下一代康普顿望远镜的量能器探测单元研究

Me V能区的γ射线天文研究远落后于其它能区,导致该能区的天文物理信息至今还没被充分挖掘,因此,研制下一代高灵敏度的康普顿望远镜对于开展Me V能区的γ射线天文研究具有重要的科学意义。量能器作为康普顿望远镜的重要组成部分,应具有高能量分辨率和高位置分辨率,为此,设计了一种双端读出的γ射线探测器作为量能器的基本探测单元,并对其进行细致的研究。结果表明:通过双端读出信号幅值,可以确定γ射线的总能量以及在晶体中的相互作用位置,采用硅光电倍增管(Silicon Photomultiplier,Si PM)匹配铊激活碘化铯(Cs I(Tl))晶体时,探测单元获得比采用光电二极管(Photodiode,PD)和雪崩光电二极管(Avalanche Photodiode,APD)都更好的性能,对662 ke Vγ射线的能量分辨率可达5.9%(Full Width at Half Maxima,FWHM),位置分辨率约为5.7 mm(FWHM)。该探测单元能够很好地满足下一代康普顿望远镜对量能器的性能要求。     

The silicon tracker readout electronics of the gamma-ray large area space telescope

A unique electronics system has been built and tested for reading signals from the silicon-strip detectors of the Gamma-ray Large Area Space Telescope mission. The system amplifies and processes signals from 884 736 36-cm strips using only 160 W of power, and it achieves close to 100% detection efficiency with noise occupancy sufficiently low to allow it to self trigger. The design of the readout system is described, and results are presented from ground-based testing of the completed detector system.     

Hartree-Fock Compton profiles for the elements

Orbital and total-atom Compton profiles are given for the elements. Hartree-Fock wavefunctions were used in the numerical calculations for atomic numbers 1 ≤ Z ≤ 36 and relativistic Dirac-Hartree-Fock wavefunctions for atomic numbers 36 ≤ Z ≤ 102.     

Development of a direction finding gamma-ray detector

This paper describes a direction finding gamma-ray detector, which consists of three different scintillators; NaI (Tl), CsI (Tl) and BGO. The detector positively increases directional sensitivity to incident gamma-rays, and can measure direction, energy and number of gamma-rays. This detector will be useful to carry out monitoring of nuclear power plants or radiation facilities in emergencies. It will be also effective in searching for radiation sources such as radioisotopes and radioactive contaminations. Experimental results have shown the proposed directional detector has a potential for practical use in real fields and will contribute to radiation emergency preparedness.     

Development of a compact high resolution gamma-ray detector for E-CT applications

A compact gamma-ray detector with good spatial resolution for emission computed tomography (E-CT) applications has been developed. The detector is composed of NaI(Tl) scintillation pixels array and Hamamastu R2486-05 PSPMT. Having a pixel size of 2 mm × 2 mm and an overall dimension of 48.2 mm × 48.2mm × 5 mm, it has 484 pixels in a 22×22 matrix. An average spatial resolution of 2.5mm (FWHM) was achieved. The slope of position linearity is constant within 10% in a range of 40mm. After corrections, the average value of differential non-linearity and absolute non-linearity were 0.16mm and 0.535mm respectively, and a 17% at FWHM of total energy resolution for 241Am was obtained.     

Development of Compton imaging system for nuclear material monitoring at pyroprocessing test-bed facility

The Korea Atomic Energy Research Institute (KAERI) has constructed a test-bed facility, named PRIDE (PyRoprocess Integrated inactive DEmonstration), for demonstration of pyroprocessing technology. Even though the PRIDE facility utilizes depleted uranium, instead of actual spent fuel, as process material, it will play an important role not only from the process perspective, but also from the safeguards standpoint. In the present study, a Compton imaging system based on pixelated GAGG:Ce scintillation detectors was constructed and tested to determine its utility for accurate imaging of nuclear material locations and, thus, its applicability as a safeguards monitoring system at the PRIDE facility. In a lab-scale performance evaluation, when the dose rate induced by a ¹³⁷Cs point-like source was ～0.1 μSv/h, the source location was imaged within 5 min. The image resolutions were 22° and 7.6° for real-time monitoring using a back-projection algorithm and for near-real-time monitoring using a statistical iterative algorithm, respectively. The developed Compton imaging system was finally applied to low-enriched uranium and also to depleted uranium, which latter is the process material of the PRIDE facility, and it was indicated that the Compton imaging system can localize nuclear materials within a few minutes under conditions similar to those prevailing at the PRIDE facility. The results of this study show that the Compton imaging system, and Compton imaging technology in general, has a great potential for utilization as a nuclear material monitoring tool at the PRIDE facility.     

Development of a miniature gamma-ray endoscopic probe for tumorlocalization in nuclear medicine

Two types of miniature gamma-ray endoscopic probes developed for insertion into a body cavity to detect invisibly small or deeply located tumors are described. One is a single detector system using a small BGO (Bi₄Ge₃O₁₂) crystal connected with a fiber optic light guide, and the other is a dual detector system using a pair of single detector probes of the same size combined with a random coincidence technique. The performance of these detectors was tested by using a point source and a hollow cylindrical water phantom that simulated a body cavity. Measured and calculated results indicated that a dual detector system can be used for realistic tumor localization in a body cavity, and a single detector system may be applied only for the detection of tumors in which radiopharmaceuticals that emit gamma rays of energy below about 200 keV are accumulated     

Development of high-performance heavy density concrete using different aggregates for gamma-ray shielding

Primary and secondary containment structures are the major components of the nuclear power plant (NPP). The performance requirements of the concrete of containment structures are mainly radiological protection, structural integrity and durability, etc. For this purpose, high-performance heavy density concrete with special attributes can be used. The aggregate of concrete plays an essential role in modifying concrete properties and the physico-mechanical properties of the concrete affect significantly on its shielding properties. After extensive trials and errors, 15 concrete mixes were prepared by using the coarse aggregates of barite, magnetite, goethite and serpentine along with addition of 10% silica fume (SF), 20% fly ash (FA) and 30% ground granulated blast-furnace slag (GGBFS) to the total content of OPC for each mix. To achieve the high-performance concrete (HPC- grade M60), All concrete mixes had a constant water/cement ratio of 0.35, cement content of 450 kg/m³ and sand-to-total aggregate ratio of 40%. Concrete density has been measured in the case of fresh and hardened. The hardened concrete mixes were tested for compressive strength at 7, 28 and 90 days. In some concrete mixes, compressive strength was also tested up to 90 days upon replacing sand with the fine portions of magnetite, barite and goethite. The attenuation measurements were performed by using gamma spectrometer of NaI (Tl) scintillation detector. The utilized radiation sources comprised ¹³⁷Cs and ⁶⁰Co radioactive elements with photon energies of 0.662 MeV for ¹³⁷Cs and two energy levels of 1.173 and 1.333 MeV for ⁶⁰Co. Some shielding factors were measured such as half-value layer (HVL), tenth-value layer (TVL) and linear attenuation coefficients (μ). Experimental results revealed that, the concrete mixes containing magnetite coarse aggregate along with 10% SF reaches the highest compressive strength values exceeding over the M60 requirement by 14% after 28 days of curing. Whereas, the compressive strength of concrete containing barite aggregate was very close to M60 and exceeds upon continuing for 90 days. The results indicated also that, the compressive strength of the high-performance heavy density concrete incorporating magnetite as fine aggregate was significantly higher than that containing sand by 23%. Also, concrete made with magnetite fine aggregate improved the physico-mechanical properties than the corresponding concrete containing barite and goethite. Therefore, high-performance concrete incorporating magnetite as fine aggregate enhances the shielding efficiency against γ-rays.     

一个用于多重示踪技术的康普顿成像装置

提出了一个由位置灵敏度高纯锗探测器组成、用于多重示踪技术的康普顿成像装置。简要介绍了康普顿成像系统的工作原理以及影响其空间分辨率的各种因素。用蒙特卡洛方法模拟了所提出的康普顿成像装置对处于不同位置、发射不同能量γ射线的点源可达到的效率和空间分辨率。用现有的2个多单元高纯锗探测器进行了三个点源成像实验,证明所提出的康普顿成像装置适用于多重示踪技术。     

基于LabVIEW的远程γ能谱测量系统的开发

本文讨论了一套基于LabVIEW的远程γ能谱测量系统的设计技术:(1)数据采集及客户端软件编程技术,(2)基于DataSocket的网络通讯技术.利用该系统测量了137Csγ能谱,其性能优于基于Java applet技术的同类系统.     

Real-Time Compton Imaging for the GammaTracker Handheld CdZnTe Detector

We are currently developing a handheld radioisotope identifier containing 18 position-sensitive CdZnTe crystals. In addition to isotope identification, the device performs basic Compton imaging to determine the location of suspected sources. This paper presents two computationally efficient algorithms for this purpose. The first algorithm traces individual Compton cones onto the unit sphere, whereas the second algorithm computes the intersection of two Compton cones and the unit sphere. Simulations demonstrate that the algorithms are suitable for determining the directionality, even with features such as uncertainty calculations omitted. The one-cone algorithm works more efficiently at high count rates, but the two-cone algorithm generates fewer image artifacts.     

BH1307型康普顿散射谱仪

主要介绍了康普顿散射谱仪的性能、工作原理、结构装置和实验方法。     

Zener diodes for gamma-ray radiation dosimetry

The fundamental properties of Zener diodes and junction field-effect transistors have been studied to use them as a relative dose monitor or a radiation-damage monitor. The response observed at liquid nitrogen temperature, i.e., radiation-induced change in the breakdown voltage of the Zener diode, or change in the breakdown voltage of the pn junction between the gate and the channel (or between the substrate gate and the channel) of the junction field-effect transistor as a function of dose, has shown good linearity. The diode of Toshiba 05Z18 has been found to be useful for doses between 1 and 100 MGy with the fading of response less than 10% for 100 h after irradiation. On the other hand, the junction field-effect transistors of Mitsubishi 2SK33 has proved useful in the region between 0.1 and 10 MGy with the build-up of responses less than 5% for 100 h. The response of both the junction field-effect transistor and the Zener diode has shown a reproducibility within ±5%. For fast readout, a simple system consisting essentially of a constant-current source together with a digital voltmeter has been constructed. For practical application, the devices from which soldered leads are taken off can be used simply to measure relative doses in various materials     

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     

Unbiased Monte Carlo simulation of the Compton profile

Recent comparisons between analytical (deterministic) computations using the code SHAPE, and Monte Carlo (MC) simulations of Compton scattering using different codes show discrepancies in the shape of the Compton peak (the so-called Compton profile), specially for medium-low energy X-ray excitation. Considering the analytical computations as a reference model, the standard approach adopted for generating the Compton profile in different MC codes (EGSnrc, MCNP, MCSHAPE) has been studied comparatively in order to discover a reason for the difference. Apparently there is a bias in the profile generation which is common to all the codes and is related to the assumption of completely populated atomic orbitals contributing to the scattering. Such an assumption does not agree with the equivalence condition between the integrated Compton profile in the Impulse Approximation (IA) and the Waller-Hartree (WH) scattering function.In this article, we report the comparisons mentioned above for a paradigmatic case and propose an unbiased MC algorithm for the simulation of the Compton scattering.