This PDF file contains the front matter associated with SPIE Proceedings Volume 9595 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

The problem of accurately detecting extremely low levels of nuclear radiation is rapidly increasing in importance in nuclear counter-proliferation, verification, and environmental and waste management. Because the ²³⁹Pu gamma signature may be weak, for instance, even when compared to the natural terrestrial background, coincidence counting with the ²³⁹Pu neutron signature may improve overall ²³⁹Pu detection sensitivity. However, systems with sufficient multiple-particle detectors require demonstration that the increased sensitivity be sufficiently high to overcome added cost and weight. We report the results of measurements and calculations to determine sensitivity that can be gained in detecting low levels of nuclear radiation from use of a relatively new detector technology based on elpasolite crystals. We have performed investigations exploring cerium (Ce³⁺)-doped elpasolites C_s2LiYCl₆:Ce³⁺_0.5% (CLYC) and C_s2LiLa(Br₆)_90%(Cl₆)_10%:Ce³⁺_0.5% (CLLBC:Ce). These materials can provide energy resolution (r(E) = 2.35σ(E)/E) as good as 2.9% at 662 keV (FWHM). The crystals show an excellent neutron and gamma radiation response. The goals of the investigation were to set up the neutron/gamma pulse shape discrimination electronics for elpasolite detectors; perform limited static source benchmarking, testing, and evaluation to validate system performance; and explore application of a maximum likelihood algorithm for source location. Data were measured and processed through a maximum likelihood estimation algorithm, providing a direction to the radioactive source for each individual position. The estimated directions were good representations for the actual directions to the radioactive source. This paper summarizes the maximum likelihood results for our elpasolite system.

Scintillation light is widely believed to be Poisson or super-Poisson. We tested this hypothesis by measuring the temporal correlation between two detectors detecting scintillation light resulting from the same gamma-ray event in SrI₂:Eu . Poisson light is expected to yield zero temporal correlations, while super-Poisson light is expected to yield positive, and sub-Poisson light is expected to yield negative temporal correlation. Scintillation light in SrI₂:Eu was found to be negatively correlated. Therefore, we conclude that the scintillation light in SrI₂:Eu is sub-Poisson.

This paper presents a microsystem for remote sensing of high energy radiation in extremely low flux density conditions. With wide deployment in mind, potential applications range from nuclear non-proliferation, to hospital radiation-safety. The daunting challenge is the low level of photon flux densities – emerging from a Scintillation Crystal (SC) on to a ~1 mm-square detector, which are a factor of 10000 or so lower than those acceptable to recently reported photonic chips (including ‘single-photon detection’ chips), due to a combination of low Lux, small detector size, and short duration SC output pulses – on the order of 1 μs. These challenges are attempted to be overcome by the design of an innovative ‘System on a Chip’ type microchip, with high detector sensitivity, and effective coupling from the SC to the photodetector. The microchip houses a tiny n+ diff p-epi photodiode (PD) as well as the associated analog amplification and other related circuitry, all fabricated in 0.5micron, 3-metal 2-poly CMOS technology. The amplification, together with pulse-shaping of the photocurrent-induced voltage signal, is achieved through a tandem of two capacitively coupled, double-cascode amplifiers. Included in the paper are theoretical estimates and experimental results.

A Compton spectrometer has been re-commissioned for measurements of flash radiographic sources. The determination of the energy spectrum of these sources is difficult due to the high count rates and short nature of the pulses (~50 ns). The spectrometer is a 300 kg neodymium-iron magnet which measures spectra in the <1 MeV to 20 MeV energy range. Incoming x-rays are collimated into a narrow beam incident on a converter foil. The ejected Compton electrons are collimated so that the forward-directed electrons enter the magnetic field region of the spectrometer. The position of the electrons at the magnet’s focal plane is a function of their momentum, allowing the x-ray spectrum to be reconstructed. Recent measurements of flash sources are presented.

Degradation of room temperature operation of TlBr radiation detectors with time is thought to be due to electromigration of Tl and Br vacancies within the crystal as well as the metal contacts migrating into the TlBr crystal itself due to electrochemical reactions at the metal/TlBr interface. Scanning Auger electron spectroscopy (AES) in combination with sputter depth profiling was used to investigate the metal contact surface/interfacial structure on TlBr devices. Device-grade TlBr was polished and subjected to a 32% HCl etch to remove surface damage and create a TlBr_1-xCl_x surface layer prior to metal contact deposition. Auger compositional depth profiling results reveal non-equilibrium interfacial diffusion after device operation in both air and N₂ at ambient temperature. These results improve our understanding of contact/device degradation versus operating environment for further enhancing radiation detector performance.

In response to the critical need of more effective bio-dosimetric techniques to improve cancer risk estimation, this paper focuses on the design of an advanced biomedical instrumentation that could be used for radiation risk analysis on space missions. A designed concept for a hodoscope for radiation detection and tracking is tested via Monte Carlo simulation. The device consists of a set of layers of scintillating fibers, above and below a biological sample, in a design that allows for the determination of the direction of incoming and outgoing radiation. The efficiency of energy deposition on each of the different layers of the device is studied for proton radiation. The study of the response for different incoming energy is the main focus, but fiber-size is also a designed parameter considered in this study. The optimum energy range as found to be around 30 MeV’s – 50MeV’s depending on arrangement. It is found that energy deposited by protons in the optimum range in 1 mm-diameter fibers, is large enough for detection. Since smaller fibers allow for larger resolution, it is concluded that they are preferable than 2 mm fibers. Alternative arrangements consisting respectively of 3 and 4 layers of fibers on each side of the sample are tested and compared. It is observed that although one more coordinate for the source is needed, the 3-layers array is a viable alternative when that extra information is available. With this arrangement, the device is sensitive to lower energy photons.

We are investigating scintillator performance in radiographic imaging systems at x-ray endpoint energies of 0.4 and 2.3 MeV in single-pulse x-ray machines. The effect of scene magnification and geometric setup will be examined along with differences between the detector response of radiation and optical scatter. Previous discussion has reviewed energy absorption and efficiency of various imaging scintillators with a 2.3 MeV x-ray source. The focal point of our study is to characterize scintillator blur to refine system models. Typical detector geometries utilize thin tiled LYSO:Ce (cerium-doped lutetium yttrium orthosilicate) assembled in a composite mosaic. Properties of individual tiles are being studied to understand system resolution effects present in the experimental setup. Comparison of two different experiments with different geometric configurations is examined. Results are then compared to different scene magnifications generated in a Monte-Carlo simulation.

In recent years gamma ray imagers such as the GammaCam^TM and Polaris have demonstrated good imaging performance in the field. Imager performance is often summarized as “resolution”, either angular, or spatial at some distance from the imager, however the definition of resolution is not always related to the ability to image an object. It is difficult to quantitatively compare imagers without a common definition of image quality. This paper examines three categories of definition: point source; line source; and area source. It discusses the details of those definitions and which ones are more relevant for different situations. Metrics such as Full Width Half Maximum (FWHM), variations on the Rayleigh criterion, and some analogous to National Imagery Interpretability Rating Scale (NIIRS) are discussed. The performance against these metrics is evaluated for a high resolution coded aperture imager modeled using Monte Carlo N-Particle (MCNP), and for a medium resolution imager measured in the lab.

In ‘radiation remote sensing’ multiple unknown high energy sources are generally involved. The detectors, upon sensing the corresponding mixed signals, must separate their contributions blindly for further analysis. A practical way to perform this separation could be through the Independent Component Analysis algorithm. However, the challenge faced is that theoretically there is no correlation among events, even those arising from the same source – thereby disabling meaningful ICA analysis. We overcome this hurdle by use of a thin barrier and by providing wide detector pulses. The radiation events that interact with the barrier take a longer time to reach the detector due to their increased path length. They also lose some energy, which makes them increasingly prone to capture in the barrier once they have scattered. These observations are confirmed through Monte-Carlo simulations upon Gamma-ray sources. Normalized crosscovariance up to 0.22 was found, but is actually controllable through appropriate selection of the detector shaping-pulse width. Experiments on a physical setup confirm these findings. Finally, the application of the ICA approach is demonstrated to demix, or separate, the individual contributions of the sources to the observed detector signals.

The spatial response of pressurized helium-4 fast neutron scintillation detectors is characterized using collimated neutron source measurements and MCNPX-PoliMi simulations. A method for localizing the position of each detected event is also demonstrated using the two-sided photomultiplier readout. Results show that the position of particle interaction along the axis of the active volume has a measurable effect on the scintillation light response of the detector. An algorithm is presented that uses the probability distribution of relative interaction positions to perform source localization, further demonstrating the applicability of these detectors as tools for the detector of hidden shielded nuclear material.

The Los Alamos Neutron Science Center (LANSCE) is a linear accelerator in Los Alamos, New Mexico that accelerates a proton beam to 800 MeV, which then produces spallation neutron beams. Flight path FP15R uses a tungsten target to generate neutrons of energy ranging from several hundred keV to ~600 MeV. The beam structure has micropulses of sub-ns width and period of 1.784 ns, and macropulses of 625 μs width and frequency of either 50 Hz or 100 Hz. This corresponds to 347 micropulses per macropulse, or 1.74 x 10⁴ micropulses per second when operating at 50 Hz. Using a very fast, cooled ICCD camera (Princeton Instruments PI-Max 4), gated images of various objects were obtained on FP15R in January 2015. Objects imaged included blocks of lead and borated polyethylene; a tungsten sphere; and a tungsten, polyethylene, and steel cylinder. Images were obtained in 36 min or less, with some in as little as 6 min. This is novel because the gate widths (some as narrow as 10 ns) were selected to reject scatter and other signal not of interest (e.g. the gamma flash that precedes the neutron pulse), which has not been demonstrated at energies above 14 MeV. This proof-of-principle experiment shows that time gating is possible above 14MeV and is useful for selecting neutron energy and reducing scatter, thus forming clearer images. Future work (simulation and experimental) is being undertaken to improve camera shielding and system design and to precisely determine optical properties of the imaging system.

The self-magnetic pinch (SMP) diode is an intense radiographic source fielded on the Radiographic Integrated Test Stand (RITS-6) accelerator at Sandia National Laboratories in Albuquerque, NM. The accelerator is an inductive voltage adder (IVA) that can operate from 2-10 MV with currents up to 160 kA (at 7 MV). The SMP diode consists of an annular cathode separated from a flat anode, holding the bremsstrahlung conversion target, by a vacuum gap. Until recently the primary imaging diagnostic utilized image plates (storage phosphors) which has generally low DQE at these photon energies along with other problems. The benefits of using image plates include a high-dynamic range, good spatial resolution, and ease of use. A scintillator-based X-ray imaging system or “gamma camera” has been fielded in front of RITS and the SMP diode which has been able to provide vastly superior images in terms of signal-to-noise with similar resolution and acceptable dynamic range.

Time-domain electromagnetic method used in unexploded ordnance (UXO) detection has always faced the problem of the losing of early-time response due to tailed-current. In this article, the response of UXO like targets with different tailed-current are calculated and measured, and the influence of tailed-current on UXO prospecting is talked. The targets include a sphere, an iron pipe and a shell, and the tailed-current is set with switch-off time varies from 0μs to 230μs. According to magnetic surface modes(MSM), the step response of a compact steel target exhibits an early algebraic regime wherein the response transitions from t^-1/2 to t^-3/2 decay, followed by a late regime characterized by an exponentially decay. In fact, the transmitter current cannot be turned off immediately, especially for system with multiturn coil and large current. The switch-off process is decided by system parameters such as coil induction, coil resister, damping resister and maximum voltage across the coil. The response of the targets will be distorted dramatically by the tailed-current. The targets responses of tailed-current with different switch-off time are calculated through a convolution algorithm and measured with a specially designed system. The results show that the responses of UXO like targets are influenced by the tailed-current in two ways. Firstly, the primary response of the tailed-current will lead to signal saturation in the early times. Secondly, the off-time responses of UXO like targets are distorted by the tailed-current. All the influences will affect the system ability on detecting and discriminating the UXO like targets. An extra-fast switch-off system and deconvolution strategies are good advices to solve the problems.

Overhauser magnetometer is a high-precision device for magnetostatic field measurement, which can be used in a wide variety of purposes: UXO detection, pipeline mapping and other engineering and environmental applications. Traditional proton magnetometer adopts DC polarization, suffering from low polarization efficiency, high power consumption and low signal noise ratio (SNR). Compared with the traditional proton magnetometer, nitroxide free radicals are used for dynamic nuclear polarization (DNP) to enhance nuclear magnetic resonance (NMR). RF excitation is very important for electron resonance in nitrogen oxygen free radical solution, and it is primarily significant for the obtention of high SNR signal and high sensitive field observation. Therefore, RF excitation source plays a crucial role in the development of Overhauser magnetometer.

In this paper, an improved design of a RF circuit is discussed. The new RF excitation circuit consists of two parts: Quartz crystal oscillator circuit and RF power amplifier circuit. Simulation and optimization designs for power amplifier circuit based on software ADS are presented. Finally we achieve a continuous and stable sine wave of 60MHz with 1-2.5 W output power, and the second harmonic suppression is close to -20dBc. The improved RF circuit has many merits such as small size, low-power consumption and high efficiency, and it can be applied to Overhauser magnetometer to obtain high sensitive field observation.

There are many types of X-ray diodes that are used for X-ray flux or spectroscopic measurements and for estimating the spectral shape of the VUV to soft X-ray spectrum. However, a need arose for a low cost, robust X-ray diode to use for experiments in hostile environments on multiple platforms, and for experiments that utilize forces that may destroy the diode(s). Since the typical proposed use required a small size with a minimal single line-of-sight, a parallel array could not be used. So, a stacked, filtered multi-channel X-ray diode array was developed, called the MiniXRD. To achieve significant cost savings while maintaining robustness and ease of field setup, repair, and replacement, we designed the system to be modular. The filters were manufactured in-house and cover the range from 450 eV to 5000 eV. To achieve the line-of-sight accuracy needed, we developed mounts and laser alignment techniques. We modeled and tested elements of the diode design at NSTec Livermore Operations (NSTec / LO) to determine temporal response and dynamic range, leading to diode shape and circuitry changes to optimize impedance and charge storage. We fielded individual and stacked systems at several national facilities as ancillary ‘ride-along’ diagnostics to test and improve the design usability. We present the MiniXRD system performance which supports consideration as a viable low-cost alternative for multiple-channel low-energy X-ray measurements. This diode array is currently at Technical Readiness Level (TRL) 6.