基于双探测器校正的分段γ扫描技术研究

将探测器对准废物桶两个不同偏心位置进行测量,由两个位置计数率比值,确定桶内放射源所在等效半径位置,从而计算其活度。对非均匀样品进行了测量,结果显示,测量结果误差在10%以内。     

Modern detectors for radiation monitors

The possibilities of using modern photon and neutron detectors for developing radiation monitors, specifically, LaBr₃, Bi₄Ge₃O₁₂, CdWO₄, LiI, ZnO, Lu₂SiO₅(Ce), CdTe, and HgI₂, microtubes from organic scintillators, nanomaterials, and detectors based on gaseous and solid-state electronic multipliers are examined. A comparison is made of conventional detectors based on NaI(Tl) and CsI(Tl), plastic scintillators, and ³He counters. The advantages of the new detectors are better energy resolution, high detection efficiency, low supply voltage, processing convenience, and cost. These detectors will increase the sensitivity of radiation monitors in monitoring unauthorized transport of nuclear and other radioactive materials, identify in real time the materials being monitored, and simplify the detecting apparatus and the development of monitors.     

Elongate X-ray detectors for application in security inspectionsystems

We have developed, manufactured, and investigated a novel type of long X-ray detector up to 1000 mm long with two exit windows. The sensitive element of the detector is an elongated polished rectangular plate of inorganic scintillator. The detector is highly sensitive to X-rays in the energy region 50-250 keV. The factors influencing the sensitivity and longitudinal uniformity of the detector response have been considered     

Evaluation of K X-ray escape and crosstalk in CdTe detectors andmulti-channel detectors

The simple structure of CdTe semiconductor detectors facilitates their downsizing, and their possible application to radiographic sensors has been studied. The escape of K X-rays from these detectors increases with reduction of their dimensions and affects the measurements of X- and gamma-ray spectra. K X-rays also produce crosstalk in multi-channel detectors with adjacent channels. Therefore, K X-rays which escape from the detector elements degrade both the precision of energy spectra and spatial resolution. The ratios of escape peak integrated counts to total photon counts for various sizes of CdTe single detectors were calculated for gamma rays using the Monte Carlo method. Also, escape and crosstalk ratios were simulated for the CdTe multi-channel detectors. The theoretical results were tested experimentally for 59.54-keV gamma rays from a ²⁴¹Am radioactive source. Results showed that escape ratios for single detectors were strongly dependent on element size and thickness. The escape and crosstalk ratios increased with closer channel pitch. Our calculated results showed a good agreement with the experimental data. The calculations made it clear that K X-rays which escaped to neighboring channels induced crosstalk more frequently at smaller channel pitch in multi-channel detectors. A radiation shielding grid which blocked incident photons between the boundary channels was also tested by experiment and by calculation. It was effective in reducing the probability of escape and crosstalk     

The optimum lead thickness for lead-activation detectors

The optimum lead thickness for lead-activation detectors has been studied in this paper. First existence of the optimum lead thickness is explained theoretically. Then the optimum lead thickness is obtained by two methods, MCNP5 calculation and mathematical estimation. At last factors which affect the optimum lead thickness are discussed. It turns out that the optimum lead thickness is irrelevant to incident neutron energies. It is recommended 2.5 cm generally.     

Neutron response functions for superheated droplet detectors

Neutron response functions for superheated droplet detectors have been analyzed from threshold up to 2 MeV incident energy, taking into account a gradual threshold function, in terms of temperature and incident energy. A method for obtaining fitted parameters is described. Detection mechanisms up to 14 MeV are discussed     

Near-infrared detectors for ITER LIDAR Thomson scattering

In this paper we discuss strategies for the development of fast photodetectors suitable for operation in the λ > 850 nm near-infrared (NIR) spectral region in the ITER core LIDAR Thomson scattering (TS) system. Detection of this spectral range is necessary if a Nd:YAG laser operating at the fundamental wavelength (λ = 1.06 μm) will be used as the input laser source. Different types of NIR photodetectors are potentially suitable for use in ITER LIDAR TS: the transferred electron (TE) InGaAsP/InP hybrid photodiodes and microchannel plate photomultipliers (MCP PMTs), the In_xGa_1?xAs MCP image intensifiers and PMTs, and the detectors based on transmission Si photocathodes. But their characteristics of either sensitivity, active area or speed of response, do not match the ITER specifications and all devices require some developmental work. For each of these detector types we review the characteristics of devices presently available and suggest a realistic development strategy suitable to extend their performances to meet the ITER specifications. Finally the expected performance of the ITER LIDAR TS system for different detector choices are compared by calculating the expected signal-to-noise ratio of the measured plasma temperature and density.     

Hybrid direct conversion detectors for digital mammography

Hybrid pixel detector arrays that convert X-rays directly into charge signals are under development at NOVA for application to digital mammography. This technology also has wide application possibilities in other fields of radiology and in industrial imaging for applications in nondestructive evaluation and inspection. These detectors have potentially superior properties compared to either emulsion based film, which has nonlinear response to X-rays, or phosphor-based detectors in which there is an intermediate step of X-ray to light photon conversion. Potential advantages of direct conversion detectors are high quantum efficiencies (QE) of 98% or higher (for 0.3 mm thick CdZnTe detector with 20 keV X-rays), improved contrast, high sensitivity and low intrinsic noise. These factors are expected to contribute to high detective quantum efficiency (DQE). The prototype hybrid pixel detector developed has 50×50 microns pixel size, and is designed to have linear response to X-rays, and can support a dynamic range of 14 bits. Modulation Transfer Function (MTF) is measured on a l-mm silicon detector system where 10% or better modulations are obtained at 10 lp/mm spatial frequency. Preliminary DQE measurements of the same system yields a value of 55% at zero spatial frequency. Here, the authors report data of their first full size prototype readout ASIC chips hybridized with both silicon and CdZnTe detector arrays and present initial MTF and DQE measurement results as well as some test images     

Large-volume thallium bromide detectors for gamma-ray spectroscopy

Thallium bromide (TlBr) is a wide-bandgap compound semiconductor characterized with high photon stopping power. In this study, large-volume γ-ray detectors (approximately 3.8 × 3.8 × 3.8 mm³) have been fabricated from TlBr crystals grown by the horizontal travelling molten zone (TMZ) method using zone-purified material. In order to extract the energy information of the incident radiation from the thick detectors, the short charge-collection time technique has been applied to the detectors. By this technique, the induced charge on the electrode is measured for a period of time that is short compared to the carrier transit time in order to minimize the deviation of the measured induced charge. The large-volume TlBr detectors irradiated with ²²Na and ¹³⁷ Cs γ-ray sources at room temperature have exhibited energy resolutions of 18.7% and 17.4% (FWHM) for the 511- and 662-keV peaks, respectively. To our knowledge, this is the first time that full-energy peaks have been obtained from TlBr detectors several millimeters thick. The time stability of the detector operation is also studied     

Recent results for the CMS tracker silicon detectors

The paper reports on a detailed study of the radiation resistance of p⁺ on n silicon microstrip detectors for the CMS tracking system. From this study, it is seen that the use of low-resistivity substrates with 〈100〉 crystal lattice orientation promises excellent performance of the Inner Tracker after heavy irradiation in the Large Hadron Collider environment. Furthermore, the advantage of using detectors thicker than 300 μm in the Outer Tracker is discussed together with experimental measurements on prototypes     

The use of scintillator-photodiode detectors for dosimetric monitoring

Translated from Atomnaya Énergiya, Vol. 69, No. 6, pp. 392–394, December, 1990.