St. Petersburg State University.Department of Physics.Division of Computational Physics.

COMPUTER SIMULATION OF CURRENT PRODUCED BY PULSE

OF HARD RADIATION

Vadim V. Galitsyn

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Contents

- Introduction- Actuality- Solution method- Results

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Introduction

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The aim of this work is to determine the role of a different physical processes for the formation of a current pulse produced by a hard radiation with a initial gamma energy between 20 keV and 4 MeV. It is necessary for better understanding of detector registration efficiency.

Relativistic electrons Speed of light of the current propagation in the detector Secondary physical processes effect

Actuality

Examples:

- ALICE- ATLAS- LHCb- Future CBM

The actuality is in a possible upgrade of detectors of relativistic charged particles.

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GEANT4 toolkit

We consider to simulate interaction of particles and passage through matter with a GEANT4 Software package

GEANT4 is an open source toolkit for the simulation of the passage of particles through a matter written on C++

Official GEAN4 web site, http://geant4.cern.ch

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How it worksStep 1 of 4. The Volume Space

Physical Volume.

The matter.

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We used Air and Water matter to simulate gamma passage through.

There are many different volume forms possible to create with the GEANT4.

Cubical geometry of a detector was considered.

How it worksStep 2 of 4. Gamma source and detection plane

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Setting up:

● Gamma beam direction

● Number of gamma

● Gamma energy (between 20 keV and 4 MeV energy range)

● Fixing detection virtual plane position (perpendicular to gamma direction)

Gamma source

Physical Volume.

The matter.

Detection plane

* We were interested by time distribution of secondary electrons at the detection plane and role of the different physical processes for current pulse formation

How it worksStep 3 of 4. Physics

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Before we run the simulation we must to determine which physical processes we want to see and what particles are we working with

Processes:Photo effect, Compton scattering, Pairing effect

Particles:Gamma, Electron, Positron

Gamma source

Physical Volume.

The matter.

Detection plane

How it worksStep 4 of 4. Experiment start-up

GEANT4 graphical output window

● GEANT4 show experiment parameters on the screen; we can see particles tracks online

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How it worksWhat we are looking for?

All processes

Current pulse form on detection plane. 1.5 MeV gamma source. Water.

Compton Scattering

Ionization EffectJASS, 2006

Computer cluster

From 30 minutes to several hours needed to perform calculations for one run consisting of 107 events

We are using high performance clusters for simulations

In our case (full data parallelism) speedup depends linearly on computing nodes (theoretical limit of the Amhdal’s law)

Linearspeedup

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Results (Water)

Passage of gamma quanta through2 mm water layer

4000

The role of different processes in current pulse formation in water

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Results (Air)The role of a different processes in current pulse formation in the air

Passage of gamma quanta through 1 m air layer at atmosphere pressure

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Results

Photo electric effect Compton Scattering Pairing effect

Air

Theory

GEANT4

20 keV

120 keV

Water55 keV

87 keV

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Conclusions

• The role of different physical processes for the formation of current pulse was defined

• The differences between a theory and experiment was detected

• The forms of a current produced by a pulse of hard radiation were defined

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Appendix

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Acknowledgement

S. A. Nemnugin

F. F. Valiev

S. U. Slavyanov

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Thank you for attention

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