In this paper, a method is presented for the detection of special nuclear materials (SNMs) in shielded containers, which is both sensitive and applicable under field conditions. The method uses an external pulsed neutron source to induce fission in SNM and subsequent detection of the fast prompt fission neutrons. The detectors surrounding the container under investigation are liquid scintillation detectors able to distinguish gamma rays from fast neutrons by means of pulse shape discrimination method (PSD). One advantage of these detectors, besides the ability for PSD analysis, is that the analog signal from a detection event is of very short duration (typically few tens of nanoseconds). This allows the use of very short coincidence gates for the detection of the prompt fission neutrons in multiple detectors, while benefiting from a low background coincidence rate, yielding a low detection limit. Another principle advantage of this method derives from the fact that the external neutron source is pulsed. By proper time gating, the interrogation can be conducted by epithermal source neutrons only. These neutrons do not appear in the fast neutron signal following the PSD analysis, thus providing a fundamental method for separating the interrogating source neutrons from the sample response in the form of fast fission neutrons. This paper describes laboratory tests with a configuration of eight detectors in the Pulsed Neutron Interrogation Test Assembly (PUNITA). Both the photon and neutron signature for induced fission is observed, and the methods used to isolate these signatures are described and demonstrated.

References

References
1.
Enqvist
,
A.
,
Flaska
,
M.
,
Dolan
,
J. L.
,
Chichester
,
D. L.
, and
Pozzi
,
S. A.
,
2011
, “
A Combined Neutron and Gamma-Ray Multiplicity Counter Based on Liquid Scintillation Detectors
,”
Nucl. Instrum. Methods Phys. Res., Sect. A
,
652
(
1
), pp.
48
51
.
2.
Pozzi
,
S. A.
,
Clarke
,
S. D.
,
Flaska
,
M.
, and
Peerani
,
P.
,
2009
, “
Pulse-Height Distributions of Neutron and Gamma Rays From Plutonium-Oxide Samples
,”
Nucl. Instrum. Methods Phys. Res., Sect. A
,
608
(
2
), pp.
310
315
.
3.
Clarke
,
S. D.
,
Flaska
,
M.
,
Pozzi
,
S. A.
, and
Peerani
,
P.
,
2009
, “
Neutron and Gamma-Ray Cross-Correlation Measurements of Plutonium Oxide Powder
,”
Nucl. Instrum. Methods Phys. Res., Sect. A
,
604
(
3
), pp.
618
623
.
4.
Ocherashvili
,
A.
,
Roesgen
,
E.
,
Beck
,
A.
,
Caspi
,
E. N.
,
Mosconi
,
M.
,
Crochemore
,
J.-M.
, and
Pedersen
,
B.
,
2012
, “
SNM Detection by Means of Thermal Neutron Interrogation and a Liquid Scintillation Detector
,”
J. Instrum.
,
7
, p. C03037.
5.
Favalli
,
A.
,
Mehner
,
H.-C.
,
Crochemore
,
J.-M.
, and
Pedersen
,
B.
,
2009
, “
Pulsed Neutron Facility for Research in Illicit Trafficking and Nuclear Safeguards
,”
IEEE Trans. Nucl. Sci.
,
56
(
3
), pp.
1292
1296
.
6.
Ocherashvili
,
A.
,
Mosconi
,
M.
,
Crochemore
,
J.-M.
,
Beck
,
A.
,
Roesgen
,
E.
,
Mayorov
,
V.
, and
Pedersen
,
B.
,
2013
, “
Fast Neutron Coincidences From Induced Fission as a Method for Detection of SNM
,”
35th European Safeguards Research and Development Association Symposium
(
ESARDA
), Bruges, Belgium, May 27–30, Vol.
49
, pp.
42
51
.
7.
The MathWorks,
2004
, “
MATLAB 7.0 and Statistics Toolbox 7.1
,” The MathWorks, Natick, MA.
8.
X-5 Monte Carlo Team Diagnostics Applications Group Los Alamos National Laboratory
,
2003
, “
MCNP™—A General Monte Carlo N-Particle Transport Code Version 5
,” Volume I: Overview and Theory, Los Alamos National Laboratory, Report No.
LA-CP-03-0245
.
9.
Ensselin
,
N.
,
Harker
,
W. C.
,
Krick
,
M. S.
,
Langner
,
D. G.
,
Pickrell
,
M. M.
, and
Stewart
,
J. E.
,
1998
, “
Application Guide to Neutron Multiplicity Counting
,” Report No.
LA-13422-M
.
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