Development of a gamma ray monitor using a CdZnTe semiconductor detector

Modelling and calculations are presented for the spectrum of initial DNA damage produced by 100 eV to 100 keV energetic electrons. Analysis of the initial spectrum of damage, based upon the source (direct energy deposition and reactions with diffusing OH radicals) and complexity of damage, indicates that the majority of the interactions cause no damage to DNA and any damage that does occur is most likely to be a simple single strand break (SSB). The fraction of complex damage for energetic electrons is lower than that induced by low energy electrons and ultrasoft X rays but still represents an appreciable fraction (20-30%) of the total double strand breaks (DSBs). Relative yields of strand breaks are investigated for dependence on the assumed energy deposition threshold and on the probability of the hydroxyl radicals to produce a single strand break. The ratio of direct to indirect damage does not change significantly across the electron energy range investigated and the values lie well within the experimental data. The direct energy deposition in DNA represents a larger proportion of the damage although the contribution from the hydroxyl radicals is also substantial, both in terms of the absolute yield of the breaks and the complexity of the damage.     

A high energy gamma ray calibration source

A high energy gamma ray calibration source is obtained by the fast neutron irradiation of polytetrafluoride and lead.     

A versatile digital signal annunciator for monitor/control panelinstrumentation

An application-specific integrated circuit (ASIC) design for a four-signal annunciator chip is developed. The design incorporates the ability to select three modes of operation of the sound alarm, economic lamp logic for visual indication, an all-digital built-in widely adjustable delay network for the sound alarm, operator acknowledge, autoacknowledge, two separate tones for the sound alarm-one to identify signal detection and the other to identify signal clearance-and logic circuits for cascading any number of chips and robust glitch-free operation. A 3-μm CMOS standard-cell-based layout design in Caltech Intermediate Four (CIF) is obtained. The core area and chip area are 6050 μm×4904 μm and 7426 μm×6188 μm, respectively, and the gate complexity is equivalent to 1537 in two-input NAND gates. Fan-out delay is 34.40 ns, and the estimated power dissipation is ≈11 mW     

A model for secondary gamma ray transport in hydrogenous media

A new analytical model was introduced for secondary gamma rays due to either (γ, γ) or (n, γ) reactions in a homogeneous, hydrogenous medium, where Compton scattering is the main effect of interaction with matter.For the case of a gamma point source, an expression for the secondary gamma flux distribution due to (γ, γ) reactions was obtained on the basis of the flux distribution in a reference medium. Expressions for the spatial moments and buildup factor were derived.A general form of the secondary gamma flux distribution due to (n, γ) reactions was obtained in terms of the gamma point source flux, and of the thermal neutron flux in reference media. Spatial moments of the (n, γ) secondary gamma flux distribution were calculated.     

Neutron detection gamma ray sensitivity criteria

The shortage of ³He has triggered the search for effective alternative neutron detection technologies for national security and safeguards applications. Any new detection technology must satisfy two basic criteria: (1) it must meet a neutron detection efficiency requirement, and (2) it must be insensitive to gamma-ray interference at a prescribed level, while still meeting the neutron detection requirement. It is the purpose of this paper to define measureable gamma ray sensitivity criteria for neutron detectors. Quantitative requirements are specified for: intrinsic gamma ray detection efficiency and gamma ray absolute rejection. The gamma absolute rejection ratio for neutrons (GARRn) is defined, and it is proposed that the requirement for neutron detection be 0.9<GARRn<1.1 at a 10 mR/h exposure rate. An example of the results from a ³He based neutron detector is provided showing that this technology can meet the stated requirements. Results from tests of some alternative technologies are also reported.     

Mirrors for an imaging gamma ray telescope

A method is given for making mirrors suitable for large parabolic light collectors. The present application is for collecting Cherenkov light from air showers.     

脉冲中子、伽马探测系统性能表征与设计技术

探测系统是获取辐射场特征信息的核心器件,是实施脉冲辐射探测的关键和技术基础,其性能直接决定测试数据的质量和测试方法的选择.对影响脉冲辐射探测的性能指标进行系统描述、表征是探测系统设计、研制、实际应用和综合性能评价的基础.用于复杂能谱脉冲中子、伽马混合辐射场时间谱、强度谱测量的探测系统,主要性能包括探测灵敏度、时间响应、能量响应、线性电流和中子、伽马分辨能力等指标参数,这些参数的获得与实现,需要根据中子、伽马射线与物质相互作用的基本原理,构建相应的探测结构和技术原理.在设计上,综合权衡能量收集和电荷收集方式选择、几何效率完备和高信噪比结合、信号响应和直照响应分离、探测效率与时间特性兼顾、综合性能与使用可靠性一致等设计原则,综合应用这些原则构成了探测系统设计方法.     

SIMULATE Program: a gamma ray spectroscopy tool

A software package which simulates the virtual creation of gamma ray spectra emitted from a combination of radioactive sources, as seen by a semiconductor or scintillation detector, is presented . It partially utilizes Monte Carlo techniques based on the physics of gamma ray spectroscopy. In addition, certain algorithms are used to compensate for the premature termination of the fate of the detected photons of any particular energy.     

A gamma ray reference pulser which does not interfere with the data spectrum

The construction and use of a CaF₂(Eu) pulser is described. The pulser is doped with ²⁴¹Am and supplies a 60 keV reference peak to the host crystal; the alpha particle is absorbed in the pulser. Operation of the pulser in the coincident mode with the host crystal allows only the 60 keV photopeak to be viewed in the reference crystal. Operation in the anti-coincident mode allows only the data spectrum to be observed.     

Experimental simulation of A-bomb gamma ray spectra: revisited

It has been reported recently that the A-bomb gamma ray spectra received by the colon of the average Japanese survivor of Hiroshima and Nagasaki may be experimentally simulated using a hospital-based Philips SL15 linear accelerator. The simulated A-bomb gamma radiation may be used in radiobiology experiments to determine, amongst other things, the biological effectiveness of the A-bomb gamma radiation. However, in that study, the electron beams from the linear accelerator were poorly defined and photon contamination was ignored. In the study reported here, a Varian Clinac 2100C linear accelerator has been used for the same purpose but with photon contamination included in better defined output electron beams. It is found that the A-bomb gamma radiation can still be matched to an acceptable degree (<10%). The cause of the slightly poorer fit was due mainly to the different ranges of energies available from the linear accelerators used. The absorbed dose received by model breasts was also estimated in this study for the same situations as in the previous study. The ratio of the breast to colon doses was found to be only (3.9 +/- 4.0)% low compared with the expected values of 1.17 and 1.16 for Hiroshima and Nagasaki, respectively. These results provide further confirmation of the acceptability of the simple cylindrically symmetrical body models employed in these studies to represent the average Japanese survivor.     

The multiple scattering profile in gamma ray Compton studies

The spectrum of 662 keV gamma radiation, multiply scattered by a nickel sample, has been measured directly in a Compton scattering experiment at a scattering angle of 104°. Under these conditions the multiple profile extends well beyond the single and this affords an opportunity to check the Monte Carlo simulation commonly used to correct the single line shapes (Compton profiles). Measurements in reflection and transmission geometries on thin samples produced markedly different multiple profiles which were found to agree with the simulations within the statistical accuracy of the comparison. This provides the first direct validation of the multiple scattering correction procedure in Compton profile analysis.     

Cryostat cold-finger support for shielded Ge gamma ray detectors

A sturdy support with low thermal conductance has been developed to locate cold fingers carrying tungsten-alloy shielded Ge gamma-ray detectors. Typically, heat conductance through the support increases liquid nitrogen consumption by only about 0.25 ? per day.     

A technique for the evaluation of signal enhancement with application to gamma ray spectra

A procedure is presented which permits the quantitative evaluation of deconvolution algorithms with regard to their ability to enhance or improve the resolution of spectral signals. The approach used here revealed that the maximum realizable enhancement can be expressed in terms of a single variable which is a function of response width, peak area, background level and nearest neighbour spacing. The evaluation procedure was designed primarily to test nonlinear algorithms, a class which can ensure positivity of solution and thereby control noise growth in the recovery process. The effects of response width, system gain, background level and proximity of nearest neighbours are addressed and the utility of the test is demonstrated by evaluation of specific algorithms.     

Design and calibration of a gamma ray transmission density probe

A dual probe gamma ray transmission gauge has been designed in LNETI for the measurement of soil porosities and bulk densities. The gauge makes use of a 4 cm GM counter and of a ¹³⁷Cs source, and can be operated at a source-detector distance of either 20 or 30 cm.The gauge performance and main parameters were studied experimentally as well as by means of a computer simulation. The experiments were carried out both in the laboratory and on the field. Monte Carlo simulations were performed for both Cs and Co sources and the two source-detector distances. Reported here are calibration curves for sensitivity, relative statistical errors and resolution. Good agreement has been found between simulated and experimental data.     

Experimental simulation of A-bomb gamma ray spectra for radiobiology studies

Improved radiation protection of humans requires a better understanding of the mechanisms of radiation action and accurate estimates of radiation risk for both internal and external radiations. The Japanese atomic bomb survivors represent one of the most important sources of human data on the late carcinogenic effects of ionising radiations. The present study was undertaken to investigate whether it would be possible to use hospital radiotherapy/radiobiology equipment to mimic the spectra encountered in Hiroshima and Nagasaki. The estimated total gamma ray fluence spectra (including both prompt and delayed photons) at both Hiroshima and Nagasaki, for distances of 500, 1000, 1500 and 2000 m have been evaluated using DS86 data and previously unpublished information for delayed gamma radiations which constitute the major contribution to survivor doses. Monte Carlo (EGS4) simulations were performed to transport these photons through the body in order to investigate the variation in electron spectra for various body organs. The electron spectra obtained for these fluences at, for example, the colon, have been matched with combinations of electron spectra produced by linear accelerators to within 5% SD. These will, for the first time, enable a direct link to be made between radiobiological studies (for example, on mammography spectra) and the epidemiological data from Japan, which currently underpin radiation risk estimates.     

TL detectors for gamma ray dose measurements in criticality accidents

Determination of gamma ray dose in mixed neutron+gamma ray fields is still a demanding task. Dosemeters used for gamma ray dosimetry are usually in some extent sensitive to neutrons and their response variations depend on neutron energy i.e., on neutron spectra. Besides, it is necessary to take into account the energy dependence of dosemeter responses to gamma rays. In this work, several types of thermoluminescent detectors (TLD) placed in different holders used for gamma ray dose determination in the mixed fields were examined. Dosemeters were from three different institutions: Ruder Boskovi? Institute (RBI), Croatia, JoZef Stefan Institute (JSI), Slovenia and Autoridad Regulatoria Nuclear (ARN), Argentina. All dosemeters were irradiated during the International Intercomparison of Criticality Accident Dosimetry Systems at the SILENE Reactor, Valduc, June 2002. Three accidental scenarios were reproduced and in each irradiation the dosemeters were exposed placed on the front of phantom and 'free in air'. Following types of TLDs were used: 7LiF (TLD-700), CaF2:Mn and Al2O3:Mg,Y-all from RBI; CaF2:Mn from JSI and 7LiF (TLD-700) from ARN. Reported doses were compared with the reference values as well as with the values obtained from the results of all participants. The results show satisfactory agreement with other dosimetry systems used in the Intercomparison. The influence of different types of holders and applied corrections of dosemeters' readings are discussed.     

Self-scattering in gamma ray sources used in compton scattering experiments

The energy degradation of various monochromatic gamma ray sources due to self-scattering has been studied by Monte Carlo simulation techniques. A direct measurement of the energy spectrum of the ¹⁹⁸Au source used for Compton scattering experiments at the Hahn-Meitner Institute (HMI) confirms the predictions of the emission of a low energy tail. The effect of the tail on Compton profiles is examined and a method of correction is proposed and applied to measurements made at the HMI.     

环境γ射线监测工作质量控制探讨

环境辐射γ射线监测做为一项新监测项目,在质量控制方面并没有成熟具体措施。作者通过实际工作,查阅大量的资料,总结了一整套的质量控制措施,在实践中使用取得了良好的效果。     

A PC-based coherent sonar for experimental underwater acoustics

An important tool for experimental underwater acoustics research is a versatile sonar system for transmitting, receiving, anti recording acoustic waveforms. In this paper the design, implementation and performance of a variable-frequency (25 kHz to 500 kHz) coherent sonar are presented. The significance of the design lies in its simplicity and versatility. These attributes are a result of a sampling technique that provides quadrature samples of the complex envelope of a bandpass signal without analog demodulation using a single A/D converter. Implementation of the design is accomplished using an ISA bus personal computer (PC), a commercially available digital signal processing (DSP) board, and a small amount of custom electronics. Performance of the sonar, in terms of magnitude and phase errors, is determined from wideband noise characterization, a linear-system model, and transmit/receive measurements