QUADOS IRSN - ENEAold.enea.it/com/web/news/attiv/p_guald/P7_Menard_Summary.pdfQUADOS IRSN. Task 1:...

QUADOSQUADOS IRSNIRSN

ProblemProblem P7P7

Stéphanie MénardStéphanie MénardIRSNIRSN

DosimetryDosimetry DepartmentDepartment92262 Fontenay92262 Fontenay--auxaux--RosesRoses

FRANCEFRANCE


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


What do we measure with a spectrometer ?

• Pulse height distributions => Energy

• Peak count rates => Fluence


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


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


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


Example of a GeHP detector simulated byA.L. Weber (IRSN/DSMR/SATE)

X-Ray photograph of Ge 2D plot


Description of the geometry

- Al cryostat

Al holder

Ge detector (core)

Ge dead layer

Be window

γ


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)


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


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


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 )



• Pulse height distribution divided into several areas• Energy limits of the areas depend on the incident

photon energy



• 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


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,


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



• 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


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



• 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


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


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


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


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


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


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


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


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


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 …)


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.


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


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


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


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


Task 2

• Results of the participants compared to the author’s results have the same trends than the results of task 1.


Task 3 (optional)

• Influence of the Al Holder• Any change on peak efficiencies

P7- A

P7-D

P7-E

P7-N

P7-C


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


Task 3 (optional)

• Important influence of the Al Holder observed only in the computations without Doppler broadening


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.


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

QUADOS IRSN - ENEAold.enea.it/com/web/news/attiv/p_guald/P7_Menard_Summary.pdfQUADOS IRSN. Task 1:...

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