Large area (> m2) position-sensitive readout of scintillators is important for passive/active gamma and neutron imaging for counter-terrorism applications. The goal of the LAMPA project is to provide a novel, affordable, large-area photodetector (8” x 8”) by replacing the conventional dynodes of photomultiplier tubes (PMTs) with electron multiplier microstructure boards (MSBs) that can be produced using industrial manufacturing techniques. The square, planar format of the LAMPA assemblies enables tiling of multiple units to support large area applications. The LAMPA performance objectives include comparable gain, noise, timing, and energy resolution relative to conventional PMTs, as well as spatial resolution in the few mm range. The current LAMPA prototype is a stack of 8” x 8” MSBs made commercially by chemical etching of a molybdenum substrate and coated with hydrogen-terminated boron-doped diamond for high secondary emission yield (SEY). The layers of MSBs are electrically isolated using ceramic standoffs. Field-shaping grids are located between adjacent boards to achieve good transmission of electrons from one board to the next. The spacing between layers and the design of the microstructure pattern and grids were guided by simulations performed using an electro-optics code. A position sensitive anode board at the back of the stack of MSBs provides 2-D readout. This presentation discusses the trade studies performed in the design of the MSBs, the measurements of SEY from various electro-emissive materials, the electro-optics simulations conducted, the design of the 2-D readout, and the mechanical aspects of the LAMPA design, in order to achieve a gain of > 104 in an 8-stage stack of MSBs, suitable for use with various scintillators when coupled to an appropriate photocathode.
A new scintillator crystal, now known as CLYC (Cs2LiYCl6:Ce), has been under development for over 15 years (1). It was primarily of interest for radiation detection applications because of its good energy resolution for gamma rays (< 4% for 662 keV gamma rays) and its capability for detection of thermal neutrons. The pulse shapes of the signals from the two radiations are different, which allow them to be separated electronically, permitting simultaneous detection of gamma rays and neutrons. The crystal is now commercially available. Early investigations of the neutron response by the current authors (2) revealed that CLYC also responds to fast neutrons. In fact, the good energy resolution of the response under monoenergetic neutron irradiations showed that CLYC was an excellent high-energy neutron spectrometer. This discovery has great impact on the field of neutron spectroscopy, which has numerous, although often specialized, applications. This presentation focuses on applications in counter-terrorism scenarios where neutrons may be involved. The relative importance of the fast neutron response of CLYC, compared to the thermal and gamma-ray response, will be discussed for these scenarios.
Certain insulating solids can store a fraction of the absorbed energy when irradiated by ionizing radiation. The stored
energy can be released subsequently by heating or optical stimulation. As a result, light may be emitted through
Thermoluminescence (TL) or Optically-Stimulated Luminescence (OSL) and electrons may be emitted through
Thermally-Stimulated Electron Emission (TSEE) or Optically-Stimulated Electron Emission (OSEE).
TL and OSL are widely used in current radiation dosimetry systems. However, despite considerable research effort
during the early 1970s, SEE was not commonly adopted for dosimetry applications. One of the main reasons is that SEE
is a surface phenomenon, while luminescence is a bulk phenomenon, making SEE more susceptible to humidity,
absorption of gases, minor physical defects and handling, both before and after irradiation. Nevertheless, it has been
recognized that SEE may be useful for homeland security applications in nuclear forensics, where dose accuracy is not
the primary performance metric.
In this research, we are investigating the use of SEE for nuclear forensic applications. Many common materials, both
natural and man-made, exhibit the phenomenon, providing an opportunity to use the environment itself as an in-situ
radiation detector. We have designed and constructed a unique prototype reader for conducting SEE measurements. We
have demonstrated that the SEE measurements from a variety of materials are quantitatively reproducible and correlated
to radiation exposure. Due to the broad applicability of SEE, significant additional studies are warranted to optimize this
novel technique for nuclear forensic and other applications.
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.
Tests of existing electronic neutron dosimeters by military and civilian groups have revealed significant performance
limitations. To meet the operational requirements of emergency response personnel to a radiological/nuclear incident as
well as those in the nuclear industry, a new END has been developed. It is patterned after a unique commercial neutron
spectral dosemeter known as the N-probe. It uses a pair of small special scintillators on tiny photomultiplier tubes.
Special electronics were designed to minimize power consumption to allow for weeks of operation on a single charge.
The size, performance, and data analysis for the END have been designed to meet/exceed international standards for
electronic neutron dosimeters. Results obtained with the END prototype are presented.
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. The detector 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 very weak point source offset from the detector to roughly approximate a uniform source at the detector plane. Imagery of mine surrogates is presented. Realistic Monte Carlo simulations were used to estimate performance capability, including spatial resolution and detection times.
Neutron albedo 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 1950's, but only using non-imaging detectors. Without imaging, natural variations in hydrogen content in the soil, chiefly due to moisture, and surface irregularities, produce enough false alarms to render the method impractical in all but the driest conditions. This paper describes research to design and build a prototype landmine detector based on neutron albedo imaging. Realistic Monte Carlo simulations were performed to assess the signal-to-noise ratio for various soil types and moisture contents, assuming a perfect two dimensional neutron imaging system. The study showed that a neutron albedo imager was feasible for mine detection and that image quality could be good enough to significantly improve detector performance and reduce false alarm rates compared to non-imaging albedo detection, particularly in moist soils and where surface irregularities exist. After reviewing various neutron detector technologies, a design concept was developed. It consisted 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. Performance capability, including spatial resolution and detection times, were estimated by modeling. A proof-of-principle imager is now being constructed with an expected completion date of Spring 2002. The detector design is described and preliminary results are discussed.
A DT neutron generator has been integrated into the Canadian Improved Landmine Detection Program's Thermal Neutron Activation sensor. The generator has been redesigned from a commercial version, and the moderator structure around the generator has been completely redesigned. These developments allow the DT generator and its moderator structure to be placed interchangeably into the location currently occupied by a 252Cf source and its moderator structure. Experimental and calculational studies have helped to define the optimal operating parameters for the neutron generator in this application. Performance comparisons between the old californium-based system and the new DT-generator-based system have demonstrated that the new system out-performs the old in all tested scenarios, particularly when the mine is deeply buried or when the source is not directly over the explosive. This is in excellent agreement with calculations performed in the design phase of this system. Combined with the myriad other benefits associated with DT generators over isotopic sources, these results demonstrate the desirability of using a DT generator in a TNA land mine detection system.
A thermal neutron analysis (TNA) detector was developed as a confirmatory sensor for the Canadian ILDP multisensor teleoperated vehicle mounted land mine detector system. ILDP is the only multisensor mine detection system with a confirmation sensor which can reduce false alarms to acceptable levels. The TNA has been experimentally proven to be capable of detection of anti-tank and large anti- personnel mines in acceptable short time periods in its intended role. It has performed well, in extreme climates, in Canadian and U.S. stand-alone tests and in U.S. tests of the complete ILDP system. Current research is aimed at developing a version which is ready for production and field.
To detect and locate buried landmines, the Canadian Department of National Defence (DND) is developing a teleoperated, vehicle-mounted, multisensor system called ILDP. In operation, a suite of 4 detectors scan ahead of the vehicle. Their outputs are combined through data fusion to indicate the possibility of a mine at a particular location, within a 30 cm radius. A thermal neutron activation (TNA) sensor, mounted behind the vehicle, is used to confirm the presence of explosives via detection of the 10.83 MeV gamma-ray associated with neutron capture on 14N. The TNA system developed for this uses a 100 microgram 252Cf neutron source surrounded by four 7.62 cm X 7.62 cm NaI(Tl) detectors. A combination of 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; (1) confirm the presence of all surface-laid or shallowly-buried anti-tank mines in a few seconds to a minute (depending on mass of explosive) (2) confirm the presence of anti-tank mines down to 20 cm depth in less than 5 minutes. (3) confirm the presence of large (greater than 100 g Nitrogen) anti-personnel mines in less than five minutes (4) operate in adverse climatic conditions. These results have been verified in field trials using the prototype sensor. Work is now ongoing to miniaturize the electronics, make the system robust and easy to use and investigate the use of an electronic neutron generator expected to enter service by the year 2000.