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Geoff Parker’s investigations of the yellow dung fly mating system revitalized interest in sexual selection theory, sparked development of sperm competition and sexual conflict theories, and stimulated use of this species as an important model system. Numerous studies across widespread populations have demonstrated large-male advantages in competition contests occurring on dung in cow pastures; however, recent work suggests that smaller males adopt an alternative mating tactic by avoiding dung and instead copulating with females at foraging sites. Though this finding has the potential to expand our understanding of sexual selection in yellow dung flies, such behavior has to date been documented at only one field site, raising the possibility that this phenomenon is highly localized. Here, we report the expression of size-dependent alternative mating tactics across three discrete populations. These findings provide a cautionary tale for researchers limiting their attention to aggregation sites where study organisms are most conveniently encountered.

The paper describes a novel detector for neutrons in the 1 to 20-MeV energy range with combined imaging and spectroscopic capabilities. The Fast Neutron Imaging Telescope (FNIT) was designed to detect solar neutrons from spacecraft deployed to the inner heliosphere. However, the potential application of this instrument to Special Nuclear Material (SNM) identification was also examined. In either case, neutron detection relies on double elastic neutron-proton (n-p) scattering in liquid scintillator. We optimized the design of FNIT through a combination of Monte Carlo simulations and lab measurements. We then assembled a scaled-down version of the full detector and assessed its performance by exposing it to a neutron beam and an SNM source. The results from these tests, which were used to characterize the response of the complete FNIT detector to fast neutrons, are presented herein.

The capability to detect fast neutrons with good angular and energy resolutions is gaining increased interest for different applications such as non-destructive testing, homeland security, and space-borne solar physics. To the latter aim, we recently developed and tested a novel type of instrument, the Fast Neutron Imaging Telescope (FNIT), for neutron spectroscopy and imaging in the 1-20 MeV range. Assessments of the instrument prototype performances, based on Monte Carlo simulations and on results from calibration tests performed in a monoenergetic neutron beam, are presented here. The purpose of the study is twofold: (1) to provide a comprehensive characterization of the prototype response, notably in terms of efficiency, event selection, energy and angular resolution; (2) to validate the simulation tool to support data analysis and reduction, and also to help in the design of more complex fast neutron telescopes.

The Medium Energy Gamma-ray Astronomy (MEGA) telescope concept will soon be proposed as a MIDEX mission. This mission would enable a sensitive all-sky survey of the medium-energy gamma-ray sky (0.4–50 MeV) and bridge the huge sensitivity gap between the COMPTEL and OSSE experiments on the Compton Gamma Ray Observatory and the visionary Advanced Compton Telescope (ACT) mission. The scientific goals include compiling a much larger catalog of sources in this energy range, performing far deeper searches for supernovae, better measuring the galactic continuum and line emissions, and identifying the components of the cosmic diffuse gamma-ray emission. MEGA records and images gamma rays by completely tracking Compton and pair creation events in a stack of double-sided Si strip detectors surrounded by a pixellated CsI calorimeter. A prototype instrument has been developed and calibrated in the laboratory and at a gamma-ray beam facility. We present calibration results from the prototype and describe the proposed satellite mission.

The Medium Energy Gamma-ray Astronomy (MEGA) telescope concept will soon be proposed as a MIDEX mission. This mission would enable a sensitive all-sky survey of the medium-energy gamma-ray sky (0.4–50 MeV) and bridge the huge sensitivity gap left after the demise of the COMPTEL and OSSE experiments on the Compton Gamma-Ray Observatory. The scientific goals include compiling a much larger catalog of sources in this energy range, performing far deeper searches for long-lived nuclear lines from supernovae, novae, and supernova remnants, studying prompt decay lines from solar flares and the interstellar medium, better measuring the diffuse galactic continuum and line emissions, identifying the components of the cosmic diffuse gamma-ray emission, searching for nuclear resonance absorption features in bright continuum spectra, and studying the medium-energy properties of black holes, pulsars, and gamma-ray bursts. MEGA detects and images gamma rays by completely tracking Compton and pair creation interactions in a stack of double-sided silicon strip track detectors surrounded by a pixellated CsI calorimeter. A prototype instrument has been developed and calibrated in the laboratory and at a gamma-ray beam facility. We present calibration results and describe future plans for the prototype, and describe the proposed satellite mission.

We present a Fast Neutron Imaging Telescope (FNIT) that is sensitive to neutrons in the energy range 3 – 100 MeV, optimized to study solar neutrons in the innermost heliosphere. The detection principle is based on multiple elastic neutron–proton scatterings in parallel plastic scintillator layers. Reaction kinematics allows then to determine direction and energy spectrum of the primary neutron flux. A performance evaluation prototype has been built, and we report on first laboratory measurements and Monte Carlo simulation results.

We describe the development and tests of the prototype for a new telescope for Medium Energy Gamma-ray Astronomy (MEGA) in the energy band 0.4–50 MeV. As a successor to COMPTEL and EGRET (at low energies), MEGA aims to improve the sensitivity for astronomical sources by at least an order of magnitude. It could thus fill the severe sensitivity gap between scheduled or operating hard-X-ray and high-energy gamma-ray missions and open the way for a future Advanced Compton Telescope. MEGA records and images γ-rays by completely tracking Compton and Pair creation events in a stack of double-sided Si-strip track detectors surrounded by a pixelated CsI calorimeter. A scaled down prototype has been built and we describe technical details of its design and properties. Results from calibrations using radioactive sources and from measurements with an accelerator generated, fully polarized, γ-ray beam are presented and an outlook to future plans with MEGA is given.

We describe a Fast Neutron Imaging Telescope (FNIT) that is sensitive to neutrons in the energy range 3–100 MeV, optimized to study solar neutrons in the innermost heliosphere. The detection principle is based on multiple elastic neutron–proton scatterings in stacked organic scintillator layers. Plastic scintillator provides the proton target and is an efficient detector of charged particles. At the upper and lower face of each scintillator plate orthogonally oriented wavelength shifting fibers (B � 1 mm) collect and guide the scintillation light to a multi-anode photomultiplier tube (MAPMT). The relative anode signals of the MAPMT register the interaction location while the total intensity of the signal is a measure of the recoil proton energy. Elastic scattering kinematics allows one to determine direction and energy spectrum of the primary neutron flux. A performance evaluation prototype has been built, and we show results from first laboratory measurements. We then present Monte Carlo simulation results to outline the performance of an optimized design. � 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.

We describe the calibration measurements of the MEGA prototype, a tracking Compton and pair creation telescope. The measurements were performed at the high intensity gamma-ray source (HIγS) facility from April 21 to May 06, 2003. The main goal of this calibration was directed at higher energies, above those available from radioactive lab sources, and at polarization. A total of 15.5×10 6 triggered events at 10 energies in the range of 0.7–49 MeV and at six angles of incidence (0°–180°) were recorded.

We report on the development of custom front-end electronics for use with avalanche photodiode (APD) arrays as part of a NASA technology study for the readout of scintillating plastic fibers. APD arrays featuring 64 1 mm square pixels are used. We demonstrate that a pixel of these APD arrays coupled to relatively thin (0.25 mm) and short (15 cm) scintillating plastic fibers can be used to detect and measure the tracks of even minimum ionizing particles. An application-specific integrated circuit (ASIC) implementation of the electronics is required to produce a detector sufficiently compact for practical use in a space flight experiment featuring many thousands of channels. This paper briefly describes the detector concept and performance and presents the design and performance of a four-channel prototype ASIC fabricated using the 0.35 /spl mu/ Taiwan Semiconductor Manufacturing Company (TSMC) process.

An instrument capable of unambiguously determining the energy and direction of incident neutrons has important applications in solar physics, environmental monitoring, and medical/radiological sciences. The SOlar Neutron TRACking (SONTRAC) instrument is designed to operate in the neutron energy range of 20–250 MeV. It is based on non-relativistic double scatter of neutrons off ambient protons within a block of scintillating fibers. Using this double-scatter mode it is possible to uniquely determine neutron energy and direction on an event-by-event basis. A fully operational science model of such an instrument has been built and its performance (energy resolution, angular resolution) calibrated at MeV energies. The science model consists of a 5×5×5 cm3 cube of orthogonal plastic scintillating fiber layers. Two orthogonal imaging chains allow full 3D reconstruction of scattered proton particle tracks. We report the results of the instrument development and calibration efforts, and discuss ongoing developmental efforts to improve performance.

MARGIE (Minute of Arc Resolution Gamma ray Imaging Experiment) is proposed to be a sensitive, large field-of-view, high angular resolution, hard X-ray/gamma ray (20–511 keV) telescope capable of observing gamma ray bursts and point sources with

Polymer flip chip bonding has been used to package a multi-electrode CZT detector. During the packaging process the temperature of all components was kept less than 80°C. The size of the conductive epoxy eontacts is less than 120 μm in diameter. Thermal cycling, and random and structural vibration tests indicate reliable detector–substrate interconnection and rugged construction.

The ratio of the proton's elastic electromagnetic form factors was obtained by measuring the transverse and longitudinal polarizations of recoiling protons from the elastic scattering of polarized electrons with unpolarized protons. The ratio of the electric to magnetic form factor is proportional to the ratio of the transverse to longitudinal recoil polarizations. The ratio was measured over a range of four-momentum transfer squared between 0.5 and 3.5 GeV-squared. Simultaneous measurement of transverse and longitudinal polarizations in a polarimeter provides good control of the systematic uncertainty. The results for the ratio of the proton's electric to magnetic form factors show a systematic decrease with increasing four momentum squared, indicating for the first time a marked difference in the spatial distribution of charge and magnetization currents in the proton.

We have been developing a Compton scatter polarimeter for measuring the linear polarization of hard X-rays (100-300 keV) from astrophysical sources. A laboratory prototype polarimeter has been used to successfully demonstrate the reliability of our Monte Carlo simulation code and to demonstrate our ability to generate a polarized photon source in the lab. Our design concept places a self-contained polarimeter module on the front-end of a a 5-inch position sensitive PMT (PSPMT). We are currently working on the fabrication of a science model based on this PSPMT concept. Although the emphasis of our development effort is towards measuring hard X-rays from solar flares, our design has the advantage that it is sensitive over a rather large field-of-view (>1 steradian), a feature that makes it especially attractive for /spl gamma/-ray burst studies.

Milagro will be the first water-Cerenkov detector specifically built to study extensive air showers. It is being built in an existing man-made pond located near Los Alamos, NM. Milagro will be the only air shower detector to have an energy threshold as low as a few hundred GeV and an angular resolution as good as 0.3°. Milagro will observe the entire overhead sky at all times. We describe here the Milagro detector, it capabilities and its physics goals.

In order to gain insight on a proposed CZT imaging device with orthogonal coplanar anodes currently under development, measurements have been made on an available commercial device with pixels and control electrodes. Charge signals induced on both the pixel and control electrodes by alphas incident at two positions on the cathode side are measured and compared with model predictions. Signals produced by c-rays are also discussed. Measurements and simulations are found to be in reasonably good agreement. It is concluded that the proposed anode geometry might exhibit excellent energy resolution and good position resolution in two dimensions as well as some position information along the depth dimension. ( 1999 Elsevier Science B.V. All rights reserved.

We report on a prototype detector system designed to perform imaging and spectroscopy on 20–250 MeV neutrons. The detection techniques employed can be applied to measurements in a variety of disciplines including solar and atmospheric physics, radiation therapy and nuclear materials monitoring. The detector measures the energy and direction of neutrons by detecting double neutron–proton scatters and recording images of the ionization tracks of the recoil protons in a densely packed bundle of scintillating plastic fibers stacked in orthogonal layers. The scintillation tracks are detected and imaged by photomultipliers and image intensifier/CCD camera optics. By tracking the recoil protons from individual neutrons, the kinematics of the scatter are determined. This directional information results in a high signal-to-noise measurement. The self-triggering and track imaging features of a prototype for tracking in two dimensions are demonstrated in calibrations with 14–65 MeV neutrons, 20–67.5 MeV protons, and with cosmic-ray muons. Preliminary results of phantom imaging measurements using a proton beam are also presented. We discuss several applications for this detector technique and outline future development work.

We report on recent tests and computer simulations of a sub-millimeter pitch CdZnTe strip detector under study as a prototype imaging spectrometer. This paper presents new measurements and new analyses of previous measurements of the CdZnTe transport properties for this prototype and resolves previously reported quantitative discrepancies. Measurements of charge signals produced by /spl alpha/-particles are used to determine the transport properties. These are then used in the model to predict detection efficiencies and spectroscopic performance for /spl gamma/-rays that are compared with the data.

We describe the development of a new balloon-borne telescope known as MARGIE (Minute-of-Arc Resolution Gamma ray Imaging Experiment). It is a coded aperture telescope designed to image photons (in various configurations) over the 20–600 keV range with an angular resolution approaching 1′. MARGIE will use one (or both) of two different detection plane technologies. One such technology involves the use of Cadmium Zinc Telluride (CZT) strip detectors, for which we have successfully demonstrated a spatial resolution of

We report /spl gamma/-ray detection performance measurements and computer simulations of a sub-millimeter pitch CdZnTe strip detector. The detector is a prototype for /spl gamma/-ray astronomy measurements in the range of 20-200 keV. The prototype is a 1.5 mm thick, 64/spl times/64 orthogonal stripe CdZnTe detector of 0.375 mm pitch in both dimensions, with approximately one square inch of sensitive area. Using discrete laboratory electronics to process signals from an 8/spl times/8 strip region of the prototype we measured good spectroscopic uniformity and sub-pitch (/spl sim/0.2 mm) spatial resolution in both x and y dimensions. We present below measurements of the spatial uniformity, relative timing and pulse height of the anode and cathode signals, and the photon detection efficiency. We simulated the photon interactions and signal generation in the strip detector and the test electronics and we compare these results to the data. The data indicate that the cathode signal-as well as the anode signal-arises primarily from the conduction electrons rather than the holes. This presents a detection efficiency limitation which must be considered in the design of strip detector systems.

The literature fails to reflect general agreement over the nature of the services and procedures provided by bioethicists, and the training and core competencies this work requires. If bioethicists are to define their activities in a consistent way, it makes sense to look for common ground in shared communities of practice. We report results of a survey of the services and procedures among bioethicists affiliated with the University of Toronto Joint Centre for Bioethics (JCB). This is the largest group of bioethicists working in healthcare organizations in Canada. The results suggest there are many common services and procedures of JCB bioethicists. This survey can serve as a baseline for further exploration of the work of JCB bioethicists. Common practices exist with respect to the domains of practice, individual reporting relationships, service availability within business hours and the education and training of the bioethicist.

The energy resolution of CdTe and CdZnTe detectors is usually limited by the poor transport properties of holes. Devices segmented into small pixels have been observed to exhibit improved energy resolutions. Simulations have shown that this small pixel effect is due to the fact that small pixels are mostly sensitive to carriers moving close to the pixel, within a distance of the order of the pixel size. In this paper, signals are calculated for CdZnTe strip detectors in order to determine to what extent a similar small electrode effect is produced by strips. The free carrier density distributions following the absorption of a /spl gamma/-ray are calculated by solving the continuity equations. Combined with the strip weighting field, this provides the signal induced in the strip. Simulations are made for various detector geometries and for both the anode and cathode strips. Simulated signals are compared with actual signals measured on CdZnTe detectors.

Nearly 1500 tons of 8000 filament superconductor are required for the Superconducting Super Collider Laboratory (SSCL) main ring dipole magnets. IGC Advanced Superconductors' (IGC-ASI's) major accomplishments in achieving the goals included in the SSCL Phase 1 program are presented. Under the Phase 1 contract, IGC-ASI has assembled 12 Phase 1A and 9 Phase 1B multifilament billets. As required by the program, all the Phase 1B billets, containing one alloy 'source X', were identically processed under the IGC-ASI baseline. An analysis of data generated in the program is given. All data published are based on alloy source X. The authors discuss mechanical properties, including final die draw parameters, superconducting properties, and cable performance, including data affecting strand residual resistivity ratio (RRR). >

The Fast Neutron Imaging Telescope (FNIT) instrument is a NA-22 funded project for the design, construction, calibration and modeling of an instrument specifically tailored to measure and identify sources of fission neutrons - a key signature of Special Nuclear Material (SNM). A neutron detector that is sensitive to this energy range is of utmost importance to stop the proliferation of these materials. The proof of concept of this instrument has been successfully demonstrated with a limited FNIT prototype. After being constructed and fine-tuned at the University of New Hampshire (UNH), the prototype was calibrated with quasi-monoenergetic neutron beams at Crocker Nuclear Laboratory. Extensive Monte Carlo calculations are currently in the advance stages for the modeling of FNIT. These simulations, along with the calibration and tests that have been performed with a 252Cf source at UNH, will be used to determine the instrument efficiency and response. Further instrument simulations will allow us to determine the best methods for spectral and imaging de-convolution. Ultimately, these methods will be implemented into “on-line” software being designed for real-time analysis algorithms to be used in conjunction with a fully populated, portable neutron telescope. We present the most recent laboratory and instrument modeling results.

We have developed a design for a hard X‐ray polarimeter operating in the energy range from 50 to 500 keV. This modular design, known as GRAPE (Gamma‐Ray Polarimeter Experiment), was successfully demonstrated with partially polarized gamma‐ray sources in the lab and fully polarized photon beams at Argonne National Laboratory. In June of 2007, a GRAPE engineering model flew on a high altitude balloon flight which demonstrated the design and collected background data. A much larger payload is currently under development that will provide a significant level of sensitivity for gamma‐ray bursts on a long‐duration balloon flight. The first balloon flight of the full GRAPE instrument is currently scheduled to take place in the Fall of 2011 from Ft. Sumner, NM.

POET (Polarimeters for Energetic Transients) represents a concept for a Small Explorer (SMEX) satellite mission, whose principal scientific goal is to understand the structure of GRB sources through sensitive X‐ray and γ‐ray polarization measurements. The payload consists of two wide field‐of‐view (FoV) instruments: a Low Energy Polarimeter (LEP) capable of polarization measurements in the energy range from 2–15 keV and a high energy polarimeter (Gamma‐Ray Polarimeter Experiment or GRAPE) that would measure polarization in the 60–500 keV energy range. The POET spacecraft provides a zenith‐pointed platform for maximizing the exposure to deep space. Spacecraft rotation provides a means of effectively dealing with any residual systematic effects in the polarization response. POET provides sufficient sensitivity and sky coverage to measure statistically significant polarization (for polarization levels in excess of 20%) for ∼80 GRBs in a two‐year mission. High energy polarization data would also be obtained f...

We describe the development, testing and performance of a Fast Neutron Imaging Telescope (FNIT) with the capability of detecting and composing real-time images of a neutron source. A key signature unique to Special Nuclear Material (SNM) is the emission of fission neutrons. An efficient neutron detector that is sensitive to neutrons in the energy range of 1-10 MeV and with imaging capability represents a key tool for the interdiction of smuggling of clandestine amounts of SNM into the country. A small, modular, organic liquid scintillator detector - initially developed at the University of New Hampshire to study solar neutrons - has been tailored to locate fission neutron sources in homeland security applications. The principle of detection is based on multiple elastic neutron-proton scattering. By measuring the interaction locations and the recoil proton energies, we can determine the direction and energy spectrum of the primary neutron flux along with the location of the neutron source. Key parameters determined in the laboratory thus far have been an energy (trigger) threshold of 200 keV (proton equivalent) and a 5deg (sigma) angular resolution across a broad energy range. This paper outlines the most recent results on instrument development, the FNIT detector's response to SNM and real-time neutron imaging development.

The spare detectors from NASA Compton Gamma-Ray Observatory COMPTEL instrument have been reconfigured to demonstrate the capability at ground level to remotely locate and identify sources of g radiation or the movement of material that might shield γ-ray sources. The Gamma-Ray Experimental Telescope Assembly (GRETA) employs two 28 cm diameter scintillation detectors separated by 81 cm: one 8.5 cm thick liquid scintillator detector and one 7.5 cm thick NaI(Tl) detector. The assembly electronics and real-time data acquisition system measures the energy deposits and time-of- flight for each coincident detection and compiles histograms of total energy and incident angle as computed using the kinematics of Compton scattering. The GRETA field of view is a cone with full angle approximately 120°. The sensitive energy range is 0.3 to 2.6 MeV. Energy resolution is ~10% FWHM. The angular resolution, ~19° in the simplified configuration tested, will improve to better than 5° with well-defined enhancements to the data acquisition hardware and data analysis routines. When operated in the mode that was used in space, the instrument is capable of measuring and imaging up to 30 MeV with an angular resolution of 1.5°. The response of the instrument was mapped in the laboratory with 14 Ci 22 Na source 3 m from the instrument. Later, we conducted demonstrations under two measurement scenarios. In one, the remotely located instrument observed an increase of background radiation counts at 1.4 MeV when a large amount of lead was removed from a building and a corresponding decrease when the lead was replaced. In the other scenario, the location and isotope-identifying energy spectrum of a 500 μCi 137 Cs source 3-5 m from the instrument with two intervening walls was determined in less than one minute. We report details of the instrument design and these measurements.

FNIT (the Fast Neutron Imaging Telescope), a detector with both imaging and energy measurement capabilities, sensitive to neutrons in the range 0.8-20 MeV, was initially conceived to study solar neutrons as a candidate design for the Inner Heliosphere Sentinel (IHS) spacecraft of NASA’s Solar Sentinels program and successively reconfigured to locate fission neutron sources. By accurately identifying the position of the source with imaging techniques and reconstructing the Watt spectrum of fission neutrons, FNIT can detect samples of special nuclear material (SNM), including heavily shielded and masked ones. The detection principle is based on multiple elastic neutron-proton scatterings in organic scintillators. By reconstructing n-p event locations and sequence and measuring the recoil proton energies, the direction and energy spectrum of the primary neutron flux can be determined and neutron sources identified. We describe the design of the FNIT prototype and present its energy reconstruction and imaging performance, assessed by exposing FNIT to a neutron beam and to a Pu fission neutron source. Keywords: fast neutrons, neutron imaging, passive SNM search, container screening 1. INTRODUCTION A critical gap in national security is the inability to efficiently detect and identify problematic quantities of Special Nuclear Material (SNM). These materials, specifically uranium and transuranics, emit neutrons via spontaneous or induced fission. Unlike the other forms of radiation produced by SNM (e.g. -rays), copious and penetrating neutron emission is unique to fissionable material. From a practical point of view, shielding of fission neutrons ( e.g. in a cargo container) represents a far greater challenge and requires a considerably larger and heavier amount of passive material than shielding of other forms of radiation emitted by SNM. Neutron detection, therefore, is of particular interest for SNM identification for security and proliferation deterrence, as well as for nuclear waste detection and monitoring. While improvements in all forms of radiation detection are necessary to close the SNM security gap, there are unique problems associated with the detection and measurement of neutrons. Some of these are: • current neutron detectors used in the field ( e.g. Bonner spheres

Illicit nuclear materials represent a threat for the safety of the American citizens, and the detection and interdiction of a nuclear weapon is a national problem that has not been yet solved. Alleviating this threat represents an enormous challenge to current detection methods that have to be substantially improved to identify and discriminate threatening from benign incidents. Rugged, low-power and less-expensive radiation detectors and imagers are needed for large-scale wireless deployment. Detecting the gamma rays emitted by nuclear and fissionable ma terials, particularly special nuclear materials (SNM), is the most convenient way to identify and locate them. While there are detectors that have the necessary sensitivity, none are suitable to meet the present need, primarily because of the high occurrence of false alarms. The exploitation of neutron signatures represents a promising solution to detecting illicit nuclear materials. This work presents the development of several detector configurations such as a mobile active interrogation system based on a compact RF-Plasma neutron generator developed at LBNL and a fast neutron telescope that uses plastic scintillating-fibers developed at the University of New Hampshire. A human-portable improved Solid-State Neutron Detector (SSND) intended to replace pressurized

We describe the design optimization process and performance characterization of a next generation neutron telescope, with imaging and energy measurement capabilities, sensitive to neutrons in the 1-20 MeV energy range. The response of the fast neutron imaging telescope (FNIT), its efficiency in neutron detection, energy resolution and imaging capabilities were characterized through a combination of lab tests and Monte Carlo simulations. Monte Carlo simulations, together with experimental data, are also being used in the development and testing of the image reconstruction algorithm. FNIT was initially conceived to study solar neutrons as a candidate instrument for the inner heliosphere sentinel (IHS) spacecraft. However, the design of this detector was eventually adapted to locate special nuclear material (SNM) sources for homeland security purposes, by detecting fission neutrons. In either case, the detection principle is based on multiple elastic neutron-proton scatterings in organic scintillator. By reconstructing event locations and measuring the recoil proton energies, the direction and energy spectrum of the primary neutron flux can be determined and neutron sources identified. This paper presents the most recent results arising from our efforts and outlines the performance of the FNIT detector.

We describe the design and performance of a prototype instrument with capabilities for both imaging and spectroscopy of sources of 1-10 MeV neutrons. The laboratory prototype is composed of custom-designed liquid scintillator detectors and employs measurements of double neutron-proton scattering to determine the direction and energy of incident neutrons. The detectors provide measurements of the position, energy deposit and pulse shape for each interaction. Pulse shape discrimination and a time-of-flight measurement between coincident interactions in two detectors are used to identify the neutron events, reject background due to Compton scattered gamma radiation and provide a measure of the scattered neutron energy. Calculations employing double n-p scattering kinematics are used to accumulate images and spectra of the neutron source. The quality of these images and spectra is correlated with the energy, position and timing resolution of the detectors. The prototype instrument achieves ~5deg angular resolution and 20% energy resolution (1sigma). This paper presents the design and the most recent results.

Tihs is a viewgraph presentation of a discussion of the X-ray Polarimeter. Gamma-ray bursts are one of the most powerful explosions in the universe and have been detected out to distances of almost 13 billion light years. The exact origin of these energetic explosions is still unknown but the resulting huge release of energy is thought to create a highly relativistic jet of material and a power-law distribution of electrons. There are several theories describing the origin of the prompt GRB emission that currently cannot be distinguished. Measurements of the linear polarization would provide unique and important constraints on the mechanisms thought to drive these powerful explosions. We present the design of a sensitive, and extremely versatile gamma-ray burst polarimeter. The instrument is a photoelectric polarimeter based on a time-projection chamber. The photoelectric time-projection technique combines high sensitivity with broad band-pass and is potentially the most powerful method between 2 and 100 keV where the photoelectric effect is the dominant interaction process We present measurements of polarized and unpolarized X-rays obtained with a prototype detector and describe the two mission concepts, the Gamma-Ray Burst Polarimeter (GRBP) for thc U S Naval Academy satellite MidSTAR-2, and thc Low Energy Polarimeter (LEP) onboard POET, a broadband polarimetry concept for a small explorer mission.

The ability of Compton telescopes to perform imaging and spectroscopy in space depends directly on the speed and energy resolution of the calorimeter detectors in the telescope. The calorimeter detectors flown on space-borne or balloon-borne Compton telescopes have included NaI(Tl), CsI(Na), HPGe and liquid organic scintillator. By employing LaX scintillators for the calorimeter, one can take advantage of the unique speed and resolving power of the material to improve the instrument sensitivity and simultaneously enhance its spectroscopic performance and thus its imaging performance. We present a concept for a space-borne Compton telescope that employs LaX as a calorimeter and estimate the improvement in sensitivity over past realizations of Compton telescopes. With some preliminary laboratory measurements, we estimate that in key energy bands, typically corrupted with neutron-induced internal nuclear emissions, this design enjoys a twenty-fold improvement in background rejection.

Special nuclear material (SNM) emits high energy radiation during active and passive interrogation. This radiation can be imaged thus allowing visualization of shielded and/or smuggled SNM. Although gamma-ray imaging is appropriate for many cases, neutrons are much more penetrating through hi-Z materials, and are thus preferred in certain scenarios (e.g. weapons grade Pu or HEU smuggled inside a lead pig several inches thick). Techniques for thermal neutron imaging have already been developed, but these approaches only image the moderating material, not the true SNM source. Traditional neutron detectors such as He3 tubes and scintillators simply count neutrons. We are developing an instrument that will directly image the fast fission neutrons from an SNM source using a neutron scatter camera. This technique has been shown to be 10 times more sensitive for solar neutrons over traditional neutron counting techniques. In addition to being a 4pi neutron imager, this instrument will also be an excellent neutron spectrometer, and will be able to differentiate between different types of neutron sources (e.g. fission, gamma-n, cosmic ray, and dd or dt fusion). Our instrument will be able to pinpoint the source location. We will present results from a prototype detector and discuss key parameters that determine detector performance.

We report progress in the development of precision scintillating plastic fiber bundles for 3-d tracking experiments. Specifically, we present an approach for the design and fabrication of the tracking detector for the SOlar Neutron TRACking experiment (SONTRAC), an imaging spectrometer for measurement of 20-200 MeV neutrons in a space environment. SONTRAC operates by measuring the tracks of the recoil protons from n-p scatters in a closely packed bundle of scintillating plastic fibers. The energy and angular resolution of the instrument depends on the accuracy and precision with which the length and orientation of each track can be measured. Early prototype fiber bundles yielded distorted track images due to irregular orientation and registration of the fibers. These fiber detector bundles, composed of 250 mum square scintillating plastic fibers on a nominal 300 mum pitch, contain fibers with registration errors as large as 1 mm. The next fiber bundles will use 290 mum round fibers on 300 mum pitch. The goal is for every fiber in the array to be registered within 300 mum of a rectilinear 3-d grid. We present the requirements, materials, assembly fixtures and procedures for the fabrication of these higher fidelity SONTRAC fiber bundle detectors. We present photographs and measurements of a small prototype fiber bundle constructed using these new techniques.

Simulation of the charge sharing properties of single-sided CZT strip detectors with small anode pads are presented. The effect of initial event size, carrier repulsion, diffusion, drift, trapping and detrapping are considered. These simulations indicate that such a detector with a 150 mum pitch will provide good charge sharing between neighboring pads. This is supported by a comparison of simulations and measurements for a similar detector with a coarser pitch of 225 mum that could not provide sufficient sharing. The performance of such a detector used as a gamma-ray imager is discussed.

We report progress in the study of thick single-sided charge-sharing cadmium zinc telluride (CZT) strip detector modules designed to perform spectroscopy and 3-D imaging of gamma-rays. We report laboratory measurements including spectroscopy, efficiency and 3-D imaging capability of prototype detectors (15 15 7.5 cu mm) with 11x11 unit cells. We also report on Monte Carlo simulations (GEANT4 v7.1) to investigate the effect of multihits on detector performance in both spectroscopy and imaging. We compare simulation results with data obtained from laboratory measurements and discuss the implications for future strip detector designs. Keywords: CZT, strip detectors, gamma-ray

We report on recent progress in the development of the Fast Neutron Imaging Telescope (FNIT), a detector with both imaging and energy measurement capabilities, sensitive to neutrons in the 2-20 MeV range. FNIT was initially conceived to study solar neutrons as a candidate design for the Solar Sentinels program under formulation at NASA. This instrument is now being configured to locate fission neutron sources for homeland security purposes. By accurately identifying the position of the neutron source with imaging techniques and reconstructing the energy spectrum of fission neutrons, FNIT can locate problematic amounts of Special Nuclear Material (SNM), including heavily shielded and masked samples. The detection principle is based on multiple elastic neutron-proton (n-p) scatterings in organic scintillators. By reconstructing the n-p event locations and sequence and measuring the recoil proton energies, the direction and energy spectrum of the primary neutron flux can be determined and neutron point sources identified. The performance of FNIT is being evaluated through a series of Monte Carlo simulations and lab tests of detector prototypes. The Science Model One (SM1) of this instrument was recently assembled and is presently undergoing performance testing.

The Solar Neutron Tracking (SONTRAC) telescope was originally developed to measure the energy spectrum and incident direction of neutrons produced in solar flares, in the energy range 20-250 MeV. While developed primarily for solar physics, the SONTRAC detector may be employed in virtually any application requiring both energy measurement and imaging capabilities. The SONTRAC science model (SM) is presently being operated at the University of New Hampshire (UNH) as a ground-based instrument to investigate the energy spectrum, zenith and azimuth angle dependence of the cosmic-ray induced sea-level atmospheric neutron flux. SONTRAC measurements are based on the non-relativistic double scatter of neutrons off ambient protons within a block of scintillating fibers. Using the n-p elastic double-scatter technique, it is possible to uniquely determine the neutron's energy and direction on an event-by-event basis. The 3D SM consists of a cube of orthogonal plastic scintillating fiber layers with 5 cm sides, read out by two CCD cameras. Two orthogonal imaging chains allow full 3D reconstruction of scattered proton tracks

We report on the development of a next generation neutron telescope, with imaging and energy measurement capabilities, sensitive to neutrons in the 2-20 MeV energy range. The fast neutron imaging telescope (FNIT) was initially conceived to study solar neutrons as a candidate instrument for the inner heliosphere sentinels (IHS) program under formulation at NASA. This detector is now being adapted to locate special nuclear material (SNM) for homeland security purposes by detecting fission neutrons and reconstructing the image of their source. In either case, the detection principle is based on multiple elastic neutron-proton scatterings in organic scintillator. By reconstructing the scattering coordinates and measuring the recoil proton energy, the direction and energy of each neutron can be determined and discrete neutron sources identified. We describe the performance of the FNIT prototype, report on the current status of R&D efforts and present the results of recent laboratory measurements

The study of particle acceleration, particle transport and interaction mechanisms associated with high-energy phenomena at the Sun is of general astrophysical relevance. In this context an exemplary overview is given of ground-based and spaceborne instruments to measure the energy spectrum of solar neutrons, and of the significance of such observations.

This paper discusses the latest progress in the development of GRAPE (Gamma‐Ray Polarimeter Experiment), a hard X‐ray Compton Polarimeter. The purpose of GRAPE is to measure the polarization of hard X‐rays in the 50–300 keV energy range. We are particularly interested in X‐rays that are emitted from solar flares and gamma‐ray bursts (GRBs). Accurately measuring the polarization of the emitted radiation from these sources will lead to a better understating of both the emission mechanisms and source geometries. The GRAPE design consists of an array of plastic scintillators surrounding a central high‐Z crystal scintillator. We can monitor individual Compton scatters that occur in the plastics and determine whether the photon is photo absorbed by the high‐Z crystal or not. A Compton scattered photon that is immediately photo absorbed by the high‐Z crystal constitutes a valid event. These valid events provide us with the interaction locations of each incident photon and ultimately produces a modulation pattern for the Compton scattering of the polarized radiation. Comparing with Monte Carlo simulations of a 100% polarized beam, the level of polarization of the measured beam can then be determined. The complete array is mounted on a flat‐panel multi‐anode photomultiplier tube (MAPMT) that can measure the deposited energies resulting from the photon interactions. The design of the detector allows for a large field‐of‐view (> π steradian), at the same time offering the ability to be close‐packed with multiple modules in order to reduce deadspace. We present in this paper the latest laboratory results obtained from GRAPE using partially polarized radiation sources along with a brief description of our future plans for the GRAPE design.

Advanced scintillator materials such as LaBr3:Ce and LaCl3:Ce hold great promise for future hard X-ray and gamma-ray astrophysics missions due to their high density, high light output, good linearity, and fast decay times. Of particular importance for future space-based imaging instruments, such as coded-aperture telescopes, is the precise spatial location of individual gamma-ray interactions. We have investigated the position and energy resolution achievable within monolithic (5 cm times 5 cm times 1 cm) LaBr3:Ce and LaCl3:Ce crystals using position-sensitive light readout devices, including a position-sensitive photomultiplier tube and a multi-anode photomultiplier tube. We present the results of these tests and discuss the applicability of such advanced scintillators to future high-energy imaging astrophysics missions.

We present results from a proton accelerator beam test to measure radiation damage and activation in advanced scintillator materials. Samples of LaBr3:Ce and LaCl2:Ce were exposed to protons from 40-250 MeV at the Proton Irradiation Facility of the Paul Scherrer Institute in Switzerland. Twelve energy bands were used to simulate the spectrum of the South Atlantic Anomaly (SAA), with different samples exposed to the equivalent of 4 months, 1 year, and 5 years of SAA passage. No significant decrease in light output was found due to radiation damage, indicating that these new scintillator materials are radiation tolerant. High-resolution spectra of the samples were obtained before and after irradiation with a germanium spectrometer to study activation. We present a detailed analysis of these spectra and a discussion of the suitability of these scintillator materials for detectors in future space missions.

We report progress in the study of a thick CZT strip detector module designed to perform gamma-ray spectroscopy and 3-D imaging. We report preliminary performance measurements of 7.5 mm thick single-sided charge-sharing strip detector prototype devices. This design features both row and column contacts on the anode surface. This electron-only approach addresses problems associated with poor hole transport in CZT that limit the thickness and energy range of double-sided strip detectors. This work includes laboratory and simulation studies aimed at developing compact, efficient, detector modules for 0.05 to 1 MeV gamma measurements while minimizing the number and complexity of the electronic readout channels. This is particularly important in space-based coded aperture and Compton telescope instruments that require large area, large volume detector arrays. Such arrays will be required for the NASA Black Hole Finder Probe (BHFP)and Advanced Compton Telescope (ACT). This new design requires an anode pattern with contacts whose dimensions and spacing are roughly the size of the ionization charge cloud. The first prototype devices have 125 μm anode contacts on 225 μm pitch. Our results demonstrate the principle of operation but suggest that even finer anode contact feature sizes will be necessary to achieve the desired performance.

This paper discusses the latest progress in the development of GRAPE (Gamma-Ray Polarimeter Experiment), a hard X-ray Compton Polarimeter. The purpose of GRAPE is to measure the polarization of hard X-rays in the 50-300 keV energy range. We are particularly interested in X-rays that are emitted from solar flares and gamma-ray bursts (GRBs). Accurately measuring the polarization of the emitted radiation from these sources will lead, to a better understating of both the emission mechanisms and source geometries. The GRAPE design consists of an array of plastic scintillators surrounding a central high-Z crystal scintillator. We can monitor individual Compton scatters that occur in the plastics and determine whether the photon is photo absorbed by the high-Z crystal or not. A Compton scattered photon that is immediately photo absorbed by the high-Z crystal constitutes a valid event. These valid events provide us with the interaction locations of each incident photon and ultimately produces a modulation pattern for the Compton scattering of the polarized radiation. Comparing with Monte Carlo simulations of a 100% polarized beam, the level of polarization of the measured beam can then be determined. The complete array is mounted on a flat-panel multi-anode photomultiplier tube (MAPMT) that can measure the deposited energies resulting from the photon interactions. The design of the detector allows for a large field-of-view (>pi steradian), at the same time offering the ability to be close-packed with multiple modules in order to reduce deadspace. We plan to present in this paper the latest laboratory results obtained from GRAPE using partially polarized radiation sources., 10 pages; conference paper presented at the SPIE conference "UV, X-Ray, and Gamma-Ray Space Instrumentation for Astronomy XIV." To be published in SPIE Conference Proceedings, vol. 5898

Inner heliosphere measurements of the Sun can be conducted with the proposed Solar Sentinel spacecraft and mission. One of the key measurements that can be made inside the orbit of the Earth is that of lower energy neutrons that arise in flares from nuclear reactions. Solar flare neutrons below 10 MeV suffer heavy weak-decay losses before reaching 1 AU. For heliocentric radii as close as 0.3 AU, the number of surviving neutrons from a solar event is dramatically greater. Neutrons from 1-10 MeV provide a new measure of heavy ion interactions at low energies, where the vast majority of energetic ions reside. Such measurements are difficult because of locally generated background neutrons. An instrument to make these measurements must be compact, lightweight and efficient. We describe our progress in developing a low-energy neutron telescope that can operate and measure neutrons in the inner heliosphere and take a brief look at other possible applications for this detector.