Hands on 2: a simple setup

Introduction

In this hands on you will learn: Note: We do not use Qt GUI for HandsON2.

The code for this hands-on session is here ( for your reference, the complete solution is also availavble here). Copy the the tar ball to your local area.

  $ cd <tutorial> #change to your working directory
  $ tar xzf HandsOn2.tar.gz
  $ cd HandsOn2
  $ ls #Take a look at the files

Follow the instructions of Hands On 1 to configure with cmake the example and build it.
Try out the application:

  $ cmake .
  $ make -j 2 -f Makefile
  $ ./SLACtut

The following should appear:


The default behavior of the application when started without command line arguments is to start the (G)UI (if enabled). You should find Idle> prompt on your terminal screen. Familiarize with the Geant4 UI.

Exercise 0.a:

Question 1: Try ls, help and help <UI_command>.
Question 2: Run 10 events.

  Idle> /run/beamOn 10
  Idle> exit

Exercise 0.b:

Now run the application with a macro file as command line argument:

  $ ./SLACtut run1.mac


Check the content of the macro file run1.mac, start the application again interactively and using the help system check the syntax of the few commands used in the macro file.
Note: Other macro files in the HandsOn2 direcory do not work until you finish all the exercises.

Defining Materials

Important note

Throughout this tutorial, where to edit the code is clearly marked in the corresponding file. Open the specified file and search a comment line that matches to the exercise name. That is the place you should add your code. If you are working on Exercise X.Y, here is the place.

File name to be edited
  //============================
  // Exercise X.Y
      put your code here

Exercise 1.a:

In this example, we have a specific method DetectorConstruction::ConstructMaterials() where all materials that are used in the application are built. Such method is not mandatory, but it may help to organize your code.
Create a CsI (Cesium Iodide) material starting from the elements.

Some of its properties:

After adding the needed code, re-compile (no need to do the cmake step again) and start once more the application. Note that at the moment we have created the material (and so Geant4 kernel knows about it), but it is not yet used in any geometry element.
Observe Geant4 output, at the beginning of the application the list of materials will be shown, starting from the line The materials defined are : . At the end of the method DetectorConstruction::ConstructMaterials() there is a line that prints on screen the complete list of defined materials. Note the paragraph relative to CsI and its properties.
The UI command: /material/g4/printMaterial CsI can be issued at run-time to print the details of CsI. Check the other UI commands available in the /material directory.

Solution

DetectorConstruction.cc File:
  G4Element* el_i = new G4Element("Iodine","I", 53,126.9*g/mole);
  G4Element* el_cs = new G4Element("Cesium","Cs",55,132.9*g/mole);
  G4Material* mat_csi = new G4Material("CsI",4.51*g/cm3,2);
  mat_csi->AddElement(el_i,1);
  mat_csi->AddElement(el_cs,1);

Exercise 1.b:

Use NIST database to create Lead material.

Hint: You can use UI command /material/nist/listMaterials to dump on screen the list of all Gean4-NIST compounds" materials. Search for the name relative to lead.
Build again the application and run it again. Note that now the list of materials includes lead element with all isotopes with natural abundances.
Hint: You can always use the command /material/g4/printMaterial <name> to print interactively the information on a specific material of your interest.

Solution

DetectorConstruction.cc File:
 nistManager->FindOrBuildMaterial("G4_Pb");

A very simple geometry

In this example we will create a first geometry element. The goal of this exercise is to show how to define a shape, a logical volume and a placement.

Exercise 2.a

Add a box of to the setup.

The box has full dimensions (X times Y times Z): 300x60x100 cm, select CsI as material. Place the box inside the logical volume second arm. It should be placed at the very back of this mother volume. At the end of the tutorials this simple box will become a calorimeter.
Re-compile and check that you obtain the correct behavior:


Solution

DetectorConstruction.cc File:
  G4Material* material = G4Material::GetMaterial("CsI");
  G4VSolid* hadCalorimeterSolid = new G4Box("HadCalorimeterBox",1.5*m,30.*cm,50.*cm);
  G4LogicalVolume* hadCalorimeterLogical = new G4LogicalVolume(hadCalorimeterSolid,material,"HadCalorimeterLogical");
  new G4PVPlacement(0,G4ThreeVector(0.,0.,3.*m),hadCalorimeterLogical,"HadCalorimeterPhysical",secondArmLogical,false,0,checkOverlaps);

Exercise 2.b

Change material of the box and observe effect on physics simulation.

Modify the material of the box: instead of CsI, use the material scintillator. Simulate a single electron. Note how the material affects the shower dimensions:



The material is already created in the ConstructMaterials method, it has a long name becasue it is a particular type of plastic. You need just to retrieve it by name when using it in the G4LogicalVolume.

Command line based scoring

In this exercise we will collect simulation information using command line scoring. A scoring mesh will be defined on top of the volume created in Exercise 2.a, different quantities will be recorded, and we will show how to display and save in a text file.

Exercise 3.a

Enable command line scoring.

Instantiate a scoring manager in the main() function.

Solution

tutorial.cc File:
  // Activate UI-command base scorer
  G4ScoringManager * scManager = G4ScoringManager::GetScoringManager();
  scManager->SetVerboseLevel(1);

Exercise 3.b

Score some quantities: energy deposit, number of steps.

Using only UI commands create a scoring box mesh that is placed on top of the calorimeter box. The mesh should have the same dimension as the calorimeter and have (X times Y times Z) 30x6x10 voxels. Score the following quantities:

Dump the scored quantities to files and verify the content.
Hint: use the help command to understand the format of command line scoring UI commands.

Starting from the content of the file scoring.mac reproduce in an interactive session the various steps used to score the quantities. Some of the UI commands used here depends on the UI commands used before. For example the commands used to define a particle filter are used in combination with the preceding command defining the quantity to score. The command /score/close signals that all scoring volumes and associated quantities are now completed and configured.

There are two separate concepts to grasp when scoring: one is the scoring mesh (e.g. the shape, dimension and number of bins of the used 3D grid), the other is the list of quantities measured in each cell of the grid.
You can have multiple quantities associated to a given mesh, but you can also have multiple meshes in the same application even with different geometries and possibily overlapping.

Solution

The macro scoring.mac shows all the UI commands needed in this exercise. It can be used directly to create the output file:
  $ ./SLACtut scoring.mac
Note:Reduce the number of simulated events (default 2000) if the simulation takes too long.

scoring.mac File:
 /run/initialize
 ########################################
 #
 # define scoring mesh
 #
 /score/create/boxMesh boxMesh_1
 #
 #Create a mesh large as the box
 /score/mesh/boxSize 150. 30. 50. cm
 #Position it over the box
 /score/mesh/translate/xyz 0 0 8 m
 #mesh voxel size of 5cm
 /score/mesh/nBin 30 6 10
 # All these quantities are associated
 # with the mesh with name "boxMesh_1"
 /score/quantity/energyDeposit eDep
 /score/quantity/nOfStep nOfStepGamma
 /score/filter/particle gammaFilter gamma
 /score/quantity/nOfStep nOfStepEMinus
 /score/filter/particle eMinusFilter e-
 /score/quantity/nOfStep nOfStepEPlus
 /score/filter/particle ePlusFilter e+
 #
 /score/close
 #
 /run/verbose 1
 /gun/particle e-
 /run/beamOn 2000
 ########################################
 #
 # Dump scores to a file: tell G4 which
 # mesh and which quantity should go in the output file
 #
 /score/dumpQuantityToFile boxMesh_1 nOfStepGamma nOfStepGamma.txt

Exercise 3.c

Visualize scored quantities.

Using UI commands draw on the screen different scored quantities. For example the energy deposit looks like:

Solution

The macro file draw.mac shows how to draw scored quantities, in also shows how to draw slices using loops in UI commands.
This macro should be executed after scoring.mac:
  $ ./SLACtut
  Idle> /control/execute scoring.mac
  Idle> /control/execute draw.mac


draw.mac File:
 ########################################
 #
 # drawing projections
 #
 /score/drawProjection boxMesh_1 eDep
 /score/drawProjection boxMesh_1 nOfStepGamma
 /score/drawProjection boxMesh_1 nOfStepEMinus
 /score/drawProjection boxMesh_1 nOfStepEPlus
 #
 ########################################
 #
 # drawing slices
 #
 /vis/scene/create
 /vis/sceneHandler/attach scene-1
 /score/colorMap/setMinMax ! 0. 800.
 /control/loop drawSlice.mac iColumn 0 10 3

The macro files perform several views at the same time (/score/drawProjection commands), try out the views one at the time in the command line.

Created by: Andrea Dotti (adotti AT slac DOT stanford DOT edu) May 2018
Updated by: Makoto Asai (asai AT slac DOT stanford DOT edu) August 2019