The development of a thermal neutron activation (TNA) system as a confirmatory non-metallic land mine detector

Abstract

In order to detect and locate buried landmines for peacekeeping, the Canadian Department of National Defence (DND), under the Improved Landmine Detection Project, is developing a vehicle-mounted, two-phase mine detection system. The first phase constitutes a suite of detectors used to indicate the possibility of a mine at a particular location (to _+30 cm in accuracy). In the second phase a Thermal Neutron Activation (TNA) system is used to confirm the presence of explosives via detection of the 10.83 MeV gamma-ray associated with nitrogen decay. The TNA system developed for this uses a 100 p~g 252Cf neutron source surrounded by four 3"x3" NaI(T1) detectors. Combining the use of state-of-the art radiation transport codes for design, judicious choice of specialized shielding materials and development of high-rate, fast-pulse processing electronics, has led to a system which can; (i) confirm the presence of all surface-or lightly-buried anti-tank mines in a few seconds to a minute (depending on mass of explosive), (ii) confirm the presence of anti-tank mines down to 20 cm depth in less than 5 minutes, (iii) confirm the presence of large (>100 g nitrogen) anti-personnel mines in less than five minutes, (iv) operate in adverse climatic conditions. These results have been verified in field trials and the system is due to be fielded in 1999.

A militarily fielded thermal neutron activation sensor for landmine detection

“…1 For the landmine scenario, very few environmental gamma rays are present in the nitrogen ROI ð$9:5211:1 MeVÞ, due to low isotopic abundance, low capture cross-sections or both. Although the 10.607 MeV line from thermal neutron capture on 29 Si can be marginally visible at low source strengths [9], comparisons of spectra for low-and high-strength sources have shown [3] that the pile-up spectrum dwarfs any silicon contribution at the source strengths used in the operational TNA. Cosmic rays also contribute to the ROI background spectrum, but are negligible compared to the pile-up spectrum.…”

“…The output of each module contains all needed signals for data processing and recording to allow pulse-height display and control by a host computer. This integrated and miniaturized system is based on signal processing concepts and design that were developed and proven in the prototype TNA system [3].…”

“…Limited in-house [3] and independent [14] performance evaluations have been done with the prototype TNA operated separately from the other ILDS detectors. These results are of limited use for the production instrument, both because the former had significant problems with temperature stability and background correction when the tests were done and because the background compensation methods now used are markedly improved.…”

“…The prototype TNA detector has been described previously [3,4]. In this paper, we will describe the production version of the TNA, which is based on the prototype.…”

Landmine detection with the neutron backscattering method

“…Techniques that can give information on the content of the mine are thermal neutron analysis (TNA) [6], [7] and pulsed fast neutron analysis (PFNA), or a combination of the two [8]. Also, information on the content of the mine can be gathered from the energy of neutrons that elastically interact in the hidden explosive, also known as elastically backscattered spectrometry (EBS) [9].…”