r&d on the geant4 radioactive decay physics monte carlo 2010

08.10.10| TU Darmstadt | Institut für Kernphysik | Steffen Hauf | 1

R&D on the Geant4 Radioactive Decay PhysicsMonte Carlo 2010

Steffen Hauf, Markus Kuster, Philipp-M. Lang, Maria Grazia Pia, Zane Bell, Dieter H.H. Hoffmann, Georg Weidenspointner, Andreas Zoglauer

Credit: CNES, NASA


Introduction

Radioactive decay simulation as part of larger MC code important for variety of applications.

Examples of GEANT4 dosimetry Biophysics Medical physics Accelerator physics (i.e. LHC) Manned space mission (i.e. ISS, Moon,

Mars) Unmanned probes (i.e. JIMO),

observatories (i.e. IXO) National Security ...


Introduction

Geant4 radioactive decay simulation originally developed as part of ESA contract.

Uses tabulated data to obtain decay parameters (halflife, branching, levels, intensities).

After decay delegates nucleus and decay products to other Geant4 processes (photo-deexitation) .

RadDecay

Other Processes

Ground State


Introduction

Problem: Tabulated data is poorly referencedSolution: New database based on current available ENDF data

Combined effort with international nano5 collaboration to create common GEANT4 data model.

Problem: Only sporadic validation of resultsSolution: Comparision with experiments for variety of isotopes.

gamma ray spectroscopy at Oak-Ridge Laboratories

activation and decay experiment at GSI Phelix Laser

Problem: No native support for long term activation

can bias decay times, this removes particles from MC

MEGALib and Cosima have adressed this, include these concepts into nano5


Problem 1: Data Source

As part of nano5: common GEANT4 data model

Should include references to data origin

Should allow generic unit testing

Should be „easy“ to update Common superstructure but

adaptable for physics process needs

Deviation of energy levels in keV in Geant4 database compared to ENSDF


Problem 2: Experimental Verification „Simple and General“ approach at Oak Ridge Labs:Use GEANT4 to decay various isotopes in front of Ortec HPGe detector.

We know:•measurement time•isotope•background•detector geometry to certain extentsystematics under controlWe do not want fit using efficiency

Measured so far: 2 2Na, 5 4Mn, 5 6Mn, 5 7Co, 6 0Co, 1 1 6In, 1 3 3Ba


Effects of Geant4 Version and Physics Settings

Gamma spektrum of 1 3 7Cs for different Geant versions compared to experimental data(gray)Tested: G4.9.1, 4.9.1* w.

Compton mod, G4.9.2

Spectra are very similar for all Geant4 versionstested

Differ in particle speciesproduced (see next slide)

Same trends for deviationfrom experiment

True for other isotopes aswell



Gamma spektrum of 1 3 7Cs (black) compared to experimental data(gray)

G4.9.1 low energy physics G4.9.2 low energy physics

Spectrum is very similar but contributing particles (e- blue, photon yellow) change



Gamma spektrum of 1 3 7Cs (black) compared to experimental data(gray)

G4.9.1 low energy physics G4.9.2 standard em physics

Spectrum is very similar but contributing particles (e- blue, photon yellow) change


Effects of Detector Geometry

Introduction of a „dead“ layer at detector entrance side (i.e. 1 3 7Cs)

Continuum and high energy peak representation improves,low energy peak worsens

sensitivedead

source

d



Most energy is deposited in front part of HPGe crystal and at outer and bore edge.

In real world detector this area will have strongly curved electric field lines causing non-trivial charge transport and collection

Dead layer shows that selectivly changing efficiency of this region can positively influence modelling of continuum



Majority of energy is deposited in frontal detector regions

Holds true in continuum and peak areas of spectrum

Cumulative energy deposition in respect to location in detector

entrance window

detector rear


Laser Accelerated Protons for Testing Activation and Decay Simulation

Target Normal Sheath Acceleration

Proton Spectrum

M. Schollmeier, PhD Thesis TU Darmstadt 2008

M. Roth TU Darmstadt

Parameters

Laser intensity:

Proton flux:

Pulse duration: pico seconds

Parameters

Laser intensity:

Proton flux:

Pulse duration: pico seconds

Simulation Verification

Activation of shielding material

Interaction of MeV protons with

detector and shielding materials

Simulation Verification

Activation of shielding material

Interaction of MeV protons with

detector and shielding materials



Due to beam problems so far only one preliminary shot on 2.25mm Sn.

Beam time proposal for additional 18 shots at GSI PHELIX laser was handed in

Stacks are halfed: one side Sn target, other side: radiochromatic films and copper absorbers

After shot: gamma spectroscopy in HPGe detector

Sn RC- Stack



Courtesy: K

. Harres



Analysis of radiochromatic films results in input spectrum for GEANT4 simulation (solid)

Input in General Particle Source (GPS)

Adequate similarity to cosmic proton spectrum (dotted)

Comparison between cosmic and laser accelerated proton spectrum



Activation and decay measurement in one run

Simple geometry, add complexity if needed

Physics as used for IXO/Simbol-X simulations (LowEn-EM, hadron)

Only particles with parent process „Radioactive Decay“ are registered.

Protons are „killed“ at boundry Sn-Detector.

Sn

HPGe

p+


Summary and Outlook

Radioactive decay database needs to be checked for consistenceNew data model which includes references would aid updating and validation

Simple experiment with HPGe detector can be qualatively modelled but simulation isn't completely accurateHPGe simulation is not sensitive to Geant4 version or physics setups (within modest parameter changes)HPGe simulation is sensitive to geometrical changes near detector. Further investigation underway

Additional experiment with laser accelerated protons proposed

r&d on the geant4 radioactive decay physics monte carlo 2010

Documents

geant4 database

use geant4

geant4 versionstesteddiffer

decay experiment

decay products

decay times

common geant4 data modelshould

tabulated data