19th july 2002, salamanca 1 efficiency calibration of a germanium gamma-ray detector using geant4 *...
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19th July 2002, Salamanca
1
Efficiency calibration of a Germanium
gamma-ray detector using GEANT4
* Dpto. Física Atómica, Molecular y Nuclear
** Dpto. Física Aplicada I
Universidad de Sevilla
Santiago Hurtado*, Manuel García-León*, Rafael García-Tenorio**
19th July 2002, Salamanca
2Detector geometry
D
L
R
r
d
Ge tf
th
REGe
(Reverse Electrode Germanium)
DIMENSION NOMINAL
Crystal radius R 27.0 mm
Crystal lenght L 55.0 mm
Window distance
5.0 mm
Hole radius 5.0 mm
Hole depth 41.0 mm
Thickness hole dead layer
0.5 mm
Thickness front dead layer
0.3 m
Be window
19th July 2002, Salamanca
3Experimental setup
15 cm
Point source Marinelli beaker
Radionuclides: 210Pb, 241Am, 137Cs, 40K, 133Ba, 152Eu
19th July 2002, Salamanca
4
REGePhysicsList
Cut values
, e- and e+
LowEnergyPhysics
Simulation Class diagram
REGe
REGeVisManager
RegisterGraphicsSystem
->VRML1FILE
REGePrimaryGenerator
particleGun
REGeDetectorConstruction
G4Tubs,G4Material,...
->REGe geometry setup
REGeCristalHit
Hit-> Pos,Edep,weight
REGeCristalSD
HitsCollection
REGeRunAction
Histogramfilename
REGeEventAction
HitsCollection->
Histogramfilename
GSPM
GenerateBiasFlux
ROOT-C++
19th July 2002, Salamanca
5Variance Reduction technique
Zone I Zone II
Zone III
Zone IV
Zone V
HzRr1
min tan
zRr1
max tan
0)/(tan
0)/(tan21
1
xxy
xxyc
)/(sin 12 rRr
2min rc 2max rc
maxmaxmin11 cos)cos(coscos
minminmax2 )(
4/))(cos(cos minmaxmaxmin w
(x,y,z)
Zone II algorithm
r
R
H
min
max
Ge
19th July 2002, Salamanca
6Computing time reduction
Computing time reduction
10
100
1000
10000
100000
1000000
Pb-210 Am-241 Cs-137 K-40
Tim
e (s
)
Point ISO
Marinelli ISO
Point BIAS
Marinelli BIAS
19th July 2002, Salamanca
7ROOT-C++ Analysis
Histogram
FWHMexp
Area calculation
MC
19th July 2002, Salamanca
8Point results
Point efficiency
0
0.10.2
0.3
0.4
0.50.6
0.7
0.8
0 0.2 0.4 0.6 0.8
Exp. Efficiency (%)
Cal
c. E
ffic
ien
cy (
%)
Eff. MC
Eff. MC opt.
19th July 2002, Salamanca
9Marinelli results
Marinelli Efficiency
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 1 2 3 4 5
Exp. efficiency (%)
Cal
c. E
ffic
ien
cy (
%)
Eff. MC
Eff. MC opt.
Eff. Tranf
19th July 2002, Salamanca
10Optimized geometry & Efficiency transfer
R
D
L
r
d
Ge tf
th
D, R -> 240Am , 210Pb , 133Ba (POINT)
L -> 240Am , 210Pb (MARINELLI)
d, r, th -> 137Cs , 40K (POINT-MARINELLI)
(exp))( )/( refcalc
a refaT
)(
)(
)/( MCref
MCarefaT
D+2 mm , R-0.75 mm , L-3 mm ,
D-3 mm , r+2 mm
19th July 2002, Salamanca
11Conclusions
• GEANT4 provides a good agreement: exp. & MC data
• GEANT4 is useful to setup complicated experimental geometries
• Versatility of GEANT4 (C++)
improves lab experiments (coincidence- summing, background simulation, ...)