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The crystal growth of CsCaI 3 :Eu with improved quality over prior efforts for use in X-ray and gamma-ray detection applications is reported. Boules were grown using the vertical Bridgman technique in quartz ampoules at 15, 22, and 35 mm diameters. CsCaI 3 :Eu crystals show evidence of a heavily twinned microstructure likely caused by a solid-solid phase transformation of the crystal during the cooling process. Energy resolution (FWHM) in large and small samples taken from crystalline boules varies between 13% and 4.5% for 662 keV gamma rays indicating volumetric non-uniformity. Scintillation decay time is shown to increase with volume. Proportionality of the light yield of CsCaI 3 :Eu is reported for the first time. [ABSTRACT FROM AUTHOR]

In \gamma -ray detectors, monolithic scintillation crystals offer the possibility of preserving the scintillation light distribution especially when painted black. The statistical moments of this distribution provide accurate information on the three photon impact coordinates, including their depth of interaction (DOI). Digital SiPMs (dSiPMs) return digital information based on pixels about the collected light distribution, since the signal is a digital sum of the trigger bins. In this work we present, for the first time, an accurate analysis of the statistical moments of the light distribution using monolithic painted black crystals and state-of-the-art dSiPMs. Two 32.6 \times 32.6 ~\mm^2 monolithic LYSO crystals covering the entire photodetectors area have been used in coincidence with 10 mm in thickness. The photosensor tiles were kept at a stable temperature of T = 20\,^\circ\ C. Energy resolution of about 18% was reached in relation to the zeroth moment. The first moment, related to the impact position, determined a spatial resolution of about 3 mm near the crystal center, but quadratically degrading towards the crystal borders. The DOI resolution, measured by means of the second moment, was found to be nearing 4 mm in the crystal center region. The third order moment, the so-called skewness, is related to the degree of truncation and once calibrated minimizes the compression effects. A corrected spatial resolution of about 3 mm was then measured for the entire crystal surface. DOI resolution improved at the crystal’s center, reaching 3.5 mm, but a degradation towards the borders remained due to truncation of the scintillation light distribution. [ABSTRACT FROM AUTHOR]

In this paper, we report on the recent development of a 32-channel low-noise front-end readout ASIC for cadmium zinc telluride (CdZnTe) X-ray and \gamma -ray detectors. Each readout channel includes a charge sensitive amplifier, a CR-RC shaping amplifier and an analog output buffer. The readout ASIC is implemented using TSMC 0.35 - \mu \m mixed-signal CMOS technology, the die size of the prototype chip is 2.2~\mm \times 4.8~\mm. At room temperature, the equivalent noise level of a typical channel reaches 133~\e^ - (rms) with the input parasitic capacitance of 0 pF for the average power consumption of 2.8 mW per channel. The linearity error is less than \pm 2\% and the input energy dynamic range of the readout ASIC is from 10 keV to 1 MeV. The crosstalk between the channels is less than 0.4%. By connecting the readout ASIC to a CdZnTe detector, we obtained a \gamma -ray spectrum, the energy resolution is 1.8% at the 662-keV line of ^137Cs source. [ABSTRACT FROM AUTHOR]

Various analytical functions proposed to express the full energy photopeak efficiency (FEPE) of gamma ray detectors have been investigated for their performance tofit the percentage FEPE of Amcrys-H made 2" x 2" NaI(Tl) scintillation detector. Initially, the experimental measurements on FEPEs of various gamma sources were used to validate the theoretical Monte Carlo (MC) simulations. The maximum deviation observed between the experimental efficiencies and MC simulations is -12.51%, which is observed for 356 keV of 133Ba. The percentage FEPEs obtained through validated MC simulations are then fitted against gamma energy in the range 122-1332 keV using the recommended efficiency functions to obtain the percentage FEPE as a smooth function of gamma energy for the source to detector distance of 5 cm. The analytical function recommended by McNelles, Campbell and Singh is identified as the most suitable for the detector type considered and this, in turn, is used to obtain fitting coefficients for all other source to detector distances. The fitted equations are found to provide the percentage FEPEs, which are well within ±6% deviation with respect to the theoretical MC simulations for most of the energies and distances. For the source to detector distances of 15 and 25 cm, the gamma energy of 500 keV is found to have the maximum deviations up to 7.6%. [ABSTRACT FROM AUTHOR]

We describe a pulsed positron beam that is optimised for positronium (Ps) laser-spectroscopy experiments. The system is based on a two-stage Surko-type buffer gas trap that produces 4 ns wide pulses containing up to 5 x 105 positrons at a rate of 0.5-10 Hz. By implanting positrons from the trap into a suitable target material, a dilute positronium gas with an initial density of the order of 107 cm-3 is created in vacuum. This is then probed with pulsed (ns) laser systems, where various Ps-laser interactions have been observed via changes in Ps annihilation rates using a fast gamma ray detector. We demonstrate the capabilities of the apparatus and detection methodology via the observation of Rydberg positronium atoms with principal quantum numbers ranging from 11 to 22 and the Stark broadening of the n = 2 → 11 transition in electric fields. [ABSTRACT FROM AUTHOR]

The progress of modern detector arrays was based on their good angular resolution, which has a great impact on gamma-ray spectroscopy with relativistic fragmentation beams and, thus, allows studies of the most exotic nuclei and discovery of superdeformed states of high spins. Recently, a fast timing array was designed for the future Facility for Antiproton and Ion Research for studying the very short-lived nuclei (of several subnanoseconds) at the extremes of existence. For this purpose, several gamma-ray detector array geometries were designed and simulated to maximize the solid angle and enhance the timing precision and efficiencies. Therefore, the probability correction approach has been applied in the present work to calibrate the newly designed gammaray conical array for the fast timing array. The calculated full-energy peak efficiency values for the array were compared to the simulated ones by the GEANT 4 code published in the literature. Results showed a reasonably low-percentage relative difference between the calculated and the reported simulated results <4.5% on average. [ABSTRACT FROM AUTHOR]

Monte Carlo simulations of one of the possible configurations of the imaging phase for the DEGAS spectrometer situated at the DESPEC/NUSTAR experiment have been performed. The geometry consists of the coupling of the high-resolution γ spectroscopy array, AGATA, with a high-resolution segmented planar detector utilized as an implantation detector in a compact configuration. The sensitivity and performance of the array in terms of efficiency and imaging capability is deduced. [ABSTRACT FROM AUTHOR]

A device to characterize position-sensitive germanium detectors has been implemented at GSI. The main component of this so called scanning table is a gamma camera that is capable of producing online 2D images of the scanned detector by means of a PET technique. To calibrate the gamma camera Compton imaging is employed. The 2D data can be processed further offline to obtain depth information. Of main interest is the response of the scanned detector in terms of the digitized pulse shapes from the preamplifier. This is an important input for pulse-shape analysis algorithms as they are in use for gamma tracking arrays in gamma spectroscopy. To validate the scanning table, a comparison of its results with a second scanning table implemented at the IPHC Strasbourg is envisaged. For this purpose a pixelated germanium detector has been scanned. [ABSTRACT FROM AUTHOR]

This paper reports on a new Ce-doped Tl-based scintillator, Tl 2 LaCl 5 (TLC), for gamma-ray detection. 10 mm diameter crystals have been successfully grown using the vertical Bridgman method. The emission peak of TLC is detected at 383 nm under X-ray excitation. The light yield of TLC is 76,000 ph/MeV. The samples show excellent energy resolution of 3.4% (FWHM) at 662 keV. The non-proportionality is less than 1%, from 32 keV to 1275 keV. The major scintillation decay time is 36 ns. [ABSTRACT FROM AUTHOR]

So to search for WIMPs physicists need only look for recoiling nuclei in detectors deep underground, where they're shielded from other types of radiation that can also cause recoil events. However, physicists are only now starting to probe the heart of the possible ranges of mass and interaction strength for WIMPs, contends Rafael Lang, a physicist and XENON team member at Purdue University. Physicists working with the world's biggest dark-matter detector - a behemoth in the United States known as LUX-ZEPLIN (LZ) - released their first results today. [Extracted from the article]

Plastic scintillators have been used for gamma ray detection in the fields of dosimetry and homeland security because of their desired characteristics such as a fast decay time, a low production cost, availability in a large-scale, and a tissue-equivalence. Gaussian energy broadening (GEB) in MCNP simulation is an effective treatment for tallies to calculate the broadened response function of a detector similarly to measured spectra. The full width at half maximum (FWHM) of a photopeak has been generally used to compute input parameters required for the GEB treatment. However, it is hard to find the photopeak in measured gamma spectra with plastic scintillators so that computation of the input parameters for the GEB has to be taken with another way. In this study, an iterative method for the GEB treated MCNP simulation to calculate the response function of a plastic scintillator is suggested. Instead of the photopeak, Compton maximum and Compton edge were used to estimate energy broadening in the measured spectra and to determine the GEB parameters. In a demonstration with a CsI(Tl) scintillator, the proposed iterative simulation showed the similar gamma spectra to the existing method using photopeaks. The proposed method was then applied to a polystyrene scintillator, and the simulation result were in agreement with the measured spectra with only a little iteration. [ABSTRACT FROM AUTHOR]

Dosimetric instruments must constantly monitor radiation dose levels in different areas of nuclear reactor. Tehran Research Reactor (TRR) has seven beam tubes for different research purposes. All the beam tubes extend from the reactor core to Beam Port Floor (BPF) of the reactor facility. During the reactor operation, the gamma rays exiting from each beam tube outlet produce a specific gamma dose rate field in the space of the BPF. To effectively monitor the gamma dose rates on the BPF, gamma ray detection systems must be installed in optimal positions. The selection of optimal positions is a compromise between two requirements. First, the installation positions must possess largest gamma dose rates and second, gamma ray detectors must not be saturated in these positions. In this study, calculations and experimental measurements have been carried out to identify the optimal positions of the gamma ray detection systems. Eight three dimensional models of the reactor core and related facilities corresponding to eight scenarios have been simulated using MCNPX Monte Carlo code to calculate the gamma dose equivalent rate field in the space of the BPF. These facilities are beam tubes, thermal column, pool, BPF space filled with air, facilities such as neutron radiography facility, neutron powder diffraction facility embedded in the beam tubes as well as biological shields inserted into the unused beam tubes. According to the analysis results of the combined gamma dose rate field, three positions on the north side and two positions on the south side of the BPF have been recognized as optimal positions for installing the gamma ray detection systems. To ensure the consistency of the simulation data, experimental measurements were conducted using TLDs (600 and 700) pairs during the reactor operation at 4.5 MW. [ABSTRACT FROM AUTHOR]

Mechanically polishing cadmium zinc telluride (CdZnTe) wafers for x-ray and gamma-ray detectors often is inadequate in removing surface defects caused by cutting them from the ingots. Fabrication-induced defects, such as surface roughness, dangling bonds, and nonstoichiometric surfaces, often are reduced through polishing and etching the surface. In our earlier studies of mechanical polishing with alumina powder, etching with hydrogen bromide in hydrogen peroxide solution, and chemomechanical polishing with bromine-methanol-ethylene glycol solution, we found that the chemomechanical polishing process produced the least surface leakage current. In this research, we focused on using two chemicals to chemomechanically polish CdZnTe wafers after mechanical polishing, viz. bromine-methanol-ethylene glycol (BME) solution, and hydrogen bromide (HBr) in a hydrogen peroxide and ethylene-glycol solution. We used x-ray photoelectron spectroscopy (XPS), current-voltage ( I- V) measurements, and Am-241 spectral response measurements to characterize and compare the effects of each solution. The results show that the HBr-based solution produced lower leakage current than the BME solution. Results from using the same chemomechanical polishing solution on two samples confirmed that the surface treatment affects the measured bulk current (a combination of bulk and surface currents). XPS results indicate that the tellurium oxide to tellurium peak ratios for the mechanical polishing process were reduced significantly by chemomechanical polishing using the BME solution (78.9% for Te 3 dO and 76.7% for Te 3 dO) compared with the HBr-based solution (27.6% for Te 3 dO and 35.8% for Te 3 dO). Spectral response measurements showed that the 59.5-keV peak of Am-241 remained under the same channel number for all three CdZnTe samples. While the BME-based solution gave a better performance of 7.15% full-width at half-maximum (FWHM) compared with 7.59% FWHM for the HBr-based solution, the latter showed a smaller variation in performance of 0.39% FWHM over 7 days compared with 0.69% for the BME-based solution. [ABSTRACT FROM AUTHOR]

The development of a reliable technique for making good electrical contacts to semi-insulating (Cd,Mn)Te monocrystalline plates meant for x- and gamma radiation detectors, a technique of crystal surface preparation and a technique of passivation of the surfaces between electrodes were the main objectives of the studies. The investigations of the electrical contacts were focused on the amorphous/nanocrystalline contact layers. The effects of passivation of the inter-electrode surfaces on the magnitude of the surface leakage currents were studied. [ABSTRACT FROM AUTHOR]

The influence of the gas-static processing on the optical, structural and electrophysical properties of Au–CdZnTe–Au structures, used in X- and gamma-ray detectors, was investigated. The processing, which is described in detail in the experimental part, was done in a laboratory-scale setup “GAUS-4/2000-35” with the following process parameters: pressure=0.32±0.02 GPa, temperature ~170 °C, time=2 h. The influence of the mentioned processing on the photoluminescence, the Raman scattering, the electric resistance, the I–V characteristics and the spectrometric parameters of the Au–CdZnTe–Au structures was determined. The physical mechanisms, through which the gas-static processing induces changes in the structural and functional properties, were analyzed. It was observed that the gas-static processing (with the above-mentioned process parameters) of the Au–CdZnTe–Au structures leads to a significant increase of the electric resistance of the structures; it also leads to the increase of the intensity of the photoelectric absorption peak when the respective detector is registering X- and gamma-radiation with energy near 32.19 keV. The Raman and photoluminescence data indicates the formation of the surface oxides TeO x and the compensation of Cd vacancies by Au atoms. The assumption that, under the discussed processing, two different rival processes modify the Au–CdZnTe junction due to the influence of the increased temperature ~170 °C and pressure ~0.3 GPa, was suggested. The first process is the formation of TeO 2 oxide (which increases the electric resistance) on the contact; the second process is the destruction of the surface films of the oxides and the absorbed gases. Most likely, the first process is dominant, which was evidenced by the Raman and photoluminescence measurements. [ABSTRACT FROM AUTHOR]

Asbstract The French Atomic Energy Commission (CEA), with the support of the European Space Agency (ESA), is partner of the Soft Gamma-Ray Detector (SGD) and the Hard X-ray Imager (HXI) onboard the 6th Japanese X-ray scientific satellite ASTRO-H (JAXA) initiated by the Institute of Space and Astronautical Science (ISAS). Both scientific instruments, one hosting a series of Compton Gamma Cameras and the other being a focal plane of a grazing incidence mirror telescope in the hard X-ray domain, are equipped with Cadmium Telluride based detectors. ASTRO-H will be operated in a Low Earth Orbit with a 31° inclination at ~550 km altitude, thus passing daily through the South Atlantic Anomaly radiation belt, a specially harsh environment where the detectors are suffering the effect of the interaction with trapped high energy protons. As CdTe detector performance might be affected by the irradiation, we investigate the effect of the accumulated proton fluence on their spectral response. To do so, we have characterized and irradiated representative samples of SGD and HXI detector under different conditions. The detectors in question, from ACRORAD, are single-pixels having a size of 2 mm by 2 mm and 750 µm thick. The Schottky contact is either made of an Indium or Aluminum for SGD and HXI respectively. We ran the irradiation test campaign at the Proton Irradiation Facility (PIF) at PSI, and ESA approved equipment to evaluate the radiation hardness of flight hardware. We simulated the proton flux expected on the sensors over the entire mission, and secondary neutrons flux due to primary proton interactions into the surrounding BGO active shielding. We eventually characterized the detector response evolution, emphasizing each detector spectral response as well as its stability by studying the so-called Polarization effect. The latter is provoking a spectral response degradation against time as a charge accumulation process occurs in Schottky type CdTe sensors. In this paper, we report on the test campaigns at PIF and will show up our experimental setup. We will pursue describing the irradiation conditions associated with our GEANT 4 predictions and finally, we report the main results of our campaigns concluding that the proton effect does not severely affect the CdTe response neither the detector stability while the secondary neutrons might be more active to reduce the performance on the long run. [ABSTRACT FROM AUTHOR]

The liquid xenon (LXe) γ-ray detector for the MEG II experiment is based on a highly granular scintillation readout with Multi-Pixel Photon Counters (MPPCs). Here we report on the development of a large-area MPPC sensitive to LXe scintillation light in deep-UV range for the MEG II LXe detector. A prototype model of the deep-UV MPPC with an active area of 12 × 12 mm 2 was successfully tested in LXe, showing an excellent performance such as a high photon detection efficiency for the LXe scintillation light (about 20% at Δ V = 2.5 V ), a high internal gain (about 10 6 at Δ V = 2.5 V ) and an excellent single photoelectron resolution. The sensor chip of the MPPC is segmented into four sectors, which are then connected in series in order to reduce the overall sensor capacitance. The signal fall time of about 135 ns for the non-segmented sensor was significantly reduced down to 25 ns with the series-connected sensor segments. The preliminary results on the performance of the deep-UV MPPC are presented. [ABSTRACT FROM AUTHOR]

This paper is the fifth in a series of articles on the basic physics of light yield nonproportionality in scintillators. Here, we compare and contrast the nonproportionality as registered by gamma rays and high-energy electrons. As has been noted in the past, these two types of data have different curve shapes (for plots of the light yield against electron or gamma energy). Herein, we show how the experimental gamma nonproportionality curve can be calculated from the electron response by accounting for the distribution of high energy electrons created by the gamma photon via the photoelectric interaction. Similarly, we measure and model the gamma-induced resolution as a function of energy and compare this data to predictions from our model. The utility of the model is explored using data acquired with the scintillators SrI2(Eu), GYGAG(Ce) and CsI(Na). [ABSTRACT FROM PUBLISHER]

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]

In positron emission tomography (PET) systems, light sharing techniques are commonly used to readout scintillator arrays consisting of scintillation elements, which are smaller than the optical sensors. The scintillating element is then identified evaluating the signal heights in the readout channels using statistical algorithms, the center of gravity (COG) algorithm being the simplest and mostly used one. We propose a COG algorithm with a fixed number of input channels in order to guarantee a stable calculation of the position. The algorithm is implemented and tested with the raw detector data obtained with the Hyperion-II^D preclinical PET insert which uses Philips Digital Photon Counting’s (PDPC) digitial SiPMs. The gamma detectors use LYSO scintillator arrays with 30 \times 30 crystals of 1 \times 1 \times 12~\mm^3 in size coupled to 4 \times 4 PDPC DPC 3200-22 sensors (DPC) via a 2-mm-thick light guide. These self-triggering sensors are made up of 2 \times 2 pixels resulting in a total of 64 readout channels. We restrict the COG calculation to a main pixel, which captures most of the scintillation light from a crystal, and its (direct and diagonal) neighboring pixels and reject single events in which this data is not fully available. This results in stable COG positions for a crystal element and enables high spatial image resolution. Due to the sensor layout, for some crystals it is very likely that a single diagonal neighbor pixel is missing as a result of the low light level on the corresponding DPC. This leads to a loss of sensitivity, if these events are rejected. An enhancement of the COG algorithm is proposed which handles the potentially missing pixel separately both for the crystal identification and the energy calculation. Using this advancement, we show that the sensitivity of the Hyperion-II^D insert using the described scintillator configuration can be improved by 20–100% for practical useful readout thresholds of a single DPC pixel ranging from 17–52 photons. Furthermore, we show that the energy resolution of the scanner is superior for all readout thresholds if singles with a single missing pixel are accepted and correctly handled compared to the COG method only accepting singles with all neighbors present by 0–1.6% (relative difference). The presented methods can not only be applied to gamma detectors employing DPC sensors, but can be generalized to other similarly structured and self-triggering detectors, using light sharing techniques, as well. [ABSTRACT FROM PUBLISHER]

True coincidence summing (TCS) occurs when two or more photons are emitted from the same decay of a radioactive nuclide and are detected within the resolving time of the gamma ray detector. TCS changes the net peak areas of the affected full energy peaks in the spectrum and the nuclide activity is rendered inaccurate if no correction is performed. TCS is independent of the count rate, but it is strongly dependent on the peak and total efficiency, as well as the characteristics of a given nuclear decay. The TCS effects are very prominent for well detectors because of the high efficiencies, and make accounting for TCS a necessity. For CANBERRA׳s recently released Small Anode Germanium (SAGe) well detector, an extension to CANBERRA׳s mathematical efficiency calibration method (In Situ Object Calibration Software or ISOCS, and Laboratory SOurceless Calibration Software or LabSOCS) has been developed that allows for calculation of peak and total efficiencies for SAGe well detectors. The extension also makes it possible to calculate TCS corrections for well detectors using the standard algorithm provided with CANBERRAS׳s Spectroscopy software Genie 2000. The peak and total efficiencies from ISOCS/LabSOCS have been compared to MCNP with agreements within 3% for peak efficiencies and 10% for total efficiencies for energies above 30 keV. A sample containing Ra-226 daughters has been measured within the well and analyzed with and without TCS correction and applying the correction factor shows significant improvement of the activity determination for the energy range 46–2447 keV. The implementation of ISOCS/LabSOCS for well detectors offers a powerful tool for efficiency calibration for these detectors. The automated algorithm to correct for TCS effects in well detectors makes nuclide specific calibration unnecessary and offers flexibility in carrying out gamma spectral analysis. [ABSTRACT FROM AUTHOR]

We draw attention to, and present a summary archive of the data from, the Pioneer Venus Orbiter Gamma-ray Burst Detector (OGBD), an instrument not originally conceived with Venus science in mind. We consider the possibility of gamma-ray flashes generated by lightning and model the propagation of gamma rays in the Venusian atmosphere, finding that if gamma rays originate at the upper range of reported cloud top altitudes (75 km altitude), they may be attenuated by factors of only a few, whereas from 60 km altitude they are attenuated by over two orders of magnitude. The present archive is too heavily averaged to reliably detect such a source (and we appeal to investigators who may have retained a higher-resolution archive), but the data do provide a useful and unique record of the cosmic ray flux at Venus 1978–1993. We consider other applications of future orbital gamma ray data, such as atmospheric occultations and the detection of volcanic materials injected high in the atmosphere. [ABSTRACT FROM AUTHOR]

Single crystals of Ce-doped Cs 3 LaCl 6 and Cs 3 LaBr 6 show promising scintillation properties in gamma-ray detection. Their thermal response in the range from 40 K to 500 K is discussed in this work. The steady state photoluminescence spectra, photoluminescence decay time, and X-ray excited radioluminescence of Ce-doped and undoped Cs 3 LaCl 6 and Cs 3 LaBr 6 were studied. The photoluminescence and radioluminescence emission intensity of the Ce-doped crystals decreases less than 25% from 40 K to 500 K. The photoluminescence decay time of Ce 3+ increases with increasing temperature. [ABSTRACT FROM AUTHOR]

t– Recent advances in manufacturing technology have enabled the use of multi-channel pixelated detectors in gamma-ray imaging applications. When obtaining gamma-ray measurements, it is important to obtain pulse height information in order to avoid unnecessary events such as scattering. However, as the number of channels increases, more electronics are needed to process each channel׳s signal, and the corresponding increases in circuit size and power consumption can result in practical problems. The time-over-threshold (ToT) method, which has recently become popular in the medical field, is a signal processing technique that can effectively avoid such problems. However, ToT suffers from poor linearity and its dynamic range is limited. We therefore propose a new ToT technique called the dynamic time-over-threshold (dToT) method [4] . A new signal processing system using dToT and CR-RC shaping demonstrated much better linearity than that of a conventional ToT. Using a test circuit with a new Gd 3 Al 2 Ga 3 O 12 (GAGG) scintillator and an avalanche photodiode, the pulse height spectra of 137 Cs and 22 Na sources were measured with high linearity. Based on these results, we designed a new application-specific integrated circuit (ASIC) for this multi-channel dToT system, measured the spectra of a 22 Na source, and investigated the linearity of the system. [ABSTRACT FROM AUTHOR]

This paper is the fourth in a series of articles published on the light yield nonproportionality of scintillators and its impact on the detector’s energy resolution. Herein, we focus on modeling the resolution degradation induced by delta-rays. To do this, we begin with Møller’s classic equation to describe collisions between incident high-energy electrons and those in the scintillator medium, which lead to the delta-rays. The trajectories of delta-rays having energies above a specified cut-off value are further analyzed to determine the resolution degradation induced by fluctuations in their light yield and ionization density. Our conclusion is that the delta-ray contribution to resolution is typically smaller but comparable to that arising from the primary electron. We have considered the cases for two illustrative scintillators: NaI(Tl) and LSO(Ce). [ABSTRACT FROM PUBLISHER]

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]

In this paper, the capabilities of a wide-area gamma ray photosensor based on a SiPM array are investigated. For this purpose, we have mounted an array of 144 (12\times12) SiPMs with individual active area of 3 \times 3~\mm^2 and a pitch of 4.2~\mm, thus covering an active area of 50.2 \times 50.2~\mm^2. The measurements were performed by coupling the SiPM array to LYSO crystal arrays of different pixel size (2\times2~\mm^2, 1.5 \times 1.5~\mm^2, and 1 \times 1~\mm^2) and 10–12 mm thicknesses. The SiPM array was controlled by means of three ASICs, and the SiPM signals were multiplexed in order to determine the gamma ray impact position by means of implementing the Anger logic algorithm in the ASIC. The optimum bias voltage and temperature dependence of the gamma ray sensor were determined. An energy resolution as good as 8%, for individual crystal pixels, were reached at 5 V overvoltage. The ASICs design allows one to “activate” different photosensor array areas. This feature has been used to evaluate the detector performance as a function of the crystal pixel size and the photosensor dark noise contribution. In this work we also show the system capability to provide depth-of-interaction (DOI) information by means of implementing a two-layer staggered approach. We have found that accurate DOI information is obtained when the ASICs enabled an SiPM active area as high as 32\times 32~\mm^2(8 \times 8 SiPMs). [ABSTRACT FROM PUBLISHER]

Gamma-ray detector systems are important instruments in a broad range of science and new setup are continually developing. The most recent step in the evolution of detectors for nuclear spectroscopy is the construction of large arrays of detectors of different forms (for example, conical, pentagonal, hexagonal, etc.) and sizes, where the performance and the efficiency can be increased. In this work, a new direct numerical method (NAM), in an integral form and based on the efficiency transfer (ET) method, is used to calculate the full-energy peak efficiency of a single hexagonal NaI(Tl) detector. The algorithms and the calculations of the effective solid angle ratios for a point (isotropic irradiating) gamma-source situated coaxially at different distances from the detector front-end surface, taking into account the attenuation of the gamma-rays in the detector׳s material, end-cap and the other materials in-between the gamma-source and the detector, are considered as the core of this (ET) method. The calculated full-energy peak efficiency values by the (NAM) are found to be in a good agreement with the measured experimental data. [ABSTRACT FROM AUTHOR]

Herein, ferrispinel of the system Ni 1− x Zn x FeGaO 4 with 0.0≤ x ≥0.5, have been prepared by solid state reaction to investigate the effect of gamma rays irradiations using 60 Co source on the structure and photoluminescence properties. The structure and Photoluminescence properties of unirradiated and irradiated samples with radiation dose (114 KGy) were investigated by using X-ray diffractometer (XRD) and spectrofluorophotometer (PL). The correlation between photoluminescence and structural distortion due to an irradiation was discussed. It was found that γ-irradiation induced a remarkable change in both structure and photoluminescence properties appearing as a change in the emission energy values and the observed quantum yield. In most results the sample x =0.3 showed anomalous behavior and was explained on the basis of disordered cluster. The data recommended the use of this ferrispinel material as a radiation–detector; accordingly, XRD and PL are used as dosemetric properties for γ − irradiated materials. [ABSTRACT FROM AUTHOR]

Coplanar grid (CPG) CdZnTe detectors have been used as gamma-ray spectrometers for years. Comparing with pixelated CdZnTe detectors, CPG CdZnTe detectors have either no or poor spatial resolution, which directly limits its use in imaging applications. To address the issue, a 2×2 CPG array CdZnTe detector with dimensions of 7×7×5 mm 3 was fabricated. Each of the CPG pairs in the detector was moderately shrunk in size and precisely designed to improve the spatial resolution while maintaining good energy resolution, considering the charge loss at the surface between the strips of each CPG pairs. Preliminary measurements were demonstrated at an energy resolution of 2.7–3.9% for the four CPG pairs using 662 keV gamma rays and with a spatial resolution of 3.3 mm, which is the best spatial resolution ever achieved for CPG CdZnTe detectors. The results reveal that the CPG CdZnTe detector can also be applied to imaging applications at a substantially higher spatial resolution. [ABSTRACT FROM AUTHOR]

The Soft Gamma-ray Detector (SGD) is one of the instrument payloads onboard ASTRO-H, and will cover a wide energy band (60–600 keV) at a background level 10 times better than instruments currently in orbit. The SGD achieves low background by combining a Compton camera scheme with a narrow field-of-view active shield. The Compton camera in the SGD is realized as a hybrid semiconductor detector system which consists of silicon and cadmium telluride (CdTe) sensors. The design of the SGD Compton camera has been finalized and the final prototype, which has the same configuration as the flight model, has been fabricated for performance evaluation. The Compton camera has overall dimensions of 12 cm×12 cm×12 cm, consisting of 32 layers of Si pixel sensors and 8 layers of CdTe pixel sensors surrounded by 2 layers of CdTe pixel sensors. The detection efficiency of the Compton camera reaches about 15% and 3% for 100 keV and 511 keV gamma rays, respectively. The pixel pitch of the Si and CdTe sensors is 3.2 mm, and the signals from all 13,312 pixels are processed by 208 ASICs developed for the SGD. Good energy resolution is afforded by semiconductor sensors and low noise ASICs, and the obtained energy resolutions with the prototype Si and CdTe pixel sensors are 1.0–2.0 keV (FWHM) at 60 keV and 1.6–2.5 keV (FWHM) at 122 keV, respectively. This results in good background rejection capability due to better constraints on Compton kinematics. Compton camera energy resolutions achieved with the final prototype are 6.3 keV (FWHM) at 356 keV and 10.5 keV (FWHM) at 662 keV, which satisfy the instrument requirements for the SGD Compton camera (better than 2%). Moreover, a low intrinsic background has been confirmed by the background measurement with the final prototype. [ABSTRACT FROM AUTHOR]

Positron Emission Tomography (PET) systems using detectors with Depth of Interaction (DOI) capabilities could achieve higher spatial resolution and better image quality than those without DOI. Up till now, most DOI methods developed are not cost-efficient for a whole body PET system. In this paper, we present a DOI decoding method based on flood map for low-cost conventional block detector with four-PMT readout. Using this method, the DOI information can be directly extracted from the DOI-related crystal spot deformation in the flood map. GATE simulations are then carried out to validate the method, confirming a DOI sorting accuracy of 85.27%. Therefore, we conclude that this method has the potential to be applied in conventional detectors to achieve a reasonable DOI measurement without dramatically increasing their complexity and cost of an entire PET system. [ABSTRACT FROM AUTHOR]

The boron concentration in water was determined using neutron scattering and transmission, and prompt gamma ray neutron activation analysis methods. The experimental setup is based on a Pu-Be neutron source, 3 He neutron detectors and an NaI(Tl) gamma-ray detector. Water samples of different volumes and known amounts of boron were prepared. Transmitted and scattered neutrons and prompt gamma rays resulting from neutron capture reactions within the samples were simultaneously measured. The sensitivities of the neutron scattering and transmission measurements were determined to be better than those of the prompt gamma ray neutron activation analysis. The neutron scattering measurements were determined to be more sensitive than those of the neutron transmission measurements. [ABSTRACT FROM AUTHOR]

This paper is the third in a series of articles on the basic physics of nonproportionality in scintillators. Here, we focus on the temperature dependence of six scintillators, NaI(Tl), CsI(Tl), CsI(Na), CeBr_3, LaBr_3(Ce), and undoped SrI_2, and report their nonproportionality curves at -40^\circC, 0^\circC and + 40^\circC. We fit the data to a modified form of our previously employed model, including the competition of carrier trapping with the Onsager-mediated attraction between electrons and holes. [ABSTRACT FROM PUBLISHER]