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We developed a high spatial resolution and sensitive detector particularly suitable for radiation dose measurements in radiotherapy at small fields and X-ray imaging applications. The detector is based on a silica optical fiber whose sensitive terminal is functionalized by grafting Ag-doped ZnS scintillating materials that emit blue luminescence under X-ray irradiation. Due to the small scintillating head of the detector, the acquisition signal is quite low, and it is measured by a sensitive photon counter plugged at the other terminal of the fiber. The weaker signal can be enhanced significantly by adding a metal coating over the scintillator. Therefore, this study presents the effect of metal thickness and density on the signal amplification at high irradiation energies of 6 MeV and 15 MeV using a Linear Accelerator (LINAC). In addition, the stem effect was characterized for regular to small field beam size and shows that the detector is almost free from stem contribution during high energy irradiation. [ABSTRACT FROM AUTHOR]

Quaternary Cd0.9Zn0.1Te1–ySey (CZTS) single crystals, a novel room-temperature nuclear radiation detector semiconductor material, have been grown using a modified vertical Bridgman method (VBM) and a traveling heater method (THM). The percentage concentration of selenium in the VBM-grown crystal was 3% and that in the THM-grown crystal was 2%. While the THM Frisch collar detector ($4.4\times 4.4\times10.7$ mm $^{3}$) produced a highly resolved pulse height spectra (PHS) with a resolution of ~1.06% for 662-keV gamma rays without any correction, the VBM-grown detector ($10\times 10\times 2$ mm $^{3}$) offered a high-energy resolution of ~2% after the application of a digital bi-parametric correction. The high-resolution performance of these detectors has been attributed to the addition of Se in the Cd0.9Zn0.1Te (CZT) matrix. Ab-initio calculations based on density functional theory (DFT) also confirmed that the addition of Se in the CZT matrix helps to reduce the formation of TeCd and the TeZn antisites. The VBM-grown crystals were characterized using powder X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). While the XRD results revealed sharp diffraction peaks confirming the crystalline nature of the grown crystal, the EDS results confirmed the targeted stoichiometry of the elemental composition. The bulk resistivity of the grown crystal was calculated to be $\sim 3\times 10^{10}\,\,\Omega$ -cm from the current–voltage characteristics recorded at room temperature in a planar configuration, ensuring that the grown CZTS crystals have low dark current as required for detector-grade crystals. [ABSTRACT FROM AUTHOR]

In this letter we report a direct correlation between the space charge limited current flow and radiation detection properties of CdxZn1-xTe1-ySey (CZTS) detector. CZTS is a recently discovered quaternary wide bandgap semiconductor for room-temperature gamma photon detection. The CZTS single crystals have been grown in-house using a modified Bridgman technique. Planar detectors were fabricated and characterized in terms of charge carrier flow and radiation detection measurements. An anomalous current flow falling outside the Lampert’s triangle in $\textit {logJ}-\textit {logV}$ plot, has been observed which is not generally seen in semiconductor detectors governed by space-charge limited current flow mechanism. The anomalous behavior has been attributed to the presence of electron traps. The devices were tested for their radiation detection properties by acquiring pulse height spectra using 241Am and a 137Cs isotopes as a source of alpha particles and gamma photons, respectively. It was further noticed that the only detectors which worked satisfactorily as radiation detectors, did not exhibit the anomalous current flow mechanism. [ABSTRACT FROM AUTHOR]

Large-volume detector-grade Cd0.9Zn0.1Te (CZT) single crystals were grown using a vertical Bridgman technique. The bulk resistivity of the as-grown crystal was found to be ~ 5 × 1010 Ω-cm from current–voltage measurements. A 19.0 ×19.0 × 5.0 mm3 block of the crystal was used to fabricate a detector with 10 × 10 pixelated anode configuration integrated with interpixel guard rings. The detector was tested for its radiation detection properties using 662-keV gamma rays from a 137Cs source. The pixels exhibited well-resolved gamma pulse-height spectra (PHS) with percentage energy resolution ~1.6% at 662 keV. A few pixels exhibited tailing of the photopeak on the lower energy side indicating the presence of hole traps. Biparametric plots (BPs) were obtained from digitally recorded preamplifier pulses. The BPs showed anomalous behavior, which was correlated with the gamma interactions in the active region of the detector in virtual Frisch grid configuration. The BPs also enabled to extract PHS free from the extensive tailing of the photopeak. [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]

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This paper considers the use of maximum likelihood estimation to localize a stationary source from total gamma ray counts, in an open area setting with a highly fluctuating background. As this turns out to be a highly nonconcave maximization, convergence rates of global convergent algorithms, such as simulated annealing, can be very slow and iterative algorithms such an Newton’s method for maximization can be captured by local maxima while fast. Thus, the selection of the initial estimate is critical to how well they perform. This paper proposes a way to generate such an initial estimate using an averaging process that is shown to be asymptotically convergent to the maximum likelihood source estimate. This ensures that with a sufficiently large number of samples, the initial estimate is indeed within of the basin of attraction of such iterative algorithms. Analytical results are supported by numerical simulations based on a measured background data and synthetically injected source data. [ABSTRACT FROM AUTHOR]

Quality and performance of a detection system are the crucial parameters in all nuclear physics experiments. This system serves as a source of all signals and noises to be processed. Better performance, higher amplification and lower noises occurrence simplify subsequent signal analysis. In the field of Mössbauer spectroscopy, the spectrum quality and Mössbauer effect are crucial parameters which are affected especially by the quality of the detection system. These parameters were evaluated for different types of a detection setup. Finally an improvement of the spectrum quality by 15% and Mössbauer effect by 7% has been achieved for the natural iron reference absorber measurement in comparison with previous version of the detection system. [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]

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 BGO endcap calorimeter was successfully operated in the CMD-2 detector at the VEPP-2M collider. It consists of 680 BGO crystals, each with a size of 25\times 25\times 150~mm^3, arranged in two identical endcaps, with a total weight of 450 kg. The light readout used vacuum phototriodes. The endcap calorimeter has been now upgraded to operate in the CMD-3 detector at the new VEPP-2000 collider. The major part of the endcap calorimeter, BGO crystals, remains the same. The main upgrade is the use of silicon PIN photodiodes and new electronics. The reason of changing a photosensitive device is a strong non-uniform magnetic field in the endcap calorimeter volume making the operation of the vacuum photosensitive devices impossible. We also had to reduce the space available for the endcap calorimeter. Hamamatsu PIN photodiodes S3590–08 were chosen as optimal devices as they are insensitive to magnetic fields and are both compact and stable. An order of magnitude larger capacitance of silicon photodiodes requires a design and production of the new custom electronics. The upgrade is expected to bring an overall improvement of the calorimeter parameters. The endcap calorimeter has been installed in the detector and operated during the data taking that started in 2010. Data analysis shows an improvement of the energy resolution compared to the CMD-2 detector. [ABSTRACT FROM PUBLISHER]

Data on the photon nonproportional response of 33 inorganic scintillation materials are systemized and analyzed. The main trends of nonproportionality for different groups of inorganic scintillators, especially for oxides and halides, are highlighted. The dependence of the shape and degree of photon nonproportional response versus chemical composition, dopant type, index of refraction and other fundamental properties of the materials is studied. Better proportionality appears to be correlated with higher index of refraction of the compound. Another related factor is the width of the valence band in halide compounds. With larger valence band width from fluorides, to chlorides, to bromides, and to iodides, a better proportionality is observed. [ABSTRACT FROM AUTHOR]

We manufactured transparent optical ceramic of Pr 0.2–1% doped Lu3Al5 O12 (Pr:LuAG) by the sintering method. We compare its optical and scintillation properties with the single crystal counterpart grown by the conventional Czochralski method. So far the scintillation ceramic of Pr:LuAG appeared inferior to its single crystal analog especially in terms of light yield. However, in the present case our ceramic Pr 0.25%-doped sample exhibited by 20% higher light yield compared to single crystal under \gamma-ray excitation. Furthermore, in the ceramic sample the slower scintillation decay components were suppressed and the defect related host emission as well. The optimized technology of optical ceramics thus appears very competitive to single crystals and opens great practical prospectives for the former materials in the field of fast scintillators. [ABSTRACT FROM PUBLISHER]

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

The Vertical Gradient Freeze (VGF) method has been used to grow high resistivity Cadmium Zinc Telluride (CZT) for high energy radiation applications. In this work, the effect of lapping and polishing the lateral edges of planar detectors is studied. Expectations that improved surface morphology of the edges should correlate with reduced surface leakage current are shown to be erroneous. The effect of various types of lateral edge treatments on detector performance was observed before and after each surface modification. Complementary results were obtained using I-V, Cathodoluminescence (CL), and gamma ray response measurements using 133Ba. As a result, a quick and easy method is reported which minimizes leakage current and actually enhances detector performance through the introduction of surface defects. It is demonstrated that the introduction of radiative recombination centers helps reduce surface leakage current in the detector by a factor of up to 200%, depending on the surface treatment. The purpose of this work is to identify material processing steps for fabricating planar devices based on CZT for gamma ray spectroscopy. [ABSTRACT FROM AUTHOR]

Preparation of SrI_2 and Eu:SrI_2 ceramics is reported on for the first time. Translucent ceramics were sintered by hot-pressing. Thermal analysis on SrI_2 and EuI_2 starting powders was used to identify dehydration temperatures and informed the choice of sintering conditions. Optical transmission was found to decrease with increasing temperature and time. Microstructure studies (grain size and texture) were used to evaluate variations in optical transmission between samples. Scintillation characterization was carried out on 5 wt% Eu:SrI_2 ceramics. X-ray radio-luminescence spectra showed both the characteristic Eu^2+ emission band and a lower-intensity, broad emission in the visible. Scintillation lifetimes were shorter than those previously reported for single-crystal samples, and afterglow was substantially lower. A light yield of 21 000 ph/MeV was calculated from the photopeaks under \gamma-irradiation. Like single-crystal samples, Eu:SrI_2 ceramics were found to have a very proportional response with \gamma-ray energy. [ABSTRACT FROM AUTHOR]

Liquid scintillators loaded with boron-10 or lithium-6 are capable to detect gamma rays, fast neutrons and also thermal neutrons. One of the popular methods applied in order to distinguish events originating from different particles is the pulse shape discrimination (PSD). The previously presented study of boron-10 loaded liquid scintillators using the PSD method showed different discrimination performance in scintillators such as BC523A, BC523A2, EJ339A2 and EJ309B5. It triggered a further study of the light pulse shapes in these scintillators originating from events related to gamma rays, fast and thermal neutrons. The light pulse shapes, measured using the single photon method, were recorded together with the 2-dimensional n/gamma discrimination data. Next, the recorded light pulses were gated using energy and the PSD information to extract pulses characteristic of the only one kind of particles. Finally, the analysis of the light pulse shapes with multi-exponential fits and calculation of decay time constants and intensities of components were performed. The results were compared with the data obtained for liquid scintillators not sensitive to thermal neutrons BC501A, EJ301 and EJ309. [ABSTRACT FROM AUTHOR]

The Improved Landmine Detector System, a militarily fielded, teleoperated vehicle-mounted multi-sensor landmine detector, uses a thermal neutron analysis (TNA) detector to con- firm the presence of a mine by detecting the bulk nitrogen in its explosives. To improve the nitrogen sensitivity or measurement times of the TNA detector, higher gamma ray rates will be required. The chief bottleneck to achieving the maximum possible performance from the present TNA or future versions is the relatively slow fluorescent decay time of the NaI(Tl) scintillators which are currently used. An experimental investigation was undertaken to compare a number of modern, fast inorganic scintillators to NaI(Tl) with respect to parameters relevant to TNA landmine detection, including efficiency, energy resolution, linearity, avail- able size and cost. This paper presents results in the context of the high-rate, high-gamma-energy environments expected in such a TNA application. Large (7.62 cm x 7.62 cm) LaBr3 :Ce scintillators, and to a lesser degree LaCl3 :Ce, were found to stand-out as as the principal candidates for the detector upgrade to the TNA confirmation system. Their properties also make them ideal candidates for fast neutron analysis and associated particle imaging bulk explosives detectors. [ABSTRACT FROM AUTHOR]

The authors constructed a prototype Time-Encoded Signature (TES) system, complete with automated detection algorithms that can be used to detect point-like gamma-ray sources in search applications where detectors observe large variability in background count rates beyond statistical (Poisson) noise. The person-carried system consists of two cesium iodide scintillators placed on opposite sides of a lead shield. This geometry mitigates systematic background variation and induces a unique signature upon encountering point-like sources. This manuscript focuses on the development of detection algorithms that identify point-source signatures while remaining computationally simple. The latter constraint derives from the instrument's mobile (and thus low power) operation. The authors evaluated algorithms using both simulated and field data. The results of this analysis demonstrate the capability to detect sources at a wide range of source-detector distances using computationally simple algorithms. [ABSTRACT FROM AUTHOR]

Room-temperature semiconductor CdZnTe (CZT) detectors are currently limited to total detector volumes of 1-2 cm³, which is dictated by poor charge transport characteristics. Because of this size limitation, one of the problems in accurately determining isotope identification is the enormous background from Compton scattering events. Eliminating this background will not only increase the sensitivity and accuracy of measurements, but will also help to resolve peaks buried under the background and peaks in close vicinity to others. We are currently developing a fission products detection system based on Compton-suppressed CZT and LaCl3 (Ce) detectors. In this application, the detection system is required to operate in a high radiation field. Therefore, a small 10 mm × 10 mm × 5 mm CZT and Φ13 mm × 15 mm LaCl3 detector are placed inside the center of a well-shielded Φ76 mm by 76 mm long Na! detector. So far, we have been able to successfully reduce Compton background by a factor of 3.7 to 4.0 for a 137Cs spectrum. In this work, we will discuss the performance of this detection system using both CZT and La Cl3 detectors. The results are compared with MCNP calculations. [ABSTRACT FROM AUTHOR]