Maria Grazia Pia, INFN Genova Low Energy Electromagnetic Physics Maria Grazia Pia INFN Genova on...

Maria Grazia Pia, INFN Genova

Low Energy Electromagnetic Physics

Low Energy Electromagnetic Physics

http://www.ge.infn.it/geant4/lowE

Maria Grazia PiaINFN Genova

on behalf of Geant4 Low Energy Electromagnetic Working Group

Monte Carlo 2005Chattanooga, 18-21 April 2005


Boulby mine

Courtesy of NASA/CXC/SAO

Bepi Colombo

Radiotherapy

Brachytherapy

Dark matter searchesXMM

From deep undergroun

d to galaxies

From crystals to human beings

Radiobiology


Low Energy Electromagnetic PhysicsLow Energy Electromagnetic Physics

A set of processes extending the coverage of electromagnetic A set of processes extending the coverage of electromagnetic interactions in Geant4 down to “interactions in Geant4 down to “low”low” energy energy

– 250/100 eV (in principle even below this limit) for electrons and photons– down to approximately the ionisation potential of the interacting material for

hadrons and ions

Processes based on detailed modelsProcesses based on detailed models– shell structure of the atom– precise angular distributions

Specialised models depending on particle typeSpecialised models depending on particle type– data-driven models based on the Livermore Libraries for e- and photons– analytical models for e+, e- and photons (reengineering Penelope into Geant4)– parameterised models for hadrons and ions (Ziegler 1977/1985/2000, ICRU49)– original model for negative hadrons


The process in a nutshellThe process in a nutshellRigorous software process

– Iterative and incremental model– Based on the Unified Process: bidimensional, static + dynamic dimension– Use case driven, architecture centric– Continuous software improvement process

User Requirements Document – Updated with regular contacts with users

Analysis and design– Design validated against use cases

Unit, package integration, system tests + physics validation– We do a lot… but we would like to do more– Limited by availability of resourcesavailability of resources for core testing– Rigorous quantitative tests, applying statistical methods

Peer design and code reviews– We would like to do more… main problem: geographical spread + overwork

Close collaboration with users


User requirementsUser requirementsGEANT4 LOW ENERGY ELECTROMAGNETIC PHYSICS

GGEEAANNTT44 LLOOWW EENNEERRGGYY

EELLEECCTTRROOMMAAGGNNEETTIICC PPHHYYSSIICCSS

User Requirements Document Status: in CVS repository

Version: 2.4 Project: Geant4-LowE Reference: LowE-URD-V2.4 Created: 22 June 1999 Last modified: 26 March 2001 Prepared by: Petteri Nieminen (ESA) and Maria Grazia Pia (INFN)

User User RequirementsRequirements

Posted on the WG

web site

Elicitation through interviews and surveys useful to ensure that UR are complete and

there is wide agreement

Joint workshops with user groups

Use cases

Analysis of existing Monte Carlo codes

Study of past and current experiments

Direct requests from users to WG coordinators

Various methodologies adopted to Various methodologies adopted to capturecapture URsURs


OOADOOAD

Rigorous adoption of OO methods

openness to extension and evolution

Technology as a support to physics


Testing

Suite of unit tests (at least 1 per class)

Cluster testing

3 integration/system tests Suite of physics tests (in progress with publications)

Regression testing

Testing process

Testing requirements Testing procedures etc.

Physics validation

Geant4 Low Energy Electromagnetic Physics

Version 2

27 May 2001

The Role of Testing in the Software Process of the Geant4 Low-Energy Electromagnetic Physics Working Group

P. Nieminen and M.G. Pia

1 Introduction

Testing forms a vital part of the software process in developments as advanced and complex as those currently in progress in the Geant4 Low-Energy e-m physics Working Group. The purpose of this document is to outline the procedures to be followed regarding testing both during development of new software, and during updates and corrections to existing code.

2 Testing objectives and goals

The objective of testing is to ensure the new, or updated, code performs as intended. Testing should reveal any potential deviancies from expected behaviour of the code both from physics and performance point of view. The goal is high-quality code ready for public release, ultimately leading to easier maintenance and substantial timesaving for developers in the course of the software lifecycle.

3 Test designs and testing schedules

3.1 Test requirements

1. Testing should be performed according to agreed and documented procedures.

2. Traceability through requirements-design-implementation-tests should be implemented.

3. The design should be tested for satisfying the user requirements.

4. The code implementation should be tested for compliance with the design.

5. The code should be tested for correct functionality.

6. The code should be tested for compliance with Geant4 coding guidelines.

7. The code should be tested for satisfactory quality, clarity and readability.

8. Every class of the lowenergy category shall be exercised in an appropriate system test (directly or indirectly).

9. The code should be tested on all Geant4 supported platforms.

10. The code shall be submitted to the entire set of tests above to be considered for release.

11. Tests and test tools should be documented.

12. The test code should be kept under configuration management (in Geant4 CVS repository).

13. Reference outputs, data sets for validation tests etc. should be kept in appropriate agreed locations, accessible to the whole WG.

14. Test tools should be maintained.

15. Modifications of the tests (including test tools, reference outputs, data sets etc.) should be performed according to agreed and documented procedures.

16. The most recent test results should be made available to WG coordinators for code to be included in a monthly global tag or in a Geant4 public release, according to the guidelines described in the "Testing process" section.

XP practice “write a test before writing the code” recommended to WG developers!

IIntegrated with developmentntegrated with development(not “something to do at the end”)(not “something to do at the end”)


Photons and electrons: processes based on the Livermore library

Photons and electrons: processes based on the Livermore library

Based on evaluated data libraries from LLNL:– EADL (Evaluated Atomic Data Library) – EEDL (Evaluated Electrons Data Library)– EPDL97 (Evaluated Photons Data Library)

especially formatted for Geant4 distribution (courtesy of D. Cullen, LLNL)

Validity range: 250 eV - 100 GeV– The processes can be used down to 100 eV, with degraded accuracy– In principle the validity range of the data libraries extends down to ~10 eV

Elements Z=1 to Z=100– Atomic relaxation: Z > 5 (transition data available in EADL)


Calculation of cross sectionsCalculation of cross sections

12

1221

/log

/loglog/logloglog

EE

EEEEE

iii nE

1

E1 and E2 are the lower and higher energy for which data (1 and 2) are available

ni = atomic density of the ith element contributing to the material composition

Interpolation from the data libraries:

Mean free path for a process, at energy E:


PhotonsPhotons


Compton scatteringCompton scattering

Energy distribution of the scattered photon according to the Klein-Nishina formula, multiplied by scattering function F(q) from EPDL97

The effect of scattering function becomes significant at low energies– suppresses forward scattering

Angular distribution also based on EPDL97

2

0

020

220 cos42

h

h

h

h

h

hr

4

1

d

dKlein-Nishina cross section:

Rayleigh scatteringRayleigh scatteringAngular distribution: F(E,q)=[1+cos2(q)]F2(q)

– where F(q) is the energy-dependent form factor obtained from EPDL97


Photoelectric effectPhotoelectric effectCross section

– Integrated cross section (over the shells) from EPDL + interpolation– Shell from which the electron is emitted selected according to EPDL

Final state generation– Direction of emitted electron = direction of incident photon– Improved angular distribution in preparation

Deexcitation via the atomic relaxation sub-process– Initial vacancy + following chain of vacancies created

conversion conversionPair and triplet production cross sections

The secondary e- and e+ energies are sampled using Bethe-Heitler cross sections with Coulomb correction

e- and e+ assumed to have symmetric angular distribution

Energy and polar angle sampled w.r.t. the incoming photon using Tsai differential cross section


PolarisationPolarisation

250 eV -100 GeV

y

O z

x

h

h A

C

Polar angle

Azimuthal angle

Polarization vector

22

0

020

220 cossin2

h

h

h

h

h

hr

2

1

d

d

More details: talk on Geant4 Low Energy Electromagnetic Physics

Other polarised processes under development

Ncossin1sincossincos 22

coskcoscossin

N

1jcossinsin

N

1iN 2'

||

sinksinsinjcosN

1'

Cross section:

Scattered Photon Polarization

10 MeV

small

large

100 keV

small

large

1 MeV

small

large

Low Energy Low Energy Polarised Polarised ComptonCompton


Electron BremsstrahlungElectron Bremsstrahlung

Parameterisation of EEDL data – 16 parameters for each atom– At high energy the

parameterisation reproduces the Bethe-Heitler formula

– Precision is ~ 1.5 %

Plans– Systematic verification over Z

and energy


Bremsstrahlung Angular DistributionsBremsstrahlung Angular Distributions

Three LowE generators available in GEANT4:

G4ModifiedTsai, G4Generator2BS and G4Generator2BN

G4Generator2BN allows a correct treatment at low energies (< 500 keV)


Electron ionisationElectron ionisation

Parameterisation based on 5 parameters for each shell

Precision of parametrisation is better then 5% for 50 % of shells, less accurate for the remaining shells

Work in progress to improve the parameterisation and the performance


Processes à la PenelopeProcesses à la Penelope

The whole physics content of the Penelope Monte Carlo code has been re-engineered into Geant4 (except for multiple scattering)

– processes for photons: release 5.2, for electrons: release 6.0

Physics models by F. Salvat et al.

Power of the OO technology:– extending the software system is easy– all processes obey to the same abstract interfaces– using new implementations in application code is simple

Profit of Geant4 advanced geometry modeling, interactive facilities etc.

– same physics as original Penelope


Hadrons and ionsHadrons and ions

Variety of models, depending on – energy range– particle type– charge

Composition of models across the energy range, with different approaches

– analytical– based on data reviews + parameterisations

Specialised models for fluctuations

Open to extension and evolution


Algorithms encapsulated in

objects

Physics models handled through abstract classes

Hadrons and ionsHadrons and ions

Interchangeable and transparent access to data sets

Transparency of physics, clearly exposed to users


Hadron and ion processesHadron and ion processesVariety of models, depending on energy range, particle type and charge

Bethe-Bloch model of energy loss, E > 2 MeV 5 parameterisation models, E < 2 MeV

based on Ziegler and ICRU reviews

3 models of energy loss fluctuations

Density correction for high energy Shell correction term for intermediate energy Spin dependent term Barkas and Bloch terms Chemical effect for compound materials Nuclear stopping power

Positive charged hadronsPositive charged hadrons

Positive charged ionsPositive charged ions

Negative charged hadronsNegative charged hadrons

Scaling:

0.01 < < 0.05 parameterisations, Bragg peak

based on Ziegler and ICRU reviews

< 0.01: Free Electron Gas Model

Parameterisation of available experimental data Quantum Harmonic Oscillator Model

ion

pp m

mTT ),()( 2

ppionion TSZTS Effective charge model Nuclear stopping power

Model original to Geant4 Negative charged ions: required, foreseen


Some results: protonsSome results: protons

Straggling

Stopping power Z dependence for various energiesZiegler and ICRU models Ziegler and ICRU, Fe Ziegler and ICRU, Si

Nuclear stopping powerBragg peak (with hadronic interactions)


Positive charged ions

• Scaling:

• 0.01 < < 0.05 parameterisations, Bragg peak based on Ziegler and ICRU reviews

< 0.01: Free Electron Gas Model

ion

pp m

mTT ),()( 2

ppionion TSZTS

Effective charge modelEffective charge model Nuclear stopping powerNuclear stopping power

Deuterons


Models for antiprotonsModels for antiprotons

> 0.5 Bethe-Bloch formula

0.01 < < 0.5 Quantum harmonic oscillator model

< 0.01 Free electron gas model

Proton

G4 Antiproton

Antiproton from Arista et. al

Antiproton exp. data

Proton

G4 Antiproton

Antiproton from Arista et. al

Antiproton exp. data


Atomic relaxationAtomic relaxation

See next talk


Geant4 validation vs. NIST databaseGeant4 validation vs. NIST database

All Geant4 physics models of electrons, photons, protons and compared to NIST database

– Photoelectric, Compton, Rayleigh, Pair Production cross-sections– Photon attenuation coefficients– Electron, proton, stopping power and range

Comparison of Geant4 Standard and Low Energy Electromagnetic packages against NIST reference data

– document the respective strengths of Geant4 electromagnetic models

Quantitative comparison– Statistical goodness-of-fit tests

See talk by B. Mascialino on Wednesday


Electrons: dE/dxElectrons: dE/dx

Ionisation energy loss in various materials

Compared to Sandia database

More systematic verification planned

Also Fe, Ur


The problem of validation: finding reliable dataThe problem of validation: finding reliable data

Note: Geant4 validation at Note: Geant4 validation at low energy is not always easylow energy is not always easy

experimental data often exhibit large differences!

Backscattering low energies - Au


ApplicationsApplications

A small sample in the next slides– various talks at this conference concerning Geant4 Low Energy

Electromagnetic applications

Many valuable contributions to the validation of LowE physics from users all over the world

– excellent relationship with our user community

Maria Grazia Pia, INFN Genova M.Piergentili, INFN Genova

LINAC for IMRTLINAC for IMRT

Kolmogorov-Smirnov Test: p-value=1

Kolmogorov-Smirnov Test: p-value=0.1-0.9


MicroSelectron-HDR source

DosimetryEndocavitary brachytherapy

DosimetryEndocavitary brachytherapy

DosimetrySuperficial brachytherapy

DosimetrySuperficial brachytherapy

Leipzig applicator

Dosimetry Interstitial brachytherapy

Dosimetry Interstitial brachytherapy

Bebig Isoseed I-125 source


Hadrontherapy beam line at INFN-LNS, Catania

Hadrontherapy beam line at INFN-LNS, Catania

G.A.P. Cirrone, G. Cuttone, INFN LNS


Bepi Colombo Bepi Colombo Mission to MercuryMission to Mercury

Bepi Colombo Bepi Colombo Mission to MercuryMission to Mercury

Study of the elemental composition of Mercury by means of

X-ray fluorescence and PIXE

Insight into the formation of the Solar System

(discrimination among various models)


Shielding in Interplanetary Space Missions

Shielding in Interplanetary Space Missions

Aurora ProgrammeAurora Programme

Dose in astronaut resulting from Galactic Cosmic Rays

Fe - 52 Si - 28

O - 16 C - 12

pGCR (all ion components)

ESAREMSIM Project


ConclusionsConclusions

New physics domain in HEP simulation

Wide interest in the user community

A wealth of physics models

A rigorous approach to software engineering

Significant results from an extensive validation programme

A variety of applications in diverse domains

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