This paper discusses our initial investigation of fast neutron detection with a Cs 2 LiYCl 6 (CLYC) scintillator. CLYC has been already developed for dual mode detectors (thermal neutrons and gamma rays). Described are results collected under mono-energetic irradiation from a Van de Graaff generator and a continuous irradiation from a 252 Cf source. There are two reactions in which fast neutrons are captured 35 Cl(n,p) 35 S and 6 Li(n,t)α; both have been observed. They produce a proton and a pair of α/t particles, respectively. The response to mono-energetic fast neutrons due to the 35 Cl(n,p) reaction produces a peak and due to the 6 Li(n,t) reaction a continuum in the energy spectra. The relation between the peak (continuum) position and the excitation energy is linear within evaluated energy range. This allows for fast neutron spectroscopy. The α/β ratios for both reactions were found to be different and somewhat dependent on the excitation energy. The decay times under the proton excitation slightly differ from these under the α/t excitation, while both are significantly different from the gamma ray excited curves. This is important for pulse shape discrimination. Using continuous excitation from 252 Cf initial efficiency was estimated for the 35 Cl(n,p) reaction. For a 1-inch right cylinder crystal the measured intrinsic efficiency is at least 0.06%, while calculated is 0.5%. The discrepancy is due to experimental inaccuracies. The relative detection efficiency scales linearly with the volume. A convolution of the theoretical 252 Cf fast neutron distribution and the 35 Cl(n,p) cross-section curve was found to match the experimental data.

In this paper we introduce a new scintillator for fast neutron and gamma ray detection, Cs2NaYCI6:Ce (CNYC). The material belongs to the elpasolite crystal family. The fast neutron detection is based on the 35Cl(n,p)35S reaction. The proton produced carries the energy proportional to the excitation energy. We show neutron energy spectra measured under continuous excitation (Cf-2S2, Am/Be) and mono-energetic excitation (from a Van de Graaff generator). The latter show clear peaks in the energy spectra. Gamma detection is also discussed. The 7% (FWHM) energy resolution was measured at 662 keV. The light yield was estimated to be lower than 10,000 photons/MeV. The material shows good proportionality, as most elpasolite scintillators. Therefore improvement in the energy resolution is expected should better light yield be achieved. Decays times and pulse shape discrimination is also discussed. The latter is critical in extracting neutron data.

The response of Cs2LiYCl6:Ce (CLYC) scintillator material to fast neutrons has been measured using a Van de Graaff accelerator. Beams of monoenergetic neutrons in the energy range 0.359 MeV to 4.703 MeV were used to irradiate a 9 mm × 9.5 mm × 12 mm CLYC crystal. Following pulse-shape discrimination to separate neutron and gamma-ray events, peaks are observed in the neutron spectrum and assigned to fast-neutron events in the scintillator. One of the peaks is interpreted as being due to the 35Cl(n, p)35S reaction, and it is shown that the proton energy released in this reaction varies linearly with the energy of the incoming neutron. The linearity of the response may enable CLYC to be used for fast-neutron spectroscopy with well defined spectral peaks. The response of CLYC to thermal neutrons and gamma rays is well known, and the material has potential for simultaneous thermal-neutron detection, fast-neutron spectroscopy, and gamma-ray spectroscopy.

Detection of radionuclides emitting short-range radiation, such as alpha and low-energy beta particles, has always presented a challenge, particularly when such radionuclides are dispersed over a wide area. In this situation, conventional detection methods require the area of interest to be surveyed using a fragile probe at very close range - a slow, error-prone, and potentially dangerous process that may take many hours for a single room. The instrument under development uses a novel approach by imaging radiation-induced fluorescence in the air surrounding a contaminated area, rather than detecting the radiation directly. A robust and portable system has been designed and built that will allow contaminated areas to be rapidly detected and delineated. The detector incorporates position-sensitive photo-multiplier tubes, UV filters, a fast electronic shutter and an aspherical phase mask that significantly increases the depth-of-field. Preliminary tests have been conducted using sealed Am-241 sources of varying activities and surface areas. The details of the instrument design will be described and the results of recent testing will be presented.

On-site detection and measurement of the activity and extent of alpha (α) contamination presents a significant challenge to radiation detection personnel. Due to the short range of these particles, conventional detection techniques involve bringing a probe within a few centimetres of the suspect area. Performing a thorough survey of an area is a time consuming, painstaking, and potentially dangerous task, as personnel may be exposed to harmful radiation. Conventional detectors may have fragile Mylar windows which are highly prone to breakage. The instrumentation under development employs a novel approach: instead of detecting the radiation directly, it detects radiation-induced air fluorescence surrounding the contaminated area. Optical imaging is used to determine the spatial extent of the contamination, providing a much more rapid, accurate and robust tool for in-situ contamination measurements. A mobile, near-field, wide-angle, fast optical system has been designed and constructed to detect and image this radiation-induced air fluorescence. It incorporates large-area position-sensitive photo-multiplier tubes, UV filters, a specially constructed fast electronic shutter, and an aspherical phase mask to significantly increase the instrument's depth-of-field. First tests indicate that a 0.3 μCi α source can be detected in less than 10 seconds at a standoff distance of 1.5 meters.

The Improved Landmine Detector System, a militarily fielded, teleoperated vehicle-mounted multi-sensor landmine detector, uses a thermal neutron analysis (TNA) detector to confirm the presence of a mine by detecting the bulk nitrogen in its explosives. To improve the nitrogen sensitivity or measurement times of the TNA detector, higher gamma ray rates will be required. The chief bottleneck to achieving the maximum possible performance from the present TNA or future versions is the relatively slow fluorescent decay time of the NaI(Tl) scintillators which are currently used. An experimental investigation was undertaken to compare a number of modern, fast inorganic scintillators to NaI(Tl) with respect to parameters relevant to TNA landmine detection, including efficiency, energy resolution, linearity, available size and cost. This paper presents results in the context of the high-rate, high-gamma-energy environments expected in such a TNA application. Large (7.62 cm times 7.62 cm) LaBr 3 :Ce scintillators, and to a lesser degree LaCl 3 :Ce, were found to stand-out as as the principal candidates for the detector upgrade to the TNA confirmation system. Their properties also make them ideal candidates for fast neutron analysis and associated particle imaging bulk explosives detectors.

The Improved Landmine Detector System is a vehicle-mounted multi-sensor landmine detector, conceived and developed by Defence R&D Canada (DRDC). Suspicious targets are identified by fusing data from scanning sensors. A Thermal Neutron Activation (TNA) detector, developed by DRDC and Bubble Technology Industries (BTI), then confirms the presence of a mine by detecting the bulk nitrogen in its explosives. While the first generation TNA detector has been fielded by the Canadian Forces, DRDC and BTI have continued development and optimization of a second generation TNA sensor based around an electronic neutron generator source. By implementing faster detectors, faster electronics and more intense neutron sources, it is possible that this system could achieve 10 to 15 times higher rates, allowing correspondingly higher sensitivity or shorter detection times for landmines. The chief bottleneck to achieving the maximum possible performance from the present TNA or a future system is the relatively slow fluorescent decay time of the NaI(Tl) scintillators which are currently used. An experimental investigation was undertaken to compare a number of modern, fast inorganic scintillators to NaI(Tl) with respect to parameters relevant to TNA, including efficiency, energy resolution, linearity, available size and cost. This paper presents results in the context of the high-rate, high-gamma-energy environments expected in a TNA application. Large (7.62 cm × 7.62 cm) LaBr3:Ce scintillators, and to a lesser degree LaCl3:Ce, were found to stand-out as as the principal candidates for the detector upgrade to the TNA confirmation system. Their properties also make them ideal candidates for fast neutron activation and associated particle imaging bulk explosives detectors.

Nuclear methods have long been one of the few techniques available to aid in the detection and identification of potentially dangerous objects in a non-intrusive manner. The application of neutron-based methods has been particularly successful in bulk material detection and identification, owing to the neutron's capability to penetrate deep into materials, and its nuclide-specific interactions which can be used to make direct measurements of a target's elemental composition. Defence R&D Canada - Suffield's initial work in the area of penetrating radiation resulted in the development of the recently commercialized Minespec, a Thermal Neutron Analysis (TNA) system for buried-explosives detection. Co-developed with Bubble Technology Industries Inc., as the confirmation detector for a multi-sensor anti-tank landmine detection system, continuing improvements to the TNA system have included the inclusion of an electronic pulsed neutron generator - an upgrade that presents the possibility of utilizing Fast Neutron Analysis (FNA) methods to improve the system's detection capability. In this paper we will discuss the Minespec system and report on our investigations regarding the possibility for incorporating an FNA component to provide complementary information to assist in anti-tank landmine detection.

Neutron moderation land mine detection involves irradiating the ground with fast neutrons and subsequently detecting the thermalized neutrons which return. This technique has been studied since the 1950s, but only using non-imaging detectors. Without imaging, natural variations in moisture content, surface irregularities, and sensor height variations produce sufficient false alarms to render the method impractical in all but the driest conditions. This paper describes research to design and build a prototype land mine detector based on neutron moderation imaging. After reviewing various neutron detector technologies, a design concept was developed. It consists of a novel thermal neutron imaging system, a unique neutron source to uniformly irradiate the underlying ground, and hardware and software for image generation and enhancement. A proof-of-principle imager has been built, but with a point source offset from the detector to roughly approximate a very weak uniform source at the detector plane. Imagery from the detector of mine surrogates is presented. Realistic Monte Carlo simulations were performed using the same two dimensional neutron imaging geometry as the detector in order to assess its performance. The target-to-background contrast was calculated for various soil types and moisture contents, explosive types and sizes, burial depths, detector standoffs, and ground height variations. The simulations showed that the neutron moderation imager is feasible as a land mine detector in a slow scanning or confirmation role and that image quality should be sufficient to significantly improve detector performance and reduce false alarm rates compared to non-imaging albedo detection, particularly in moist soils, where surface irregularities exist and when the sensor height is uncertain. Performance capability, including spatial resolution and detection times, was estimated.