从(艹氐)闪烁谱仪获得入射中子谱的计算机程序

在从实验测量的反冲质子脉冲高度谱获得入射中子能谱时,用Monte Carlo方法计算响应矩阵的运算量太大,本文叙述了获得中子谱的解析方法并编制了一套在IBM-PC/XT微机上使用的计算机程序,其中考虑了中子在芪晶体中的二次散射修正和反冲质子的壁端效应修正。用T(d,n)中子源对本程序进行了检验,得到了它的中子谱。     

Effect of γ-radiation on HfO2 based MOS capacitor

Radiation effects on Metal Oxide Semiconductor (MOS) capacitors with a HfO₂ gate insulator have been studied. Because HfO₂ is a promising high-k dielectric material for microelectronic applications, radiation effects on its performance in MOS devices is of interest. New results on radiation effects on HfO₂, particularly at low gamma radiation doses, are presented. The results are compared with other systems including those of Al₂O₃ plus silicon based Si MOS capacitors. Both devices with different gate thicknesses were irradiated with Co-60 gamma source for varying exposure time. The midgap and flatband voltage shifts in these devices were measured and analyzed. Results show that gamma radiation does not cause significant variations in the HfO₂ MOS especially at low doses.     

Energy Loss Distribution of Recoil Protons in Stilbene Scintillator

Formulas are derived for calculating the energy loss distribution of recoil protons in a cylindrical organic scintillator with a broad beam of fast neutrons in the energy range 1 to 15 MeV perpendicularly incident on its base. The assumptions are: (1) the scintillator is composed solely of hydrogen and carbon; (2) only elastic scattering from hydrogen and carbon is considered in relation to the interaction of fast neutrons with the scintillator; (3) single and double scattering alone are considered; (4) wall effect is neglected for recoil protons produced in the second collisions; (5) the radius and the thickness of the scintillator are greater than the range of recoil protons of the highest energy.

As an example, the calculated results are shown for stilbene crystals of 1″ dia. and 1/8″ to 1″ thick. In scintillators of thicknesses below 1/4″, and for incident fast neutrons in the energy range from 3 to 15 MeV, the contribution of double scattering to the energy loss distribution of recoil protons is below about 10% of that of single scattering, while wall effect is quite significant, in particular, for incident neutrons of high energy.     

质子和中子的单粒子效应等效性实验研究

通过实验方法确定了高能质子和中子引起的单粒子效应等效关系，实验中采用金箔散射法降低了质子束流强度，并利用热释光剂量计（TLD）进行质子注量的监测，采用新研制的存储器长线实时监测系统，进行了64K位至4M位的SRAM器件单粒子效应实验，确定了两种粒子引起单粒子效应等效关系。     

Energy and angular distribution of recoil proton of fast neutron in scintillation fiber： a simulation study

Due to their low cost,big reaction cross-section with neutrons,flexibility,and convenience for long distance data transfer,plastic scintillation fibers (PSF) have been increasingly used as detectors or sensors for high-energy neutron radiography.In this paper,Geant4 Monte Carlo simulation tool was used to obtain some chalacteristics of energy and angular distributions of recoil protons in plastic scintillation fibers irradiated by fast neutrons.The plastic fiber with BCF-20 as the core and an acrylic outer cladding was used in the simulation.The results show that there is a big range of energy and angular distribution of recoil protons in energies varying inversely with the recoil angle.     

Application of CR-39 Track Detector to Neutron Spectrum Measurement

A new technique for estimating the neutron energy spectrum with CR-39 track detectors has been proposed for application to a singly pulsed neutron field where prevailing counters cannot operate properly. The CR-39 sample exposed to neutrons was intermittently etched, then the major and minor radii of respective etch pits were measured for each etching stage and the growth curve was obtained. The analysis method of growth curves was also designed, with which both the energy and the angle of recoil protons could be evaluated and converted into the energy of neutrons incident normally.

The neutron irradiation experiments were carried out with the 46 MeV electron linear accelerator at the Research Reactor Institute, Kyoto University. It was confirmed from comparing with the reference spectrum measured by the neutron time-of-flight method that the present growth-curve method is useful for the estimation of the neutron energy distribution between about 0.3 and 2 MeV. Moreover, we have experimentally examined the unfolding method suggested by Matiullah and Durrani in order to extend the application of CR-39 detector to higher energies.     

Radiation Dosage Due to Neutrons Produced in a Vehicle by Protons in the Trapped Radiation Belt

The rate of production of neutrons by geomagnetically trapped protons incident on a vehicle was measured by a neutron counting system carried into the trapped radiation belt by a pod flow piggy back on an Atlas rocket on December 19, 1961. The flux of neutrons produced by radiation belt protons incident on the pod was determined to be at least 700 neutrons/(cm2 sec); the actual value depends somewhat on the energy spectrum of the neutrons. This flux was estimated to be equivalent to a dose rate in tissue of 0.10 rems/hr. On the basis of proton flux measurements made in the radiation belt by Freden and White, a calculation was made of the tissue dosage which would have been received in the same environment directly from protons. These calculations were made by obtaining a numerical integration of the dE/dx times RBE times flux product over the entire energy spectrum. The total dose calculated amounted to 2.78 rems/ hr. Further calculations were made to estimate the dose rates which would have been received by tissue in the same environment but with varying amounts of shielding around the vehicle. The proton dose is, of course, reduced by the shield but the neutron dose actually increases as the shielding thickness is increased. It is seen that the neutron dose equals the proton dose at .3 rems/hr. when aluminum shielding of 2.6" surrounds the vehicle and it exceeds the proton dose with thicker shielding.     

Characterization of displacement cascade damage produced in Cu3Au by fast-particle irradiation

Zones of reduced long-range order created at displacement cascade sites in well-ordered Cu₃Au may be directly imaged in the transmission electron microscope so that quantitative information can be obtained on individual cascade events. This technique has been used to characterise the cascade damage created by three fast particles (3.5 MeV protons, a source of moderated fission neutrons and a source of fusion neutrons with energies peaking at 14.8 MeV) with the aim of comparing the experimental observations with the relevant collision models. In each case, disordered zone number densities, sizes and shapes were determined, and were found to be characteristic of each irradiation, with the sizes of disordered zones and the proportion of zones of complex shape increasing on going from 3.5 MeV protons to fission neutrons to fusion neutrons. The quantitative results are largely consistent with the different calculated primary recoil spectra, although in the fusion neutron case some discrepancies are found which cannot readily be explained by limitations in the experimental technique. More specifically, more and larger disordered zones are found than expected from the calculated recoil spectrum. Subcascade formation was observed only in the neutron irradiations, with the distributions of sizes and shapes of individual sub-cascades being very similar in the two cases (in marked contrast to those obtained from sizing total cascade events). Finally, the production of point-defect clusters at cascade sites was studied. The efficiency of cascade collapse increased on going from 3.5 MeV protons to fission neutrons to fusion neutrons.     

Radiation Effects on MOS Devices: Dosimetry, Annealing, Irradiation Sequence, and Sources

This paper reports on some investigations of dosimetry, annealing, irradiation sequences, and radioactive sources, involved in the determination of radiation effects on MOS devices. Results show that agreement in the experimental and theoretical surface to average doses support the use of thermo-luminescent dosimeters (manganese activated calcium fluoride) in specifying the surface dose delivered to thin gate insulators of MOS devices. Annealing measurements indicate the existence of at least two energy levels, or activation energies, for recovery of soft oxide MOS devices after irradiation by electrons, protons, and gammas. Damage sensitivities of MOS devices were found to be independent of combinations and sequences of radiation type or energies. Comparison of various gamma sources indicated a small dependence of damage sensitivity on the Cobalt facility, but a more significant dependence in the case of the Cesium source. These results were attributed to differences in the spectral content of the several sources.     

Determination of energy absorption in a mixed flux of fast neutrons and γ-rays by an ionization method

The possibility of separate determinations of the energy absorption of fast neutrons and -rays in the mixed radiation flux from a reactor has been studied with ioni/ation chambers. Three chambers with different hydrogenous fillers were used: polyethylene with an ethylene filler; graphite with a CO₂ filler and a chamber made from aerion, a conducting plastic, which was filled with a mixture of ethylene and CO₂. Calculations have been carried out to ascertain the sensitivity of these chambers to neutrons with energies ranging from 0.2–8 Mev. Variation of the neutron spectrum over wide limits has no effect on the accuracy in the determination of the absorbed dose in the hydrogenous substrates. A calculation shows that the error in the determination of the absorbed energy for fast neutrons is approximately 15% and is a weak function of the relative doses of neutrons and -rays.In conclusion the authors wish to express their gratitude to Yu. F. Chernilin for help in this experiment and T. B. Radzievskii for discussion of the results.     

Proton simulation of displacement effects induced in metals by 14 mev neutrons

In designing a D-T fusion reactor, one must know the effect of a high flux of 14 MeV neutrons on structural materials. Available laboratory sources of 14 MeV neutrons are not intense enough to expose samples to the expected flux. Bombardment with other particles is one way of simulating the anticipated neutron environment. The energy spectrum of atoms recoiling from collisions with bombarding particles can be calculated from elastic-scattering and nonelastic-reaction data for the incident species. This analysis shows that 16 MeV protons closely simulate the displacement effects caused by 14 MeV neutrons. In niobium the average atom recoiling from a 14 MeV neutron interaction has 65 keV of damage energy. The mean damage energy deposited per cm³ of niobium by a fluence of one 14 MeV neutron per cm² is 14 keV. The equivalent quantity for 16 MeV protons incident on niobium is 33 keV.     

Relation between material configuration and radiation shielding capability - application of radiation shielding characteristic functions

For the purpose of finding a principle for material configuration which an ideal radiation shielding in slab geometry should obey, radiation energy dependence of material configuration is studied. In the course of study, radiation shielding capability for each system of different material configuration is evaluated by using radiation shielding characteristic functions defined as dose rates of transmitted radiations in response to isotropic incidence of radiations to the slab shield with pulse-like narrow energy distributions.In shielding neutrons by steel and water layers, recommendable material configuration depends on energy distribution of incident neutrons; all steel layers should be located in the source side of all water layers, if incident neutron energies are above 5 MeV: either homogeneous array of steel and water layers or above mentioned material configuration is recommendable, if incident neutron energies are between 2 MeV and 5 MeV: all water layers should be located in the source side of all steel layers, if incident neutron energies are below 2 MeV or incident neutrons have energy spectrum of fission neutrons.Above recommendation can be understood well by considering both energy dependence of neutron cross sections of each material and the maximum amount of energy degradation at elastic scattering in each material.In designing a neutron shield, shielding of secondary gamma rays is important as well as neutron shielding. This importance is demonstrated for several types of actual cask walls which are composed of many material layers by using the characteristic functions of neutrons and gamma rays for cask walls.     

Slowing Down of Neutrons to Very Low Temperature by Cold Solid Hydrogenous Moderators

The slowing down of neutrons to very low energy has been examined with particular reference to cold neutron production. The neutron spectrum formed in very cold light water ice has been measured with time-of-flight technique. It is observed that at extremely low temperature the neutron temperature is much higher than the moderator temperature, whereas in the intermediate range of temperature the neutron temperature does not differ much from the moderator temperature.

It is suggested that there is a limiting neutron temperature below which it does not fall, even when the moderator temperature drops further. This observation can lead to information on the nature of the mechanism for removing small amounts of energy from slow neutrons in cold solid hydrogenous moderators. By using a simplified model for the cold solid hydrogenous moderators, it is shown that low frequency lattice vibrations play an important role in producing cold neutrons. Also, quantitative analysis indicates that while the cold neutron temperature depends only slightly on the neutron absorption, the gain in cold neutron flux is strongly affected by the neutron absorption.     

Use of new ENDF/B-VI proton and neutron cross sections for singleevent upset calculations

Single-event upsets (SEU) in microelectronics are calculated from newly-developed silicon nuclear reaction recoil data for incident protons and neutrons with energies up to 150 MeV. This paper focusses on the nuclear reaction physics that is important for calculating recoil spectra, and burst generation rate spectra. Comparisons are made with previous results, obtained from intranuclear cascade calculations as well as from previous ENDF data below 20 MeV, to demonstrate new features in the present calculations. Calculated SEU cross sections are compared with measured data     

Neutron response functions and detection efficiency of a spherical proton recoil proportional counter

<正>The neutron response function and detection efficiency of a spherical proton recoil proportional counter (SP) play key roles in precise measurement of neutron spectra of the interior materials.In this paper,the response functions and detection efficiency of three SPs developed at CAEP are simulated by Geant4.The simulated spectra are compared with pulse-height spectra measured at 0.165,0.575,1.4,and 14.1 MeV of incident neutrons.And the calculated detector efficiencies agree within 5%with the data obtained by neutron activation.     

圆柱氧化钍装置上的中子及伽马穿透能谱实验测量

利用D-T中子对氧化钍圆柱装置进行了辐照。样品直径为30 cm、厚度为15 cm。在不同的布局状态下,采用芪晶体闪烁体基于反冲质子法对1 MeV~15 MeV中子能谱进行了实验测量;基于反冲电子法对中子辐照下和辐照后的0.5 MeV以上伽马能谱进行了测量。对能谱中的分布规律、与布局状态的关系进行了比对分析。     

Nonlinearity of pulse height of recoil helium in 3Heproportional counters

The pulse height distribution in ³He proportional counters has been investigated to accurately quantify the response function to be used in fast neutron spectroscopy. The measurements were performed as a function of the operating voltage, the counting gas mixture, and the incident neutron energy. The special emphasis of this study has been put on the nonlinearity of the pulse height of a recoil helium induced by the ³He(n,n)³He reaction. A distinct deviation of 14% at maximum to lower energies was found in the position of the recoil edge with the energy axis calibrated by the full energy peaks of the ³He(n,p)T reaction produced with neutrons of thermal energy and 2.413 MeV. It was confirmed that the nonlinear effects, such as an initial recombination and a space-charge effect, take place more significantly in the energy loss process of a recoil helium because of its higher linear energy transfer (LET) in the filling gas compared to that of a proton and triton pair emitted from the ³ He(n,p)T reaction. The deviation becomes larger with an increase of the average LET in the gas mixture. The experimental results suggested that the nonlinear effect caused by a higher LET recoil helium is inevitable for the filling gas, even if the operating voltage is changed to an acceptable range     

Correlation of Radiation Types with Radiation Effects

The effects produced by different types of nuclear radiation can be compared by making use of the available information on radiation-effects mechanisms. One can separate radiation-effects manifestations into three categories: transient radiation effects, which are due to excited and ionized electrons; displacement radiation effects, which are manifestations of atoms displaced from their normal lattice sites in crystalline solids; and chemical radiation effects, which are due to molecular rearrangements occurring as a second stage to ionizing interactions. The effects produced by different primary radiations can be compared by first identifying the manifestation as belonging to one of these three types. For displacement effects one should then compute the relative cross sections for producing displaced atoms and the average size of the displacement cascade produced by the primary recoil atom. Similarly, for transient and chemical effects one should compute the ionization density produced by the incident radiation. Examples of the pertinent cross sections have been calculated for electrons, gamma rays, protons, and neutrons of various energies.     

The neutron tissue dose

This paper is devoted to the determination of dosimetric characteristics of intermediate-energy neutrons. A calculation of the interaction of neutrons with paraffin for the normal incidence of an extended beam of neutrons in the energy interval from 100 ev to 1 Mev, which has been performed by means of an electronic computer, is given here. The computation results are used for calculating the components of the neutron tissue dose resulting from the moderation process in the tissue. The dose resulting from the neutron capture is calculated on the basis of the authors' data on the distribution of slow neutrons in paraffin and on neutron reflection from the surface of a hydrogenous medium. The depth distributions of neutron dose components for thermal neutrons and neutrons with energies of 100 ev, 1, 30, 240, 500 kev, and 1 Mev were obtained. The depth distributions of the biological dose for neutrons of the same energy and the biological dose values pertaining to the unit neutron flux were obtained.     

Calculations of the transport of neutrons and secondary gamma rays through concrete for incident neutrons in the energy range 15 to 75 MeV

Earlier work by Alsmiller et al. considered coupled neutron and secondary-gamma-ray transport through a thick shield of silicon dioxide with 5% water by weight for neutron sources with energies of 50, 100, 200, 300 and 400 MeV. In that work, the approximation was made that gamma rays were produced only by neutron capture. In the present work, coupled neutron and secondary-gamma-ray transport through a thick shield of concrete for neutron sources with energies of 15, 25 and 75 MeV is considered. In this study, gamma-ray production for all interactions involving neutrons with energies up to 15 MeV was included; i.e., the approximation made here is that gamma-ray production can be neglected for interactions by neutrons with energies > 15 MeV.For incident neutron energies of 15, 25, 50, and 75 MeV, results of total and gamma-ray dose equivalents are given as a function of depth into the slab. For the 50- and 75-MeV incident neutron energies, the gamma-ray dose equivalent was found to be no more than 5% of the total dose equivalent at all depths considered ( 1500 g/cm²). For the 15- and 25-MeV incident neutron energies, however, the gamma-ray dose equivalent dominates at greater depths into the slab. A conservative estimate of the effect of including gamma rays produced in interactions with neutrons of energies > 15 MeV indicates that the calculated total dose equivalent would increase by no more than 5%.