A Monte Carlo code for AGATA based on Geant4 E.Farnea INFN Sezione - - PowerPoint PPT Presentation

A Monte Carlo code for AGATA based on Geant4

E.Farnea INFN Sezione di Padova, Italy

Why Geant4?

• The code is well mantained and in widespread use

Object-oriented, suitable for big projects

• C++ based
• Leaves the user responsibility on geometry definition,

detector response and read out, event generation

Possibility to import complex geometries from CAD systems?

Philosophy of the program

Command-line UI based on tcsh

Built-in commands to change simulation parameters without recompiling

Additional possibilities through switches at the start

• f the program

Sequences of commands automatized through macro files

Graphics enabled only when needed

Concentrate on the production of list-mode output files rather than making on-line analysis

Class structure of the program

Agata

*Agata RunAction *Agata EventAction Agata PhysicsList Agata VisManager Agata

SteppingAction

*Agata Analysis *Agata

GeneratorGamma

*Agata

GeneratorNeutron

*Agata

GeneratorAction

CSpec1D CSpec2D Agata

GeneratorOmega

Agata

SteppingOmega

*Agata Detector Construction *Agata Detector Shell *Agata Detector Simple *Agata

SensitiveDetector

Agata

DetectorReadOut

*Agata

DetectorArray

Agata HitDetector CConvex Polyhedron Agata DummySD

Messenger classes are not shown!

*Agata

GeneratorEmitter

* Possibility to change parameters via a messenger class

*Agata

DetectorAncillary

AgataDetectorConstruction

Generate here only material definition, experimental hall and other passive objects (target, reaction chamber)

Handles actual detector arrangement using auxiliary classes

Implemented geometries selectable via switch at the start of the main program: single germanium detector (AgataDetectorSimple), germanium 4π shell (AgataDetectorShell) and the AGATA array (AgataDetectorArray)

• ✶

• ❀

γ

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γ

• ❀

γ

• ❀

γ

• ❚

• ❀

γ

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γ

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γ

• ❀

γ

AgataDetectorArray

Irregular polyhedra generated with the CConvexPolyhedron class (D.Bazzacco)

Actual detector shape can consider the intersection of such polyhedra with a closed-end cylinder

Vertexes of the polyhedra calculated with an external program (MarsView by D.Bazzacco)

Available data files for the geometries with 180 crystals and 120 crystals (grouped in triple or quadruple clusters, or with the shape used in GRETA)

Possibility to add extra passive materials to emulate an ancillary device (AgataDetectorAncillary)

Start with a platonic solid e.g. an icosahedron On its faces, draw a regular pattern of triangles grouped as hexagons and pentagons. E.g. with 110 hexagons and (always) 12 pentagons Project the faces on the enclosing sphere; flatten the hexagons.

A radial projection of the spherical tiling generates the shapes of the detectors. Ball with 180 hexagons. Space for encapsulation and canning obtained cutting the

• crystals. In the example 3

crystals form a triple cluster Add encapsulation and part of the cryostats for realistic MC simulations Al capsules 0.7 mm spacing 0.8 mm thick Al canning 2 mm spacing 2 mm thick

Configuration A=180

Configuration A=180 – solids

Solid 1 Solid 2 Solid 3

Configuration A=120

Configuration A=120 – solids

Solid 1 Solid 2

ε

ε

To reduce cost of germanium, A-180 could be squeezed to similar size as A-120. Efficiency reduces also but all nice symmetries remain; smaller crystals simplify PSA .

γ γ

Ω

γ

γ

γ

γ

AGATA Crystals: 10 cm long, 8 cm diameter (at the back). Balanced volumes. Arranged in triple-clusters with capsules and cryostats

• Eff. (%)

P/T (%)

AgataDetectorReadOut

An alternative segmented read out geometry can be enabled

The effective shape

• f the segments can

be approximated with “elementary” shapes

200 dx dy dz total Segmentation: 10, 10, 4x17.5 mm

Segmented polyhedron The whole array (A=120)

AgataSensitiveDetector

• Standard Geant4 tracking: follow the particles

from the last created one to the primary particle

Possibility to overcome this tracking order for gammas and neutrons (ignoring the secondary particles produced)

AgataPhysicsList

Generation of gammas (photoelectric effect, Compton scattering, pair production, Rayleigh scattering)

Possibility to consider the Compton profile (using the G4LECS package, see:

Generation of neutrons (elastic and inelastic scattering, capture)

Generation of other particles needed for these processes (leptons and hadrons)

AgataGeneratorAction

Cascade modelled as Mn neutrons followed by Mγ γ

High-multiplicity events are emulated by packing single-particle events generated in the proper order

Use auxiliary classes to handle time and position (AgataGeneratorEmitter), direction and energy of the emission (AgataGeneratorGamma, AgataGeneratorNeutron)

AgataGeneratorEmitter

Possibility to choose between point and diffused source

Possibility to consider a recoil velocity with variable direction and module

Possibility to consider delayed radiation with displacement of the source

AgataGeneratorGamma

Several centre of mass spectra available: monochromatic, regular band, irregular band, flat distribution, statistical spectrum

Laboratory energy and direction are calculated using the proper relativistic transformations, starting from an isotropical centre of mass distribution (with the possibility to limit the angular region of emission)

Linear polarization can be optionally considered (switch at the start of the program)

AgataGeneratorNeutron

Possibility to choose between monochromatic and evaporative centre of mass spectra

Laboratory energy and direction are calculated using the proper relativistic transformations, starting from an isotropical centre of mass distribution (with the possibility to limit the angular region of emission)

Program configuration

The program is being developed on a PC running Linux (RedHat 9.0)

Compiler: gcc 3.2

CLHEP version: 1.8.0.0

Geant4 version: 4.5.1 with update patch and two modified classes (G4VIntersectionSolid, G4AssemblyDetector) plus G4LECS package

Minor problems in moving from Geant4.5.0 to 4.5.1

Things to do ...

The work is still in progress!

Test other geometries

Interaction with tracking algorithms

Interaction with other groups (ancillaries, data analysis, mechanical design, ...)

Documentation!

If interested in the program for further developments, contact farnea@pd.infn.it or bazzacco@pd.infn.it