Active Interrogation of Depleted Uranium Using a Single Pulse, High-Intensity Photon and Mixed Photon-Neutron Source

Abstract

Active interrogation is a method used to enhance the likelihood of detection of shielded special nuclear material (SNM); an external source of radiation is used to interrogate a target and to stimulate fission within any SNM present. Radiation produced by the fission process can be detected and used to infer the presence of the SNM. The Atomic Weapons Establishment (AWE) and the Naval Research Laboratory (NRL) have carried out a joint experimental study into the use of single pulse, high-intensity sources of bremsstrahlung x-rays and photoneutrons in an active interrogation system. The source was operated in both x-ray-only and mixed x-ray/photoneutron modes, and was used to irradiate a depleted uranium (DU) target which was enclosed by up to of steel shielding. Resulting radiation signatures were measured by a suite of over 80 detectors and the data used to characterise detectable fission signatures as a function of the areal mass of the shielding. This paper describes the work carried out and discusses data collected with proportional counters, NaI(Tl) scintillators and Eljen EJ-309 liquid scintillators. Results with the x-ray-only source demonstrate detection ( ) of the DU target through a minimum of of steel, dropping to when using a mixed x-ray/photoneutron source. The proportional counters demonstrate detection ( ) of the DU target through the maximum steel shielding deployed for both photon and mixed x-ray/photoneutron sources.Index Terms-Active interrogation, bremsstrahlung x-ray, electron accelerators, nuclear security, photoneutron, special nuclear material (SNM).

Pulsed Power Active Interrogation of Shielded Fissionable Material

“…6(b)), where a lower, yet clearly distinguishable, signal is observed above the blank- target shot for a steel thickness of 19.1 cm. The results for the neutron pulse shape selected events in the liquid scintillation detection array, as discussed in [14] [15], show that the array measured counts that are comparable in magnitude to that observed by the , albeit with a steeper falloff as the shielding was increased. At a of g cm the array measured a signal that is indistinguishable from the blank-target.…”

“…However, in the regime of low overall counts above background (for greater than g cm ), the differences for increased steel thickness become less pronounced with statistical fluctuations dominating. The results from the NaI(Tl) array, as discussed in [14] [15], show that the unshielded DU target shot resulted in detection three orders of magnitude above the blank-target shot. For steel shielding with of g cm the array measured roughly three times more signal-above the blank-target shot-than is required to trigger the data acquisition system.…”

“…The goal of this campaign was to demonstrate that a high-confidence measurement of an unshielded/shielded fissionable target (DU: depleted uranium, ) could be achieved using a wide variety of neutron and -ray detection arrays in the harsh active interrogation environment in a timeframe of s. This manuscript is intended to complement the results presented in Clemett et al [14], which describes the portion of this campaign conducted using three types of interrogating sources while the DU target was shielded with highmaterial only. Measurement of the delayed -ray signature, as well as the delayed neutron signature, using NaI(Tl) detectors and a small array of moderated thermal and fast neutron detectors, respectively, are discussed in that publication.…”

Low-dose material-specific radiography using monoenergetic photons

“…The detection of shielded special nuclear material (SNM) has been named one of engineering’s grand challenges of the 21st century by the Department of Homeland Security [3]. Containers can be probed for presence of SNM by bombarding the cargo with γ rays, x rays, or neutrons, for imaging or detection of isotope-specific signatures [4–7]. These active interrogation methods can be more robust than passive interrogation for detection of special nuclear material (SNM), especially in the presence of shielding [8, 9].…”