A Laboratory Demonstration of High-Resolution Hard X-Ray and Gamma-Ray Imaging Using Fourier-Transform Techniques

A laboratory imaging system has been developed to study the use of Fourier-transform techniques in high-resolution hard x-ray and ?-ray imaging, with particular emphasis on possible applications to high-energy astronomy. We discuss considerations for the design of a Fourier-transform inlager and describe the instrumentation used in the laboratory studies. Several analysis methods for image reconstruction are discussed including the CLEAN algorithm and maximum entropy methods. Images obtained using these methods are presented.     

Wafer-Bonded Silicon Gamma-Ray Detectors

A wafer-bonded silicon power transistor has been shown to function as an x-ray detector. The device consists of two thin device wafers bonded onto either side of a 2 mm-thick high-resistivity silicon wafer. The hydrophobic bonding process was performed at 400deg C. This low temperature wafer bonding technique should enable the development of large-area, position-sensitive detectors, using thick, high-resistivity intrinsic silicon bonded to thin readout wafers fabricated using conventional CMOS technology. These devices should enable fabrication of thicker intrinsic silicon detectors than currently available. Thick, position-sensitive detectors based on double-sided strip detectors and pixellated detectors are possible. To demonstrate this, a 1 mm thick gamma-ray detector was created from two 0.5 mm thick wafers that were patterned with gamma-ray strip detectors. The energy resolution of the detector is 8.9 keV FWHM for 60 keV gamma rays at room temperature with a leakage of 0.9 nA while operating at 700 V and fully depleted. Improvements in the technique should allow for thicker detectors with better energy resolution.     

Large-Volume Coaxial Germanium Gamma-Ray Spectrometers

Germanium lithium-drift p-i-n diodes for high resolution 7-ray spectroscopy have been made with sensitive volumes in the range 16 to 54 cm3 (1 to 3.3 in. 3) using the coaxial method of drift. Details of the construction, mounting and preparation as spectrometers are given. The shape of the undrifted p-type core has been determined by scanning with a collimated 7-ray beam and by copper plating the surface of a sectioned diode. The characteristics as spectrometers, using 7-rays of energies in the range 0.1 to 7.5 MeV, are shown. At 122 keV energy, resolutions of 5.0 and 4.4 keV (fwhm) were obtained with diodes of sensitive volumes 23 and 54 cm3 respectively. A 16 cm3 volume diode had a resolution of 4.8 keV at 1533 keV 7-ray energy, and a 45 cm3 diode had resolutions of 6.5 and 19 keV at energies of 1.1 and 5.1 MeV respectively. The diodes were operated at bias voltages in the range 600 to 1500 V. Intrinsic full energy peak efficiencies are shown for different diode sizes over a range of 7-ray energies. For the 54 cm3 volume diode, these efficiencies are 21% and 8% respectively for 7-ray energies of 0.5 and 1.0 MeV with a source to diode distance of 30 cm. The larger diodes show a greatly enhanced peak/total ratio, and the higher efficiencies make these spectrometers extremely useful in reaction y-ray, y-7 coincidence, and n, y studies.     

Gamma-Ray Energy of 4DK

Abstract

The stability of a power reactor with multiple transport lags and nonlinear characteristics embodied in the controller is analyzed by parameter plane method. The analysis covers two reactor models: (a) A rather simple model, symbolically representing the features of a nonlinear controller, one transport lag and the reactor with temperature feedback, and (b) A more realistic model depicting a practical chemical fine-control reactor system characterized by multiple transport lags and mixing effect associated with the chemical fluid, the nonlinear characteristics of chemical injection valves, and the spatial distribution of poison inside the reactor, as well as the reactor temperature feedback. These analyses yield much useful information about the stability of both systems, such as the conditions of reactor stability and of the occurrence of limit cycles, as well as the aspects of discontinuous change of the limit cycle frequency. Use of this parameter plane method will greatly simplify evaluation of the stability of even a fairly complex reactor control system that depends not only on the system parameters but also on the nonlinear controller characteristics and initial input signal amplitude.     

Gamma-Ray Spectrum of Cerium-145

The safety of activity-containing asphalt products kept in enclosed storage was evaluated from considerations of radiolysis and hydrogen evolution. The samples examined were mainly homogeneous asphalt products containing 43% of sludge produced in routine operation of the asphalt plant at the Japan Atomic Energy Research Institute (JAERI), the samples were irradiated with external ⁶⁰Co x-ray source to a dose of 10⁹R.

The bulk of the gases evolving from the asphalt product is hydrogen, which constitutes 75~95% of the total gas evolution. The total amount of gases generated during infinite time is proportional to the total exposure dose; hydrogen evolves at a rate of 5.5 × 10³ cm³/g-MR. The amount of total gas evolution is governed solely by the quantity of asphalt, and is independent of the sludge contained therein. Nor do differences in the rate of dose appear to have any significant effect. In so far as concerns smallness of radiolysis, slightly better performance can be expected from straight than from blown asphalt.

There is no danger of explosion of the asphalt products currently generated at JAERI (10~⁶Ci/kg), which can be expected to accumulate in infinite time no more than about 3 cm³ from a 200 l product. Only asphalt products containing activity in concentrations exceeding 10¹ Ci/kg risk explosion when kept in enclosed storage, through accumulation of hydrogen in quantity exceeding the explosion limit in a relatively short time.     

Gamma-Ray Streaming through Multibend Cylindrical Ducts

The ray analysis method is applied to the problem of γ-ray streaming through multibend cylindrical ducts. In this application, the total path length of a γ-ray photon through the shielding material is determined by calculating one by one the positions of the intersections between the straight line representing the direction of photon travel and the surfaces of the shield or of the wall of the bent duct, as the photon passes from duct into wall and out of wall into duct.

Based on this procedure of calculation, two computer programs have been prepared for the estimation of collision-free and total γ-ray doses as well as single and total scattered γ-ray doses behind a shield with multibend cylindrical duct.

The results of calculation with these programs are compared with the experimental values obtained by Shure and Marshall, and fairly good agreement is obtained.     

Half-Life and Gamma-Ray Energies of Lanthanum-144

A procedure using a complexing agent (NTA) in paper electromigration has been devised to achieve rapid separation of fission product lanthanum. This technique permits direct observation of the decay of the 42 sec ¹⁴⁴La without interference from the radiation of other fission products. The γ-ray spectrum of ¹⁴⁴La has been measured with a high-resolution Ge(Li) detector, and the following r-transitions were observed: 397, 434, 541, 586, 704, 734, 845, 951 and l,292keV. Their relative intensities were also determined. From the decay plots of the two strong photopeaks at 397 and 541 keV, the half-life of the ¹⁴⁴La was determined as 42.4±0.6sec which is more accurate than that of 41±3sec previously reported.

It is concluded that the separation procedure used in the present study can be adapted to the isolation of other short-lived fission products as well whenever their metal ions from the complexes by different values of the equilibrium constant.     

Laboratory Gamma-Ray Images Using the ZEBRA Telescope

A series of approximately 100 laboratory images have been made with the ZEBRA astronomical telescope using a range of radioactive sources. These images were aimed at assessing the performance of the telescope and included combinations of point sources, extended sources, ring sources as well as vignetted sources. Besides linear reconstruction techniques a range of non linear image restoration processes are discussed.     

半导体二极管γ瞬时辐射效应

本文研究了半导体二极管瞬时电离辐射效应,给出了在闪光X射线机上的试验结果。     

γ射线剂量率的线性化数字显示方法

计数管测量的Υ射线脉冲计数率与剂量率成非线性关系。本文利用分段线性近似和斜率归一化的方法求数字显示剂量率.方法简单、直观、线性误差小。     

Automatic Analysis of Gamma-Ray Spectra on Small Computers

A program for the automatic analysis of Ge(Li) gamma-ray spectra is described. Owing to its reduced size it can be used on small (16 K memory words) computers. For the design of the program, the steps of manual methods of analysis have been followed as closely as possible. Most of the subroutines are written in Fortran II language.     

A Coaxial Ge(Li) Gamma-Ray Spectrometer

A single-open-end coaxial type Ge(Li) γ-ray detector with an effective volume of 8.7cm³ and a capacitance of 35 pF was made by Li-drifting for 440 hr at an applied voltage of 140 V at 40°C in thermomodule-controlled constant-temperature water coolant. The FWHM energy resolution with an E810F preamplifier was 4.2 and 8.0 keV for γ-rays of 122 and 1,173 keV respectively. The pulse height distributions of γ-rays from an irradiated natural U sample and ¹⁰⁵Rh isotope were measured.     

New Gamma-Ray Exposure Estimation Method for Radiation Accident

There occurred in 1971 an accidental exposure to γ-rays from an ¹⁹²Ir source received by persons not regularly occupied in radiation work. To serve in planning the therapeutical treatment, a method for estimating the γ-ray exposure received by these persons was devised.

The method is based on the idea of using bearing jewels collected from the patients' wrist watches as monitor sample for tests on their thermoluminescence. Applying this method, it was estimated that the exposure sustained by the three patients in question was 761, 77 and 40 R. The method thus developed should prove useful for estimating the exposure sustained by patients involved in a radiation accident.     

Prompt Gamma-Ray Analysis of Steel Slag in Concrete

Blast furnace slag (BFS) is added to Portland cement concrete to increase its durability, particularly its corrosion resistance. Monitoring the concentration of BFS in concrete for quality control purposes is desired. In this study, the concentration of BFS in concrete was measured by utilizing an accelerator-based prompt gamma-ray neutron activation analysis (PGNAA) setup. The optimum size of the BFS cement concrete specimen that produces the maximum intensity of gamma rays at the detector location was calculated through Monte Carlo simulations. The simulation results were experimentally validated through the gamma-ray yield measurement from BFS cement concrete specimens having different radii. The concentration of BFS in the cement concrete specimens was assessed through calcium and silicon gammaray yield measurement from cement concrete specimens containing 5 to 80 wt% BFS. The yield of calcium gamma rays decreases with increasing BFS concentration in concrete while the yield of silicon gamma rays increases with increasing BFS concentration in concrete. The calcium-to-silicon gamma-ray yield ratio has an inverse relation with BFS concentration in concrete.     

Determination of Activation Cross Section by Gamma-Ray Spectrometry

A quick and easy way of determining activation cross sections by the analysis of γ-ray spectra is described. To determine cross sections by this method, it is not necessary to measure the neutron flux density, to undertake any chemical separation process, nor to use enriched target substances. To ascertain the validity of the method, the activation cross section of ¹⁰²Ru(n,γ) ¹⁰²Ru reaction was obtained, resulting in the value of 1.37±0.132 barns, which compares well with published data of 1.44±0.16 barns, determined by another method.     

γ测量中级联修正完全解决方法

HPGe探测器在低位测量γ射线强度时，因γ级联效应不可避免，对测量结果应进行必要的级联修正。目前，较为普遍的修正方案是简化衰变纲图，给出近似计算修正系数。这种方法只能处理一些纲图比较简单或γ引起级联影响比较小的情况。本工作在借鉴国外理论研究结果的基础上提出1个γ级联完全解决方案，并自主开发了级联修正系数计算程序。为了考察该方案的可靠性，用¹⁵²Eu标准源的实验数据进行了检验。并检验结果表明，该方法基本能够处理各种复杂衰变方式的级联修正。      

硅光电管-闪烁体探测器γ谱仪研制

实验研制了硅光电管-闪烁体探测器γ谱仪。该γ谱仪用硅光电倍增管代替普通光电倍增管作为闪烁体探测器的光学读出端,配置闪烁体探测器,构成新型γ谱仪。测试结果表明:新型γ谱仪随温度漂移变化程度大;能量线性较好,线性相关度R为0.9987;配置LaBr_3:10%Ce~(3+)晶体,其能量分辨率为4.3%~4.9%;配置NaI(TI)晶体,其能量分辨率为8.4%。     

Half-Lives and Gamma-Ray Energies of Short-Lived Molybdenum Isotopes

Short-lived molybdenum isotopes produced by the ²³⁶U(n, f) reaction were isolated by rapid paper electrophoretic technique. Gamma-ray spectra of the isolated molybdenum fraction were measured with high resolution Ge(Li) detector. The half-lives of ¹⁰³Mo (70±1 sec), ¹⁰⁴Mo (66±2 sec) and ¹⁰⁵Mo (30±3 and 40±5 sec) were determined by analyzing the genetic relationships of the known photopeaks of their technetium daughters. Decay analysis of observed photopeaks free from interference resulted in the detection of many new short-lived photopeaks with half-lives of 10–70 sec, and which were not relevant to technetium isotopes. These new photopeaks were ascribed to ^103-106Mo, based on examination of their decay behavior.