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Since the discovery of X-rays by Röntgen in 1895, radiation detection technology have developed rapidly and have been widely used in many fields such as medical imaging, security inspection, industrial non-destructive testing, nuclear safety monitoring, resource exploration, basic science and space science. In terms of detection materials and working principles, radiation detectors can be divided into gas detectors, scintillator detectors and semiconductor detectors. This article focuses on semiconductor detectors, starting from the interaction between various radiation and semiconductor materials, as well as the working principle and signal processing process of semiconductor detectors, and discusses the performance requirements and main points of detector design of semiconductor radiation detectors in different types of radiation and different application requirements. The performance and research progress of semiconductor materials in the field of radiation detection are reviewed according to the order of element family. [ABSTRACT FROM AUTHOR]

The electrical signals generated by radiation detectors are often subject to undesired effects that can affect the energy resolution of the detector. These effects may be caused by the measurement system itself or by the high rate of events. Traditional methods for shaping the signals and mitigating these effects often have limitations, such as requiring explicit information about the signals. In this paper, the authors propose a deconvolution method based on least square filtering and non-negative sparsity theory to address these limitations. The method is evaluated using simulated data representing a gamma ray detector with a NaI(Tl) crystal and a photomultiplier tube (PMT). The electrical pulses in this system are pre-processed using a CR coupling circuit and a RC integrator. The energy resolution obtained with the traditional method was 6.60%, while the proposed method resulted in an energy resolution of 5.65%. In addition to improving accuracy, the proposed method also reduces implementation complexity. [ABSTRACT FROM AUTHOR]

Finding and tracking radioactive sources have numerous security applications in civilian energy installations, military facilities, and ports of entry. The price of radiological sensors varies proportionally to size and imaging characteristics such as angular resolution, and the cheapest devices are nearly isotropic–i.e., they integrate radiation from a sphere of directions centered at the sensor. While many radiation sensors have high aspect ratios or odd shapes, the sensors used here are right cylinders, with a near identical directional efficiency such that for analysis purposes, other aspects, such as counting statistics, would make nonisotropy of the sensor negligible. In this article, we propose a simple and robust way to integrate measurements from both isotropic radiological sensors and depth sensors, whose reliability and resolution benefit from recent advances in computer vision and imaging. Our key idea is to convert all sensor measurements into proximity signals based on radial distance variations over time. Based on this sensor fusion model, we show that for moving radiological sources even a simple Kalman filter can trade-off the complementary strength of high-resolution depth sensors and isotropic radiological sensors. We show novel results with a LIDAR sensor and a thermal stereo pair, and demonstrate applications such as tracking and rendering non-line-of-sight imagery behind obstacles and detecting multiple radiological sources in the same scene. [ABSTRACT FROM AUTHOR]

Compact multi-channel radiation detectors rely on low noise front-end application specific integrated circuits (ASICs) to achieve high spectral resolution. Here, a new ASIC developed to readout virtual Frisch-grid cadmium zinc telluride (VFG CZT) detectors for gamma ray spectroscopy is presented. Corresponding to each ionizing event in the detector, the ASIC measures the amplitude and timing at the anode, the cathode and four pad sense electrodes associated with each sensor in a detector array. The ASIC is comprised of 52 channels of which there are 4 cathode channels and 48 channels which can be configured as either anode channels with a baseline of 250 mV or pad sense channels to process induced signals with a baseline of 1.2 V. With a static power dissipation of 3 mW, each channel performs low-noise charge amplification, high-order shaping, peak and timing detection along with analog storage and multiplexing. The overall channel linearity was better than ± 1% with timing resolution down to 700 ps for charges greater than 8 fC in the 3 MeV range. With a 4 × 4 array of 6 mm × 6 mm × 20 mm virtual Frisch-grid bar sensors connected and biased, an electronic resolution of ≈ 270 e−rms for charges up to 100 fC in the 3.2 MeV range was measured. Spectral measurements obtained with the 3D correction technique demonstrated resolutions of 1.8% FWHM at 238 keV and 0.9% FWHM at 662 keV. [ABSTRACT FROM AUTHOR]

Two high performance single crystal diamond (SCD) radiation detectors for neutrons and gamma ray have been fabricated. One was coated with a 5 μm 6LiF (95% enriched in 6Li) layer in order to detect the neutrons and the other one is without any conversion layer for comparison. The detectors are irradiated with the 241Am-Be and 252Cf neutron sources and 152Eu gamma source to test their performance. Under neutron sources, the neutron signal peak was clearly observed in the detector with the 6LiF conversion layer. Meanwhile, both detectors are responsive to the gamma rays at the low energy. The 152Eu gamma source was specially used to verify the gamma ray detection ability of the fabricated SCD detectors. The results show that the detector's count rate and the gamma peak center position in the PHS depend on the incident gamma spectra critically. Combined, these results demonstrate that the design and fabrication process of the detectors are feasible. [ABSTRACT FROM AUTHOR]

Abstract The transient responses of the CMOS image sensor (CIS) detectors during radiation are one of the key issues to the detector design, reliability and applicability in space and nuclear environments. The transient radiation experiments of the CIS detectors irradiated by gamma rays and X rays were carried out to compare the difference and the similarity of the transient responses. The CISs have 4 Megapixels and pinned photodiode (PPD) pixel architecture with a standard 0.18 μ m CMOS technology. The white spots and lines of the dark images induced by gamma rays and X rays during radiation are analyzed to compare the difference and the similarity of transient response characteristics. The comparison of the DSNU fluctuation of the CIS detectors versus the continuous frames induced by gamma rays and X rays are also analyzed. The theoretical analysis of the difference is presented by radiation particle transportation simulation using GEANT4. The mechanisms of the transient responses in the CIS detectors are demonstrated by combining the experimental results and theoretical analysis. [ABSTRACT FROM AUTHOR]

Mobile radiation sensing techniques for surge deployment and wide area search are important for nuclear security applications. Radiation sensors were developed for the use with robotic platforms of unmanned aerial systems (UAS). Ambient temperature neutron and gamma CLYC sensor and high resolution CZT gamma sensor were integrated into the UAS as plug-and-play interchangeable components allowing easy attachment to a robot in field conditions. The time and position data were added via Robot Operating System to measured intensities of photon peaks and neutron rates enabling the input for the UAS flight control. The contour mapping of a radiation area by multiple UAS was simulated. [ABSTRACT FROM AUTHOR]

A well-type HPGe detector model with the existence of a particular dead area in the HPGe crystal was developed for use in Monte Carlo simulation codes to better model gamma-ray efficiency characteristics. Dissimilarities of counting efficiencies between simulation and calibration were successfully minimized for the case of point and volume sources. Simulations using the resulting model are applicable to the activity measurement of samples both in the hole and on top of the endcap of the well-type HPGe detector. [ABSTRACT FROM AUTHOR]

For the first time, a diamond sensor was operated for the characterisation of a high average-intensity gamma-ray beam. Data was collected for gamma beam energies between 2 and 7 MeV, at the HIγS facility of TUNL. The nanosecond-fast resolution of diamond detectors is exploited to distinguish bunches of gamma rays 16.8 ns apart. It allows a precise direct determination of the time-structure of the gamma beam. The strong potential of such a detector for precise absolute flux, position and polarisation measurements is exposed. It is thus shown that diamond detectors are a decisive and unique tool for the detailed characterisation of upcoming gamma sources, such as ELI-NP and HIγS-2. [ABSTRACT FROM AUTHOR]

Some of the more attractive semiconducting compounds for ambient temperature radiation detector applications are impacted by low charge collection efficiency due to the presence of point and volumetric defects. This has been particularly true in the case of BiI3, which features very attractive properties (density, atomic number, band gap, etc.) to serve as a gamma ray detector, but has yet to demonstrate its full potential. We show that by applying growth techniques tailored to reduce defects, the spectral performance of this promising semiconductor can be realized. Gamma ray spectra from >100 keV source emissions are now obtained from high quality Sb:BiI3 bulk crystals with limited concentrations of defects (point and extended). The spectra acquired in these high quality crystals feature photopeaks with resolution of 2.2% at 662 keV. Infrared microscopy is used to compare the local microstructure between radiation sensitive and non-responsive crystals. This work demonstrates that BiI3 can be prepared in melt-grown detector-grade samples with superior quality and can acquire the spectra from a variety of gamma ray sources. [ABSTRACT FROM AUTHOR]

For radiation monitoring at the sites of such nuclear power plant accidents as Fukushima Daiichi, radiation detectors are needed not only for gamma photons but also for alpha and beta particles because some nuclear fission products emit beta particles and gamma photons and some nuclear fuels contain plutonium that emits alpha particles. In some applications, imaging detectors are required to detect the distribution of plutonium particles that emit alpha particles and radiocesium in foods that emits beta particles and gamma photons. To solve these requirements, we developed an imaging detector that can measure the distribution of alpha and beta particles as well as gamma photons. The imaging detector consists of three-layer scintillators optically coupled to each other and to a position sensitive photomultiplier tube (PSPMT). The first layer, which is made of a thin plastic scintillator (decay time: ~5 ns), detects alpha particles. The second layer, which is made of a thin Gd 2 SiO 5 (GSO) scintillator with 1.5 mol% Ce (decay time: 35 ns), detects beta particles. The third layer made of a thin GSO scintillator with 0.4 mol% Ce (decay time: 70 ns) detects gamma photons. Using pulse shape discrimination, the images of these layers can be separated. The position information is calculated by the Anger principle from 8×8 anode signals from the PSPMT. The images for the alpha and beta particles and the gamma photons are individually formed by the pulse shape discriminations for each layer. We detected alpha particle images in the first layer and beta particle images in the second layer. Gamma photon images were detected in the second and third layers. The spatial resolution for the alpha and beta particles was ~1.25 mm FWHM and less than 2 mm FWHM for the gamma photons. We conclude that our developed alpha–beta–gamma imaging detector is promising for imaging applications not only for the environmental monitoring of radionuclides but also for medical and molecular imaging. [ABSTRACT FROM AUTHOR]

It has been observed that large polyvinyl toluene (PVT)-based gamma-ray detectors can suffer internal “fogging” when exposed to certain outdoor environmental conditions over long periods of time. When observed, this change results in reduced light collection by photomultiplier tubes connected to the PVT. Investigation of the physical cause of these changes has been explored, and a root cause identified. Water penetration into the PVT from hot, high-humidity conditions results in reversible internal water condensation at room temperature, and permanent micro-fracturing of the PVT at very low environmental temperatures. Mitigation procedures and methods are being investigated. [ABSTRACT FROM PUBLISHER]

^3He shortage has provoked a renewed interest for organic scintillation detectors (good neutron detection efficiency) with neutron-gamma discrimination capability. Pulse Shape Discrimination (PSD) with plastic scintillators has recently shown important progresses and raises a great interest as plastic detectors are not toxic and not inflammable contrary to liquid scintillation detectors. In this context, the French Atomic and Renewable Energy Commission (CEA), within the FP7 European project SCINTILLA, is studying the possibility to produce large size plastic scintillators as candidates for ^3He tube replacements together with the related FPGA electronics. To support the design of plastic scintillators with enhanced neutron-gamma discrimination power, software based on ROOT data analysis software was developed to couple photon-neutron transport with MCNP PoliMi and optical photon tracking in the scintillator with Litrani. This new tool called “POLITRANI” allows to build realistic electronic pulses delivered by radiation detectors, and thus to study PSD sensitivity to various factors such as plastic shape, size, coating, scintillation decay time for neutrons vs. gamma rays, and radiation scattering in the detector. Parameters of the FPGA-based electronics can also be investigated, such as sampling frequency, trigger, and length of the integration gate. [ABSTRACT FROM PUBLISHER]

In recent years, real-time neutron/\gamma -ray pulse-shape discrimination has become feasible for use with scintillator-based detectors that respond extremely quickly, on the order of 25 ns in terms of pulse width, and their application to a variety of nuclear material assays has been reported. For the in-situ analysis of nuclear materials, measurements are often based on the multiplicity assessment of spontaneous fission events. An example of this is the ^240Pueff assessment stemming from long-established techniques developed for ^3He-based neutron coincidence counters when ^3He was abundant and cheap. However, such measurements when using scintillator detectors can be plagued by low detection efficiencies and low orders of coincidence (often limited to triples) if the number of detectors in use is similarly limited to 3 or 4. Conversely, an array of > 10 detector modules arranged to optimize efficiency and multiplicity sensitivity, shifts the emphasis in terms of performance requirement to the real-time digital analyzer and, critically, to the scope remaining in the temporal processing window of the firmware in these systems. In this paper we report on the design, development and commissioning of a custom-built, 16-channel real-time pulse-shape discrimination analyzer specified for the materials assay challenge summarized above. The analyzer incorporates 16 dedicated and independent high-voltage supplies along with 16 independent digital processing channels offering pulse-shape discrimination at a rate of 3\times10^6 events per second. These functions are configured from a dedicated graphical user interface, and all settings can be adjusted on-the-fly with the analyzer effectively configured one-time-only (where desired) for subsequent plug-and-play connection, for example to a fuel bundle organic scintillation detector array. [ABSTRACT FROM PUBLISHER]

We have developed a 4-layer depth-of-interaction (DOI) detector which consists of four layers of scintillation crystal arrays and a position sensitive photomultiplier tube (PS-PMT). To control the behavior of scintillation light in each DOI crystal array, some reflectors between crystals are removed so that all crystal responses in the four layers are expressed in one two-dimensional (2D) position histogram by implementing an Anger-type calculation of the PS-PMT signals. Since the method utilizes spread of scintillation light through the boundary of the crystals with no reflectors, positioning performance in the 2D position histogram depends on the crystal dimensions, the crystal surface finish, and gap materials. In this work, we propose an adjustment method for crystal identification performance of the 4-layer DOI detector by selecting the optimal refractive index for the gap materials between the crystals in which the reflectors are removed. We fabricated single-layer detectors and 4-layer detectors using LYSO scintillators and evaluated the crystal identification performance, while varying the refractive index of the gap materials (by using different optical cements). As a result, we found the 2D position histogram changes as a function of the refractive index of the optical cement between crystals and the optimal refractive indices can be determined for the detector using the LYSO crystals. We concluded that the crystal response of the 2D position histograms can be adjusted and crystal identification performance can be optimized by changing the refractive index of the gap materials. [ABSTRACT FROM AUTHOR]

Abstract: The Large High Altitude Air Shower Observatory (LHAASO) is a multipurpose project with a complex detector array for high energy gamma ray and cosmic ray detection. The array of 1km2 is composed of five types of detectors to measure shower arrival direction, total number of secondary particles, muon content, Cherenkov image and high energy gamma rays near shower core, respectively. The main scientific goals are (1) searching for galactic cosmic ray origins by extensive spectroscopy investigations of gamma ray sources above 30TeV; (2) all sky survey for gamma ray sources at energies higher than 300GeV; (3) energy spectrum and composition measurements of cosmic rays over a wide range covering knees with fixed energy scale and known fluxes for all species at the low energy end. In this paper, the progress on relevant detector developments is reported, including constructions of prototype detectors at Tibet site and coincidence operation with the ARGO-YBJ resistive plat chamber full coverage array at 4300m a.s.l. The energy spectrum of cosmic ray hydrogen and Helium nuclei up to 0.8PeV is reported as the first piece of physics measurements by the LHAASO experiment. [Copyright &y& Elsevier]

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. [ABSTRACT FROM PUBLISHER]

Gamma-ray efficiency calculations for a germanium detector have been made for a Compton suppression system. Results have shown that for radionuclides that have gamma rays in coincidence the photopeaks can be severely depressed leading to erroneous results. While this can be overcome in routine neutron activation analysis using a comparator method, special consideration must be given to determine the suppression for coincident gamma rays when calculating the efficiency curve and for radionuclide activities. This is especially important for users of the k method and for fission product identification using Compton suppression methods. [ABSTRACT FROM AUTHOR]

Total body nitrogen (TBN) can be used to estimate total body protein, an important body composition component at the molecular level. A system using the associated particle technique in conjunction with prompt gamma neutron activation analysis has been developed for the measurement of TBN in vivo. The system uses a compact D, T neutron generator (~10 n/s) coupled to an internal alpha-particle detector, and a counting system with six bismuth germinate detectors. 14 Subjects were scanned from shoulders to hips (20 min scan time, <0.4 mSv dose) generating complex spectra dominated by signals from C, O, H, and N, with significant peak overlap. Fractional contributions from these elements to regions of interests (ROI) spanning a 4-8 MeV range were determined by algorithms comparing ratios of interrelated ROIs. In addition, multi-component least squares fitting was done to further resolve individual peak activities (MATLAB R2011b). Total body potassium (TBK) was also measured using a whole body gamma counter. Predicted TBN values, based on fat-free mass estimated from TBK, were compared to measured TBN results. Measured versus predicted results for all subjects were not statistically different. Separating subjects by gender also showed no difference between measured and predicted values. The associated particle system showed good agreement with predicted TBN values, but measurement precision was not better than that commonly seen in traditional prompt gamma thermal neutron activation analysis systems. [ABSTRACT FROM AUTHOR]

We proposed a Compton Backscattering Coincidence (CBC) Technique to reduce background gamma-rays. Properties of the CBC technique were investigated with the EGS5 Monte Carlo simulation code and basic experiments. In this method, a sensitive area can be confined between two detectors while in a conventional method a sensitive area can't be confined because the sensitivity decreases as the solid angle decreases. Two detector configurations using two \ LaBr3 scintillators or HPGe-pure \ CaF2 scintillators were tested to validate the feasibility of the proposed technique. [ABSTRACT FROM PUBLISHER]

Abstract: Detector grade CZT single crystals have been grown from zone refined Cd, Zn, and Te (∼7N) precursor materials using a tellurium solvent method. Infrared transmission imaging has shown an average tellurium inclusion size of ∼8μm in the as-grown crystal. Radiation detectors were fabricated in planar and virtual Frisch grid geometry and characterized for their spectroscopic performance. Charge transport properties revealed a high drift mobility of∼1200cm2/Vs and a mobility–lifetime product of ∼2.8×10−3 cm2/V. A detector with planar configuration (dimensions 6.9×6.9×4.8mm3) showed an energy resolution of 4.7% for 59.5keV gamma rays. The detector in a Frisch grid configuration (dimensions 4.2×6.2×6.5mm3) exhibited an energy resolution of 1.4% for 662keV gamma rays. Digital spectroscopic measurements were carried out using a high-resolution digitizer card. A biparametric correlation scheme was employed to study the effect of charge loss on energy resolution of the planar detector. Based on this correlation scheme, a digital correction method was applied and improved pulse-height spectrum was obtained for 662keV gamma rays using the planar detector with spectral features comparable to those of the virtual Frisch grid detector. [Copyright &y& Elsevier]

The ionic conductivity of TlBr, TlI and their solid solutions, candidates for high energy radiation detection, was examined using impedance spectroscopy. The orthorhombic to cubic phase change in TlI was observed via a steep change in conductivity with increasing temperature, whereas the TlBr-TlI solid solution was cubic throughout the measured temperature range, in agreement with the literature. The intrinsic conductivity of the cubic phase of each material showed nearly identical behavior, indicating that I substitution for Br has little to no effect on the combined defect formation and transport parameters in the studied range. Additionally, optical transmission was correlated with I concentration. [ABSTRACT FROM PUBLISHER]

The crystals of 0.1, 0.5, 1, and 3% Ho doped Lu3Al5O12 (Ho:LuAG) grown by the micro-pulling-down method were examined for their scintillation properties. At wavelengths longer than 300 nm, Ho:LuAG crystals demonstrated around 60% transparency with many absorption peaks attributed to Ho^3+ 4f^10-4f^10 transitions. When excited by ^241Am \alpha-ray to obtain radio luminescence spectra, broad host emission and four sharp Ho^3+4f^10-4f^10 emission peaks were detected in the visible region. Light yields and decay time profiles of the samples irradiated by ^137Cs\gamma-ray were measured using photomultiplier tubes R7600 (Hamamatsu). Ho 0.5%:LuAG showed the highest light yield of 3100 \pm 310 photons/MeV among the present samples. The decay time profiles were well reproduced by two components exponential approximation consisting of 0.5–1 \mus and 3–6 \mus. [ABSTRACT FROM PUBLISHER]

Abstract: In a pixelated detector, an electron cloud can be collected by and shared between several adjacent pixels. By including these charge-sharing events, the Compton-imaging efficiency can be improved for 3D position sensitive room-temperature CdZnTe gamma-ray detectors. Simulated photopeak events that trigger three separate pixels with two pixels being adjacent to each other, which are called three-pixel side-neighbor photopeak events, were divided into six categories based on interaction type. Analysis of this simulation shows that the most effective strategy is to treat all side-neighbor events as charge-sharing events and to combine all side-neighbor signals into a single interaction. By including these side-neighbor events in the Compton image reconstruction, we can improve the imaging efficiency by 45% and 160% for 662keV and 1333keV incident photons, respectively. The simulation also shows that 76% of these combined events reconstruct to rings that pass the source direction. Measured data is presented to validate the simulation results. [Copyright &y& Elsevier]

Abstract: Performance tests of a movable gamma-ray waste drum scanning system were carried out in this study. The scanner consists of a single HPGe detector on a movable cart with a 90° collimation angle to the observed item. The detection efficiency for 137Cs was determined using the ISOTOPIC software. The activities of 35 low-level radioactive waste drums were measured using this system and compared with the results of two other measurement systems. This movable scanning system gave the same result as the other two systems with a relative spread (one standard deviation) of about 7.2%. [Copyright &y& Elsevier]

A method of determining the characteristics of photon radiation from an instantaneous release of gas-aerosol radioactive impurity on the basis of the indications of ARMS sensors recording the dose rate of external irradiation was examined. The dose rate distribution was modeled by the Monte Carlo method by prescribing different energy spectra of the photon radiation for point and linear sources. The average energy of the photon radiation was determined from histograms of the reconstructed spectra; this made it possible to find all necessary parameters for making predictive estimates of the dose loads on workers and the general public during radiation accidents. The average energies computed for the a priori and reconstructed photon spectra showed satisfactory agreement. The relative computational error was no greater than 2% for ascending and hump-shaped spectra and the optimal number of iterations did not exceed 2500. For a descending spectrum, the estimation error for the average photon energy was 5-6% but the number of iterations exceeded 12000. [ABSTRACT FROM AUTHOR]

We performed Monte-Carlo simulations of X-ray interactions and charge transport within a photon counting cadmium zinc telluride (CZT) detector. We study various physical processes affecting the width and shape of detected pulses and find that the energy resolution depends on the pulse width variance. One impact factor (and main topic of this work) is the temporal splitting of pulses due to the simultaneous creation of two or more charge clouds by K-fluorescence within the same pixel. Measured energies are underestimated if the timing constants of detector and electronics are below or in the order of the arrival time differences of the charge clouds. Pulse temporal splitting is of minor relevance if other effects like charge sharing or polarization by hole trapping are present which cause a stronger degradation of the pulse height spectrum. [ABSTRACT FROM AUTHOR]

This paper proposes a soft error characterization methodology to analyze multiple faults caused by single-event-induced charge sharing in standard-cell based ASIC designs. Fault injection campaigns have been executed using data provided by placement analysis as well as a pulse width modeling through electrical simulation. Experimental results demonstrate that the error rate can be largely overestimated if placement is not considered. [ABSTRACT FROM PUBLISHER]

Abstract: Bismuth tri-iodide is a wide band-gap semiconductor material that may be able to operate as a radiation detector without any cooling mechanism. This material has a higher effective atomic number than germanium and CdZnTe, and thus should have a higher gamma-ray detection efficiency, particularly for moderate and high energy gamma-rays. Unfortunately, not much is known about bismuth tri-iodide, and the general properties of the material need to be investigated. Bismuth tri-iodide does not suffer from some of the material issues, such as a solid state phase transition and dissociation in air, that mercuric iodide (another high-Z, wide band-gap semiconductor) does. Thus, bismuth tri-iodide is both easier to grow and handle than mercuric iodide. A modified vertical Bridgman growth technique is being used to grow large, single bismuth tri-iodide crystals. Zone refining is being performed to purify the starting material and increase the resistivity of the crystals. The single crystals being grown are typically several hundred mm3. The larger crystals grown are approximately 2cm3. Initial detectors are being fabricated using both gold and palladium electrodes and palladium wire. The electron mobility measured using an alpha source was determined to be 260±50cm2/Vs. An alpha spectrum was recorded with one of the devices; however the detector appears to suffer from polarization. [Copyright &y& Elsevier]

Abstract: We have built a fast neutron bismuth activation counter that measures activation counts from pulsed 14-MeV neutron generators for incident neutron fluences between 30 and 300neutrons/cm2 at 15.2cm (6in.). The activation counter consists of a large bismuth germanate (BGO) detector surrounded by a bismuth metal shield in front of and concentric with the cylindrical detector housing. The 14MeV neutrons activate the 2.6-millisecond (ms) isomer in the shield and the detector by the reaction 209Bi (n,2nγ) 208mBi. The use of millisecond isomers and activation counting times minimizes the background from other activated materials and the environment. In addition to activation, the bismuth metal shields against other outside radiation sources. We have tested the bismuth activation counter, simultaneously, with two data acquisition systems (DASs) and both give similar results. The two-dimensional (2D) DAS and three dimensional (3D) DAS both consist of pulse height analysis (PHA) systems that can be used to discriminate against gamma radiations below 300keV photon energy, so that the detector can be used strictly as a counter. If the counting time is restricted to less than 25ms after the neutron pulse, there are less than 10 counts of background for single pulse operation in all our operational environments tested so far. High-fluence neutron generator operations are restricted by large dead times and pulse height saturation. When we operate our 3D DAS PHA system in list mode acquisition (LIST), real-time corrections to dead time or live time can be made on the scale of 1ms time windows or dwell times. The live time correction is consistent with nonparalyzable models for dead time of 1.0±0.2μs for our 3D DAS and 1.5±0.3μs for our 2D DAS dominated by our fixed time width analog to digital converters (ADCs). With the same solid angle, we have shown that the bismuth activation counter has a factor of 4 increase in sensitivity over our lead activation counter, because of higher counts and negligible backgrounds. [Copyright &y& Elsevier]