反应堆二次中子源源强计算及验证

研究建立了反应堆二次中子源源强的机理性计算方法,并计算了某核电厂反应堆第2循环装料时的二次中子源源强。为验证二次中子源源强的计算结果,计算了反应堆装料第2步完成后堆外源量程探测器的计数率,并与实测结果进行对比。源量程探测器计数率计算结果与实测结果符合得非常好,验证了二次中子源源强计算结果的正确性以及所建立的计算方法的合理性。     

陕西西岳庙古琉璃胎料来源的INAA研究及多元统计分析

用仪器中子活化分析研究了陕西立地坡明代地层和陕西西岳庙宋、元、明、清早期、清晚期4个地层出土的古琉璃胎中的主量和微量元素, 并对实验数据进行多元统计分析. 结果表明, 陕西西岳庙从宋到清早期古琉璃胎料很稳定, 其原料可能来自本地； 清晚期古琉璃胎料与宋到清早期的古琉璃之间存在明显的区别, 明代3个样品和清晚期的古琉璃制造原料与立地坡出土的古琉璃其成分相近, 西岳庙清晚期的古琉璃可能来自陕西立地坡窑烧制.     

中子活化分析原理及应用简介

介绍了中子活化分析的基本原理,详细给出中子活化方程的推导过程．概述其主要特点．通过实例对其应用进行了说明。     

Spatial dosimetry and spectrometry with neutron activation of remaining Ag from nuclear emulsion

Certain characteristics of nuclear emulsion make it suitable for dosimetric measurements in space. It serves as an integrating medium of all ionizing effects i.e. the total dose absorbed within the detector, which leads to developable grains. Their number or the mass of silver, remaining after processing can be determined by neutron activation of the Ag nuclides. Using emulsions with different sensitivity thresholds (Ilford K5÷K0) allows to differentiate to a certain degree LET-classes of the ionizing radiation, and to obtain a rough composition of the flux over a wide range of dose. The results of the calibration with gamma rays, protons and oxygen for emulsions of different sensitivities are given. Results from various space experiments (Bion 10, 1, , 2, 2) are presented too.     

反应堆内中子注量率新型探测器的理论研究

利用核泵浦激光强度与入射中子注量率的相关性,探讨了反应堆活性区核泵浦激光中子探测器的理论可行性.从核泵浦激光机理出发,对该中子探测系统——核泵浦激光3He?Ar?Xe气体体系的能量沉积密度和激光的本征效率进行了深入的理论研究.提出了较完整的理论模型,讨论了该系统对中子注量率的响应函数及其检测灵敏度随工作时间的变化情况,论证了该中子探测系统的理论可行性.     

The NA-2 Neutron Generator and its Applications

The NA-2 neutron generator, developed for use in activation analysis in the Central Research Institute for Physics, was described in an earlier paper 1, in 1965. Keeping the basic design concepts unaltered but utilizing the practical experiences obtained during this one-year period of operation several modifications have been made in the construction on to improve the operational parameters of the equipment. In the present paper this improved type and its applications are described.     

A TEM study of the stability of intermetallic precipitates in Zircaloy nuclear reactor components

Transmission electron microscopy (TEM) has been used to characterise the radiation-induced changes in Zr(Cr,Fe)₂ intermetallic precipitates present in Zircaloy-2 and -4 nuclear reactor components. The results show that the precipitates become completely amorphous at low fluences (<1 × 10²⁴ n·m⁻²) during low temperature neutron irradiation (about 330 K) with no associated chemical composition change. At higher temperatures (about 573 K), a duplex amorphous-crystalline structure is produced. The precipitates retain a crystalline core surrounded by a peripheral amorphous layer that advances inwards with increasing fluence. The amorphous outer layer is coincident with a depletion of Fe that is dispersed into the surrounding hcp -phase matrix. Subsequent post-irradiation heat-treatment below the amorphous phase recrystallisation temperature results in the back-diffusion of Fe into the precipitates.     

Transmutation studies using SSNTD and radiochemistry and the associated production of secondary neutrons

Experiments using 1.5 GeV, 3.7 GeV and 7.4 GeV protons from the Synchrophasotron, LHE, JINR, Dubna, Russia, on extended Pb- and U-targets were carried out using SSNTD and radiochemical sensors for the study of secondary neutron fluences. We also carried out first transmulation studies on the long-lived radwaste nuclei ¹²⁹I and ²³⁷Np.

In addition, we carried out computer code simulation studies on these systems using LAHET and DCM/CEM codes. We have difficulties to understand rather large transmutation rates observed experimentally when they are compared with computer simulations. There seems to be a rather fundamental problem understanding the large transmutation rates as observed experimentally in Dubna and CERN, as compared to those theoretical computer simulations mentioned above.     

Neuere Ergebnisse in der metallurgischen Analyse durch Aktivierung mit 14-MeV-Neutronen

Der Vortrag informiert über neuere Untersuchungen zur Bestimmung des Sauerstoffgehalts verschiedener Metalle, insbesondere des Aluminiums und dessen Legierungen sowie üher die Anwendung programmierbarer Kleinrechner für derartige Analysen durch Aktivierung mit 14-MeV-Neutronen. Als ebenfalls vorteilhaft erwies sich diese Analysentechnik für die Bestimmung von Cer, das als Mikrolegierungsetement für verschiedene Metelle Anwendung findet. Es wird über die Moglichkeiten der Cer-Bestimmung in Metalleu mit unterschiedlichen Cer-Gehalten und im Cer-Mischmetall berichtet.     

Constraint on nuclear symmetry energy imposed by f-mode oscillation of neutron stars

Due to improvements in the sensitivity of gravitational wave (GW) detectors, the detection of GWs originating from the fundamental quasi-normal mode (f-mode) of neutron stars has become possible. The future detection of GWs originating from the f-mode of neutron stars will provide a potential way to improve our understanding of the nature of nuclear matter inside neutron stars. In this work, we investigate the constraint imposed by the f-mode oscillation of neutron stars on the symmetry energy of nuclear matter using Bayesian analysis and parametric EOS. It is shown that if the frequency of the f-mode of a neutron star of known mass is observed precisely, the symmetry energy at twice the saturation density (E_sym(2ρ₀)) of nuclear matter can be constrained within a relatively narrow range. For example, when all the following parameters are within the given intervals: 220 ≤ K₀ ≤ 260 MeV, 28 ≤ E_sym(ρ₀) ≤ 36 MeV, 30 ≤ L ≤ 90 MeV, −800 ≤ J₀ ≤ 400 MeV, − 400 ≤ K_sym ≤ 100 MeV, −200 ≤ J_sym ≤ 800 MeV, E_sym(2ρ₀) will be constrained to within ${48.8}_{-5.5}^{+6.6}$ MeV if the f-mode frequency of a canonical neutron star (1.4 M_⊙) is observed to be 1.720 kHz with a 1% relative error. Furthermore, if only f-mode frequency detection is available, i.e. there is no stellar mass measurement, a precisely detected f-mode frequency can also impose an accurate constraint on the symmetry energy. For example, given the same parameter space and the same assumed observed f-mode frequency mentioned above, and assuming that the stellar mass is in the range of 1.2–2.0 M_⊙, E_sym(2ρ₀) will be constrained to within ${49.5}_{-6.8}^{+8.1}\,\mathrm{MeV}$. In addition, it is shown that a higher slope of 69 ≤ L ≤ 143 MeV will give a higher posterior distribution of E_sym(2ρ₀), ${53.8}_{-6.4}^{+7.0}\,\mathrm{MeV}$.     

Exploring nuclear symmetry energy with isospin dependence in neutron skin thickness of nuclei

We propose an alternative way to constrain the density dependence of the symmetry energy from the neutron skin thickness of nuclei which shows a linear relation to both the isospin asymmetry and the nuclear charge with a form of Z^2/3. The relation of the neutron skin thickness to the nuclear charge and isospin asymmetry is systematically studied with the data from antiprotonic atom measurement, and with the extended Thomas-Fermi approach incorporating the Skyrme energy density functional. An obviously linear relationship between the slope parameter L of the nuclear symmetry energy and the isospin asymmetry dependent parameter of the neutron skin thickness can be found, by adopting 70 Skyrme interactions in the calculations. Combining the available experimental data, the constraint of -20 MeV L 82 MeV on the slope parameter of the symmetry energy is obtained. The Skyrme interactions satisfying the constraint are selected.     

The role of cool-flame chemistry in quasi-steady combustion and extinction of n-heptane droplets

Experiments on the combustion of large n-heptane droplets, performed by the National Aeronautics and Space Administration in the International Space Station, revealed a second stage of continued quasi-steady burning, supported by low-temperature chemistry, that follows radiative extinction of the first stage of burning, which is supported by normal hot-flame chemistry. The second stage of combustion experienced diffusive extinction, after which a large vapour cloud was observed to form around the droplet. In the present work, a 770-step reduced chemical-kinetic mechanism and a new 62-step skeletal chemical-kinetic mechanism, developed as an extension of an earlier 56-step mechanism, are employed to calculate the droplet burning rates, flame structures, and extinction diameters for this cool-flame regime. The calculations are performed for quasi-steady burning with the mixture fraction as the independent variable, which is then related to the physical variables of droplet combustion. The predictions with the new mechanism, which agree well with measured autoignition times, reveal that, in decreasing order of abundance, H₂O, CO, H₂O₂, CH₂O, and C₂H₄ are the principal reaction products during the low-temperature stage and that, during this stage, there is substantial leakage of n-heptane and O₂ through the flame, and very little production of CO₂ with no soot in the mechanism. The fuel leakage has been suggested to be the source of the observed vapour cloud that forms after flame extinction. While the new skeletal chemical-kinetic mechanism facilitates understanding of the chemical kinetics and predicts ignition times well, its predicted droplet diameters at extinction are appreciably larger than observed experimentally, but predictions with the 770-step reduced chemical-kinetic mechanism are in reasonably good agreement with experiment. The computations show how the key ketohydroperoxide compounds control the diffusion-flame structure and its extinction.     

基于JMCT软件的中子活化数值模拟程序的开发和检验北大核心CSCD

中子活化产物和辐射特征的数值模拟程序是研究材料活化效应的重要工具。在JMCT软件的基础上开发了具备材料中子活化效应模拟能力的数值模拟程序,并将其命名为“中子活化数值模拟程序”,旨在将其应用于军控核查、核安全等领域的研究中。对该程序在核弹头内部中子输运和活化计算的准确性进行了验证,发现该程序对核弹头内部中子输运和活化的计算精度优良。利用该程序研究了混凝土地面核素在裂变核材料的裂变中子辐照下的活化效应,计算结果进一步验证了中子活化数值模拟程序的功能。     

基于252Cf裂变中子源的核信息系统频谱分析

 针对²⁵²Cf裂变中子源所构造的核信息系统,在阐述随机核信号功率谱密度的算法原理基础上,借助于Matlab分析工具,采用分块平均法,对系统3个测量通道的随机核信号,先做相关计算,再对总的相关函数进行傅里叶变换,求得总功率谱,最后做平均得到所需的功率谱密度,得到了核信息系统的频谱图,并获得了相关函数多重性、相干性和功率谱密度比等重要参数。     

Fissile radionuclides in thyroid of the inhabitants of the gomel region in belarus and peculiarities of their distribution

Severe radiation damages with the following substitution of connective tissue are the effect of high doses in microvolumes of the thyroid. Calcium, strontium and uranium deposited into these sections was more as compared to a normal tissue of the thyroid. An estimation of the microdistribution of fissile radionuclides was carried out using the method of fragmental radiography. The analysis of tracks done visually using a microscope magnification of 300 revealed the local density of fission fragments up to 10³ mm⁻². The irradiation of the surrounded cells which contain the hidden genetic damages, initiated by radioiodine, does not exclude their possible promoter role in thyroid cancerogenesis.     

The Resonance Neutrons in Activation Analysis Part 1: Theory

A great majority of studies in the field of neutron activation analysis is concerned with the question of how to distinguish the activity of the radionuclide arising from the determined element from the activity of other radionuclides in the sample following activation.     

从“福岛第一核电站事故”看我国核能利用的核安全

文章简要说明了福岛第一核电站事故的起因、发展和后果,并对核电站全厂断电、反应堆压力容器及安全壳超压、氢爆等导致事故恶化的原因作了分析.文章还就导致福岛核事故的相关因素与我国核电站的安全设计及防范对策进行了分析比较.在吸取福岛核事故的经验教训方面,文章提出了若干值得引发关注的启示,作为我国在建和在役核电站的改进,以及新设计核电站的参考.文章还就我国能源的状况,核能发展的必要性,以及核能发展的方针进行了探讨.     

从“福岛第一核电站事故”看我国核能利用的核安全

文章简要说明了福岛第一核电站事故的起因、发展和后果,并对核电站全厂断电、反应堆压力容器及安全壳超压、氢爆等导致事故恶化的原因作了分析.文章还就导致福岛核事故的相关因素与我国核电站的安全设计及防范对策进行了分析比较.在吸取福岛核事故的经验教训方面,文章提出了若干值得引发关注的启示,作为我国在建和在役核电站的改进,以及新设计核电站的参考.文章还就我国能源的状况,核能发展的必要性,以及核能发展的方针进行了探讨.     

Neutron production in extended Cu-target irradiated with relativistic C-ions at Dubna, as studied with SSNTD and nuclear chemistry

An extended Cu-target was irradiated with 22 and 44 GeV carbon ions. The target was in contact with a (CH₂)_n-block for the moderation of secondary neutrons. Small holes in the moderator were filled with either lanthanium salts or uranium oxide. The reaction ¹³⁹La (n,γ) ¹⁴⁰La was studied via the decay of ¹⁴⁰La (40 h), and the reaction ²³⁸U (n, γ) ²³⁹U ²³⁹Np was studied via the decay of ²³⁹Np (2.3 d). In addition, a variety of solid state nuclear track detectors (SSNTD) were used. Results will be presented. The yields for the formation of (n, γ) products agree essentially with other experiments on extended targets carried out at the Synchrophasotron LHE, JINR (Dubna). To a first approximation, the breeding rate of (n, γ) products, as well as the specific track density, seen with several SSNTDs, doubles when the carbon energy is increased from 22 to 44 GeV. If, however, results at 44 GeV are compared in detail to those at 22 GeV, we observe an excess of (37 ± 9) % in the experimentally observed ²³⁹Np-breeding rate over theoretical estimations. Experiments using solid state nuclear track detectors are giving similar results. We also observed in the past such excess in the yield of other secondary particles in relativistic heavy ion interactions above a total energy of approximately 35–40 GeV.     

Surveying the role of excitation energy in probing nuclear dissipation

A dynamical Langevin model is employed to calculate the excess of the evaporation residue cross sections of the 194pb nucleus over that predicted by the standard statistical model as a function of nuclear dissipation strength. It is shown that large excitation energy can increase the effects of nuclear dissipation on the excess of the evaporation residues and the sensitivity of this excess to the dissipation strength, and that more higher excitation energies have little contribution to further raising this sensitivity. These results suggest that on the experimental side, producing those compound systems with moderate excitation energy is sufficient for a good determination of the pre-saddle nuclear dissipation strength by measuring the evaporation residue cross section, and that forming an extremely highly excited system does not considerably improve the sensitivity of evaporation residues to the dissipation strength.