Inelastic Scattering of 14MeV Neutrons by Heavy Nuclei

Energy spectra of neutrons scattered inelastically from natural samples of Ta, W, Au, Hg, TI, Pb and Bi have been studied at an incident energy of 14MeV, using time-of-flight technique. Angular distributions were also measured for Ta and Bi. The energy spectra from 2MeV to 4MeV were found to be qualitatively consistent with the prediction from statistical theory taking account of effects of nuclear pairing and shell structure. The Fermi gas level density parameter and the nuclear temperature were obtained by considering the contribution of the (n,2n) reaction. The variation of level density parameter plotted against mass number was found to agree with the trend predicted theoretically by Newton. Angular distributions proved to be symmetric about 90° and the spin cut-off parameter was estimated to be about 5.8 for Ta and 4.3 for Bi. Cross sections for the (n,n′2n) and (n,2n) reactions were obtained.     

Inelastic Scattering of 14MeV Neutrons by Medium Weight Nuclei

Continuous spectra of neutrons inelastically scattered from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge and As have been measured at an incident energy of 14 MeV with good statistics. Time-of-flight technique was used. In the analyses there were used three sets of inverse-reaction cross section σ_i: (1) calculated with Perey-Buck potential, (2) with Bjorklund-Fernbach potential and (3) cross section assumed to be constant. The inverse-reaction cross section does not affect appreciably the values of nuclear temperature or nuclear level density parameter for these nuclei except Ti, V and Cr. The nuclear temperature was found to be nearly constant in the mass number region of 48–75. The level density parameter as a function of mass number follows the general trend suggested by Newton. Newton's coefficient is found to be 0.092, in agreement with values obtained in other experiments. The total inelastic scattering cross sections are derived.     

单粒子翻转效应的实验研究

本文介绍了14MeV中子辐照动态随机存取存贮器进行单粒子翻转效应研究的实验装置和方法,并给出了各4种型号16KB,64KB芯片的辐照实验结果。结果表明,由于集成度和工艺结构的不同,单粒子翻转灵敏度有很大的不周,并且γ射线预辐照芯片可使它的单粒子翻转灵敏度降低到1/2到1/3(对TMS4116芯片)。本文对实验结果做了分析和讨论。     

高通量堆NTD硅系统活化剂量计算

根据单晶硅及靶桶材料成分、测量的辐照孔道中子通量谱与辐照时间,采用点燃耗程序ORIGEN与蒙特卡罗程序MCNP耦合计算高通量堆中子嬗变掺杂(NTD)硅辐照系统活化后的外照射剂量当量率及各种活化产物放射性核素衰减变化情况,同时对各种活化核素剂量率贡献及相应衰减时间进行了分析。通过计算结果与堆厅γ电离室剂量率监测对比验证及堆厅屏蔽层厚度的保守估算,表明目前NTD硅系统转运过程屏蔽设计满足辐射防护要求,并提出有益建议。     

Statistical Properties of Quantum Spectra in Nuclei

Some aspects of quantum chaos in a finite system have been studied based on the analysis of statistical behaviors of quantum spectrum in nuclei. The experiment data show the transition from order to chaos with increasing excitation energy in spherical nuclei. The dependence of the order to chaos transition on nuclear deformation and nuclear rotating is described. The influence of pairing effect on the order to chaos transition is also discussed. Some important experiment phenomena in nuclear     

Void Formation in Magnesium Aluminate Spinel Heavily Irradiated with Fast Neutrons

Single crystals of magnesium aluminate spinel (MgAl₂O₄) were heavily irradiated to fission neutron fluences from ?1 × 10²⁶ to ?2×10²⁷ n/m² (E>0.1 MeV) at 658 and 1,023 K in FFTF (Fast Flux Test Facility) to investigate their microstructural evolution under heavy neutron irradiation and to confirm their previously observed resistance to void swelling. At 658 K no voids were observed up to 2.29 × 10²⁷ n/m², but 1/4[110] interstitial loops were formed. These loops changed their habit planes from (111) to (110) with increasing neutron fluence. At 1,023 K the 1/4[110] type of interstitial loops grew to form stacking fault netuorks composed of stacking faults on each of the six equivalent (110) planes. Tiny voids were also observed to form preferentially on or near stacking faults after 1.37×10²⁷ n/m². A limited number of very small cavities, contributing to a volumetric swelling of only 0.07%, were also observed in the crystal matrix after 2.17×10²⁷ n/m². The possible mechanisms of suppression of void formation in MgAl₂O₄ are discussed.     

Measurement of Leakage Neutron Spectra from a Spherical Pile of Zirconium Irradiated with 14MeV Neutrons and Validation of Its Nuclear Data

In order to make a benchmark validation of the nuclear data for Zr, the leakage neutron spectrum from a Zr sphere of a 61-cm diameter was measured between 0.1 and 16MeV using a time-of-flight technique with a 14MeV neutron source facility, OKTAVIAN. The result was compared with the calculation using the Monte Carlo code MCNP-4A. To investigate the spectrum dependence on the individual neutron reactions, test calculations were carried out with the MCNP-4A code using the JENDL-3.2-based libraries, in which partial cross section values were reduced from the original values. From the comparison between the measured and the calculated spectra, it was found that each of the results could predict well the experiment in general. However, in detail, both ENDF/B-VI and EFF-2.4 gave considerable overestimation above 1 MeV. The JENDL-3.2 predicts the spectrum almost satisfactorily except below 0.8 MeV and around 10 MeV. The discrepancy found in JENDL-3.2 calculation is considered due to the cross section values of the (n, 2n) reaction and its secondary energy distributions (SED). The modified JENDL-3.2 library with the reduced (n, 2n) reaction values and the lower SED below 1 MeV reproduced the experiment with better agreement over the whole energy range.     

Statistical Behavoirs of Quantum Spectra in Superheavy Nuclei

From the point of view of the interplay between order and chaos, the most regular single-particle motion of neutrons has been found in the superheavy system of Z=120 and N=184 based on the Skyrme-Hartree-Fock model and in the system of Z=120 and N=12 based on the relativistic mean-field model. It has been shown that the statistical analysis of spectra indeed can give very valuable information about the stability of superheavy systems. The significance of this kind of study can go far beyond the investigation on the stability of superheavy systems and it may give a deep     

稍超瞬发临界系统缓发中子发射率研究

使用蒙特卡罗直接模拟程序计算了弱源点火条件下超瞬发临界5￠的GodivaⅠ快中子脉冲堆缓发中子发射率规律和脉冲引发时刻概率分布。计算结果表明,脉冲引发时刻概率分布的计算结果与实验结果符合较好,所获得的缓发中子发射率规律可合理解释引发时刻概率分布的实验结果。     

美国国家点火装置中低温定位器产生的背景中子通量密度的计算

W.C.Mead等人[1]对美国国家点火装置(NIF)内的氘氚燃料反应产生的信号中子与低温定位器(CTP)、靶室壁反应产生的背景中子和背景光子的通量密度进行了计算。论文对同一系统进行再次研究,得到与W.C.Mead不同的结论。论文对W.C.Mead等人的研究进行勘误和拓展,使用MCNP对NIF中CTP和靶室壁对背景中子和背景光子的产生情况进行了计算和分析。通过计算在靶室内不同半径不同角度上的背景中子通量密度,确定了在靶室内最佳信噪比的角度,同时对探测器布置在靶室内的位置提出了建议。并且在W.C.Mead等人的研究基础上,改变CTP在靶室中的位置,计算并对比了CTP在靶室内不同位置上,所产生的背景中子和背景光子通量密度。     

脉冲离子束轰击靶的热效应数值模拟

分析了脉冲离子轰击靶膜和衬底的热效应,在能量较低的情形下,离子轰击处理为靶膜表面热流输入。采用有限元程序,对能量为600keV、束流为12mA的不同束斑半径的脉冲离子流轰击Cu基Ti靶的热传导进行了数值计算,得到了热传导清晰物理图象。     

Measurements of Time Dependent Energy Spectra of Neutrons in a Small Graphite Assembly

The time-dependent energy spectra of neutrons have been measured in a small 30×30×30 cm³ graphite assembly by means of the linac-chopper method, with a view to establishing experimental evidence that there is no asymptotic spectrum in such a small assembly, and in order to study the non-asymptotic behavior of neutrons.

The arrangement of a polyethylene pre-moderator adjacent to the assembly made the measurements possible with the improvement obtained thereby of the neutron counting statistics. It was indicated from calculation that the presence of the pre-moderator had little effect—at least above the Bragg cut-off energy—on the evolution in time of the energy spectra of neutrons in the graphite assembly.

The experimental results indicated very probable disappearance of asymptotic spectra, and revealed significant enhancement of trapping at Bragg energies with the lapse of time. This is consistent with the results of pulsed neutron experiments in small assemblies conducted by Takahashi et al., and falls in line with de Saussure's approximation.

The spectra in the graphite assembly showed significant space dependence, the spectra becoming harder with increasing distance from the pre-moderator. This hardening may be attributed to the relatively faster propagation of higher energy neutrons.     

Theoretical Analysis on Time-Dependent Energy Spectra of Neutrons in a Small Graphite Assembly

A theoretical study was carried out on the time-dependent neutron spectrum in a small graphite assembly into which the neutron pulses were injected through a pre-moderator layer of polyethylene. Numerical analyses were performed by means of the usual time-step method, as well as by the spatial mode expansion time-step and two-region difference equation methods.

It was verified that addition of the pre-moderator does not substantially affect the space-time-dependent spectral behavior of neutrons in a graphite system of dimensions adopted in current experimental arrangements.

A strong space dependence of the time-dependent spectra was observed in the form of spectral hardening in increasing distance from source, which was termed “propagation hardening”.

The space-time-dependence and neutron trapping at Bragg peak energies appearing on the measured spectra were well reproduced by both the spatial mode expansion time-step and two-region calculations.     

超短脉冲激光辐照固体靶产生超热电子研究

实验研究了超短脉冲激光辐照固体靶产生的超热电子温度 ,所用方法是测量超热电子在固体中韧致辐射产生的硬X射线 ( >30keV)能量连续谱。中等强度 ( 1 0 16W /cm2 )、无预脉冲、红外超短脉冲( 74 4nm ,1 30fs,6mJ)、P极化激光 4 5°照射 5mm铜靶 ,产生了能量为 4 0 0keV的X射线信号 ,利用Maxwellian分布拟合能谱得到的超热电子温度为 85keV ,产生高能电子的主导吸收机制为真空加热。     

阴离子交换法从辐照后的Ni靶中分离64Cu

为实现从质子回旋加速器辐照后的Ni靶中提取⁶⁴Cu,建立了使用阴离子交换法从Ni靶溶解液中实施⁶⁴Cu与基体Ni及伴生Co放化分离的工艺。测定了Ni²⁺、Co²⁺ 和Cu²⁺在阴离子交换树脂AG1-X8与盐酸介质之间的静态分配系数K_d。确定了使用阴离子交换树脂柱分离提取⁶⁴Cu的工艺：首先用6 mol/L盐酸穿透Ni,再用4 mol/L 盐酸洗脱⁵⁷Co,最后用1 mol/L 盐酸解吸⁶⁴Cu。⁶⁴Cu放化回收率为87.5%±3.0%。以丰度99.07%的富集⁶⁴Ni为靶材,质子轰击后,使用本工艺分离得到的⁶⁴Cu放射性核纯度大于99.0%,化学杂质Ni、Co和Fe的浓度均小于0.05mg/L。     

中子辐照后6Li-Al合金靶片中氚的测量方法研究

建立了流气式系统捕集和化学转移法测量^6LiAl合金靶片在中子辐照过程中的渗漏氚和辐照后靶片中总氚量的方法。渗漏氚的捕集方法是：在流气式系统中，用含少量氢的惰性载气将渗漏氚载带出来，经高温催化氧化后被乙二醇鼓泡器捕集；靶片中的氚转移法是用NaOH溶液将合金靶片溶解，气相中的氚采用渗漏氚的捕集方法捕集，液相中的氚则蒸馏到馏分中。最后用液体闪烁计数器分别测量乙二醇鼓泡器和馏分中的氚量。测量结果与理论氚产量基本相符。     

Experimental Studies on the Self-Shielding Effect in Fissile Fuel Breeding Measurement in Thorium Oxide Pellets Irradiated with 14 MeV Neutrons

The 14 MeV neutrons produced in the D-T fusion reactions have the potential of breeding Uranium-233 fissile fuel from fertile material Thorium-232. In order to estimate the amount of U-233 produced, experiments are carried out by irradiating thorium dioxide pellets with neutrons produced from a 14 MeV neutron generator. The objective of the present work is to measure the reaction rates of 232 Th + 1 n → 233 Th → 233 Pa → 233 U in different pellet thicknesses to study the self-shielding effects and adopt a procedure for correction. An appropriate assembly consisting of high-density polyethylene is designed and fabricated to slow down the high-energy neutrons, in which Thorium pellets are irradiated. The amount of fissile fuel ( 233 U) produced is estimated by measuring the 312 keV gammas emitted by Protactinium-233 (half-life of 27 days). A calibrated High Purity Germanium (HPGe) detector is used to measure the gamma ray spectrum. The amount of 233 U produced by Th 232 (n, γ) is calculated using MCNP code. The self-shielding effect is evaluated by calculating the reaction rates for different foil thickness. MCNP calculation results are compared with the experimental values and appropriate correction factors are estimated for self-shielding of neutrons and absorption of gamma rays.     

闪烁光纤在快中子辐照下部分特性的蒙特卡罗模拟

采用蒙特卡罗方法对闪烁光纤在快中子辐照下的特性进行了研究。利用Geant4模拟计算得到了快中子照射下,闪烁光纤中的能量沉积效率与光纤长度、半径及入射中子能量的变化曲线,同时对量子效率随上述参数的变化关系进行了模拟分析。研究结果表明选择合适尺寸的闪烁光纤和入射中子能量对于快中子成像技术具有重要的意义,并为实际测量工作中的参数选择提供了的理论指导。     

Halo Structure of the Isobaric Analog States in Some Mirror Nuclei

Using ANC method the rms radius of the last nucleon in the 2s1/2 isobaric analog states of 21Ne/2lNa and 17O / 17F is extracted from transfer reaction data. The results are summarized in Tab. 1. The 2s1/2 single proton states in 21Na and 17O have the rms radii almost twice as large as that for their core nuclei (2.88 fin for 20Ne and 2.71 fm for 16O) and are proton halo states, while their isobaric analog states in 2INe and I7O can be considered as neutron skin states, because the neutrons in these states have one third of the probability staying out of the nuclear interaction range. The obvious difference in the rms radii between a mirror pair indicates the binding energy difference between the