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## Electromagnetic physics validation

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### Electromagnetic physicsvalidation

Katsuya Amako,Susanna Guatelli, Vladimir Ivanchenko, Michel Maire, Barbara Mascialino, Koichi Murakami, Sandra Parlati, Andreas Pfeiffer, Maria Grazia Pia, Takashi Sasaki, Lazslo Urban

Geant4 Workshop

Catania, October 4th-9th 2004

The project

- The project is based on a geographically spread collaboration:

INFN Genova

INFN Gran Sasso

Standard Group

KEK

THANKS TO KOICHI MURAKAMI, TAKASHI SASAKI, KATSUYA AMAKO FOR THE VERY FRUITFUL COLLABORATION!

Preliminary results were presented at last Geant4 Workshop and at IEEE-NSS in Portland. Now the project has reached a mature state.

Aim of the project

- Project for the validation of all Geant4 electromagnetic models against established references
- The project s made-up by two parts:

GOODNESS-OF-FIT

TESTING

PHYSICAL TEST

Goodness-of-Fit statistical toolkit

Chi-squared stability study

test50

Quantitative statistical comparisons allow:

- an evaluation of Geant4 physics goodness

- how the specific models behave in the same experimental condition

POSSIBILITY OF CHOOSING THE MOST APPROPRIATE MODEL

First phase: validation against the NIST database

Photon Attenuation Coefficient

Photon Cross Sections(attenuation coefficients with only one process activated)

Electrons CSDA range and Stopping Power

(no multiple scattering, no energy fluctuations)

Protons CSDA range and Stopping Power

(no multiple scattering, no energy fluctuations)

Alpha particles CSDA range and Stopping Power

(no multiple scattering, no energy fluctuations)

Elements: Be, Al, Si, Fe, Ge, Ag, Cs, Au, Pb, U

Energy range: 1 keV – 100 GeV

Testing activity has been automatised (thanks to SandraParlati and Koichi Murakami)

Photon attenuation coefficient: statistical results

NIST – XCOM

LowE Livermore

NIST – XCOM

LowE Penelope

NIST – XCOM

Standard

Photon photoelectric cross section: statistical results

NIST – XCOM

LowE Livermore

NIST – XCOM

LowE Penelope

NIST – XCOM

Standard

Photons: Compton cross section

The 1keV deviation effect is evident in both LowE Penelope and Standard packages

As an example, let us consider Ag:

Photon Compton cross section: statistical results

NIST – XCOM

LowE Livermore

NIST – XCOM

LowE Penelope

NIST – XCOM

Standard

Photons: pair production cross section

χ2/ν stability study

Be

(not compatible with the NIST)

Beryllium

deviations

χ2/ν stability study

Photon pair production cross section: statistical results

NIST – XCOM

LowE Livermore

NIST – XCOM

LowE Penelope

NIST – XCOM

Standard

Removing the 1 keV point

Photon Rayleigh cross section: statistical results

NIST – XCOM

LowE Livermore

NIST – XCOM

LowE Penelope

Test results are not consistent

Critical discussion of this result

- The disagreement between NIST reference data and data coming from the recent library EPDL97 (provided by Lawrence Livermore National Laboratory) within the range of energies between 1 keV and 1 MeV has been already underlined and discussed in a recent paper by Zaidi*.
- In his paper Zaidi concluded that EPDL97 is the most up-dated, complete and consistent data library available at the moment.

For these features, it should be considered as a standard.

* Zaidi H., 2000, Comparative evaluation of photon cross section libraries for materials of interest in PET Monte Carlo simulation IEEE Transaction on Nuclear Science 47 2722-35

χ2/ν stability study

The three models

are equivalent

Strange effect

(as a function of Z)

NIST – ESTAR

LowE Livermore

BEST

FIT

χ2/ν = -0.032 + 0.0074 Z R2=0.995 p<0.0001

BEST

FIT

NIST – ESTAR

LowE Penelope

χ2/ν = -0.032 + 0.0074 Z R2=0.995 p<0.0001

BEST

FIT

NIST – ESTAR

Standard

χ2/ν = -0.046 + 0.0073 Z R2=0.989 p<0.0001

Electrons stopping power: statistical results

NIST – ESTAR

LowE Livermore

NIST – ESTAR

LowE Penelope

NIST – ESTAR

Standard

Electrons CSDA range: statistical results

NIST – ESTAR

LowE Livermore

NIST – ESTAR

LowE Penelope

NIST – ESTAR

Standard

- LowE Ziegler 85
- LowE Ziegler 2000
- ICRU
- Standard

At low energies: free electron gas model

At middle energies (~ MeV): parametrisations

At high energies: Bethe Bloch

NIST database

Statistical comparison cannot lead to a real physics validation, but we can only compare two different models (NIST – Ziegler)

Protons: stopping power

χ2/ν stability study

LowE ICRU

Standard

LowE Ziegler 85

lOWe Ziegler 2000

NIST - PSTAR

Protons stopping power: statistical results

NIST – PSTAR

LowE Ziegler2000

NIST – PSTAR

Standard

NIST – PSTAR

LowE ICRU49

NIST – PSTAR

LowE Ziegler85

Protons: CSDA range

χ2/ν stability study

LowE ICRU

Standard

LowE Ziegler 85

LowE Ziegler 2000

NIST - PSTAR

Protons CSDA range: statistical results

NIST – PSTAR

LowE Ziegler2000

NIST – PSTAR

Standard

NIST – PSTAR

LowE ICRU49

NIST – PSTAR

LowE Ziegler85

Concerning alpha particles, this is the second iteration of production and analysis since last July.

This because thanks to the quantitative analysis we could detect a conceptual flaw in physics tablestreatment for both protons and alpha particles.

Systematic data analysis allowed to improve the physical models.

SUMMARY: photons and electrons

- Low Energy Livermore is the most compatible with the NIST reference (Rayleigh scattering is a special case)
- Low Energy Penelope is quite compatible with NIST reference except for some problems exhibited in Compton scattering and pair production cross sections
- Standard electrons are compatible with NIST, photons are quite compatible, but exhibit some problems

SUMMARY: protons and alpha particles

- While NIST represents an established reference for photon and electron processes, the reference for protons and alpha processes in controversial at least in the lower energy ranges.
- Two reference data compilations ICRU/NIST and Ziegler.
- Quantitative comparisons available for all NIST quantities for protons and alpha particles.

Conclusions

- Validation of all Geant4 Electromagnetic models against the NIST database
- Quantitative statistical analysis on all the comparisons
- Fully automated testing system (thanks to Sandra Parlati and Koichi Murakami)
- Objective comparison among Geant4 models (with respect to the NIST reference)
- Mature project and results will be presented at IEEE-NSS – paper submitted for publication next month

Future perspectives

- Final states
- angular distributions and spectra
- The first results will be shown and discussed in the parallel section Physics Book introductory talk by Susanna Guatelli

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