Portable active interrogation system

Using electronic neutron generators in active interrogation to detect shielded fissionable material

“…It is interesting to compare the data for the enriched uranium with the delayed-neutron data presented by Moss et al using test samples of a 5 kg sphere of similarly enriched uranium in a bare configuration, and when shielded by iron, lead, and polyethylene. [11] In particular it is worth noting that the neutron generator used in this reference is liquid-insulated (fluorinert FC-77), with several liters of fluid used in place of the low-density sulfur hexafluoride gas used in the MP-320, which may have slightly moderated the out going neutron spectrum and improved the induced fission rate versus that from an unmoderated spectrum. For those measurements the ENG to test item spacing was 100 cm (compared with approximately 50 cm for the tests reported here) and the test item to detector spacing was also 100 cm (again compared with approximately 50 cm for the tests reported here.)…”

“…Using an external neutron radiation source to probe a suspect SNM-containing object produces additional SNM signatures, generally stronger and less ambiguous than the passive signatures, which can allow positive/negative determinations to be made quicker and with lower material detection limits than with passive screening alone. [5][6][7][8][9][10][11][12][13][14][15][16][17] The most commonly used active neutron interrogation techniques for SNM detection involve the use of electronic neutron generators (ENGs), which produce nearly monoenergetic fast neutrons at either 2.5 or 14.1 MeV, operating as pulsed neutron sources. For these measurements the ENGs generate short pulses of neutrons, ranging from 0.01 ms to 1 ms, and typically pulse at frequencies on the order of ~100 Hz.…”

“…[5][6][7][8]10,11,15] These measurements can include the detection of gamma rays and/or neutrons and the technique has proven useful in many situations. One challenge with this technique is that the intensity of these post-fission 'delayed' signatures is not high, at least in comparison with the gamma-ray and neutron signatures originating directly from fission.…”

Addressing different active neutron interrogation signatures from fissionable material

“…Moss et al have shown that kg quantities of HEU within light shielding may be easily detected by measuring Edelayed neutrons in between pulses in just a few seconds. [12] A considerable effort has been expended recently to develop and test active neutron interrogation systems with the intention of measuring the DA neutron signal from a threat object and it deserves some elaboration. [13][14][15][16][17][18][19] In DA measurements a pulsed radiation source is used to inject a population of neutrons into a test object (either directly using a neutron source or indirectly using bremsstrahlung).…”

Neutron interrogation of high-enriched uranium by a 4MeV linac

“…For producing interrogating neutrons, a lot of methods have widely been applied. In the fields of safeguards and illicit trafficking of NM, pulsed D-T neutron generators (14 MeV) represent a sensitive and versatile variant of active interrogation systems, by counting delayed fission product neutrons [1,2], or gammas [3]. Larger and more effective systems designed basically for inspecting sea cargo rely on photoneutron interrogation by -up to 24 MeV -linacs [4,5].…”