GEANT4 Introductory Course

Transcription

1 GEANT4 Introductory Course Instituto de Estudos Avançados Instituto Tecnológico de Aeronáutica, São José Dos Campos, Brazil July 28 th August 1 st, 2014 Advanced Features Miguel A. Cortés-Giraldo adaptation of original lectures by Makoto Asai (SLAC) and Vladimir Ivanchenko (CERN)

2 Outline 2 Geometry Physical Volumes Parameterized Replica Nested parameterization Touchable Geometry checking tools Geometry optimization ( voxelization ) Parallel geometry Moving objects GDML/CAD interface Particle Generator IAEAphsp classes

3 G4PVParameterised 3 G4PVParameterised(const G4String& pname, G4LogicalVolume* plogical, G4LogicalVolume* pmother, const EAxis paxis, const G4int nreplicas, G4VPVParameterisation* pparam G4bool psurfchk=false); Replicates the volume nreplicas times using the parameterization pparam, within the mother volume pmother. paxis is a suggestion to the navigator along which Cartesian axis replication of parameterized volumes dominates. kxaxis, kyaxis, kzaxis : one-dimensional optimization kundefined : three-dimensional optimization

4 Parameterized Physical Volumes 4 User should implement a class derived from G4VPVParameterisation abstract base class and define following as a function of copy number: where it is positioned (transformation, rotation) Optional: the size of the solid (dimensions) the type of the solid, material, sensitivity, vis attributes All daughters must be fully contained in the mother Daughters should not overlap to each other. Limitations: Applies to simple CSG solids only Granddaughter volumes allowed only for special cases Consider parameterised volumes as leaf volumes 3 Typical use-cases: Complex detectors with large repetition of volumes, regular or irregular Medical applications the material in animal tissue is measured as cubes with varying material

5 G4PVParameterized: Example 1 5 G4VSolid* solidchamber = new G4Box("chamber", 100*cm, 100*cm, 10*cm); G4LogicalVolume* logicchamber = new G4LogicalVolume (solidchamber, ChamberMater, "Chamber", 0, 0, 0); G4VPVParameterisation* chamberparam = new ChamberParameterisation(); G4VPhysicalVolume* physchamber = new G4PVParameterised("Chamber", logicchamber, logicmother, kzaxis, NbOfChambers, chamberparam);

6 G4PVParameterized: Example 2 6 class ChamberParameterisation : public G4VPVParameterisation { public: ChamberParameterisation(); virtual ~ChamberParameterisation(); virtual void ComputeTransformation // position, rotation (const G4int copyno, G4VPhysicalVolume* physvol) const; }; virtual void ComputeDimensions // size (G4Box& trackerlayer, const G4int copyno, const G4VPhysicalVolume* physvol) const; virtual G4VSolid* ComputeSolid // shape (const G4int copyno, G4VPhysicalVolume* physvol); virtual G4Material* ComputeMaterial // mat, sensitivity, visatt (const G4int copyno, G4VPhysicalVolume* physvol, const G4VTouchable *parenttouch=0); // G4VTouchable should *not* be used for ordinary // parameterization

7 G4PVParameterized: Example 3 7 void ChamberParameterisation::ComputeTransformation (const G4int copyno, G4VPhysicalVolume* physvol) const { G4double Xposition = // w.r.t. copyno G4ThreeVector origin(xposition,yposition,zposition); physvol->settranslation(origin); physvol->setrotation(0); } void ChamberParameterisation::ComputeDimensions (G4Box& trackerchamber, const G4int copyno, const G4VPhysicalVolume* physvol) const { G4double XhalfLength = // w.r.t. copyno trackerchamber.setxhalflength(xhalflength); trackerchamber.setyhalflength(yhalflength); trackerchamber.setzhalflength(zhalflength); }

8 G4PVParameterized: Example 4 8 G4VSolid* ChamberParameterisation::ComputeSolid (const G4int copyno, G4VPhysicalVolume* physvol) { G4VSolid* solid; if(copyno == ) solid = mybox; else if(copyno == ) solid = mytubs; return solid; } G4Material* ComputeMaterial // material, sensitivity, visatt (const G4int copyno, G4VPhysicalVolume* physvol, const G4VTouchable *parenttouch=0); { G4Material* mat; if(copyno == ) { mat = material1; physvol->getlogicalvolume()->setvisattributes( att1 ); } return mat; }

9 Outline 9 Geometry Physical Volumes Parameterized Replica Nested parameterization Touchable Geometry checking tools Geometry optimization ( voxelization ) Parallel geometry Moving objects GDML/CAD interface Particle Generator IAEAphsp classes

10 Replicated Volumes 10 The mother volume is completely filled with replicas, all of which are the same size (width) and shape. Replication may occur along: Cartesian axes (X, Y, Z) slices are considered perpendicular to the axis of replication Coordinate system at the center of each replica a daughter logical volume to be replicated Radial axis (Rho) cons/tubs sections centered on the origin and un-rotated Coordinate system same as the mother Phi axis (Phi) phi sections or wedges, of cons/tubs form Coordinate system rotated such as that the X axis bisects the angle made by each wedge mother volume

11 G4PVReplica 11 G4PVReplica(const G4String &pname, G4LogicalVolume *plogical, G4LogicalVolume *pmother, const EAxis paxis, const G4int nreplicas, const G4double width, const G4double offset=0.); offset may be used only for tube/cone segment. Features and restrictions: Replicas can be placed inside other replicas. Normal placement volumes can be placed inside replicas, assuming no intersection/overlaps with the mother volume or with other replicas. No volume can be placed inside a radial replication. Parameterized volumes cannot be placed inside a replica.

12 Replica Axis, Width, Offset Cartesian axes - kxaxis, kyaxis, kzaxis Center of n-th daughter is given as -width*(nreplicas-1)*0.5+n*width Offset shall not be used 12 width Radial axis - kraxis Center of n-th daughter is given as width*(n+0.5)+offset Offset must be the inner radius of the mother Phi axis - kphi Center of n-th daughter is given as width*(n+0.5)+offset Offset must be the starting angle of the mother width width offset offset

13 G4PVReplica: Example 13 G4double tube_dphi = 2.* M_PI * rad; G4VSolid* tube = new G4Tubs("tube",20*cm,50*cm,30*cm,0.,tube_dPhi); G4LogicalVolume * tube_log = new G4LogicalVolume(tube, Air, "tubel", 0, 0, 0); G4VPhysicalVolume* tube_phys = new G4PVPlacement(0,G4ThreeVector(-200.*cm,0.,0.), "tubep", tube_log, world_phys, false, 0); G4double divided_tube_dphi = tube_dphi/6.; G4VSolid* div_tube = new G4Tubs("div_tube", 20*cm, 50*cm, 30*cm, -divided_tube_dphi/2., divided_tube_dphi); G4LogicalVolume* div_tube_log = new G4LogicalVolume(div_tube,Pb,"div_tubeL",0,0,0); G4VPhysicalVolume* div_tube_phys = new G4PVReplica("div_tube_phys", div_tube_log, tube_log, kphi, 6, divided_tube_dphi);

14 Outline 14 Geometry Physical Volumes Parameterized Replica Nested parameterization Touchable Geometry checking tools Geometry optimization ( voxelization ) Parallel geometry Moving objects GDML/CAD interface Particle Generator IAEAphsp classes

15 Nested Parameterization 15 Suppose your geometry has three-dimensional regular repetition of same shape and size of volumes without gaps between volumes. And material of such volumes are changing according to the position. E.g. voxels made by CT Scan data (DICOM) Instead of direct three-dimensional parameterized volume, use replicas for the first and second axes sequentially, and then use one-dimensional parameterization along the third axis. It requires much less memory for geometry optimization and gives much faster navigation for ultra-large number of voxels.

16 Nested Parameterization 16 Given geometry is defined as two sequential replicas and then one-dimensional parameterization, Material of a voxel must be parameterized not only by the copy number of the voxel, but also by the copy numbers of ancestors G4VNestedParameterisation is a special parameterization class derived from G4VPVParameterisation base class. ComputeMaterial() method of G4VNestedParameterisation has a touchable object of the parent physical volume, in addition to the copy number of the voxel. Index of first axis = thetouchable->getcopynumber(1); Index of second axis = thetouchable->getcopynumber(0); Index of third axis = copy number 0

17 G4VNestedParameterization 17 G4VNestedParameterisation is a kind of G4VPVParameterization. It can be used as an argument of G4PVParameterised. All other arguments of G4PVParameterised are unaffected. Nested parameterization of placement volume is not supported. All levels used as indices of material must be repeated volume. There cannot be a level of placement volume in between.

18 Outline 18 Geometry Physical Volumes Parameterized Replica Nested parameterization Touchable Geometry checking tools Geometry optimization ( voxelization ) Parallel geometry Moving objects GDML/CAD interface Particle Generator IAEAphsp classes

19 Step Point and Touchable 19 As mentioned already, G4Step has two G4StepPoint objects as its starting and ending points. All the geometrical information of the particular step should be taken from PreStepPoint. Geometrical information associated with G4Track is identical to PostStepPoint. Each G4StepPoint object has: Position in world coordinate system Global and local time Material G4TouchableHistory for geometrical information. G4TouchableHistory object is a vector of information for each geometrical hierarchy: copy number transformation / rotation to its mother

20 Copy Number 20 Suppose a phantom is made of 4x5 cells. and it is implemented by two levels of replica. 0 1 CopyNo 2 = In reality, there is only one physical volume object for each level. Its position is parameterized by its copy number. 0 1 CopyNo 2 = To get the copy number of each level, suppose what happens if a step belongs to two cells. Remember geometrical information in G4Track is identical to "PostStepPoint" CopyNo 2 = 2 CopyNo 2 = You cannot get the correct copy number for "PreStepPoint" if you directly access to the physical volume. Use touchable to get the proper copy number, transform matrix, etc.

21 Touchable 21 G4TouchableHistory has information of geometrical hierarchy of the point. G4Step* astep; G4StepPoint* presteppoint = astep->getpresteppoint(); G4TouchableHistory* thetouchable = (G4TouchableHistory*)(preStepPoint->GetTouchable()); G4int copyno = thetouchable->getvolume()->getcopyno(); G4int mothercopyno = thetouchable->getvolume(1)->getcopyno(); G4int grandmothercopyno = thetouchable->getvolume(2)->getcopyno(); G4ThreeVector worldpos = presteppoint->getposition(); G4ThreeVector localpos = thetouchable->gethistory() ->GetTopTransform().TransformPoint(worldPos);

22 Outline 22 Geometry Physical Volumes Parameterized Replica Nested parameterization Touchable Geometry checking tools Geometry optimization ( voxelization ) Parallel geometry Moving objects GDML/CAD interface Particle Generator IAEAphsp classes

23 Debugging Geometries 23 A protruding volume is a contained daughter volume which actually protrudes from its mother volume. Volumes are also often positioned in a same volume with the intent of not provoking intersections between themselves. When volumes in a common mother actually intersect themselves are defined as overlapping. Geant4 does not allow for malformed geometries, neither protruding nor overlapping. The behavior of navigation is unpredictable for such cases. The problem of detecting overlaps between volumes is bounded by the complexity of the solid models description. Utilities are provided for detecting wrong positioning: Optional checks at construction Kernel run-time commands Graphical tools (DAVID, OLAP) protruding overlapping

24 Optional Checks at Construction 24 Constructors of G4PVPlacement and G4PVParameterised have an optional argument, psurfchk. G4PVPlacement(G4RotationMatrix* prot, const G4ThreeVector &tlate, G4LogicalVolume *pdaughterlogical, const G4String &pname, G4LogicalVolume *pmotherlogical, G4bool pmany, G4int pcopyno, G4bool psurfchk=false); If this flag is true, overlap check is done at the construction. Some number of points are randomly sampled on the surface of creating volume. Each of these points are examined If it is outside of the mother volume, or If it is inside of already existing other volumes in the same mother volume. This check requires lots of CPU time, but it is worth to try at least once when you implement your geometry of some complexity.

25 Outline 25 Geometry Physical Volumes Parameterized Replica Nested parameterization Touchable Geometry checking tools Geometry optimization ( voxelization ) Parallel geometry Moving objects GDML/CAD interface Particle Generator IAEAphsp classes

26 Smart Voxelization 26 In case of other Monte Carlo tools, the user had to carefully implement his/her geometry to maximize the performance of geometrical navigation. While in Geant4, user s geometry is automatically optimized to most suitable to the navigation. "Voxelization" For each mother volume, one-dimensional virtual division is performed. Subdivisions (slices) containing same volumes are gathered into one. Additional division again using second and/or third Cartesian axes, if needed. "Smart voxels" are computed at initialisation time When the detector geometry is closed Does not require large memory or computing resources At tracking time, searching is done in a hierarchy of virtual divisions

27 Detector Description Tuning 27 Some geometry topologies may require special tuning for ideal and efficient optimisation for example: a dense nucleus of volumes included in very large mother volume Granularity of voxelisation can be explicitly set Methods Set/GetSmartless() from G4LogicalVolume Critical regions for optimisation can be detected Helper class G4SmartVoxelStat for monitoring time spent in detector geometry optimisation Automatically activated if /run/verbose greater than 1 Percent Memory Heads Nodes Pointers Total CPU Volume k Calorimeter k Layer

28 Outline 28 Geometry Physical Volumes Parameterized Replica Nested parameterization Touchable Geometry checking tools Geometry optimization ( voxelization ) Parallel geometry Moving objects GDML/CAD interface Particle Generator IAEAphsp classes

29 Parallel Navigation 29 Occasionally, it is not straightforward to define sensitivity, importance or envelope to be assigned to volumes in the mass geometry. Typically a geometry built machinery by CAD, GDML, DICOM, etc. has this difficulty. New parallel navigation functionality allows the user to define more than one worlds simultaneously. New G4Transportation process sees all worlds simultaneously. A step is limited not only by the boundaries of the mass geometry but also by the boundaries of parallel geometries. Materials, production thresholds and EM field are used only from the mass geometry. In a parallel world, the user can define volumes in arbitrary manner with sensitivity, regions with shower parameterization, and/or importance field for biasing. Volumes in different worlds may overlap.

30 examplen07 30 Mass geometry: Sandwich of rectangular absorbers and scintilators Parallel scoring geometry: Cylindrical layers

31 Outline 31 Geometry Physical Volumes Parameterized Replica Nested parameterization Touchable Geometry checking tools Geometry optimization ( voxelization ) Parallel geometry Moving objects GDML/CAD interface Particle Generator IAEAphsp classes

32 Moving Objects 32 In some applications, it is essential to simulate the movement of some volumes. E.g. particle therapy simulation Geant4 can deal with moving volume In case speed of the moving volume is slow enough compared to speed of elementary particles, so that you can assume the position of moving volume is still within one event. Two tips to simulate moving objects: 1. Use parameterized volume to represent the moving volume. 2. Do not optimize (voxelize) the mother volume of the moving volume(s). If moving volume gets out of the original optimized voxel, the navigator gets lost.

33 4-D Radiotherapy Treatment Plan Source: Lei Xing, Stanford University Ion chamber 33 Lower Jaws Upper Jaws MLC April, 2011, Geant4 Geometry

34 Outline 34 Geometry Physical Volumes Parameterized Replica Nested parameterization Touchable Geometry checking tools Geometry optimization ( voxelization ) Parallel geometry Moving objects GDML/CAD interface Particle Generator IAEAphsp classes

35 GDML and CAD Interfaces 35 Up to now, the course has shown how to define materials and volumes from C++. This part of slides shows some alternate ways to define geometry at runtime by providing a file-based detector description. Silicon Pixel & Microstrip Tracker for Collider Detector N. Graf, J. McCormick, LCDD, SLAC

36 GDML: Geometrical Description Modeling Language 36 An XML-based language designed as an application independent persistent format for describing the geometries of detectors. Implements geometry trees which correspond to the hierarchy of volumes a detector geometry can be composed of Allows materials to be defined and solids to be positioned Because it is pure XML, GDML can be used universally Not just for Geant4 Can be format for interchanging geometries among different applications. Can be used to translate CAD geometries to Geant4 XML is simple Rigid set of rules, self-describing data validated against schema XML is extensible Easy to add custom features, data types XML is Interoperable to OS s, languages, applications XML has hierarchical structure Appropriate for Object-Oriented programming Detector/sub-detector relationships

37 Part of GDML Structure 37 Simple Elements <element Z="8" formula="o" name="oxygen" > <atom value="16" /> </element> Material by number of atoms ( molecule ) <material name="water" formula="h2o"> <D value="1.0" /> <composite n="2" ref="hydrogen" /> <composite n="1" ref="oxygen" /> </material> Material as a fractional mixture of elements or materials, ( compound ): <material formula="air" name="air" > <D value=" " /> <fraction n="0.7" ref="nitrogen" /> <fraction n="0.3" ref="oxygen" /> </material>

38 GDML Solids 38 Box Cone Segment Ellipsoid Elliptical Tube Elliptical Cone Orb Paraboloid Parallelepiped Polycone Polyhedron Sphere Torus Segment Trapezoid (x&y vary along z) General Trapezoid Tube with Hyperbolic Profile Cut Tube Tube Segment Twisted Box Twisted Trapezoid Twisted General Trapezoid Twisted Tube Segment Extruded Solid Tessellated Solid Tetrahedron

39 Importing GDML File 39 GDML files can be directly imported into Geant4 geometry, using the GDML plug-in: #include G4GDMLParser.hh Generally you will want to put the following lines into your DetectorConstruction class: G4GDMLParser parser; parser.read( geometryfile.gdml ); G4VphysicalVolume* W=parser.GetWorldVolume(); To include the Geant4 module for GDML, Install the XercesC parser (version or 3.0.0) Set appropriate environment variables when G4 libraries are built. Examples available in: $G4INSTALL/examples/extended/persistency/gdml

40 Converting STEP to GDML 40 Imperfect, but still helpful solutions are tools to convert STEP to GDML and provide the user a way to add materials information There are two cases where existing CAD programs have added GDML export features. Since these CAD programs can also read in STEP, they can be used as STEP to GDML converters. (Neither option is free, neither option works perfectly) ST-Viewer FastRad GDML export extension was funded by European Space Agency Not free except for limited, trial mode that can handle only a small number of volumes Discussion of these solutions takes place in the Geant4 Persistency forum: Useful technical note: Linking computer-aided design (CAD) to Geant4-based Monte Carlo simulations for precise implementation of complex treatment head geometries., Constantin et. al., Phys Med Biol Apr 21;55(8):N Epub 2010 Mar 26

41 Outline 41 Geometry Physical Volumes Parameterized Replica Nested parameterization Touchable Geometry checking tools Geometry optimization ( voxelization ) Parallel geometry Moving objects GDML/CAD interface Particle Generator IAEAphsp classes

42 Phase-Space Files in IAEA Format 42 Phase-Space (phsp) File: is a collection of a set of data corresponding to particles crossing a given plane, usually knows as phase-space plane or scoring plane. The variables stored are: Position Coordinates. Momentum Direction Cosines. Kinetic Energy. Statistical Weight. Other variables (n_stat, latch...) Phsp files are a powerful utility to perform Monte Carlo simulations in medical field; the most popular codes (EGSNRC, PENELOPE) include interfaces to use them. This tool is provided externally to the Geant4 official release.

43 The Phase-Space Project of the IAEA 43

44 Design of the G4IAEAphsp Classes 44 Stand-alone set of classes developed for GEANT4. This ensures portability and compatibility with future versions of the IAEA routines. M. A. Cortés-Giraldo et al., Int. J. Radiat. Biol. 88: (2012)

45 G4IAEAphspReader 45 collimator gantry

46 Thanks for your attention 46