DocumentCode :
3527886
Title :
An analysis of Intense Pulsed Active Detection (IPAD) for the detection of special nuclear materials
Author :
Swanekamp, Stephen B. ; Apruzese, John P. ; Commisso, Robert J. ; Mosher, David ; Schumer, Joseph W.
Author_Institution :
Plasma Phys. Div., Naval Res. Lab., Washington, DC, USA
fYear :
2010
fDate :
Oct. 30 2010-Nov. 6 2010
Firstpage :
881
Lastpage :
888
Abstract :
This paper analyzes the Intense Pulsed Active Detection (IPAD) approach for active detection of fissile material, highlights some of its merits, and compares it to the multiple-pulse-train LINAC approach. In both cases, bremsstrahlung photons are used to induce fissions. IPAD´s single, 100-ns bremsstrahlung pulse offers the possibility to utilize prompt as well as delayed neutrons emitted during the fission process. A combination of the ITS and MCNPX codes is used to characterize the dose to human tissue and both the prompt and delayed neutron emissions from the induced fissions for incident bremsstrahlung spectra between 6 and 50 MeV. No effects from shielding or from the interaction of the bremsstrahlung with the environment (water, air, etc) have been included in these computations, but these effects are a topic of ongoing work. Curves are developed that give the number of useful prompt neutrons per unit dose and the total number of delayed neutrons per unit dose that are independent of both the total electron charge delivered to the bremsstrahlung converter and the source-to-object distance. Useful prompt neutrons are defined to be those with energies exceeding the highest energy photo-neutron expected from 207Pb for a given bremsstrahlung endpoint energy. The analysis shows that endpoint energies between 9 and 13 MeV are optimum for the production of useful prompt neutrons/dose. Because the prompt signal is very fast, the detection of just two useful prompt neutrons gives a false alarm rate from cosmic-ray neutrons of less than 1 in 106. The analysis for delayed neutrons shows that above 14 MeV endpoint energies, both the neutron production and the dose increase as the endpoint energy squared. This suggests that, for a fixed body dose, no additional delayed neutrons are created above an endpoint energy of 14 MeV. A comparison of the multiple-pulse pulse-train LINAC approach and the single-pulse IPAD approach for detecting delayed neutrons- - is also presented. Because the 3-s detection time for the IPAD system is so much shorter than the 120-s detection time for the LINAC system, the IPAD system produces a signal that is much easier to separate from the cosmic-ray neutron background. This shorter time allows an IPAD system to detect fissile objects with 100% detection rate at a false alarm rate from cosmic-ray neutrons of less than 10-6 compared with a 50% detection rate for a 10% false alarm rate for the LINAC approach. Alternatively, the same detection efficiency as the LINAC approach is obtained with the detector about 2.7 times farther away from the fissile object.
Keywords :
bremsstrahlung; dosimetry; neutron detection; neutron sources; shielding; IPAD system; ITS code; LINAC system; MCNPX code; bremsstrahlung converter; bremsstrahlung endpoint energy; bremsstrahlung photons; bremsstrahlung pulse; cosmic-ray neutron background; delayed neutron emission; detection efficiency; detection time; false alarm rate; fissile material; fissile objects; fission process; high energy photoneutron; human tissue; incident bremsstrahlung spectra; intense pulsed active detection approach; multiple-pulse pulse-train LINAC approach; neutron production; prompt neutron emission; prompt signal; shielding; single-pulse IPAD approach; source-to-object distance; special nuclear materials; total electron charge; Detectors; Electronic mail; Lead; Materials; Neutrons; Photonics; Production;
fLanguage :
English
Publisher :
ieee
Conference_Titel :
Nuclear Science Symposium Conference Record (NSS/MIC), 2010 IEEE
Conference_Location :
Knoxville, TN
ISSN :
1095-7863
Print_ISBN :
978-1-4244-9106-3
Type :
conf
DOI :
10.1109/NSSMIC.2010.5873887
Filename :
5873887
Link To Document :
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