geant4.ciemat-051122

7/27/2019 GEANT4.CIEMAT-051122

http://slidepdf.com/reader/full/geant4ciemat-051122 1/54

Pedro Arce Introducción a GEANT4 1

Introducción a GEANT4:

componentes

http://geant4.cern.ch

Pedro Arce Dubois

CIEMAT, Madrid

- -

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Outline

Geometry

Magnetic field

Particle generator

G4Run/G4Event/G4Track/G4Step /G4Trajectory

Sensitive detector

Electromagnetic physics: standard

Electromagnetic physics: low energy (J.M. Pérez)

Production cuts

User interface

Visualisation

Hadronic physics

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Geometry

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G4VSolid

= solid shape + dimensions

CSG (Constructed Solid Geometry): G4Box,

G4Cons, G4Trap, G4Sphere, G4Polycone, etc.

BREP (Boundary REPresented):

G4BREPSolidPolycone, G4BSplineSurface, etc. (muchslower navigation)

BOOLEAN: a solid is made adding, substracting or

intersecting two

STEP interface: to import BREPs from CAD

systems

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G4LogicalVolume

Contains all information of a detector element exceptposition

Minimum: solid + material

Sensitive detector

Visualisation

Magnetic field

User limits

Parameterisations of physics

...

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G4VPhysicalVolume

Information about placement of a volume

Several times of placement: G4PVPlacement

• Is is a volume instance positioned once in a mother

G4PVParameterized

• Parameterized by the copy number

• Shape, size, material, position and rotation can be parameterized

G4PVReplica

• Slicing a volume into smaller pieces (if it has a symmetry)

G4PVDivision

• Slicing a volume into smaller pieces (if it has a symmetry)

• Internally implemented as parameterization (no G4ReplicaNavigation)

• Allows offset

• Allows constructor with only number of divisions or size of division

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http://slidepdf.com/reader/full/geant4ciemat-051122 7/54Pedro Arce Introducción a GEANT4 7

Individual copies of a volume

How to identify a volume uniquely?

Example:- one LV A placed in 5 positions (5 PV) inside World- one LV B placed in 12 positions (12 PV) inside A

GEANT4 constructs 5+12 PV, not 5 PV of A and 5x12=60 PV of B

And even a PV can represent multiple copies (Parameterisations orReplicas)

- How can I have access to the 60 different copies of B (forexample, for finding where is a hit)?

ANSWER:

each of the 60 volumes B will be a distinct G4VTouchable

But, for efficiency reasons, G4VTouchable´s are only created attracking time, when a particle enters the corresponding volume

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How to use touchables: (from GEANT4 example novice/N02)

• G4TouchableHistory (:public G4VTouchable) has the information of thevolume hierarchy at each of the two points of the current step

Individual copies of a volume

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Magnetic Field

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Magnetic field: chords

The path is calculated using the chosen integration method and then

it is broken into linear chord segments that closely approximate the

curved path

The chords are used to interrogate the Navigator, to see whether the

track has crossed a volume boundary

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Particle Generator

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Primary Generator

G4Event has a list of G4PrimaryVertex’s

• G4double X0, Y0, Z0;• G4double T0;

• G4double Weight0;

G4PrimaryVertex has a list of G4PrimaryParticle’s • G4int PDGcode;• G4ParticleDefinition * G4code;

• G4double Px, Py, Pz;• G4int trackID;• G4double charge;• G4double polX, polY, polZ;• G4double Weight0;• G4double properTime;

Geant4 provides some concrete implementations ofG4VPrimaryGenerator

G4ParticleGun: one particle G4HEPEvtInterface: reading event particles from text files

G4GeneralParticleSource: big flexibility

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G4HEPEvtInterface

A concrete implementation of G4VPrimaryGenerator

Suitable to /HEPEVT/ common block, which many of

(FORTRAN) HEP physics generators are compliant to.

ASCII file input A good example for experiment-specific primary

generator implementation

Another interface to HepMC class, which a few new

(C++) HEP physics generators are compliant to, isplanned.

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G4GeneralParticleSource

A concrete implementation of G4VPrimaryGenerator

Generate radioactive decay fragmentsPrimary vertex is randomly chosen within a surface of a certainvolume.

spectrum (defined in terms of energy or momentum)

angular distribution with respect to a user-defined axis or surface

normalspatial distribution of particles from 2D or 3D planar surfaces orbeam line in Gaussian profile or generated homogeneously within avolume.

It also provides the option of biasing the sampling distribution. This isadvantageous, for example, for sampling the area of a spacecraft

where greater sensitivity to radiation effects is expected (e.g. where

radiation detectors are located) or increasing the number of high-

energy particles simulated, since these may produce greater numbers

of secondaries.

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G4GeneralParticleSource

2D Surfacesources

3D Surfacesources

Volume sources Angulardistribution

Energy spectrum

circle

ellipse

square

rectangle

Gaussian beam profile

sphere

ellipsoid

cylinder

paralellapiped

(incl. cube &cuboid)

sphere

ellipsoid

cylinder

paralellapiped

(incl. cube &cuboid)

isotropic

cosine-law

user-defined

(through

histograms)

mono-energetic

Gaussian

Linear

Exponential

power-law bremsstrahlung

black-body

CR diffuse

user-defined

(through

histograms or point-wise data)

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G4Run /G4Event / G4Track / G4Step

G4Trajectory

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Step

• Step has two points and also ´delta´information of a particle (energy loss

on the step, time-of-flight spent in the step, etc.)

• Each point knows the volume. In case a step is limited by a volume

boundary, the end point physically stands on the boundary, and it

logically belongs to the next volume

Current volume: G4Track::GetNextVolume(); =G4Step::GetPostStepPoint()->GetPhysicalVolume();

Previous volume: G4Track::GetVolume(); =G4Step::GetPreStepPoint()->GetPhysicalVolume();

What you see with „/tracking/verbose 1‟ is the current volume

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Trajectory

• Trajectory is a record of a track history. It stores some information

of all steps done by the track as objects of G4VTrajectoryPoint class

• The user can create its own trajectory class deriving from

G4VTrajectory and G4VTrajectoryPoint base classes for storing any

aditional information

• While Tracks are killed when its tracking finishes, Trajectories are

kept for an event lifetime:

• Think of your favorite application....

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Attaching user information

Abstract classes

User can use his/her own class derived from the provided base class

G4Run, G4VHit, G4VDigit, G4VTrajectory, G4VTrajectoryPoint

Concrete classes

User can attach a user information class objectG4Event - G4VUserEventInformation

G4Track - G4VUserTrackInformation

G4PrimaryVertex - G4VUserPrimaryVertexInformation

G4PrimaryParticle - G4VUserPrimaryParticleInformation

G4Region - G4VUserRegionInformation

• User information class object is deleted when associated Geant4

class object is deleted

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Sensitive Detector

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Detector sensitivity

A logical volume becomes sensitive if it has a pointerto a concrete class derived from G4VSensitiveDetector.

A sensitive detector either

constructs one or more hit objects or

accumulates values to existing hitsusing information given in a G4Step object.

NOTE: you must get the volume information from the

“PreStepPoint”.

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Sensitive detector and Hit

Each“

Logical Volume”

can have a pointer to a sensitivedetector

Hit is a snapshot of the physical interaction of a track or

an accumulation of interactions of tracks in the sensitive

region of your detector

A sensitive detector creates hit(s) using the information

given in G4Step object. The user has to provide his/her

own implementation of the detector responseHit objects, which still are the user’s class objects, are

collected in a G4Event object at the end of an event

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Hit class

Hit is a user-defined class derived from G4VHit. You can store various types information by implementing

your own concrete Hit class.

For example:

Position and time of the step

Momentum and energy of the track

Energy deposition of the step

Geometrical information

or any combination of above

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G4HCofThisEvent

A G4Event object has a G4HCofThisEvent object at the endof (successful) event processing. G4HCofThisEvent object

stores all hits collections made within the event.

o Pointer(s) may be NULL if collection(s) are not created in the

particular event.o Hits collections are stored by pointers of G4VHitsCollection base

class. Thus, you have to cast them to types of individual concrete

classes.

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Electromagnetic Physics:Standard

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Physics Process

OOD allow to implement or modify any physics processwithout affecting other parts of the software

Tracking is independent from physics processes(Transportation is also a process)

The generation of the final state is independent from theaccess and use of cross sections

Transparent access via virtual functions to•

cross sections (formulas, data sets, etc.)• models underlying physics processes

G4VProcess: base class for all processes

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Standard e.m. Physics Processes

Cover physics from 10 keVup to PeV

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Features of Standard e.m. processes

Multiple scattering

new model computes mean free path

length and lateral displacement

Ionisation features

optimise the generation ofd-rays near boundaries

Variety of models for ionisationand energy loss

including the PhotoAbsorption

Interaction model Differential and Integral approach

for ionisation, Bremsstrahlung,positron annihilation, energyloss and multiple scattering

Multiple scattering 6.56 MeV proton , 92.6 mm Si

J.Vincour and P.Bem Nucl.Instr.Meth. 148. (1978)

399

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Ionisation energy loss distribution produced by pions, PAI model

3 GeV/c p in 1.5 cm Ar+CH4 5 GeV/c p in 20.5 mm Si

Ionisation energy loss produced by charged particles in thin layers of

absorbers

Photo Absorption Ionisation Model

Gallery of electromagnetic physics documentation and results

http://wwwinfo.cern.ch/asd/geant4/reports/gallery/

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Electromagnetic physics:

Low energy

El t F t

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Electrones y Fotones

Rango de validez: 250 eV – 100 GeV250 eV es un límite “sugerido”

Librerias de datos hasta 10 eV1 < Z < 100

Explota librerías de datos evaluadas (de LLNL):

EADL (Evaluated Atomic Data Library)

EEDL (Evaluated Electron Data Library)

EPDL97 (Evaluated Photon Data Library)

Para el cálculo de las secciones eficaces totales y la generacióndel estado final

Photon transmission, 1mm Pb

shell effects

GaAs linesFe lines

fluorescence Scattering Compton

Scattering RayleighEfecto fotoeléctrico

Producción de pares

Bremsstrahlung

Ionización

+ relajación atómica

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Atenuación de fotones: comparación con datos

de NIST

Courtesy of S. Agostinelli, R. Corvo, F. Foppiano, S. Garelli, G. Sanguineti, M. Tropeano

Test y validación por IST - Natl. Inst. for Cancer Research, Genova

Polarización 2 hhh1d

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Polarización

250 eV -100 GeV

y

O z

x

x

qa

f hnhn0

A

C

q Ángulo Polar

f Ángulo Azimuthal

Vector depolarización

fq-

nn

nn

nn

22

0

0

2

0

22

0 cossin2h

h

h

h

h

hr

2

1

d

d

•Integrar sobre f

• Muestrear q

• Relación q - Energía Energía• Muestreo de f de P(f) = a (b – c cos2 f)

More details: talk on Geant4 Low Energy

Electromagnetic Physics

Otros procesos polarizados a baja energía están bajo

desarrollo

Ncossin1sincossincos 22 fq-xfqx

fqq-ffq- cosk ˆcoscossin N

1 jˆcossinsin

N

1iˆ N 2'

||

fq-q sink ˆsinsin jˆcos N

1'

Métodos de

muestreo

Sección eficaz:

Scattered Photon Polarization

10 MeV

small

large

100 keV

small

large

1 MeV

small

large

Low Energy

Polarised Compton

P d h d i

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Procesos de hadrones e iones

Variedad de modelos, dependiendo del rango de energía, el tipo de partícula y la carga

Modelo Bethe-Bloch de perdida de energía, E > 2MeV

5 modelos parametrizados, E < 2 MeV

- basados en las revisiones de Ziegler e ICRU

3 modelos de fluctuaciones de pérdida de energía

- Correciones de densida a alta energía

- Término de correccion de capa para

energía intermedia

- Término dependiente del espín

- Términos de Barkas y Block

- Efecto químico para materiales

compuestos

- Poder de frenado nuclear

- Modelo de carga efectiva

Hadrones cargados positivos

Iones cargados positivos

Hadrones cargados negativos

Escala:

Parametrizaciones 0.01 < < 0.05, pico de

Bragg

-basados en las revisiones de Ziegler e ICRU

< 0.01: Modelo de gas de electrón libre

Parametrización de los datos experimentales

disponibles

Modelo de Oscilador Armónico Cuántico

- Modelo original de Geant4

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Algunos resultados: protones

Straggling

Pode de frenadoDependencia en Z a varias energías

Modelos Ziegler e ICRUZiegler e ICRU, Fe Ziegler e ICRU, Si

Poder de frenado nuclear

Pico de Bragg (con interaccioneshadrónicas)

Algunos resultados: iones y

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Algunos resultados: iones y

antiprotones

antiprotones

protones

Perdida de energía en Silicio

Iones Ar y C

Deuterone

s

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Ejemplos de aplicaciones

Tres ejemplos avanzados desarrollados

por el grupo de “Low energy” de GEANT4desde Diciembre de 2000

telescopio rayos g

braquiterapia

telescopio rayos X

Física subsuelo y radiación de

fondo

Fluorescencia rayos X y PIXE

Aplicaciones completas que muestra la física yfacilidades interactivas avanzadas in “set-ups” realistas

Aplicaciones de

Solar system explorations

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Aplicaciones de

usuarios

Courtesy of S. Magni, BorexinoCourtesy of A. Howard, UKDM

ZEPLIN IIIDark Matter, Boulby mine

No hay tiempo de mencionarlas todas!

Courtesy SOHO EIT

Cosmic rays,

jovian electrons

Solar X-rays, e, p

Courtesy

P.Truscott, DERA

Courtesy of R. Nartallo, ESA

XMM X-ray telescope

-4

-2

0

2

4

- 9 0 - 8 0 - 7 0 - 6 0 - 5 0 - 4 0 - 3 0 - 2 0 - 1 0 0 1 0

Z (cm)

Y

( c m )

RGS EPIC

Brachythera

Bepi Colombo

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M. C. Lopes1, L. Peralta2, P. Rodrigues2, A. Trindade2 1 IPOFG-CROC Coimbra Oncological Regional Center - 2 LIP - Lisbon

Cabeza y cuella con dos haces opuestos

de tamaño de campo 5x5 y 10x10

GEANT frente a

planificadores comerciales

Una dosis de profundidad “off -

axis” tomada en una de las rodajas

cerca del isocentro

PLATO falla en las cavidades deaire y estructuras óseas y no puede

predecir con exactitud la dosis en

tejido que esta rodeado de aire

Las desviaciones son de hasta 25-

30%

Plano del hazHueso craneal

Tumor

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Production cuts

( ) ?

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What are the (production) cuts?

- Some electromagnetic processes have diverging cross sections

at low energy Ionisation: producing delta rays

Bremsstrahlung: producing gammas

…

Need to put a cut: produce only secondaries from some

energy up

- GEANT3: cuts per energy

- GEANT4: cuts per range more uniform treatment in different materials

- But cuts are converted to energy in each material and always used in

energy

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cut, step length and number of 2ary particles

Secondary particles are only produced above the energy cut Primary gives

the step in which it would loose enough energy to produce a secondary

GEANT4: secondaries that would live for a length above range cut

Example: Tracking of a muon with a cut of 1 mm in iron.

Energy of secondary electron/positron to live 1mm in iron: 1 GeV

Energy of secondary gamma to live 1mm in iron: 10 MeV Calculate in which step length the sum of the energies of all delta rays

produced by the muon (ionisation is in reality a „continuous‟ process =

ocurring at atomic lengths) is enough to produce an electron of 1 GeV

Same for gammas from bremmstrahlung adding up to 10 MeV

Same for e+e- from pair production adding up to 1 GeV

Choose between the three the smallest step length: make a step of this

length

Bigger cut bigger step ( logarithmically)

Oth C t i GEANT4

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Other Cuts in GEANT4

All cuts are always set by particle type

Tracking cuts: • Not needed as in GEANT3, cross sections are calculated down to zero

energy

UserLimits / G4UserSpecialCuts ‘process’:

• Define the step length

• Kill particle if: track length too big, time of flight too big, energy too

small, range too small

• User can define other conditions

An extra process that is attached to a G4LogicalVolume

• BUT: just proposes an step, that competes with other processes

For example: if in a volume there is an small electron cut (= produce delta rays every

small step) and in the same volume a UserLimits selects a bigger step, this UserLimit

have no effect, because ionisation proposes smaller steps than UserLimits process (and

always the smallest step is chosen)

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User Interface

GEANT4 User Interface

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GEANT4 User Interface

Several Graphical User Interfaces (GAG, MOMO, XVT)

G4UIterminal: C-shell like character terminal

G4Utcsh: G4UItcsh: tcsh-like character terminal with

command completion, history, etc

G4UIGAG: Java based GUI

G4UIOPACS: OPACS-based GUI, command completion, etc

G4UIXm: Motif-based GUI, command completion, etc

G4UIBatch: Batch job with macro file • Reading a file with a list of commands

• Write filename as executable argument

E i t l V i bl

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Environmental Variables

Users can select and plug in (G)UI by setting

environmental variables before compilation setenv G4UI_USE_GUINAME

Example (“G4UIterminal”, “GAG”, and Motif)

setenv G4UI_USE_TERMINAL 1

setenv G4UI_USE_GAG 1

setenv G4UI_USE_XM 1

Note that Geant4 library should be installed

with setting the corresponding environmental variable

G4VIS_BUILD_GUINAME_SESSION

to “1” beforehand

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Useful GUI Tools Released by Geant4 Developers

GGE: Geometry editor based on Java GUI

http://erpc1.naruto-u.ac.jp/~geant4

GPE: Physics editor based on Java GUI

http://erpc1.naruto-u.ac.jp/~geant4

OpenScientist, OPACS:

Flexible analysis environments

http://www.lal.in2p3.fr/OpenScientist

http://www.lal.in2p3.fr/OPACS

GEANT4 commands

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GEANT4 commands

Commands control what your job will doo /run/initialize

o /run/beamOn

o /tracking/verbose

o /run/particle/dumpCutValues

o ...

o /control/manual prints all available commands

Usually they are put in a file and given as name to the executable: myg4prog mycommands.lis

• All commands are processed through the singleton class G4UImanager

You can apply any command at any point in your code

G4UImanager* UI = G4UImanager::GetUIpointer();UI->ApplyCommand(“run/beamOn”);

• New commands are easily created, creating a messenger and an

action (see the many examples in OSCAR)

geant4.ciemat-051122

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