Search

Abstract: Isomeric ratios have been measured for high-spin states in , , , , , and following the projectile fragmentation of a 1 A GeV 238U beam by a 9Be target at GSI Helmholtzzentrum für Schwerionenforschung. The fragments were separated in the fragment separator (FRS) and identified by means of energy loss and time-of-flight techniques. They were brought to rest at the centre of the RISING gamma-ray detector array and intensities of gamma rays emitted in the decay of isomeric states with half-lives between 100 ns and 40 μs and spin values up to were used to obtain the corresponding isomeric ratios. The data are compared to theoretical isomeric ratios calculated in the framework of the abrasion–ablation model. Large experimental enhancements are obtained for high-spin isomers in comparison to expected values. [Copyright &y& Elsevier]

We have developed a proof-of-concept prototype, rapid-deployment, gamma-ray portal monitor that can uniquely link the radiation signatures and visible-light images of vehicles in the system's field of view from the side of a multilane roadway. The instrument uses both visible-light and gamma-ray imaging to accomplish this. Vehicles entering the field of view of the visible-light imaging system are identified and tracked by an automated target acquisition and tracking software engine. The vehicle locations provided by this code are reported to the gamma-ray imager which uses them to locate the vehicles in the gamma-ray images and to collect the vehicle-specific radiation signatures from those images. Using this technique the gamma-ray data is integrated over the entire residence time of the vehicle in the gamma-ray imager field of view. The complete instrument comprises \sim 1-m^2CsI(Na) detector area split between two units. The system has been designed to handle up to five-lanes of traffic at highway speeds, with one unit located on either side of the roadway. Because no equipment is required in the roadway, the instrument can be deployed without impacting the flow of traffic. The results of a test and evaluation campaign indicates that the system meets its design goal of detecting 37 MBq-class sources in any of five-lanes of traffic at up to 113 km/h. [ABSTRACT FROM PUBLISHER]

Arrays of Cherenkov telescopes typically use multi-level trigger schemes to keep the rate of random triggers from the night sky background low. At a first stage, individual telescopes produce a trigger signal from the pixel information in the telescope camera. The final event trigger is then formed by combining trigger signals from several telescopes. In this paper we present a Cherenkov telescope trigger scheme based on the analog pulse information of the pixels in a telescope camera. Advanced versions of all components of the system have been produced and a working prototype has been tested, showing in most cases features which surpass previous designs in terms of compactness, low noise, short delay, low power consumption and flexibility to be adapted to different observation conditions. Finally, issues related to integrating the trigger system in a telescope camera and in the whole array will be dealt with. [ABSTRACT FROM PUBLISHER]

New experimental results add information on the space–time variation pattern of nuclear radiation from radon in air at confined conditions. Using five gamma sensors placed around a canister containing radon in gas demonstrated temporal variation consisting of a long-term variation, which may be related to an annual variation, multiday (MD) signals and periodic daily radon (DR) signals. Separate processes drive the MD and DR signals. Both MD and DR signals exhibit inverse temporal variation patterns in the east–west and north–south directions. The MD and DR signal patterns along the vertical axis are associated with the north–south directed radiation pattern suggesting that the up–down axis of the system is actually inclined relative to the vertical axis of the canister, i.e. related to the latitude of the experiment. The relations of the time–space variations including the apparent tilt relative to a principal geographic direction imply a connection to global orientation. These results are in line with the proposition of an influence of a component of solar irradiation on variation patterns of nuclear radiation from radon. [ABSTRACT FROM AUTHOR]

Abstract: First generation thermal neutron activation (TNA) sensors, employing an isotopic source and NaI(Tl) gamma ray detectors, were deployed by Canadian Forces in 2002 as confirmation sensors on multi-sensor landmine detection systems. The second generation TNA detector is being developed with a number of improvements aimed at increasing sensitivity and facilitating ease of operation. Among these are an electronic neutron generator to increase sensitivity for deeper and horizontally displaced explosives; LaBr3(Ce) scintillators, to improve time response and energy resolution; improved thermal and electronic stability; improved sensor head geometry to minimize spatial response nonuniformity; and more robust data processing. The sensor is described, with emphasis on the improvements. Experiments to characterize the performance of the second generation TNA in detecting buried landmines and improvised explosive devices (IEDs) hidden in culverts are described. Performance results, including comparisons between the performance of the first and second generation systems are presented. [Copyright &y& Elsevier]

Background: Neutron-rich nuclei with protons in the fp shell show an onset of collectivity around N = 40. Spectroscopic information is required to understand the underlying mechanism and to determine the relevant terms of the nucleon-nucleon interaction that are responsible for the evolution of the shell structure in this mass region. Methods: We report on the lifetime measurement of the first 2+ and 4+ states in 70,72,74Zn and the first 6+ state in 72Zn using the recoil distance Doppler shift method. The experiment was carried out at the INFN Laboratory of Legnaro with the AGATA demonstrator, first phase of the Advanced Gamma Tracking Array of highly segmented, high-purity germanium detectors coupled to the PRISMA magnetic spectrometer. The excited states of the nuclei of interest were populated in the deep inelastic scattering of a 76Ge beam impinging on a 238U target. Results: The maximum of collectivity along the chain of Zn isotopes is observed for 72Zn at N = 42. An unexpectedly long lifetime of 20+1855 ps was measured for the 4+ state in 74Zn. Conclusions: Our results lead to small values of the B(E2;4+1→ 2+1)/B(E2;2+1→0+1) ratio for 72,74Zn, suggesting a significant noncollective contribution to these excitations. These experimental results are not reproduced by state-of-the-art microscopic models and call for lifetime measurements beyond the first 2+ state in heavy zinc and nickel isotopes. [ABSTRACT FROM AUTHOR]

Abstract: A wave hydraulic scale model was manufactured and used to investigate the characteristics of the transport of a pollutant in a coastal area. The experiments were performed using tracers having different properties. Experiments using variations of injection point and velocity were carried out by using NaCl and radioisotope (99mTc) tracers, respectively. The experimental data have been compared with the results of the numerical simulations. The conductivity meters and gamma ray detectors were installed at the bottom and middle area in the vertical direction, respectively. NaCl tracer moved into the bottom area due to the density effects, so the results showed some differences. But the experiments using the radioisotope showed better results for the comparison with the numerical simulations. It was shown that a radioisotope was one of the best tracers to investigate the pollutant transport in an aquatic environment. [Copyright &y& Elsevier]

One of the primary goals of scintillator-based gamma-ray detector development is to obtain spatial resolutions in bulk crystals at the millimeter level in all three spatial dimensions. An even more challenging goal is to disentangle multiple simultaneous energy depositions with comparable spatial resolutions. We are exploring a new technique to achieve this level of performance through the use of close-coupled, coded-aperture shadow masks placed between the crystal and a position-sensitive phototransducer. We report on simulations of such a device using Monte Carlo light transport simulations performed with GEANT4. Initial indications are promising; however, the technique will require a very high level of performance from the phototransducer. [ABSTRACT FROM PUBLISHER]

The most common method for time pick-off from signals coming from SiPMs coupled to scintillator crystals in PET applications is the Leading Edge Triggering. In this work we propose a new filtering scheme to be applied before the discriminator. It implements a type of baseline compensation aimed at the reduction of the time jitter due to the dark counts of the detector and is based on a simple analog filter, which is well suited for an ASIC implementation. We describe a circuit, built with discrete components, that implements the filter. Finally we report on the Coincidence Resolving Time measurements performed coupling the circuit to the real detector, composed of a SiPM built at FBK and a LYSO crystal, for the detection of 511 keV photons. The results obtained are promising, showing that the method is quite effective in reducing the impact of the detector noise on the timing performance of the system. [ABSTRACT FROM PUBLISHER]

We conducted low-temperature annealing experiments at temperatures slightly above and below the melting point of Te to clarify the effects of the state of Te inclusions (solid or liquid) upon the formation of 'star-like' defects in Cd-annealed CdZnTe (CZT). We also carried out post-growth annealing experiments with and without using Cd vapor to clarify the mechanism of formation of such defects. We demonstrated that these 'star-like' defects are due to the reaction between in-diffused Cd atoms and the molten Te inclusions, but we found no observable 'one-to-one' correlation between 'star-like' defects and Te inclusions. The non-uniform distribution of Te inclusions in the CZT matrix could account for this phenomenon since the punching distance of the dislocations depends on the volume fraction of inclusions within the matrix. [ABSTRACT FROM AUTHOR]

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]

Well designed scintillator detectors, including such examples as ARSA, SAUNA, and XIA's 'PhosWatch', can readily achieve the state of the art radioxenon detection limits required for nuclear explosion monitoring. They are also reliable, robust detectors that do not require cryogenic cooling for operation. All three employ the principle of beta-gamma coincidence detection to reduce background counting rates, using a BC-404 plastic scintillator to detect the betas and a CsI or NaI scintillator to detect the gamma-rays. As a consequence of this commonality of design, all three also display a 'memory effect' arising from the diffusion of Xe into BC-404. Thus, when one sample is pumped out of the detector, a fraction remains behind, embedded in the BC-404, where it artificially raises the signal counting rate for the next sample. While this is not a fatal flaw in scintillator detectors, developing a method to eliminate the memory effect would significantly enhance their utility. This paper reports efforts to develop thin, amorphous AlO films, deposited by atomic layer deposition (ALD) to act as diffusion barriers on the BC-404 surfaces exposed to radioxenon. Using radon as a convenient substitute for Xe, film thicknesses between 2 and 10 nm were originally investigated and found to show a memory effect to varying degrees. A second set of 20 and 30 nm films was then produced, which appeared to completely eliminate the radon memory effect, but, when consequentially tested with radioxenon, were found to exhibit xenon memory effects that were approximately half of the effect found on uncoated BC-404. We draw two conclusions from this result. The first is that it will be necessary to develop an improved method for depositing thicker ALD AlO films at lower temperatures while still retaining high film quality. The second is that, since xenon is required to test for the xenon memory effect, we need a test method that does not require xenon radio-isotopes in order to facilitate screening large numbers of samples. [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]

Microcalorimeter detectors provide unprecedented energy resolution for gamma-ray spectroscopy. One application is measuring the isotopic composition of plutonium-bearing samples by non-destructive gamma-ray spectroscopy to support nuclear safeguards and nonproliferation efforts. When measured with conventional high-purity germanium (HPGe) detectors, data from these samples contain significant peak overlaps requiring spectral deconvolution for analysis. The improved energy resolution of the microcalorimeter detector reduces peak overlaps leading to improvement in the statistical error component of the total measurement uncertainty. In this paper, we describe analysis code that was developed for spectral peak fitting and isotopic content determination from microcalorimeter and HPGe data. We apply the code to data collected from several plutonium standards to quantify the improvement of the statistical error derived from the improved energy resolution. [ABSTRACT FROM PUBLISHER]

Monte Carlo simulations were used to model gamma ray interactions at 1 MeV and 11 MeV within liquid krypton to understand geometry effects and energy containment. Two Monte Carlo codes were used in this work: Geant4 and MCNP5. The agreement of the two codes was shown by the comparison of the calculated average energy deposition and fraction of incident gamma energy deposited as a function of chamber lengths and gamma ray offsets. Modeling shows that good energy containment for 1 MeV gamma rays occurs for chamber depths of 20 cm. For gamma rays entering parallel to the central axis of the detector, 1 MeV showers are well contained up to approximately 1 cm of the detectors' edge. For 11 MeV gamma rays the acceptance plateau occurs at a depth of 40 cm and 20 cm from the detectors' edge. [ABSTRACT FROM PUBLISHER]

A study is presented on the detection of illicit special nuclear materials (SNM) in cargo containers using a conceptual neutron-based inspection system with xenon-doped liquefied argon (LAr(Xe)) scintillation detectors for coincidence gamma-ray detection. For robustness, the system is envisioned to exploit all fission signatures, namely both prompt and delayed neutron and gamma emissions from fission reactions induced in SNM. However, this paper focuses exclusively on the analysis of the prompt gamma ray emissions. The inspection system probes a container using neutrons produced either by (d, D) or (d, T) in pulsed form or from an associated particle neutron generator to exploit the associated particle imaging (API) technique, thereby achieving background reduction and imaging. Simulated signal and background estimates were obtained in MCNPX (2.7) for a 2 kg sphere of enriched uranium positioned at the center of a 1\ m\times 1\ m\times 1\ m container, which is filled uniformly with wood or iron cargos at 0.1 g/cc or 0.4 g/cc. Detection time estimates are reported assuming probabilities of detection of 95% and false alarm of 0.5%. [ABSTRACT FROM PUBLISHER]

Thallium bromide (TlBr) is a material of interest for use in room temperature gamma ray detector applications due to is wide bandgap 2.7 eV and high average atomic number (Tl 81, Br 35). Researchers have achieved energy resolutions of 1.3% at 662 keV, demonstrating the potential of this material system. However, these detectors are known to polarize using conventional configurations, limiting their use. While high quality material is a critical starting point for excellent detector performance, we show that the room temperature stability of planar TlBr gamma spectrometers can be significantly enhanced by treatment with both hydrofluoric and hydrochloric acid. By incorporating F or Cl into the surface of TlBr, current instabilities are eliminated and the longer term current of the detectors remains unchanged. In addition the choice of electrode metal is shown to have a dramatic effect on the long term stability of TlBr detector performance ^241Am spectra are also shown to be more stable for extended periods; detectors have been held at 4000 V/cm for 50 days with less than 10% degradation in peak centroid position. [ABSTRACT FROM PUBLISHER]

The Gamma-Ray Imaging Framework (GRIF) is an open source (LGPL) software framework for creating real-time gamma-ray imaging applications. GRIF is written in C++ using Qt, and uses ROOT and the Boost Graph Library. GRIF provides automatic multi-threading and data management to make it easy to quickly develop power gamma-ray imagining applications. The model for application developers is built around the separation of data acquisition (DAQ) and analysis units. Users are expected to use the APIs for the DAQ and analysis units to build their applications. Memory and data are managed by GRIF, so the user does not need to worry about allocating and de-allocating memory for data or thread management and locking schemes. The user only needs to post data to and read data from the GRIF memory manager. GRIF uses XML configuration files for determining data dependences between DAQ and analysis units in the system. We will give an overview of the first release of GRIF, as well as show example applications that have been built using the framework. [ABSTRACT FROM PUBLISHER]

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]

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. [ABSTRACT FROM PUBLISHER]

Liquid krypton has been used widely for electromagnetic calorimeters for charged particle and gamma ray detection above 100 MeV. Despite the significant price advantage of krypton over xenon, little work has been done with liquid krypton detectors for energies in the range 200 keV–12 MeV that is useful for applications involving neutron-induced gamma ray spectral analysis for isotope identification in elemental analysis. The presence of \beta decays arising from ^85\Kr (10.76-year half-life) combined with the 80 ns decay time of the dominant component of krypton scintillation light generates pile-up and reduces the photopeak efficiency of liquid Kr detectors. We discuss detector performance expected after careful optimization of the detector dimensions and doping the Kr with Xe to improve its scintillation light decay time characteristics. [ABSTRACT FROM PUBLISHER]

In this work we describe a procedure to reduce the number of signals detected by an array of 256 Silicon Photomultipliers (SiPMs) using a resistor network to divide the signal charge into few readout channels. Several configurations were modeled, and the pulsed signal at the readout contacts were simulated. These simulation results were experimentally tested on a specifically designed and manufactured set of printed circuit boards. Three network configurations were modeled. The modeling provided encouraging results for all three configurations. The measurements on the prototypes constructed for this study, however, provided useful position-sensitivity for only one of the network configurations. The lack of input signal amplification into the networks, the SiPM dark current, as well as the complexity of an eight layers board with parasitic capacitances, could have caused the degradation of resolving the impact photon position. This is hard to overcome with external printed circuit boards and components. [ABSTRACT FROM PUBLISHER]

Capacitive Frisch grid detectors with the dimensions of 2 mm\,\times\,2 mm\,\times\,4.4 mm were fabricated from TlBr crystals grown by the travelling molten zone method using zone-purified materials. Spectroscopic performance of the detectors was evaluated at room temperature (24^\circC), -5^\circC and -20^\circC. The TlBr detector exhibited an energy resolution of 1.6% FWHM at 662 keV with a peak-to-Compton ratio of 8.7 with the depth correction at room temperature. Improvement of the detector performance was achieved by cooling the detector-preamplifier system. The energy resolutions of 3.4%, 1.5%, 1.0% and 0.9% FWHM at 122 keV, 356 keV, 662 keV and 1332 keV, respectively, were recorded with the TlBr detector without the depth correction at -5^\circC. An energy resolution of 0.9% FWHM at 662 keV with a peak-to-Compton ratio of 18.2 was obtained from the TlBr detector with the depth correction at -20^\circC. An upper limit for the Fano factor of TlBr was estimated to be 0.43 at -20^\circC. [ABSTRACT FROM PUBLISHER]

In this study, a survey on environmental radioactivity in 16 high schools located in north eastern region of Turkey (the black sea region, province of Trabzon) was carried out. Indoor air radon (222Rn) concentrations were measured in spring and autumn 2008 seasons using LR115 solid state nuclear track detectors and gamma radioactivity levels were measured using an HPGe gamma ray detector. It was seen that mean radon activity concentrations in schools ranged from 31 to 157 Bq/m3 for spring season and from 38 to 114 Bq/m3 for autumn season. The mean gamma activity concentrations in located areas of schools are between 18–52, 21–59, 11–97 and 265–759 Bq/kg for 226Ra, 232Th, 137Cs and 40K, respectively. The annual effective doses of students and staff received due to radon and locations’ gamma radioactivity levels are calculated. [ABSTRACT FROM AUTHOR]

Abstract: Identifying the accelerators that produce the Galactic and extragalactic cosmic rays has been a priority mission of several generations of high energy gamma ray and neutrino telescopes; success has been elusive so far. Detecting the gamma-ray and neutrino fluxes associated with cosmic rays reaches a new watershed with the completion of IceCube, the first neutrino detector with sensitivity to the anticipated fluxes, and the construction of CTA, a ground-based gamma ray detector that will map and study candidate sources with unprecedented precision. In this paper, we revisit the prospects for revealing the sources of the cosmic rays by a multiwavelength approach; after reviewing the methods, we discuss supernova remnants, gamma ray bursts, active galaxies and GZK neutrinos in some detail. [Copyright &y& Elsevier]

Due to the emerging potential for trafficking of special nuclear material, research programs are investigating current capabilities of commercially available portable gamma ray detection systems. Presented in this paper are the results of three different portable high-purity germanium (HPGe) detectors used to identify short-lived fission products generated from thermal neutron interrogation of small samples of highly enriched uranium. Samples were irradiated at the Washington State University Nuclear Radiation Center's 1 MW TRIGA reactor. The three portable, HPGe detectors used were the ORTEC MicroDetective [], the ORTEC Detective [], and the Canberra Falcon []. Canberra's GENIE-2000 software was used to analyze the spectral data collected from each detector. Ultimately, these three portable detectors were able to identify a large range of fission products showing potential for material discrimination. [ABSTRACT FROM AUTHOR]

The complex system response of 3D position-sensitive gamma-ray detectors complicates modeling the recorded measurements and makes exact expressions for detection performance intractable. This makes source detection performance difficult and expensive to compute. Asymptotic analysis has the potential to simplify detection performance prediction with complex systems and has previously been applied to detection performance prediction with simulated gamma-ray detectors. In this work, we use asymptotic performance prediction methods to predict points on the receiver operating characteristic (ROC) curve for the illustrative task of detecting a ^137Cs source in background with an 18-detector CdZnTe array. We assume that the source position, source energy, background spectrum, and background spatial distribution are known. Although these assumptions are not always valid in practice, the efficiency of the prediction method makes it attractive for detection system design problems. Our results show that the asymptotic performance prediction method accurately predicts the empirically observed performance with real data recorded with a real system. Our results also characterize the performance of the detector array for the task of source detection. The accuracy and computational efficiency of the asymptotic detection performance prediction method make it a viable alternative to empirical performance evaluation. [ABSTRACT FROM PUBLISHER]

The Cherenkov Telescope Array (CTA) project aims to build the largest ground-based gamma ray observatory based on an array of Imaging Atmospheric Cherenkov Telescopes. The CTA will implement a multi-level trigger system to distinguish between the gamma ray-like induced showers and the background images induced by night sky background light. The trigger system is based on looking for coincident detections among pixels (level 0 trigger), clusters of pixels (level 1) or telescopes (level 2). In this article one prototype of a Level 1 trigger system is presented, capable of working with different Level 0 strategies and different trigger region sizes. At the same time it complies with all the requirements specified by the CTA project, specially the most critical ones as regards noise, dynamic range, latency and power consumption. All these features make the presented system very suitable to be used by the CTA telescopes. [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]

Cherenkov detectors are widely used for particle identification and threshold detectors in high-energy physics. Glass Cherenkov detectors that are sensitive to beta emissions originating from neutron activation have been demonstrated recently as a potential replacement for activation foils. In this work, we set the groundwork to evaluate large Cherenkov glass detectors for sensitivity to MeV photons through first understanding the measured response of small Cherenkov glass detectors to isotopic gamma-ray sources. Counting and pulse height measurements are acquired with reflected glass Cherenkov detectors read out with a photomultiplier tube. Simulation was used to inform our understanding of the measured results. This simulation included radioactive source decay, radiation interaction, Cherenkov light generation, optical ray tracing, and photoelectron production. Implications for the use of Cherenkov glass detectors to measure low energy gamma-ray response are discussed. [ABSTRACT FROM AUTHOR]

Cherenkov detectors are widely used for particle identification in high-energy physics and for track imaging in astrophysics. Glass Cherenkov detectors that are sensitive to beta emissions originating from neutron activation have been demonstrated recently as a potential replacement for activation foils. In this work, we evaluate Cherenkov glass detectors for sensitivity and specificity to MeV photons through simulations using Geant4. The model has been previously compared with measurements of isotopic gamma sources. It includes Cherenkov generation, light transport, light collection, photoelectron production and time response in photomultiplier tubes. The model incorporates measured, wavelength-dependent absorption and refractive index data. Simulations are conducted for glasses the size of fabricated samples and also for the same glasses in monolithic, square-meter-size. Implications for selective detection of MeV photons are discussed. [ABSTRACT FROM AUTHOR]

Abstract: A scintillator-based gamma-ray detection system that uses a radiation-resistant optical fiber was developed. The system consisted of two radiation-resistant optical fibers—one, a fiber with a scintillator, and the other, a fiber without a scintillator—which were used to obtain the gamma-ray dose rate at the measurement point. This system demonstrated a linear response with respect to the gamma-ray dose rate from 0.005 to 1.5Gy/h and a good radiation resistance over an absorbed dose of more than 300kGy. [Copyright &y& Elsevier]

Abstract: Hard X-ray Imager and Soft Gamma-ray Detector are being developed as onboard instruments for the Astro-H mission, which is scheduled for launch in 2014. In both detectors, BGO scintillators play key roles in achieving high sensitivity in low Earth orbit (LEO), by generating active veto signals to reject cosmic-ray events and gamma-ray backgrounds from radio-activated detector materials. In order to maximize background rejection power, it is also important to minimize the energy threshold of this shield. As a readout sensor of weak scintillation light from a number of BGO crystals in a complicated detector system, high performance, reverse-type Avalanche Photodiodes (APDs), with an effective area of are being employed, instead of bulky photomultiplier tubes (PMTs).Another advantage of using APDs is their low power consumption, although the relatively low gain of APDs (compared to conventional PMTs) requires dedicated analog circuits for noise suppression. In this paper, we report on the development and performance of APD detectors specifically designed for the Astro-H mission. In addition to APD performance, various environmental tests, including radiation hardness and qualification thermal cycling, will be described in detail. Moreover, a dedicated charge sensitive amplifier and analog filters are newly developed and tested here to optimize the performance of APDs to activate fast veto signals within a few from the BGO trigger. We will also report on overall performance testing of a prototype BGO detector system that mimics the data acquisition system onboard Astro-H. [Copyright &y& Elsevier]

Abstract: Astro-H is the sixth Japanese X-ray space observatory which will be launched in 2014. Two of onboard instruments of Astro-H, Hard X-ray Imager and Soft Gamma-ray Detector are surrounded by many number of large Bismuth Germanate (Bi4Ge3O12; BGO) scintillators. Optimum readout system of scintillation lights from these BGOs are essential to reduce the background signals and achieve high performance for main detectors because most of gamma-rays from out of field-of-view of main detectors or radio-isotopes produced inside them due to activation can be eliminated by anti-coincidence technique using BGO signals. We apply Avalanche Photo Diode (APD) for light sensor of these BGO detectors since their compactness and high quantum efficiency make it easy to design such large number of BGO detector system. For signal processing from APDs, digital filter and other trigger logics on the Field-Programmable Gate Array (FPGA) is used instead of discrete analog circuits due to limitation of circuit implementation area on spacecraft. For efficient observations, we have to achieve as low threshold of anti-coincidence signal as possible by utilizing the digital filtering. In addition, such anti-coincident signals should be sent to the main detector within to make it in time to veto the A–D conversion. Considering this requirement and constraint from logic size of FPGA, we adopt two types of filter, 8 delay taps filter with only 2 bit precision coefficient and 16 delay taps filter with 8 bit precision coefficient. The data after former simple filter provides anti-coincidence signal quickly in orbit, and the latter filter is used for detail analysis after the data is down-linked. [Copyright &y& Elsevier]

Abstract: AGILE pointed observations performed from July 9, 2007 to October 30, 2009 cover a very large time interval, with a γ-ray data archive useful to perform monitoring studies of medium to high brightness γ-ray sources in the 30MeV–50GeV energy range. The first AGILE Gamma-Ray Imaging Detector (GRID) catalog (Pittori et al., 2009) included a significance-limited (4σ) sample of 47 sources (1AGL), detected with a conservative analysis over the first-year of operations. We present a variability study of the 1AGL sources over the complete AGILE pointed Observation Blocks (OBs) dataset. In the analysis here reported we used data obtained with an improved full Field of View (FOV) event filter, on a much larger (about 27.5months) dataset, integrating data on the OB timescales, mostly ranging between 4 and 30days. The data processing resulted in an improved source list as compared to the 1AGL one. We present here our results on the variability of some of these sources. [Copyright &y& Elsevier]

Abstract: Recent developments (since the last review in J. of Physics G by I. Tanihata in 1996 [1]) at RIB facilities opened possibilities of detailed studies of halo nuclei. New facilities have been constructed to provide higher intensity beams of radioactive nuclei in a wide range of energies. At the time of the last review, only secondary beams by projectile fragmentation were the production source of halo nuclei for use in reaction studies. Since then, re-acceleration facilities have been developed and thus high-quality low-energy beams become available for the reaction studies. The wide variety of new data are thus available on halo nuclei and nuclei on and outside of proton and neutron drip lines. Low energy beams provided a means to determine the masses and charge radii of halo nuclei (6,8He, 11Li). Also transfer reactions have been measured in many nuclei far from the stability line. In fragmentation facilities, new experimental methods such as gamma ray detection in coincidence with breakup fragments of halo nuclei have been developed. Also the reaction cross sections have been measured in a wide range of beam energies. In addition, proton elastic scattering of halo nuclei has been measured at high energies. All together, studies of density distribution, identification of shell orbitals and spectroscopic factors of halo wave function became possible. Such studies reveal many new important information such as the change of magic numbers in nuclei far from the stability line. In this article, we would like to review the experimental developments on halo nuclei and other related drip line nuclei. Also the new view of the nuclear structure learned from such studies will be discussed. Development of selected theories on related nuclear structure problems will be mentioned briefly. [Copyright &y& Elsevier]

Testing of 20\,\times\,20\,\times\, 15 mm^3 3D position sensitive, CdZnTe detectors grown by Redlen Technologies Inc. has shown that 98 out of the 145 detectors analyzed achieved sub-1% FWHM at 662 keV for single-pixel events. Improvements in the detector performance over time reflect the improvements in detector growth and fabrication over the past several years. In addition to the spectroscopic performance of the detectors, the imaging performance of each detector was also quantified. The results show that imaging is weakly correlated to the spectroscopic performance, and more strongly correlated to the accuracy of the depth reconstruction. Other detector issues such as gain deficit and gain variation are also discussed. [ABSTRACT FROM AUTHOR]

Abstract: We present a technique to fabricate high spatial resolution and cost-effective X-ray/gamma-ray detectors using silicon photomultipliers (SiPMs) and microcolumnar structured CsI:Tl scintillator. SiPMs were placed inside a vacuum chamber and physical vapor deposition was used to directly deposit CsI:Tl onto the active surface of SiPMs. This approach leads to improved light transport from the scintillation material to the photodetector due to minimal light loss and light spread. Devices made by this technique may be used for gamma- and X-ray photon counting and imaging. Scanning electron micrographs show highly oriented microcolumnar CsI:Tl structure orthogonal to the SiPMs’ surface. These microcolumnar structures are excellent for channeling scintillation light to the SiPM and provide sub-macro-pixel resolution. We report the performance characteristics of the resultant detector in terms of position sensitivity, optical crosstalk, and signal-to-noise ratio. The performance of the detector fabricated in this manner is evaluated against other methods of coupling CsI:Tl scintillators to SiPMs. [Copyright &y& Elsevier]

Abstract: By using a new Compton camera consisting of a silicon double-sided strip detector (Si-DSD) and a CdTe doublesided strip detector (CdTe-DSD), originally developed for the ASTRO-H satellite mission, an experiment involving imaging radioisotopes was conducted to study their feasibility for hotspot monitoring. In addition to the hotspot imaging already provided by commercial imaging systems, identification of various radioisotopes is possible thanks to the good energy resolution obtained by the semiconductor detectors. Three radioisotopes of 133Ba (356 keV), 22Na (511 keV) and 137Cs (662 keV) were individually imaged by applying event selection in the energy window and the gamma-ray images were correctly overlapped by an optical picture. Detection efficiency of 1.68 ×10−4 (effective area: 1.7×10−3 cm2) and angular resolution of 3.8 degrees were obtained by stacking five detector modules for a 662 keV gamma ray. The higher detection efficiency required in specific use can be achieved by stacking more detector modules. [Copyright &y& Elsevier]

Abstract: The threshold temperature at which the thermal depinning of Abrikosov vortices starts to be pronounced, defines the upper temperature limit for secure operation of a gamma-ray superconducting detector based on Abrikosov vortices. Indeed, because of the flux creep phenomenon, unwanted spontaneous vortex jumps can take place concurrently with those resulting from the gamma-ray photon absorption, resulting in the appearance of dark counts. Low temperature magnetic force microscopy (MFM) was applied for the evaluation of the threshold temperature for a 0.3mm thick Nb polycrystalline bulk absorber with dimensions of 5×5 mm2, which was chosen for the fabrication of Josephson tunnel junctions serving as vortex sensor element of the gamma-ray detector. Vortices were generated by cooling the sample to 4.3K in a small magnetic field. A field of 0.1 mT was chosen in order to produce more than two vortices within the 7×7μm2 scan area, but with sufficiently large inter-vortex spacing such that vortex-vortex interactions would be negligible. The threshold temperature associated with the thermal depinning of a single vortex was found to be 6.3 ± 0.2K, whereas the threshold temperature associated with the thermal depinning of half of vortices was found to be 7.2 ± 0.2K. [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: A software package is presented to calculate the total counting efficiency for the decay of radionuclides in a well-type γ-ray detector. It is specifically applied to primary standardisation of activity by means of 4πγ-counting with a NaI(Tl) well-type scintillation detector. As an alternative to Monte Carlo simulations, the software combines good accuracy with superior speed and ease-of-use. It is also well suited to investigate uncertainties associated with the 4πγ-counting method for a variety of radionuclides and detector dimensions. In this paper, the underlying analytical models for the radioactive decay and subsequent counting efficiency of the emitted radiation in the detector are summarised. [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]

Abstract: The quadrupole deformations for the low-lying states in the transitional nuclei have been deduced through the measurement of their electric quadrupole transition probabilities using the Recoil Distance Doppler Shift Method. The nuclei were studied using a 268MeV 80Se beam impinging on a thin, self-supporting 24Mg target. States in 100Pd and 101Pd populated by the four and three neutron evaporation channels respectively, with reaction gamma-rays detected using the SPEEDY gamma-ray detection array. The recoiling nuclei were stopped in a copper foil and gamma-ray coincidence data taken at 10 separate target-stopper distances between and . The mean-lifetimes for the lowest lying 2+ (in 100Pd) and (in 101Pd) states were measured to be 13.3(9)ps and 10.8(8)ps respectively. These data are compared with predictions from nuclear Total Routhian Surface calculations, which are found to agree with the experimentally deduced values to within 10%. [Copyright &y& Elsevier]

Abstract: The need for an accurate representation of the detector response functions (DRFs) for sodium iodide (NaI), bismuth germinate (BGO), etc., arises in the oilwell logging business, especially important for spectral logging tools such as a geochemical logging tool. While Monte Carlo models predict the photon spectra incidents on these detectors, the DRFs are used to generate the pulse-height spectra. A Monte Carlo-based γ-ray detector response function code (GAMDRF) was developed to meet the requirements based on complete photon physics. [Copyright &y& Elsevier]