SOME ASPECTS OF MONTE CARLO SIMULATION FOR EFFICIENCY CALIBRATION OF GERMANIUM DETECTORS

Transcription

1 ICRM Gamma Spectrometry Workshop Paris, France February 2009 SOME ASPECTS OF MONTE CARLO SIMULATION S.Hurtado Universidad de Sevilla SPAIN 1

2 MONTE CARLO SIMULATION DISADVANTAGES Self-absorption correction Coincidence-summing effect 2

3 Self-absorption correction A. Experimental methods B. Semi-empirical methods standards few geometries C. Monte Carlo simulations Z and ρ (ICP-MS, XRF) 3

4 Self-absorption correction f 0 ε 0 is FEP calculated using Monte Carlo simulation for a cylindrical geometry f is the self-attenuation correction factor f t e 1 the linear attenuation coefficient m t 4

5 Self-absorption correction f calculation: transmission experiment using non-collimated point sources for m determination covering whole energy range (Garcia-Talavera 2004) ln I I 0 exp t sample m g I 0 I t 5

6 Self-absorption correction Gamma-rays incident not normal to crystal travel a longer distance t eff than t. MC simulations of various sample composition (SiO 2, CaCO 3, Fe 2 O 3, CaSO 4 2(H2O) and height give t eff (i.e. 1,03 ± 0,05 cm for t=1,0 cm) keV keV 6 ln (N 0 /N) ,7 59.5keV 0,10 0,08 ln (N 0 /N) 0,0 0,06 0,04 0,02 0, keV 0,7 (cm -1 ) -0,02 0,06 0,08 0,10 (cm -1 ) 6

7 Self-absorption correction f 1,0 0,9 0,8 0,7 0,6 0,5 0,4 0,3 T3 1,0 0,9 0,8 0,7 0,6 0,5 0,4 O5 f is calculated and fit for whole energy range f 1,0 0,9 0,8 0,7 0,6 0,5 0,4 T5 1,0 0,9 0,8 0,7 0,6 0,5 using equation: 2 Soilstandard f a b / E ( c/ E ) 0, Energy (kev) 0, Energy (kev) 7

8 Coincidence-summing effect Point A C sources d B t f t h D L Optimization of detector setup: detector parameters optimized comparing MC efficiencies with experimental ones at different positions (A / B / C) r R 8

9 Coincidence-summing effect PARAMETER NOMINAL OPTIMIZED Crystal radius R 27.0 mm 27.0 mm Crystal height L 55.0 mm 55.0 mm Distance to window D 5.0 mm 7.4 mm Hole inner radius r 0.5 mm 0.65 mm Hole height d 41.0 mm 41.0 mm Inner dead layer t h 0.5 mm 1.0 mm Front dead layer t f 0.3 m 30 m 9

10 Coincidence-summing effect COMPARISON NUCLEAR DATABASES GEANT4 Radioactive Decay Module (ENSDF) GEANT4 own classes (NUCLEIDE) 10

11 ICRM EXERCISE results for 2 cm ENSDF NUCLEIDE

12 Intensities ENSDF NUCLEIDE

13 IC coefficients ENSDF NUCLEIDE

14 Eu-152 MC spectrum 2 cm ENSDF NUCLEIDE Energy (kev) 14

15 Photoelectric Cross Section (barn) SOME ASPECTS OF MONTE CARLO SIMULATION 1E Coincidence-summing effect E-3 20 Diff (%) ,1 0, Cross Sections (Photoelectric) Ge STANDARD LOWENERGY PENELOPE NIST 1E-3 0,01 0,1 1 ENERGY (MeV) 15

16 Coincidence-summing effect Cross Sections (Compton) ion (barn) Compton Cross Secti 10 1 Ge STANDARD LOW ENERGY PENELOPE NIST Diff (%) E-3 0,01 0,1 1 ENERGY (MeV) 16

17 Coincidence-summing effect Cross Sections (Gamma conversion) Gamma Conversion Cros ss Section (barn) 0,1 0,01 Ge STANDARD LOWENERGY PENELOPE NIST 20 Diff (%) ENERGY (MeV) 17

18 Coincidence-summing effect Cross Sections (Rayleigh) Rayleigh Cross Sectio on (barn) ,1 0,01 Ge LOWENERGY PENELOPE NIST Diff (%) E-3 0,01 0,1 1 ENERGY (MeV) 18

19 Coincidence-summing effect Total Cross Section 19

20 Conclusions Cross sections selection Nuclear dataset selection Detector geometry optimization or high resolution X-ray image 20