NEUTRON SPECTROMETRY WITH He-3 PROPORTIONAL

COUNTERSM. Manolopoulou1, M. Fragopoulou1, S. Stoulos1, E.

Vagena1, W. Westmeier2, M. Zamani1

1School of Physics, Aristotle University of Thessaloniki, Hellas

2Philipps-Universität, 35032 Marburg, Germany

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Outline Operational characteristics of the counter Energy Calibration Efficiency Calibration Simulation with Geant4 and comparison

with the experimental results Neutron spectrum unfolding example

2

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0 1000 2000 3000 4000 5000 6000 7000100

1000

10000

100000

Deposited energy [MeV]

Coun

ts

0.68 MeV

0.89 MeV

1.1 MeV

3.3 MeV

5.0 MeV

5.6 MeV

He-3 counter spectra

Full energy peak

3He(n,p)3HQ=764 keV

Recoil peak 3He(n,elastic)

0.75*En

3He(n,d)2HQ=-3.3 MeV

Thermal – epithermal peak

(764 keV)

3

Counter characteristics Gas Pressure 6 Atm Gas Mixture 3He 65% Kr 33% CO2

2% Diameter 5 cm Effect. length 15 cm Cathode SS304, 0.9 mm Anode Tungsten, 25 μmCd cover 1.2

mm

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Irradiations at the Institute of Nuclear Physics, Demokritos, Athens

Proton Beam: 2.0 – 5.0 MeV 7Li(p, n)7Be En = 0.23 – 3.3 MeV Deuteron Beam: 1.4–7.8 MeV 2H(d, n)3He En = 3.7 – 10.7 MeV

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1 2 3 4 5 64%

68%132%196%260%324%388%452%516%580%644%708%772%836%900%964%

Neutron Energy [MeV]

Reso

lutio

n [%

]

Shap. Time 8 μs

0 500 1000 1500 2000 2500 30001

1,001

2,001

3,001

4,001

5,001

6,001

7,001

Channel

Dep

osite

d E

nerg

y [M

eV]

1500 V 1600 V 1700 V 1800 V

1870 V

NIM A 562(2006) 371 “Studies on the response of He-3 and He-4 proportional counters to monoenergetic fast neutrons“

Full energy peak

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0 200 400 600 800 1000 1200 1400 1600 18000

1

2

3

4

5

6

Channel

Depo

site

d En

ergy

[M

eV]

1500 V 1600 V 1700 V 1800 V

1870 V

Energy calibration of Recoil peak

6

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Comparison of energy calibration for Full-energy and Recoil peaks

0 500 1000 1500 2000 25000

2

4

6

8

Channel

Dep

osite

d En

ergy

[M

eV]

1870 V1700 V

1500 V

7

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Pulse height loss of recoil events

0 1 2 3 4 5 60.0

0.2

0.4

0.6

0.8

1.01500 V1600 V1700 V1800 V1870 V

3He recoil-nucleus energy [MeV]

Δp [

MeV

]

8

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Pulse height loss of recoil events

NIM A 618 (2010) 284-293. “Non linearity of recoil pulse height events in He-3 tubes”

9

c

c

E

E

EEEER

EEEdEEEaEaEaaERp

c

030

035430 )1ln)(5.1(0

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0 0.5 1 1.5 2 2.5 31E+00

1E+01

1E+02

1E+03

Neutron Energy [MeV]

Rela

tive

neu

tron

fluen

ce 565 keV1.2 MeV

2.5 MeV

Irradiations at the PTB calibrated neutron field

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Pulse height distributions obtained with He-3 counter

565 keV 1.2 MeV

2.5 MeV

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Geant4 simulation results

0 500 1000 1500 2000 2500 3000 3500 40001

10

100

1000(n,p)Recoil He-3Recoil C,O,Kr,+

Deposited Energy [MeV]

Coun

ts

12

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Simulation results folded with resolution function

0 500 1000 1500 2000 2500 3000 3500 40001

10

100

1000

Deposited Energy [MeV]

Coun

ts

13

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Experimental and simulated spectra

0 500 1000 1500 2000 2500 3000 3500 40001

10

100

1000

10000ExperimentalSimulated Sp.

Deposited Energy [MeV]

Coun

ts

565 keV

1.2 MeV 2.5

MeV

14

1E-08 1E-06 1E-04 1E-02 1E+00 1E+02 1E+041E-06

1E-05

1E-04

1E-03

1E-02

Neutron Energy (MeV)

Neu

tron

Flue

nce

(n.c

m-2

.D-1

)

Calculated neutron fluence during irradiation of the extended natU/Pb-assembly with 1.6 GeV deuterons

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Comparison of experimental and simulated spectra

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0 1 2 3 4 5 6 7 8 91

10

100

1000

10000

100000

Experimental SpectrumSimulation results

Deposited Energy [MeV]

Cou

nts

Neutron yield energy distribution

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0.1 1 100

1

2

3

4

5

6

Neutron Energy [MeV]

Neu

trons

/ D

eute

ron

0.10 1.00 10.000

3

6

9

12

15

18He-3 analysisDCM-DEM code

Neutron Energy [MeV]

Neu

trons

/ D

eute

ron

Conclusions He-3 proportional counter response can be simulated with

Geant4 provided that besides the spectrometry functions, recombination coefficient of 3He recoiling nucleus will be determined experimentally.

Using the calculated response with Geant4, neutron energy distribution of a neutron field in the MeV energy region can be determined for the energy range ~ 0.2 – 7 MeV.

No prior knowledge of neutron energy distribution is required.

Thank you for your attention

18VARNA 2011