QUADOSQUADOS IRSNIRSN
ProblemProblem P7P7
Stéphanie MénardStéphanie MénardIRSNIRSN
DosimetryDosimetry DepartmentDepartment92262 Fontenay92262 Fontenay--auxaux--RosesRoses
FRANCEFRANCE
QUADOSQUADOS IRSNIRSN
What are the applications of Gamma-Ray Spectrometry in Radiological Protection and in
Safety?• In the environment:
• after accidental releases of radionuclides(contamination),
• for surveys over large areas
• In the control of nuclear materials
• In workplaces in the nuclear fuel cycle
QUADOSQUADOS IRSNIRSN
What do we measure with a spectrometer ?
• Pulse height distributions => Energy
• Peak count rates => Fluence
QUADOSQUADOS IRSNIRSN
What physical information is essential ?
• To determine radionuclide activity levels– The activities are derived from measured full-energy peak
count rates– Knowledge of the detector peak response is essential but
complex:
• Peak response depends on the photon energy andangle of incidence
• Assumptions are made to make measurements in theenvironment
QUADOSQUADOS IRSNIRSN
What physical information is essential ?
• To calculate dose quantities– These quantities are derived from the energy distribution of
incident radiation field– To determine the energy spectrum: response matrix is
needed– Unfolding method is used
QUADOSQUADOS IRSNIRSN
How to determine the influence of parameterson the response ?
• Two methods– Experimental method– Numerical method
Limits of the methods- experimental : irradiation conditions (energy, angle), cost …- Numerical : assumptions on the geometry, detector noise
QUADOSQUADOS IRSNIRSN
Example of a GeHP detector simulated byA.L. Weber (IRSN/DSMR/SATE)
X-Ray photograph of Ge 2D plot
QUADOSQUADOS IRSNIRSN
Description of the geometry
- Al cryostat
Al holder
Ge detector (core)
Ge dead layer
Be window
γ
QUADOSQUADOS IRSNIRSN
Proposed Tasks
1) Determination of peak efficiencies and PHD at 8 energies ( 15, 30, 60, 100, 250, 500, 750, 1000 keV)
2) Estimation of the influence of the following parameters: - dead layer thickness- Source distance- Angle 2°
3) Estimation of the influence of the Al holder (optional)4) Influence of the incidence angle on PHD (optional)
QUADOSQUADOS IRSNIRSN
XXP7-I
Doppler B.XXP7-H
XP7-G
XP7-F
XXXXP7-E
XXXP7-D
DopplerBroadening
X(peak)
X(peak)
XP7-C
X (peak)XP7-B
Doppler B.XXXXP7-A
CommentTask 4(optional)
Task 3(optional)
Task 2Task 1Participant
QUADOSQUADOS IRSNIRSNXXP7-R
X (peak)
XP7-Q
Doppler B.XP7-P
XP7-O
XXXXP7-N
XP7-M
X(peak)
XP7-L
X(peak)
X (peak)
XP7-K
XP7-J
CommentTask 4(optional)
Task 3(optional)
Task 2Task 1Participant
QUADOSQUADOS IRSNIRSN
Monte Carlo Codes used
• MCNP 4B, 4C, 4C2, 4C3 : P7-B, P7-D, P7-E, P7-F, P7-I, P7-L, P7-N, P7-O, P7-Q, P7-R
• MCNPX 2.4.j : P7-G• EGS4-UCDOD : P7-A• EGS4 + KEK improvement: P7-H• EGSNrc (v2): P7-M• GEANT 3: P7-K• PENELOPE v2001: P7-J• Beta version of MCNP 5 : P7-P
QUADOSQUADOS IRSNIRSN
Method used to analyze the results
• How to compare pulse height distributions ?
0.00 0 .01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1010 - 8
10 - 7
10 - 6
10 - 5
10 - 4
10 - 3
10 - 2
100keV , Norm al
Pul
se H
eigh
t D
istr
ib. /
sou
rce
part
icle
Energy (M eV )
QUADOSQUADOS IRSNIRSN
Method used to analyze the results
• Pulse height distribution divided into several areas• Energy limits of the areas depend on the incident
photon energy
QUADOSQUADOS IRSNIRSN
Method used to analyze the results
• Counts per source particle in the energy binnings of these areas are summed
• The results of the sums are compared to the author’s sums.
• The number of areas depend on the photon energy ( ex: 6 areas at 30 keV, 9 at 100 keV, 5 at 1 MeV)
6 areas for 30 keV: 1-4.2,4.2-9,9-14.8,14.8-22.4,22.4-29 and 29-31.6 keV
QUADOSQUADOS IRSNIRSN
Task 1
• Determination of peak efficiencies and pulse height distributions at 8 energies
750, 1000 keV).• Peak efficiency is defined as
the number of events in the fullfull--energy peakenergy peak per emitted particle
(15, 30, 60, 100, 250, 500,
QUADOSQUADOS IRSNIRSN
Task 1: Ratios of the 9 areas obtained for photons of 100 keV
En (keV)
Rat
io(p
artic
ipa n
t/ au t
hor )
0 20 40 60 80 100
1.1
P7- AP7-CP7- DP7- EP7-FP7-GP7-H
1.2
1
0.9
0.8
QUADOSQUADOS IRSNIRSN
Task 1: Ratios of the 9 areas obtained for photons of 100 keV
• P7-A and P7-H: The effect of Doppler Broadening to response is simulated.
• The version of MCNP ( 4C2) used by the author does not take into account this effect.
• So the ratios obtained for the region 29.2-44 keV are about 3. Results corresponding to Compton edge area are lower than the author’s result.
• This effect is explained in the presentation of Dr Namito.• The participant P7-C presents this effect in his report but his
results are without Doppler Broadening
QUADOSQUADOS IRSNIRSN
Doppler Broadening effect
This effect changes theshape of pulse heightdistribution in these 3 Areas.
QUADOSQUADOS IRSNIRSNEn (keV)
Rat
io(p
artic
ipan
t/aut
hor)
0 20 40 60 80 1000.75
0.8
0.85
0.9
0.95
1
1.05
1.1
1.15
1.2
1.25
Task 1:100 keV
P7-IP7-JP7-KP7-LP7-MP7-NP7-R
QUADOSQUADOS IRSNIRSNEn (keV)
Rat
io(p
artic
ipan
t/aut
hor)
0 20 40 60 80 1000
1
2
3
4
5
Task 1: 100 keV
P7-BP7-DP7-EP7-HP7-Q
QUADOSQUADOS IRSNIRSN
Task 1: Ratios of the 9 areas obtained for photons of 100 keV
• P7-B: The source used is not isotropic and it is an annular ring source.
• P7-D: The participant simulated the 8 energies in 1 simulation using specific options of MCNP. But the results obtained were not multiplied by this factor 8 .
• P7-E: MCNP code use default parameters for a surface source. The source emission is not isotropic
• P7-H: This participant forgot to normalize the results ( source emission in an hemi-sphere)
• P7-D, P7-E and P7-H computed simulations without these errors: their results are presented on the other figures
QUADOSQUADOS IRSNIRSN
Task 1: Do the results depend on incident E ?R
atio
(par
ticip
ant/a
utho
r)
0.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
1.06
1.07
1.08
1.09P7-AP7-CP7-DP7-EP7-FP7-GP7-H
5 areas:2-168, 168-332, 332-488, 488-495, 495-504 keV
Results are close Effect of Doppler Broadening: smaller
En (keV)0 100 200 300 400 500 600 700 800
1.1Energy: 750 keV
QUADOSQUADOS IRSNIRSN
Do the results depend on incident E ?
En (keV)
Rat
io(p
artic
ipan
t/aut
hor)
0 10 20 30
0.8
0.9
1
1.1
1.2
P7-AP7-CP7-DP7-EP7-FP7-H
Energy : 30 keV
At 30 keV, resultsare close only forthe last area
QUADOSQUADOS IRSNIRSN
Task 1: Do the results depend on incident E ?
En (keV)
Rat
io(p
artic
ipan
t/aut
hor)
0 100 200 300 400 500 600 700 8000.95
0.96
0.97
0.98
0.99
1
1.01
1.02
1.03
1.04
1.05
1.06
1.07
1.08
1.09
1.1
P7-IP7-JP7-KP7-LP7-MP7-NP7-R
Energy: 750 keV
En (keV)
Rat
io(p
artic
ipan
t/aut
hor)
0 10 20 30
0.8
0.9
1
1.1
1.2
P7-IP7-JP7-KP7-LP7-MP7-N
Energy : 30 keV
QUADOSQUADOS IRSNIRSN
Task 1: Results relative to incident E ?
En (keV)
Rat
io(p
artic
ipan
t/aut
hor)
0 100 200 300 400 500 600 700 8000
0.5
1
1.5
2
2.5
3
3.5
4P7-BP7-DP7-EP7-HP7-MP7-PP7-Q
Energy: 750 keV
En (keV)
Rat
io(p
artic
ipan
t/aut
hor)
0 10 20 300
1
2
3
4
5 P7-BP7-DP7-EP7-HP7-PP7-Q
Energy: 30 KeV
QUADOSQUADOS IRSNIRSN
Task 1: Results relative to incident E ?
En (keV)
Rat
io(p
artic
ipan
t/aut
hor)
0 100 200 300 400 500 600 700 800
10-3
10-2
10-1
100
P7-BP7-DP7-EP7-HP7-MP7-0P7-PP7-Q
En (keV)
Rat
io(p
artic
ipan
t/aut
hor)
0 10 20 30
10-4
10-3
10-2
10-1
100
P7-BP7-DP7-EP7-HP7-OP7-PP7-Q
Energy: 30 KeVEnergy: 750 keV
QUADOSQUADOS IRSNIRSN
Task 1: peak efficiencies
Photon energy (keV)
Rat
io(p
artic
ipan
t/aut
hor)
101 102 1030.9
0.92
0.94
0.96
0.98
1
1.02
1.04
P7-AP7-CP7-DP7-EP7-FP7-GP7-H
Photon energy (keV)
Rat
io(p
artic
ipan
t/aut
hor)
101 102 103
0.94
0.96
0.98
1
1.02
1.04
1.06P7-IP7-JP7-KP7-LP7-NP7-R
QUADOSQUADOS IRSNIRSN
Task 1: peak efficiencies
Photon energy (keV)
Rat
io(p
artic
ipan
t/au
101 102 1030
0.5
1
1.5
2
2.5
3.5
4
P7-MP7-PP7-Q
Photon energy (keV)
Rat
io(p
artic
ipan
t/a
101 102 103
10-4
10-3
10-2
100
P7-BP7-DP7-EP7-HP7-MP7-0P7-PP7-Q
thor
) 3P7-BP7-DP7-EP7-H ut
hor)
10-1
QUADOSQUADOS IRSNIRSN
Task 1: Peak efficiencies
• P7-O: There is a problem with the description of the source (volume source and emission )
• P7-P: this participant made an error on the distance between the detector and the source: 20 cm instead of 2 cm
• P7-Q: there is a little shift of energy on the PHD of the participant at 100 keV
QUADOSQUADOS IRSNIRSN
What can we learn from this ?
• Differences observed with the variation of incident E in the areas can be explained by physics model inside Monte Carlo codes= > Doppler Broadening feature ( presentation of Y. Namito)= > Author’s results without this effect
• Factors of under-estimation or over-estimation are due to the source distribution ( annular ring, parallel beam , distance , volume source …)
QUADOSQUADOS IRSNIRSN
Task 2
• Estimation of the influence of the following parameters: - dead layer thickness ( +/- 50%, 50 and 150 µm) - Source distance (+/- 50%, 1.95 and 2.05 cm)- Angle uncertainty (2°)
• The influence of the dead layer thickness ( +/- 50%, 50 and 150 µm) depend on incident energy. At lower energies, this variation could give a factor 30 .
The presentation of Dr Achouri will focus on this point.
QUADOSQUADOS IRSNIRSN
Task 2: Influence of the dead layer thickness on the peak efficiencies
Photon energy ( keV )
Rat
ioof
the
peak
effic
i
101 102 103
10-1
100
1.5 %
enci
esar
eas
101
Influence of DL: 50/100Influence of DL : 150/100
14
0.07
QUADOSQUADOS IRSNIRSN
Task2: dead layer thickness uncertainty
Photon energy (keV)
Rat
io(p
artic
ipan
t/aut
hor)
101 102 103
0.95
1
1.05
P7-AP7-CP7-DP7-EP7-HP7-IP7-NP7-R
Dead layer uncertainty: - 50 %
Photon energy (keV)
Rat
io(p
artic
ipan
t/aut
hor)
101 102 1030.8
0.85
0.9
0.95
1
1.05
P7-AP7-CP7-DP7-EP7-HP7-IP7-NP7-R
Dead layer : + 50 %
QUADOSQUADOS IRSNIRSNPhoton energy ( keV )
Rat
ioof
the
peak
effic
ienc
ies
area
s
101 102 1030.97
0.98
0.99
1
1.01
1.02
1.03
1.04
Influence of distance: 1.95 cm/ 2.00 cmInfluence of distance: 2.05 cm / 2cm
Task 2: Influence of the distance between the source and the Ge detector
3% on peakefficiencies
QUADOSQUADOS IRSNIRSN
Task 2: source distance uncertainty
Photon energy (keV)
Rat
io(p
artic
ipan
t/aut
hor)
101 102 1030.9
0.95
1
1.05
1.1
1.15
1.2
1.25
1.3
P7-AP7-CP7-DP7-EP7-HP7-NP7-R
Distance: 1.95 cm
Photon energy (keV)
Rat
io(p
artic
ipan
t/aut
hor)
101 102 103
0.8
0.85
0.9
0.95
1
1.05
1.1
P7-AP7-CP7-DP7-EP7-HP7-NP7-R
Distance: 2.05 cm
QUADOSQUADOS IRSNIRSN
Task 2: angle uncertainty
Photon energy (keV)
Rat
io(p
artic
ipan
t/au
101 102 1030.9
0.95
1
1.1
P7-AP7-CP7-H
Angle uncertainty: 2 °
thor
) 1.05P7-N
QUADOSQUADOS IRSNIRSN
Task 2
• Results of the participants compared to the author’s results have the same trends than the results of task 1.
QUADOSQUADOS IRSNIRSN
Task 3 (optional)
• Influence of the Al Holder• Any change on peak efficiencies
P7- A
P7-D
P7-E
P7-N
P7-C
QUADOSQUADOS IRSNIRSN
Influence of the Al Holder at 100 keV
En (keV)
Rat
io(w
ithou
tAlH
olde
r/with
AlH
olde
r)
0 20 40 60 80 1000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
Without Al
Factor 5
QUADOSQUADOS IRSNIRSN
Task 3 (optional)
• Important influence of the Al Holder observed only in the computations without Doppler broadening
QUADOSQUADOS IRSNIRSN
What can we learn from this problem ?
• Factors of under-estimation or over-estimation are mainly due to the source distribution ( annular ring, parallel beam , distance , volume source …)
• Users must be aware of that.• At lower energies, physics model of the code could
introduce important factors of under-estimation of numerical PHD compared to experimental ones.
QUADOSQUADOS IRSNIRSN
Check-list for a Ge detector simulation
• Be careful of – the dead layers thickness, – Al holder, – Source ( incident angle, distance …)– Window– Physics at lower energies
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