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The presence of gamma-ray background significantly reduces detection sensitivity when searching for radioactive sources in the field, particularly in mobile systems which must contend with a variable background that is not known a priori . An extensive survey of the background was performed in the San Francisco Bay Area using both sodium iodide and high-purity germanium detectors, covering a wide variety of environments that might be encountered in an operational scenario. This data was used as a basis for source injection in a moving detector scenario in order to assess the effects of the background on different detection approaches. Both imaging and spectroscopic algorithms were implemented for the sodium iodide array, and their performances are compared for a variety of source energies and stand-off distances in the presence of the measured background.

Characterization of the electrical response of HPGe segmented detectors as a function of the interaction position is one of the current goals for the Nuclear Physics community in order to perform γ-ray tracking or even imaging with these detectors. For this purpose, scanning devices must be developed to achieve the signal-position association with the highest precision. With this aim, SALSA, a γ-camera-based scanning system, is under development at our laboratory. In this work, the optimization study aimed to obtain the best spatial resolution in the position-sensitive detectors employed as γ camera is described.

In gamma-ray spectroscopy and imaging, the natural gamma-ray background can significantly reduce detection sensitivity, especially when the source is weak and the background varies substantially. This project aims to systematically measure and characterize the spatial and temporal variations of the background in order to assess their impact on detection sensitivity and specificity for homeland security applications. An extensive survey of typical backgrounds found in the San Francisco bay area was performed, and initial measurement results are presented here.

The first Polaris system was built in September 2010 and has gone through significant testing at multiple DOD and DOE facilities as well as at the University of Michigan. It has been biased almost continuously for the 18 months of its current lifespan without any replacement of its detectors. The second Polaris system was built in June 2011 and has also been almost continuously biased during its lifespan. The continuous operation of both devices has provided the best opportunity to study the long-term stability of pixelated CdZnTe detectors. Spectroscopic performance has been monitored throughout each system's lifespan to study their performance over time and the impact on long term operation of these devices. It is shown that the charge transport properties and spectroscopic performance of these CdZnTe detectors are stable over time and devoid of fabrication or assembly issues. It is expected that future detectors will exhibit excellent stability.

LiCaAlF6 scintillators are one of the attractive scintillators for neutron detection. To reduce the effect on gamma-rays, the Ce doped LiCaAlF6 scintillators can discriminate the neutron and gamma-ray events based on the pulse shape discrimination technique. To apply the scintillators for the oil logging, the high temperature characteristics must be investigated. In this paper, the temperature dependence of the neutron-gamma discrimination based on pulse shape discrimination technique in the Ce:LiCaAlF6 scintillator is investigated as one of the high temperature characteristics. The property of pulse shape discrimination in the Ce:LiCaAlF6 has small temperature dependence ranging from 25°C to 150°C. We concluded that the Ce:LiCaAlF6 scintillators can discriminate neutron and gamma-ray events under high temperature condition up to 150°C .

We describe a setup we developed for the measurement of scintillation properties of crystals, from room temperature down to 3 K, under α and γ particle irradiation which resolves lines from both types of excitations. This setup is described here and we report some results obtained with this setup on BGO (Bi4Ge3O12) and ZnWO4 crystals.

Silicon photomultipliers (SiPMs) are expected to replace photomultiplier tubes (PMTs) in several applications that require scintillation detectors with excellent timing resolution, such as time-of-flight positron emission tomography (TOF-PET). However, the theory about the timing resolution of SiPM-based detectors is not yet fully understood. Here we propose a comprehensive statistical model to predict the timing resolution of SiPM-based scintillation detectors. It incorporates the relevant SiPM-related parameters (viz. the single cell electronic response, the single cell gain, the charge carrier transit time spread, and crosstalk) as well as the scintillation pulse rise and decay times, light yield, and energy resolution. It is shown that the proposed model reduces to the well-established Hyman model for timing with PMTs if the number of primary triggers (photoelectrons in case of a PMT) is Poisson distributed and crosstalk and electronic noise are negligible. The model predictions are validated by measurements of the coincidence resolving times (CRT) for 511 keV photons of two identical detectors as a function of SiPM bias voltage, for two different kinds of scintillators, namely LYSO:Ce and LaBr3:5%Ce. CRTs as low as 138 ps +/- 2 ps FWHM for LYSO:Ce and 95 ps +/- 3 ps FWHM for LaBr3:5%Ce were obtained, demonstrating the outstanding timing potential of SiPM-based scintillation detectors. These values were found to be in good agreement with the predicted CRTs of 140 ps FWHM and 95 ps FWHM, respectively. Utilizing the proposed model, it can be shown that the CRTs obtained in our experiments are mainly limited by photon statistics while crosstalk, electronic noise and signal bandwidth have relatively little influence.

This paper describes a study of background estimation in Modular X- and Gamma ray Sensor (MXGS) onboard ESA's Atmosphere-Space Interactions Monitor (ASIM) mission, using Geant4 simulations and Spenvis packages for particle flux generations.

This paper presents the CNES analysis of CCD dark current degradation in orbit. For the first time, data coming from several detectors in orbit have been collected and congregated to extract general trends about in-flight detector behaviours. The in-orbit degradation is therefore compared to the on-ground prediction for each detector. This work has been done in collaboration with the CNES detection subsystem office, the CNES image quality office and the CNES components & environment effects office.

This paper measures the sample to sample variation in the light yield proportionality of NaI(Tl), and so explores whether this is an invariant characteristic of the material or whether it depends on the chemical and physical properties of the tested samples. We report on the electron response of nine crystals of NaI(Tl), differing in shape, volume, age, manufacturer and quality. The proportionality has been measured at the SLYNCI facility in the energy range between 3.5 to 460 keV. We observe that while samples produced by the same manufacturer at approximately the same time have virtually identical electron response curves, there are significant sample to sample variations among crystals produced by different manufacturers or at different times. In an effort to correlate changes in the electron response with details of the scintillation mechanism, we characterized other scintillation properties, including the gamma response and the x-ray excited emission spectra and decay times, for the nine crystals. While sample to sample differences in these crystals were observed, we have been unable to identify the underlying fundamental mechanisms that are responsible for these differences.

We developed Lu0.4Gd1.6SiO5 (LGSO) crystal as a new scintillator for medical imaging applications. The size of the LGSO ingot obtained for this investigation was approximately 60 mm in diameter and 170 mm in length. The as-grown crystal was yellow in color. To eliminate the tint, the crystal was annealed in pure N2 atmosphere after the growth. As a result, the LGSO became colorless with uniform and large light output which is about 2.0 times that of GSO

The performance of hand-held radioisotope identification devices (RIDs) is still hampered by the performance of the NaI(Tl) detectors, which are commonly used in such instruments. In this paper, we continue the search for better detector options. One of the largest single elements ever made, a coplanar CdZnTe (CZT) detector (30times15times12.1 mm3 volume 5.45 cm3 designed by University of Michigan) is compared with a commercially available LaBr3(Ce) detector (ominus1''times1'' volume 12.9 cm3.) Parameters that are relevant to the performance of isotope identification devices, such as resolution and efficiency as function of the gamma-ray energy, temperature shift, linearity and others are measured and compared. According to measurement results, it seems that for this application LaBr3(Ce) detectors are a viable alternative to CZT detectors; even more so if one bears in mind that LaBr3(Ce) became commercially available only recently and detectors with larger volumes are likely to appear in the near future

One of the essential requirements of the tagged neutron inspection system, which is the principle of the EURITRACK project, is an efficient and inexpensive gamma ray detector. For this purpose properties of cylindrical 3"times3" and 5"times5" BGO, and 3"times3", two different 5"times5", and a rectangular 5"times5"times10" NaI(Tl) scintillators were explored. In this communication we report on light yield, energy and time resolution of the investigated crystals at high energies of gamma-rays. Additionally, results of Monte Carlo simulations of the crystals' efficiencies are compared to peak-to-total ratios obtained experimentally for various combinations of PMTs and the scintillators

We discuss the silicon photomultiplier as a novel photon detector for the Major Atmospheric Gamma Imaging Cerenkov Telescope and the Extreme Universe Space Observatory. For these astroparticle experiments we pursue two different developments of the SiPM. One development is pursued at MEPhI, where prototypes are available. In the course of this paper we will describe some characteristics of these devices. The second development, which is using the back illumination principle is at present in its design phase.

The performance characteristics of Frisch-ring CdZnTe (CZT) detectors are described and compared with other types of CZT devices. The Frisch-ring detector is a bar-shaped CZT crystal with a geometrical aspect ratio of /spl sim/1:2. The side surfaces of the detector are coated with an insulating layer followed by a metal layer deposited directly upon the insulator. The simple design operates as a single-carrier device. Despite the simplicity of this approach, its performance depends on many factors that are still not fully understood. We describe results of testing several detectors fabricated from CZT material produced by different vendors and compare the results with numerical simulations of these devices.

TlBr crystals, grown by hydrothermal and "Bridgman-Stockbarger" methods, were investigated as potential single and pixel detectors of X- and gamma radiation. Technology of detectors manufactured from TlBr crystals is reported. The spectra of the radionuclides Fe-55, Am-241, Cd-109, Co-57, and Cs-137, measured by single TlBr detectors are presented. Full-width at half-maximum (FWHM) energy resolutions of 500 eV at 5.9 keV; 518 eV at 9.87 keV; 670 eV at 13.92 keV; 777 eV at 22.1 keV; 2.7 keV at 59.5 keV; 3.7 keV at 88 keV; 4.4 keV At 122 keV, and 29 keV at 662 keV have been achieved. Small format (3/spl times/3) pixel detectors with pads 0.35/spl times/0.35 mm and gap 0.1 mm were also fabricated on single TlBr crystals of dimensions 2.7/spl times/2.7/spl times/1.0 mm/sup 3/. The interpixel resistivities measured at a bias of 50 V were 400-600 GOhm. The pixel leakage currents at a bias of 250 V were typically less than 0.5 nA. The best spectra were obtained at a temperature of -30/spl deg/C, a shaping time constant of 6 /spl mu/s and high voltage of 400 V. Energy resolutions of 2.2, 3.0, 3.7 and 29 keV were measured at input energies of 59.5, 88, 122, and 662 keV, respectively. Values of /spl mu//spl tau/ have been evaluated for two different ingots produced by the "Bridgman-Stockbarger" method. They are /spl mu//sub e//spl tau//sub e/=2.5/spl times/10/sup -4/ cm/sup 2/ V/sup -1/ and /spl mu//sub h//spl tau//sub h//spl sim/10/sup -6/ cm/sup 2/ V/sup -1/ for one ingot at -30/spl deg/C and /spl mu//sub e//spl tau//sub e/=7/spl times/10/sup -5/ cm/sup 2/ V/sup -1/, and /spl mu//sub h//spl tau//sub h/=1.5/spl times/10/sup -5/ cm/sup 2/ V/sup -1/ for the other ingot at -10/spl deg/C.

A miniature radiation monitor (MRM) device has been developed, which utilizes a charge-coupled device (CCD) as its sensitive element. Its shielding configuration has been designed to mitigate the displacement damage threat in space environments, while also introducing a good degree of directional sensitivity.

The clinically oriented NEMA NU-2 2000+ performance standards have been performed on an ADAC molecular coincidence detection dual-head camera. At 1 cm radius, the transverse resolution full-width at half-maximum was measured to be 5.2 (10.0) mm and the axial was 5.0 (10.6) mm. At 10 cm radius, the transverse radial resolution was 4.7 (7.4) mm and the transverse tangential was 8.5 (20.9) mm. The axial resolution was 14.0 (41.1) mm. The peak true count rate was 4370 counts/s at a concentration of 4.3 kBq/ml. The peak noise equivalent count rate (NECR) was 1620 counts/s at 2.9 kBq/ml. The system scatter fraction was 48%, The maximum relative count rate error observed at the NECR peak was -42%. The sensitivity was 1010 counts/sm/rSq in the center and 870 counts/s/MBq at an offset of 10 cm. The contrast for the hot spheres ranged from 18.5 (11.6)% to 11.6 (7.9)% for a contrast ratio of 8:1 (4:1). For the cold spheres, it ranged from 41% to 25% with an overall background variability of 7%. The residual error in scatter and attenuation correction was approximately 50%. All measurements were performed at the maximum allowed crystal-to-crystal distance of 810 mm.

The ionizing radiation response of pMOSFETs used as dosimeters (RADFETs) is compared for Co-60 gammas and high-energy protons. For comparable Co-60 and proton doses, RADFET response for high-energy protons (60-200 MeV) was found to be only 65-85% of their Co-60 response. This difference is not fully understood but is shown to be partially a result of increased columnar recombination in SiO/sub 2/ for high-energy proton irradiation.

The rapid and accurate quantification of radioactivity in the ground is important in many instances to enable appropriate decisions to be made about limiting its use. In-situ gamma spectrometry has been shown to be a potentially powerful technique for providing this information but its accuracy is dependent on knowledge of the activity variation with depth which is generally unavailable. Methods that allow this distribution to be rapidly determined have previously been published but all rely on a fixed depth-distribution model which is unrealistic. A novel technique using submerged collimated detector measurements termed the "submerged detector method" (SDM) has been proposed, and theoretically assessed in earlier work and has given promising results. In this work, the SDM is experimentally assessed at 19 sites in Wales, U.K., of variable /sup 137/Cs activity levels and profile shapes. Practicality and accuracy both in the derived activity per unit area and the profile shapes were assessed against the best of the other methods. The results confirm that the SDM gives more accurate results with the derived activity per unit area on average within /spl sim/40% of the true value and the depth distributions being more accurately determined.

A multiwire ionisation chamber filled with liquid xenon as a position sensitive detector for Positron Emission Tomography is studied. Both xenon scintillation, which provides a fast trigger, and ionisation charge for position and energy measurements are read. The detection efficiency of the detector is assessed in separate measurements of the probability of detection of the scintillation light and the charge signals due to 511 keV gamma-rays. These were measured to be about 1 and 0.82, respectively.

The NaI:Tl scintillation response has been studied for over four decades. Two of the significant conclusions that have been made from these studies (with respect to using NaI(Tl) to detect gamma rays and X-rays) are: (1) the NaI(Tl) scintillation response is nearly linear (especially over limited energy ranges) and (2) the NaI(Tl) scintillation response has significant nonproportionalities; while these conclusions may at first appear to be inconsistent with each other, upon further consideration these conclusions are not mutually exclusive. In fact, these conclusions are fully consistent with each other. Published results typically confirm only one of these conclusions (as it was likely the intention to study either linearity or proportionality, but not both) and are not always presented such that direct comparisons can be made with other results. Consequently, it is critical that both the intent of the study and the means with which the results are presented be appropriately considered. Otherwise, it is possible to make inaccurate conclusions about both linearity and proportionality. To facilitate accurate conclusions and meaningful comparisons, this study defines a fully consistent nomenclature, examines some of the subtleties which must be considered when comparing scintillation response results, and uses a review of the literature to demonstrate both the definitions and the subtleties.

Several articles have been reviewed on the scintillation response of NaI(Tl). Those publications which report results obtained with radioactive sources either dispersed throughout the NaI(Tl)-lattice or located inside the wells of NaI(Tl)-crystals match within a /spl plusmn/0.9% standard deviation of a linear scintillation response between 3 MeV and 3 keV. Several authors who plated their sources outside the crystals measured nonlinear responses of NaT(TI) with up to /spl plusmn/7% of standard deviations between 700 and 4.5 keV. The presented analysis suggests that the observed nonlinearity is not an intrinsic effect of NaI(TI) but could be caused, at least partly, by effects occurring at the radiation entrance surfaces of the crystals.

We have constructed an endcap photon detector with undoped cesium iodide (CsI) crystals for K/sup +//spl rarr//spl pi//sup +//spl nu//spl nu. >

Describes the unprecedented implementation of "in-flight" reconfigurable on-board data handling electronics using reprogrammable FPGA (field programmable gate array) technology. The electronics design was realized for a prototype of the Imager for the INTEGRAL mission that is an ESA "Horizon 2000" long term plan, now in the second selection cycle (M2). The Imager prototype was developed by an international collaboration, and was flown successfully on a balloon from Fort-Sumner, New Mexico in October 1993. The purpose of this reconfigurable electronics was to demonstrate a new engineering approach that would reduce the cost of mass and power of the payload. The accomplishment of using a flexible structure in an instrument prototype combined with the demonstration of high performance during hostile environmental flight conditions is presented. >

Considered are benefits of new interpretation models of the natural spectral gamma-ray log based the application of the analytical algorithms of radial "geometrical factors". A combined technique of computer simulation and analytical interpretation models is used to study the influence of geological and downhole conditions and statistical errors on the the accuracy of interpretations of spectral gamma logs. A comparison between analytical algorithms and those based on the reduction to standard downhole conditions is presented. The analytical structure of the new interpretation algorithms provides upper estimates of the interpretation accuracy and concurrent computation of radionuclide abundances. >

An historical review of the development of semiconductor detectors is presented. Detector physics, material requirements, and signal processing are discussed.

By taking advantage of the good energy resolution of CdTe detectors, gamma rays scattered by lead collimators can be rejected leading to excellent spacial resolution for medical probes. Since CdTe has over 100 times the photoelectric stopping power of Si at 140 keV (99mTc), the probe provides enough sensitivity that dental abscesses on the individual root tips of test animal teeth can be detected weeks before they are evident by radiographs.

Avalanche diodes, up to 20 mm2 in area, have been made with sensitivities up to 6 × 106 counts/ Roentgen. Operating at 200 volts, typical gains of 20 are achieved. This permits the detection of 6 keV X-rays and dosimetry of gamma rays down to 30 keV with background counting rates of about 0.1 c/s.

A hierarchical, distributed intelligence data acquisition system which has been used for the past two years in neutrino experiments at Brookhaven National Laboratory is described. Performance characteristics and the nature of problems encountered in bringing the system to maturity are discussed and some generalizations of the experience are suggested.

A fully portable source excited X-ray fluorescence analyzer has been developed to detect and quantify trace concentrations of gold in situ at the working face.1 The technique utilizes the 88 keV gamma-ray of 109Cd to excite gold Ks X-rays which are detected and analyzed by the instrument. The instrument must meet two very tough criteria in addition to the normal laboratory specifications of a precision spectrometer. First, it must be able to withstand the rugged environment of a mine including high temperature, high humidity, dust, and bumps. Second, it must be fully portable and capable of being carried easily by an operator into this environment without impairing his ability to move around and work.

A variety of aerial radiological monitoring systems are available to respond to a radiological accident or incident affecting large areas. These are operated by EG&G, Inc. for ERDA's Division of Operational Safety. A survey system can be airborne within approximately two hours after notification. Both airborne and terrestrial radioactivity can be measured and mapped. Special analysis procedures allow discrimination between radioactivity from most man-made radioelements and naturally occuring radioelements. A position accuracy of ±54 feet can be maintained over a large area survey. Detection sensitivity for gamma sources employing NaI detector arrays on board an airplane flying at 500 feet altitude is better than 2 ?R/hr for surface planar contaminants and approximately 10 mCi for a point gamma source.