an easy determination of the angle γ: M_z(γ) only acts on the polarization, and the product of M_z(α) M_x(β) acts on both. Therefore, it can be used to describe the difference of emission and polarization direction with respect to the reference frame. It the first particle is assumed to be unpolarized, the angle γ is sampled from a uniform random distribution to mimic an arbitrary behavior of the polarization.
After the determination of the Euler angles, a random emission direction of the second particle v2' is sampled from W2(θ, φ) in the laboratory frame as described in 2.3.2 AngularDistributionGenerator (using the same algorithm). By applying the three rotation matrices as shown above using the determined angles, it is rotated into the reference frame of the first particle:
v2 = M_z(α) M_x(β) M_z(γ) v2'
p2 = M_z(α) M_x(β) M_z(γ) p2'
In this case, the first action of M_z can not be neglected, of course.
The given polarization direction p2' is rotated in the same way.
To change parameters of the AngularCorrelationGenerator, an AngularCorrelationMessenger has been implemented that makes macro commands available. The following commands retain their functionality from the messenger of the AngularDistributionGenerator exactly (note the different parent directory, however):
-
/angcorr/particle NAME(m) -
/angcorr/energy ENERGY UNIT(m) -
/angcorr/nstates NSTATES(m) -
/angcorr/stateN VALUE(m) -
/angcorr/deltaN1N2 VALUE(m) -
/angcorr/sourceX VALUE UNIT(s) -
/angcorr/sourceDX VALUE UNIT(s) -
/angcorr/sourcePV VALUE(s)
Please refer to the documentation of these commands in section 2.3.2 AngularDistributionGenerator. The label 'm' or 's' indicates whether the commands can be used multiple times, or whether only a single use makes sense. Since the AngularCorrelationGenerator emits multiple particles in a single event, /angcorr/particle must be used several times. On the contrary, the location, size and name of the source can be defined only once, because the particles are assumed to be emitted from a common origin. Note that the polarized command does not exist here.
Any macro for AngularCorrelationGenerator must give the number of steps in the cascade of emitted particles via the macro /angcorr/steps. After that, the single steps are initiated by the /angcorr/particle command which is followed by a description of the angular distribution of the particle (see below). The description must be finished before the next call of /angcorr/particle to avoid unexpected behavior.
One new available macro command that can be used only once is:
/angcorr/steps NSTEPS: Specify the number of steps in the cascade which will be defined in the macro. This must be equal to the number of calls of/angcorr/particle
All other new macro commands can be used to specify an angular distribution and can be used NSTEPS times each:
/angcorr/direction X Y Z: Instead of specifying an angular distribution, sets a constant emission direction of the given particle. This option can only be used for the first particle. It is useful if one only wants to rotate the given angular distribution of the follow-up particle./angcorr/relativeangle ANGLE UNIT: Instead of specifying an angular distribution, determines that the current particle will be emitted at an angleANGLEwith respect to the previous particle, i.e. it will be emitted in a cone around the emission direction of the previous particle. ForANGLE == 180 deg, the particle will be emitted exactly in the opposite direction, forANGLE == 90 deg, it will be emitted in the perpendicular plane./angcorr/polarization X Y Z: Sets the polarization direction of the current particle, which will also be rotated with respect to the emission angle of the previous particle. IfX == Y == Z == 0, the particle is assumed to be unpolarized, i.e. the Euler angle γ can be chosen at random. If an angular distribution is specified by the/angcorr/stateNcommands, the emission direction will be sampled from the unpolarized angular distribution and transformed.
The first two options were found to be very useful for debugging of the code as well.
At the start of a simulation using the AngularCorrelationGenerator, the code will print a summary of the checked options along with the self-test that contains lines like
G4WT0 > ========================================================================
G4WT0 > Monte-Carlo momentum generator with 10000 3D vectors for
G4WT0 > Cascade step #2 ( Particle: geantino )
G4WT0 > Angular distribution : 0 -> 1 -> 0
G4WT0 > Polarization : ( 1, 0, 0 )
G4WT0 > Check finished. Of 10000 random 3D momentum vectors, 3315 were valid ( 33.15 % )
G4WT0 > Probability of failure: pow( 0.6685, 10000 ) = 0 %
G4WT0 > MAX_W == 3 seems to be high enough.
G4WT0 > ========================================================================
For a commented example, see the angcorr.mac macro file in the macros/examples directory, which implements a three-step cascade that uses all the features of AngularCorrelationGenerator.
utr makes use of the G4VModularPhysicsList, which allows to integrate physics modules in a straightforward way by calling the G4ModularPhysicsList::RegisterPhysics(G4VPhysicsConstructor*) method. The registered G4VPhysicsConstructor class takes care of the introduction of particles and physics processes.
The physics processes are separated into two logical groups, which contain the most probably occurring processes in NRF experiments: electromagnetic (EM) and hadronic.
Geant4 provides complete EM and hadronic modules for different energy ranges and with different precision. In utr, a selection of those, which was considered most suitable for low-energy NRF applications, can be selected via the HADRON* and EM* cmake build options (see also 3.3 Build configuration):
$ cmake -S . -B build -DEM_LIVERMORE=ON -DHADRON_ELASTIC_HP=ON
Though possible, it is safer not to include several EM or hadronic models at the same time. If in doubt, the command line output at the beginning of a Geant4 simulation can be checked to see which model is actually used for a certain process. For example, if both EM_LIVERMORE and EM_LIVERMORE_POLARIZED are switched on, that output will include lines like:
compt: for gamma SubType= 13 BuildTable= 1
Lambda table from 100 eV to 1 MeV, 20 bins per decade, spline: 1
LambdaPrime table from 1 MeV to 100 TeV in 160 bins
===== EM models for the G4Region DefaultRegionForTheWorld ======
LivermoreCompton : Emin= 0 eV Emax= 1 GeV FluoActive
KleinNishina : Emin= 1 GeV Emax= 100 TeV FluoActive
This shows that the unpolarized model is used (otherwise, LivermoreCompton would be replaced by LivermorePolarizedCompton), which may not be what the user expected.
A description of the physics lists and the implementation of the processes can be found in the GEANT4 Physics Reference Manual
Physics modules can be switched by setting the different HADRON* and EM* cmake build flags, for example:
$ cmake -S . -B build -DEM_LIVERMORE=ON -DHADRON_ELASTIC_HP=ON
An output like
================================================================================
Using the following physics lists:
G4EmLivermorePolarizedPhysics ...
G4HadronElasticPhysicsLEND ...
G4HadronPhysicsFTFP_BERT ...
================================================================================
at the beginning of a simulation will show which physics lists are currently used.
Most of the physics lists are probably a little too extensive for the intended use of utr. This is also why lots of warnings concerning very exotic particles like
*** G4Exception : PART10116
issued by : G4ParticleDefintion::SetProcessManager
ProcessManager is being set to eta2(1870) without proper initialization of TLS pointer vector.
This operation is thread-unsafe.
*** This is just a warning message. ***
may appear.
In order to include new physics modules, include them in the src/Physics.cc file.
In src/utr.cc, the random number engine's seed is set by using the current CPU time, making it a "real" random generator.
G4Random::setTheEngine(new CLHEP::RanecuEngine);
// 'Real' random results
time_t timer;
G4Random::setTheSeed(time(&timer));
If you want deterministic results for some reason, comment these lines out and uncomment
G4Random::setTheSeed(long n);
Re-compile afterwards. After this change, every restart of the simulation with unchanged code will yield the same results.
In section 2.2 Sensitive Detectors the format of the ROOT output file was already introduced. The possible branches are
- event
- ekin
- edep
- particle (given in the Monte Carlo Particle Numbering Scheme)
- volume
- x/y/z
- vx/vy/vz
By using cmake build options (see 3.3 Build configuration), the user can specify which of these quantities should be written to the ROOT file, to avoid creating unnecessarily large files.
To build and run the simulation, the following dependencies are required:
- Geant4 (Tested with version 10.5 and 10.7)
- CMake (build)
Furthermore, to use the analysis scripts:
Optional components:
- Qt as a visualization driver. Compile Geant4 with the
GEANT4_USE_QToption (tested with Qt4) - ccmake UI for CMake which gives a quick overview of available build options
- CADMesh is required for DetectorConstructions that depend on the CADMesh library (option
WITH_CADMESH). Thus, also the dependencies TetGen and ASSIMP are needed. - python3 is required for the utrwrapper script.
The most simple way to build and compile the simulation is executing
$ cmake -S . -B build
$ cmake --build buildfrom the utr directory.
This will compile the simulation using default options for everything. To change the default configuration, many CMake build options are available and described in the next section.
After the cmake --build build step, an executable utr will have been created in the build directory, which can be used to execute utr via build/utr (see also 4 Usage and Visualization).
Using CMake build options, the simulation can be configured. There are options available to
- Change the geometry
- Select physics lists
- Select the primary generator
- Select the output quantities
- Switch targets on and off
- Set the frequency of runtime updates
which are described in the following subsections.
They are used in the cmake step of the compilation process, which was described in the previous section. In general, an option OPTION of CMake is set to a specific value VALUE by typing:
$ cmake -S . -B build -DOPTION=VALUE
Most options are flags, i.e. their only possible values are ON and OFF. Only the options of the geometry configuration are string options, which take an arbitrary string as a value. The option that sets the frequency of updates takes an integer number.
As described in section 2.1 Geometry, the different available DetectorConstructions are sorted into campaigns and runs. To select a specific geometry, the build options CAMPAIGN and DETECTOR_CONSTRUCTION have to be set with the names of the corresponding directories. For example, to choose the 64Ni_271_279 geometry from the 2018 campaign, type
$ cmake -S . -B build -DCAMPAIGN=Campaign_2018 -DDETECTOR_CONSTRUCTION=64Ni_271_279
If the ccmake GUI of CMake is used, it is possible to loop over the available campaigns and detector constructions by repeatedly pressing enter. The campaign takes precedence over the detector construction, i.e. if the campaign is changed, the build needs to be reconfigured before the correct selection of detector constructions is displayed. If a new directory has been added, rerun cmake -S . -B build again in the utr/ directory to register it to CMake.
As described in section 2.4 Physics, different physics models can be selected by setting the corresponding flag to ON. By default, the following models are used by utr (the name of the flag is given in parentheses):
- EM : G4EmLivermorePolarizedPhysics (EM_LIVERMORE_POLARIZED)
- Elastic Hadronic: G4HadronElasticPhysics (HADRON_ELASTIC_STANDARD)
- Inelastic Hadronic: G4HadronPhysicsFTFP_BERT (HADRON_INELASTIC_STANDARD)
To switch to another EM physics list, for example, one would type
$ cmake -S . -B build -DEM_STANDARD=ON -DEM_LIVERMORE_POLARIZED=OFF
Note that the previously used physics list needs to be switched off as well, to avoid getting unexpected behavior if two physics lists implement the same processes.
utr offers three different primary generators (see 2.3 Event Generation), the Geant4-builtin G4GeneralParticleSource (GPS) and the generators for angular distributions and angular correlations. To replace the default GPS with either AngularDistributionGenerator or AngularCorrelationGenerator, use one of the GENERATOR options
$ cmake -S . -B build -DGENERATOR_XY=ON
Switching both generator options to ON works, but leads to unexpected behavior.
In real NRF experiments, one often removes the NRF target and puts a radioactive source in the same place. For convenience, utr provides a cmake build flag to switch off the targets in the geometry, i.e. to do a calibration measurement in the simulation.
To remove the targets in the simulation, type:
$ cmake -S . -B build -DUSE_TARGETS=OFF
To see which part is actually ignored when this flag is set to OFF, look at the currently activated DetectorConstruction.cc and search for code embedded in a
#ifdef USE_TARGETS
[...]
#endif
clause.
The options for the output file format are described in 2.6 Output File Format. By changing the corresponding flags:
- EVENT_ID
- EVENT_EDEP
- EVENT_EKIN
- EVENT_PARTICLE (given in the Monte Carlo Particle Numbering Scheme)
- EVENT_VOLUME
- EVENT_POSX, EVENT_POSY, EVENT_POSZ
- EVENT_MOMX, EVENT_MOMY, EVENT_MOMZ
the user can decide which of the quantities are written to the ROOT output file as branches. For example, to write the x coordinate of the first hit in the detector volume, type
$ cmake -S . -B build -DPOSX=ON
For the three implemented detector types (see Sensitive Detectors), the output quantities may have a different meaning.
By default, utr prints updates about the number of processed events and the execution time every 10^5 events (see 4 Usage and Visualization). To change that number, set the value of the PRINT_PROGRESS variable:
$ cmake -S . -B build -DPRINT_PROGRESS=1000
The compiled utr binary can be run with different arguments. To get an overview, type
$ build/utr --helpAny execution of utr will print (amongst the output of Geant4 itself) information about the output quantities and (since the 2018 campaign) about the position of important parts in the geometry:
==============================================================
DetectorConstruction: Info (all dimensions in mm)
> Collimator entrance position : ( 0.00, 0.00, -3894.18 )
> Ideal position of G3 target : ( 0.00, 0.00, 0.00 )
> Ideal position of 2nd target : ( 0.00, 0.00, 1574.80 )
> World dimensions : ( 3000.00, 3150.00, 8000.00 )
==============================================================
G4WT0 > ================================================================================
G4WT0 > ActionInitialization: The following quantities will be saved to the output file:
G4WT0 > EDEP
G4WT0 > PARTICLE
G4WT0 > VOLUME
G4WT0 > MOMX
G4WT0 > MOMY
G4WT0 > MOMZ
G4WT0 > ================================================================================Important optional arguments besides --help are:
$ build/utr -m MACROFILEExecutes macro file MACROFILE
$ build/utr -t NTHREADSSets the number of threads in multithreaded mode (default: 1)
$ build/utr -o OUTPUTDIRSets the output directory of utr where the ROOT files will be placed.
While running a simulation, utr will automatically print information about the progress in the following format, using the G4VUserEventAction class:
Progress: [ 160000/100000000] 0.16 % Running time: 0d 0h 0mn 4sThat means there is no need to use the /run/printProgress macro of Geant4 any more. The number of events NEVENTS after which a new progress update is printed can be set using the PRINT_PROGRESS preprocessor variable at compile-time (see also 3.3 Build configuration):
$ cmake -S . -B build -DPRINT_PROGRESS=NEVENTSRunning utr without any argument will launch a UI session where macro commands can be entered. It should also automatically execute the macro file init_vis.mac in the scripts directory, which visualizes the geometry.
If this does not work, or to execute any other macro file MACROFILE, type
/control/execute MACROFILEin the UI session. In this mode, it is important to know how the angles are defined, to be able to set the view using the /vis/viewer/set/viewpointThetaPhi command:
/vis/viewer/set/viewpointThetaPhi 180 0 degviews the setup in beam direction,
/vis/viewer/set/viewpointThetaPhi 0 0 degviews it against the beam direction. To view the geometry from above and below, use
/vis/viewer/set/viewpointThetaPhi 270 270 degand
/vis/viewer/set/viewpointThetaPhi 270 90 degrespectively.
It is also possible to create 3D visualization files that can be viewed by an external viewer like Blender (the title picture was made in Blender, for example). The macro vrml.mac in macros/examples shows how to create a .wrl file. Run it in UI mode with
/control/execute macros/examples/vrml.macThe directory OutputProcessing contains some sample ROOT and shell scripts that can be adapted by the user to process their simulation output. For example, a complete toolchain exists to extract full-energy peak efficiencies from a series of simulations (see also 5.5 fep_efficieny). Executing
$ cmake -S OutputProcessing/ -B build/OutputProcessing/
$ cmake --build build/OutputProcessing/in the utr directory should compile/copy all the scripts, generating executables in the build/OutputProcessing directory.
The compilation may fail if the ROOTSYS environment variable is not set on your system.
Executables can be run like
$ build/OutputProcessing/EXECUTABLENAME {ARGUMENTS}from the utr directory. The executables can be removed using the command
$ cmake --build build/OutputProcessing/ --target cleanin the utr directory or by simply deleting the build/OutputProcessing directory altogether.
RootToTxt converts a ROOT output file (TFile) containing an n-tuple of data (a TTree with TBranch objects) to a simple text file with the same content. If you want to convert a ROOT file ROOTFILE, type
$ build/OutputProcessing/rootToTxt ROOTFILEThe ROOT file can have a TTree with an arbitrary name and an arbitrary number of TBranch objects. The output text file has the same name as the ROOT file but with a ".txt" suffix. Be aware that conversion into text files increases the file size. Note that in the case of an utr output file this will just produce a list of all recorded events with their recorded properties and not a spectrum. For a text spectrum use getHistogram in combination with histogramToTxt.
getHistogram sorts the data from multiple output files (for example, those of several threads of the same simulation) into a ROOT histogram and saves the histogram to a new file. It is assumed that the output of the simulation has at least the branches edep and volume, and optionally also event (see also 2.6 Output File Format, and that the detector IDs (i.e. the possible values of volume), determined by the G4SensitiveDetector::SetDetectorID() method in utr (see also 2.2 Sensitive Detectors), are integer numbers between 0 and MAXID, where MAXID is the maximum detector ID.
Executing
$ build/OutputProcessing/getHistogram --help
Usage: getHistogram [OPTION...]
Create histograms of energy depositions in detectors from a list of events
stored among multiple ROOT files
-a, --addback Add back energy depositions that occurred in a
single event to the detector first listed in the
event (usually this is the first one hit)
(default: Off)
-b, --binning=BINNING Size of bins in the histogram in keV (default: 1
keV)
-B, --showbin=BIN Number of energy bin whose value should be
displayed, -1 to disable (default: -1)
-d, --inputdir=INPUTDIR Directory to search for input files matching the
patterns (default: current working directory '.' )
-e, --maxenergy=EMAX Maximum energy displayed in histogram in MeV
(rounded up to match BINNING) (default: 10 MeV)
-m, --multiplicity=MULTIPLICITY
Particle multiplicity, sum energy depositions for
each detector among MULTIPLICITY events (default:
1)
-n, --maxid=MAXID Highest detection volume ID (default: 12).
'getHistogram' only processes energy depositions
in detectors with integer volume ID numbers from 0
to MAXID.
-o, --filename=OUTPUTFILENAME Output file name, file will be overwritten!
(default: {PATTERN1}_hist.root with a trailing
'_t' in PATTERN1 dropped)
-O, --outputdir=OUTPUTDIR Directory in which the output files will be
written (default: same as INPUTDIR)
-p, --pattern1=PATTERN1 First string files must contain to be processed
(default: utr)
-q, --pattern2=PATTERN2 Second string files must contain to be processed
(default: .root)
-s, --silent Silent mode (does not silence -B option) (default:
Off
-t, --tree=TREENAME Name of tree composing the list of events to
process (default: utr)
-?, --help Give this help list
--usage Give a short usage message
Mandatory or optional arguments to long options are also mandatory or optional
for any corresponding short options.shows how to use the script. The meaning of the arguments to the most important options are:
- EMAX: All energy depositions of a detector are stored in a histogram. This parameter sets the maximum energy of the histogram in MeV (default: 10 MeV). Note that this number will automatically be rounded up to match the required bin width given through the -binning BINNING option, if necessary.
- BINNING: This optional argument sets the bin width of the histograms in keV with the first bin always being centered around 0.
- TREENAME: Name of the ROOT tree (Default: TREENAME=="utr") to be processed in all of the input files (which usually are utr output files).
- PATTERN1 and PATTERN2: Two strings that identify the set of files to be merged. See also the example below. (Default: PATTERN1=="utr", PATTERN2==".root")
- INPUTDIR: This optional argument sets the directory in which getHistogram searches for files to be processed (files containing the patterns) (Default: search in current working directory ".")
- OUTPUTFILENAME: Name of the output file to be created that will contain the histograms. Note that an exisiting file will be overwritten! The default behaviour is to use the PATTERN1 value with a possibly trailing _t removed and _hist.root appended.
- OUTPUTDIR: This optional argument sets the directory in which getHistogram writes its output histogram file (Default: Use the input directory INPUTDIR)
- MAXID: This optional argument determines the highest volume ID for which an output histogram is created. In total MAXID + 2 energy deposition histograms (for detectors 0 to MAXID, and a histogram called
sumwhich contains the sum of all other ones) are created. The optimum performance and memory usage can be obtained by numbering the sensitive volumes (usingG4SensitiveDetector::SetDetectorID(), see also 2.2 Sensitive Detectors) from 0 to MAXID. Otherwise,getHistogramwill create a lot of unnecessary histograms. For example, if MAXID=10 is set, but the simulation only contains two detectors with IDs 0 and 10, eight empty histograms from 1 to 9 will be in the output ofgetHistogram. On the other hand warnings will be printed when a volume is encountered whose number is larger than MAXID. (Default MAXID is 12) - MULTIPLICITY: Determines how many events per detector should be accumulated before adding the energy deposition to the histogram. This can be used, for example, to simulate higher multiplicity events in a detector: Imagine two photons with energies of 511 keV hit a detector and deposit all their energy. However, the two events cannot be distinguished by the detector due to pileup, so a single event with an energy of 1022 keV will be added to the spectrum in the experiment. Similarly, Geant4 simulates event by event. In order to simulate pileup of n events, set MULTIPLICITY to n. (Default: MULTIPLICITY is 1)
- BIN: Number of the histogram bin that should be printed to the screen while executing
getHistogram. This option was introduced because often, one is only interested in the content of a special bin in the histograms (for example the full-energy peak). If the histograms are defined such that bin3001contains the events with an energy deposition between2.9995 MeVand3.0005 MeVand so on, so there is an easy correspondence between bin number and energy. (The default for BIN is -1, disabling the output)
The options --silent and --addback do not have arguments. The former simply produces less verbose output when getHistogram is executed. The latter implements a simple add-back capability to sum up all energy depositions that happened during a single event. This is interesting, for example, when segmented detectors are used. In its current implementation, the add-back algorithm will accumulate all energy depositions in a single event, even if there was cross-talk between physically separated detectors. This may or may not be desired by the user. In order for the add-back to work, the parameter EVENT_ID must be written to the output files, of course (see also 2.6 Output File Format and 3.3 Build configuration).
A short example: The typical output of two different simulations on 2 threads each are the files
$ ls output
utr0_t0.root
utr0_t1.root
utr1_t0.root
utr1_t1.root
Assuming you would like to merge both threads of utr0 and write the accumulated histogram to hist.root, you execute
$ build/OutputProcessing/getHistogram -d output -t utr -p utr0 -q .root -o hist.rootThis will create an output file called hist.root with the desired histogram.
If, instead, you wanted to merge all ROOT files, do
$ build/OutputProcessing/getHistogram -d output -t utr -p utr -q .root -o hist.rootIn this simple example, already the first pattern uniquely identifies the files you want to merge. However, imagine there was a file utr0.txt in the same directory, then the second pattern could be used to exclude this.
Yet another possibility is that you would like to merge both threads of utr0 into one histogram, and both threads of utr1 into another one. The shell script loopGetHistogram.sh can be used for this task. Executing
$ cd output
$ build/OutputProcessing/loopGetHistogram 0 1 utr utrwould do just what is described above, creating the output files utr0.root and utr1.root.
A direct follow-up to getHistogram, HistogramToTxt.cpp takes a ROOT file that contains only 1D histograms (TH1 objects) and converts each histogram to a single text file. Executing
$ build/OutputProcessing/histogramToTxt --help
Usage: histogramToTxt [OPTION...] ROOT_FILE
Extract TH1 histograms from a ROOT file as separate txt histograms
-b, --begin=START Index of first histogram to extract (default: 0)
-c, --countsonly Only write bin contents (without energies)
(default: Off)
-e, --end=END Index of last histogram to extract, -1 to extract
to the last one (default: -1)
-f, --filename=PREFIX Output files' name prefix (default: ROOT_FILE's
filename without its extension)
-s, --skipempty Skip empty histograms (default: Off)
-?, --help Give this help list
--usage Give a short usage message
Mandatory or optional arguments to long options are also mandatory or optional
for any corresponding short options.shows how to use the script. For example
$ build/OutputProcessing/histogramToTxt utr0_hist.rootwould extract all TH1 histograms from the utr0_hist.root file created by getHistogram as utr0_hist_detN.txt files. Using the -c option allows for example to directly view those files in TV or HDTV as uncalibrated spectra.
The shell script loopHistogramToTxt.sh shows how to loop the script over a large number of files.
Refer to the next-to next section 5.5 fep_efficiency to see how to process these files even further.
MergeFiles creates a ROOT file which contains a TChain of multiple simulation output files. This makes it possible to access the data in all files as if they were in a single ROOT tree. MergeFiles recognizes similar arguments as GetHistogram (in fact, MergeFiles was created by 'cannibalizing' GetHistogram):
$ build/OutputProcessing/mergeFiles --help
Usage: mergeFiles [OPTION...] Merge ROOT output files
MergeFiles
-o OUTPUTFILENAME Output file name
-p PATTERN1 File name pattern 1
-q PATTERN2 File name pattern 2
-t TREENAME Name of tree
-?, --help Give this help list
--usage Give a short usage messageFor the meaning of the arguments, refer to the documentation of the GetHistogram script.
The TChain file can also be post-processed with the aforementioned scripts, in particular RootToTxt which cannot merge data on its own.
A follow-up to histogramToTxt, fep_efficiency can loop over two-column histogram files and extract the full-energy peak (FEP) efficiency, assuming that this is the content of the bin with the highest energy which has a nonzero content. Note that this may not always be what a user interprets as the 'efficiency' of a detector. A call of fep_efficiency without command-line arguments describes the usage in detail:
$ build/OutputProcessing/fep_efficiency
The script loops over text histograms [1] with names PREFIX<i>SUFFIX (where <i> denotes all integer numbers from START to STOP, including these limits), reads out the full-energy peak (FEP) content [2] and determines the FEP efficiency.
For example, the command
$ ./fep_efficiency.sh det0_utr 1 3 .txt 1000000
will loop over the following files:
det0_utr1.txt
det0_utr2.txt
det0_utr3.txt
The last argument denotes the number of simulated primary particles, which is needed to calculate the efficiency. If you do not know NSIM, simply enter an arbitrary value.
Two output files will be created, where the energies and the corresponding FEP counts/efficiencies are given in the first and second column. The number of simulated primary particles will be printed in the header.
PREFIX File name prefix
SUFFIX File name suffix
START Begin of file numbers
STOP End of file numbers
NSIM Number of simulated primary particles
[1] A text histogram is a two-column file which contains the energy in the first column and the number of counts in the second column. Such a file is returned by the histogramToTXT script of utr, for example.
[2] The full-energy peak in the histogram file is defined as the bin with the highest energy with a nonzero content.
Including fepefficiency, a complete toolchain exists for the simulation and extraction of FEP efficiencies. The typical workflow would be:
- Simulate the detection efficiency by looping over different source energies. It will be assumed that the simulated geometry contains detection volumes which are defined to be
EnergyDepositionSD(see also 2.2 Sensitive Detectors). If multiple volumes are used, the output of the volume identifier must be activated, of course (see also 2.6 Output File Format). This will create output filesutr<i>_t<t>.rootfiles, which contain the energy deposition in the corresponding volumes per event. The number<i>will correspond to a certain source energy. - Sort the energy deposition into histograms by using the getHistogram script, probably with the help of the
loopGetHistogram.shscript. ExecutingloopGetHistogram.shwill sum the single threads and create a set of files calledutr<i>.rootwhich containTH1ROOT histograms. - Convert the ROOT files to text histograms by using the histogramToTxt script, probably with the help of the
loopHistogramToTxt.shscript. This will create a set of files calleddet<j>_utr<i>.txt, where<j>corresponds to the ID of a detector. These files contain a two-column representation of the histograms. - Extract the FEP efficiency using the script described in this section.
To automate and systemize the workflow of conducting simulations with utr once the detector construction is implemented, a wrapper python script called utrwrapper.py was created in the OutputProcessing/ directory, which uses extended macro files to achieve this goal.
An extended macro file is a regular utr/GEANT4 macro file with a configuration header embedded as comment lines in the macro (lines proceeded by a '#').
utrwrapper.py reads this header and based on it prepares the simulation (e.g. creating directories, aborting on already existing output files, configuring utr with required build options and making it), conducts the simulation defined by the macro file (with required niceness, number of threads and output directory), and optionally does subsequent output processing (all steps are executed in the given order), while also optionally documenting all steps in a logfile.
Using utrwrapper.py with a proper extended macro file therefore allows to conduct (and log) the full simulation procedure in an easily reproducible way with a single command.
Executing
$ ./OutputProcessing/utrwrapper.py --help
usage: utrwrapper.py [-h] EXTENDEDMACROFILE
Run utr simulations controlled by extended macro files combining a utr macro
file with a configuration header
An extended macro file is a regular utr/GEANT4 macro file with a configuration
header embedded as comment lines in the macro (lines proceeded by a '#').
utrwrapper.py reads this header and based on it prepares the simulation
(e.g. creating directories, aborting on already existing output files, configuring
utr with required build options and making it), conducts the simulation defined
by the macro file (with required niceness, threads and output directory), and
optionally does subsequent output processing, while also optionally documenting
all steps in a logfile.
positional arguments:
EXTENDEDMACROFILE the extended macro file to process
optional arguments:
-h, --help show this help message and exit
Below is an example configuration header, illustrating its structure and
listing all available options with their effect and default values
#!/usr/bin/env utrwrapper.py
#[generalConfig] # Required section with general configuration
# # (all options are optional however)
#logging=True # Whether to create a logfile in the
# # output directory (Default: True)
#niceness=18 # Niceness to run utr with (Default: 18)
#threads=20 # Number of threads to run utr and make
# # with (Default: System's CPU count)
#utrPath=/path/to/utr # Path of utr's code (Default: Parent
# # directory of utrwrapper.py's directory)
#checkForExistingOutput=True # Whether to check for already existing
# # output files in the output directory
# # and potentially abort (Default: True)
#processOutput=True # Whether to process the output with
# # getHistogram and histogramToTxt after
# # the simulation ended (Default: True)
#outputDir=/path/to/utr/output # The output directory
#separateRawOutputAndHistograms=True # Whether to separate utr's output from
# # the processed output by two subfolders
# # (Raw_Events and Event_Histograms) in
# # the output directory (Default: True)
#cdToUtrPath=True # Whether to change the working directory
# # to utr's code directory and using all
# # other supplied paths relative to it
# # (Default: True)
#ensureTerminalMultiplexer=False # Whether to warn and abort if utrwrapper.py
# # is not run inside a tmux or GNU Screen
# # session (Default: False)
#cmakeArgs=--debug-output # Pure string of additional arguments to
# # cmake on utr, see also [utrBuildOptions]
# # section (Default: None)
#getHistogramArgs=-s # Pure string of additional arguments to
# # getHistogram, see also [getHistogramArgs]
# # section (Default: None)
#histogramToTxtArgs=--skipempty # Pure string of additional arguments to
# # histogramToTxt, see also [histogramToTxtArgs]
# # section (Default: None)
## Use multiple '#' for comments in the header (first '#' must not be indented!)
#[environmentVariables] # Semi-optional section of environment
# # variables to be supplied to the call
# # to utr (can be accessed in the
# # utr/GEANT4 macro by the /control/getEnv
# # command)
#filenamePrefix=Efficiency_ # Filename prefix of utr's output files,
# # required to identify output files when
# # processOutput or checkForExistingOutput
# # is True
#filenameSuffix= # Filename suffix of utr's output files,
# # required to identify output files when
# # processOutput or checkForExistingOutput
# # is True (Here: Suffix is an empty string
# # (no suffix), in such cases watch out to
# # not use the {filenameSuffix} variable in
# # the utr/GEANT4 macro, as GEANT4 cannot
# # handle aliases with an empty value!)
#myVar=Value # Example
#[utrBuildOptions] # Optional section with cmake build options
# # for utr of the form BUILDOPTION=VALUE
#CAMPAIGN=Campaign_2014_2015 # Example
#DETECTOR_CONSTRUCTION=150Sm # Example
#USE_TARGETS=ON # Example
#GENERATOR_ANGCORR=OFF # Example
#GENERATOR_ANGDIST=ON # Example
#ZERODEGREE_OFFSET=30 # Example
#[getHistogramArgs] # Optional section with additional longform
# # options (--LONGOPTION=VALUE) to getHistogram
# # of the form LONGOPTION=ARGUMENT
#maxenergy=10 # Example
#binning=2 # Example
#[histogramToTxtArgs] # Optional section with additional longform
# # options (--LONGOPTION=VALUE) to histogramToTxt
# # of the form LONGOPTION=ARGUMENT
#begin=1 # Example
#end=4 # Example
#countsonly= # Example
#START_OF_MACRO # Required magic string signaling the end of
# # the configuration header
#Here the actual utr/GEANT4 macro would startshows how to use the script. This usage message especially states the structure of the extended macro header along with all available options, their effects and default values.
Example extended macro files can be found in the macros/examples/ directory and be identified by their .xmac file extension.
To try utrwrapper.py, call it from a command line with one of the example extended macro files as its arguments, for example run ./OutputProcessing/utrwrapper.py macros/example/utrwrapper-efficiency-example.xmac.
For testing the AngularDistributionGenerator, a dedicated geometry can be found in /DetectorConstruction/unit_tests/AngularDistributionGenerator_Test/ and a macro file and output processing script are located in /unit_tests/AngularDistributionGenerator_Test/. The test geometry consists of a very small spherical particle source surrounded by a large hollow sphere which acts as a ParticleSD. Geantino particles emitted by this source and detected by the hollow sphere should have the desired angular distribution. This test was originally implemented to test the built-in angular distributions which are manually coded from the output of a computer algebra program, and to get a feeling of how large the value of W_max has to be.
In order to use the unit test, the following things have to be prepared:
- Build the correct geometry by setting the build variables
CAMPAIGNtounit_testsandDETECTOR_CONSTRUCTIONtoAngularDistributionGenerator_Test(see 3.2 Compilation). - Ensure that the momentum vectors of the particles are written to a ROOT file by enabling the correct flags in
ActionInitialization.hh(see 2.6 Output File Format) - Run a simulation with geantinos and the desired angular distribution. A sample macro is
/unit_tests/AngularDistributionGenerator/angdist_test.mac - Compile the analysis script
AngularDistributionGenerator_Test.cppin the same directory by typingmake. It can be executed with a number of simulation output files similar toGetHistogram(see 5. Output Processing).
When executed, the analysis script creates a file hist.root that contains a histogram in the (θ, φ) plane which shows the frequency of particles with a certain direction. This can already be visually compared to the shape of the continuous function that was used as an input. An example for a 0^+ -> 1^+ -> 0^+ cascade is shown below:
With the bad choice W_max == 1, the same analysis would result in the following histogram which is clearly different:
In order to have a more quantitative analysis, the histogram can also be fit with the input distribution as it is implemented in src/AngularDistribution.cc. For this purpose, AngularDistribution.hh is already included in AngularDistributionGenerator_Test.cpp.
To select a certain distribution, hard code the identifiers and parameters in the source code of the script where it says
//
// START OF USER-DEFINED OUTPUT
//
nstates = 3;
states[0] = 0.;
states[1] = 1.;
states[2] = 0.;
mix[0] = 0.;
mix[1] = 0.;
//
// END OF USER-DEFINED OUTPUT
//
and recompile afterwards. Running the script with the -f option (the only option that is different from GetHistogram) will fit the input distribution to the simulation output.
Now, by looking at the fit
and especially the fit residuals
one can see clear systematic deviations from the input distribution which are a clear indication that W_max == 1 is not a good choice for this distribution.
At the moment, the unit test for the AngularCorrelationGenerator is almost the same as for the AngularDistributionGenerator, except for the sample macro file and the ROOT processing script. The script has the additional parameter -n which allows to set the number of steps of the cascade that was used in the simulation to be able to sort different particles into different theta-phi histograms.
To test the physics processes of Geant4 and sensitive detector functionality of utr, a simple test geometry has been implemented. Almost all parts of the geometry are spherically symmetric to make it easy to study angular distributions of particles emitted by some process. At the origin, a cylindrical reaction target is placed. It is surrounded by three concentric spherical shells, representing each of the available detector types of utr (see 2.2 Sensitive Detectors). Beginning from the center, the order is ParticleSD, SecondarySD and EnergyDepositionSD. The first two detector types are nondestructive, therefore they are made of vacuum. The EnergyDepositionSD will only work if made of matter with which the particles can react.
The unit test can be activated by selecting the geometry in DetectorConstruction/unit_tests/Physics/ via CMake build variables (see 3.3 Build configuration). For a beam-on-target experiment, usage of a modified macros/examples/beam.mac macro is recommended. Feel free to play with different physics lists and materials.
Copyright (C) 2017-2019
U. Friman-Gayer ([email protected])
J. Kleemann ([email protected])
O. Papst ([email protected])
This code is distributed under the terms of the GNU General Public License v3 or later. See the COPYING file for more information.
We thank N. Michaelis for a detailed measurement of the DHIPS site and a preliminary implementation of the geometry.
We thank M. Schilling for implementing the DHIPS geometry and helpful suggestions.
We thank M. Peck for contributing photofission setups.
We thank M. Baumann, M. Beckstein, and D. Symochko for providing a Geant4 implementation and a technical drawing of the Galatea LaBr detectors.
We thank D. Savran for reporting and investigating architecture-dependent runtime errors.
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