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Title: Neutron interrogation system using high gamma ray signature to detect contraband special nuclear materials in cargo

Abstract

A system for inspecting cargo for the presence of special nuclear material. The cargo is irradiated with neutrons. The neutrons produce fission products in the special nuclear material which generate gamma rays. The gamma rays are detecting indicating the presence of the special nuclear material.

Inventors:
 [1];  [2];  [3];  [4];  [5];  [1]
  1. Oakland, CA
  2. Berkeley, CA
  3. San Ramon, CA
  4. Palo Alto, CA
  5. Kensington, CA
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
985656
Patent Number(s):
7,359,480
Application Number:
10/838,762
Assignee:
Lawrence Livermore National Security, LLC (Livermore, CA) OAK
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Patent
Country of Publication:
United States
Language:
English
Subject:
98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL PROTECTION

Citation Formats

Slaughter, Dennis R, Pohl, Bertram A, Dougan, Arden D, Bernstein, Adam, Prussin, Stanley G, and Norman, Eric B. Neutron interrogation system using high gamma ray signature to detect contraband special nuclear materials in cargo. United States: N. p., 2008. Web.
Slaughter, Dennis R, Pohl, Bertram A, Dougan, Arden D, Bernstein, Adam, Prussin, Stanley G, & Norman, Eric B. Neutron interrogation system using high gamma ray signature to detect contraband special nuclear materials in cargo. United States.
Slaughter, Dennis R, Pohl, Bertram A, Dougan, Arden D, Bernstein, Adam, Prussin, Stanley G, and Norman, Eric B. Tue . "Neutron interrogation system using high gamma ray signature to detect contraband special nuclear materials in cargo". United States. doi:. https://www.osti.gov/servlets/purl/985656.
@article{osti_985656,
title = {Neutron interrogation system using high gamma ray signature to detect contraband special nuclear materials in cargo},
author = {Slaughter, Dennis R and Pohl, Bertram A and Dougan, Arden D and Bernstein, Adam and Prussin, Stanley G and Norman, Eric B},
abstractNote = {A system for inspecting cargo for the presence of special nuclear material. The cargo is irradiated with neutrons. The neutrons produce fission products in the special nuclear material which generate gamma rays. The gamma rays are detecting indicating the presence of the special nuclear material.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Apr 15 00:00:00 EDT 2008},
month = {Tue Apr 15 00:00:00 EDT 2008}
}

Patent:

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  • A system for inspecting cargo for the presence of special nuclear material. The cargo is irradiated with neutrons. The neutrons produce fission products in the special nuclear material which generate gamma rays. The gamma rays are detecting indicating the presence of the special nuclear material.
  • The goal of the work reported here is to develop a concept for an active neutron interrogation system that can detect small targets of SNM contraband in cargo containers, roughly 5 kg HEU or 1 kg Pu, even when well shielded by a thick cargo. It is essential that the concept be reliable and have low false-positive and false-negative error rates. It also must be rapid to avoid interruption of commerce, completing the analysis in minutes. A new radiation signature unique to SNM has been identified that utilizes high-energy (E{sub {gamma}} = 3-7 MeV) fission product {gamma}-ray emission. Fortunately, thismore » high-energy {gamma}-ray signature is robust in that it is very distinct compared to normal background radiation where there is no comparable high-energy {gamma}-ray radiation. Equally important, it has a factor of 10 higher yield than delayed neutrons that are the basis of classical interrogation technique normally used on small unshielded specimens of SNM. And it readily penetrates two meters of low-Z and high-Z cargo at the expected density of {approx} 0.5 gm/cm{sup 3}. Consequently, we expect that in most cases the signature flux at the container wall is at least 2-3 decades more intense than delayed neutron signals used historically and facilitates the detection of SNM even when shielded by thick cargo. Experiments have verified this signature and its predicted characteristics. However, they revealed an important interference due to the activation of {sup 16}O by the {sup 16}O(n,p){sup 16}N reaction that produces a 6 MeV {gamma}-ray following a 7-sec {beta}-decay of the {sup 16}N. This interference is important when irradiating with 14 MeV neutrons but is eliminated when lower energy neutron sources are utilized since the reaction threshold for {sup 16}O(n,p){sup 16}N is 10 MeV. The signature {gamma}-ray fluxes exiting a thick cargo can be detected in large arrays of scintillation detectors to produce useful signal count rates of 2-4 x 10{sup 4} cps. That is high enough to quickly identify SNM fission by its characteristic high energy {gamma}-ray emission and characteristic fast decay time. Fortunately, the fission product {gamma}-radiation decays with a distinctive T{sub 1/2} = 20-30 sec lifetime that is well matched to cargo scan speeds of about one minute per container. Experimental characterization of the {gamma}-ray fluxes exiting thick cargos has not yet been undertaken. The work reported here leads to definite requirements for the interrogation neutron source that can be met with neutron commercially available source technology. A small (6-20 ft) deuteron accelerator producing about {approx} 1 mA, 2-5 MeV deuteron beam on a deuterium or beryllium target is required. Neutrons produced by such an accelerator are kinematically collimated in the forward direction, reducing shielding requirements while increasing the neutron flux on target to meet the intensity requirement even when there is thick intervening cargo. In addition, this technology provides a very penetrating beam in the energy range 4-8 MeV while remaining below the oxygen activation threshold. Maximum counting statistics and lowest error rates in the identification occur when the beam is pulsed with a 50 % duty cycle. The period for this pulsing must be comparable to the half-lives of the species that make up the signature, i.e. 10-60 sec. This is readily achieved with commercially available equipment and is well suited to rapid scanning of cargo containers.« less
  • A method and a system for detecting the presence of special nuclear materials in a container. The system and its method include irradiating the container with an energetic beam, so as to induce a fission in the special nuclear materials, detecting the gamma rays that are emitted from the fission products formed by the fission, to produce a detector signal, comparing the detector signal with a threshold value to form a comparison, and detecting the presence of the special nuclear materials using the comparison.