2017年 第34卷 第2期
近年来，越来越多的实验表明，很多轻奇特核结构中都有核心激发成分。本研究以丰中子晕核11Be为例，介绍核心激发成分的实验和理论研究进展，重点阐述核心激发成分对直接核反应微分截面的影响。实验上，1n移除反应及11Be（p，d）和10Be（d，p）转移反应是测量11Be核心激发成分比例的典型实验类型。理论上，发展了能够包括11Be核心激发成分的Faddeev AGS方法，XDWBA方法以及XCDCC方法。加入核心激发成分后，这些模型的计算结果可以更加合理地描述11Be在各种靶上的弹性散射和碎裂微分截面。通过对比是否包含核心激发成分的计算结果，发现其影响主要体现在弹散微分截面的大质心系角度，以及（p，d）转移反应角分布的小质心系角度。另外，对Ex=0:5s3 MeV的激发能区的碎裂反应，核心激发的影响不可忽略；对Ex=3s5:5 MeV的碎裂反应，核心激发的贡献非常重要。
It was found that many light exotic nuclei have the core-excitation components. In this paper, taking one-neutron halo nucleus 11Be for example, the experimental and theoretical research progress, as well as the influences on the direct nuclear reaction differential cross sections of this exotic component were reviewed. The 1n removal, 11Be(p, d) and 10Be(d, p) transfer reactions are typical experimental methods to investigate this component. The Faddeev AGS, the XDWBA, and the XCDCC methods are developed to include this constituent in various theoretical models. With the core-excitation component, the calculated results can more reasonably describe the elastic scattering and breakup differential cross sections of 11Be impinging on various targets. Comparing the full XCDCC calculation with that omitting core-excitation effect, we found that this component mainly affects the elastic scattering differential cross sections at large center-of-mass angles, and the (p, d) transfer reaction angular distributions at small center-of-mass angles. In addition, its effect is non-negligible for the breakup reaction within the excitation energy interval of Ex = 0:5~3 MeV, and is remarkable for Ex =3 5:5 MeV.
The excitation function of the 238U(9Be, 5n) reaction was obtained for the first time. By using a stack of uranium targets, 20 experimental data were obtained by the on-line irradiation without changing beam energy. Taking the advantage of the long lifetime and α decay mode of the residue nucleus 242Cm, the off-line measurement of the α radioactive was performed to obtain its yields. The maximum cross section is about 1 mb. The curve's shape and the maximum's position agree with the present model. The value of the cross section will help us to develop the ralated models, and push the nuclear studies in the transuranium region.
Based on the isospin-dependent quantum molecular dynamics model, the effect of high momentum distribution on nuclear stopping in medium mass nuclear collision system is studied with different neutron-proton ratio in intermediate energy heavy ion collisions, and the evolution of this effect with the incident energy. The results show that when the incident energy is small, the high momentum distribution has little effect on the nuclear stopping. However, when the reaction energy is large, the high momentum distribution has a great influence on the nuclear stopping and the influence increases with the increase of incident energy and the mass of collision nucleus. For the Ca isotopes reaction system, high momentum distribution increases the nuclear stopping of the reaction system. Therefore, high momentum distribution has an important influence on nuclear stopping in medium mass nuclear collision system, and closely related to the incident energy and the mass of collision nucleus.
In this paper we give a short review of the Method of Multiple of Internal Reflections (MIR method), which is accepted as the more accurate and rich in quantum description of nuclear reactions today. For a capture of the α particles by nuclei our approach gives (1) new parameters of the α-nucleus potential and (2) new fusion probabilities. We demonstrate that a fully quantum description of this process provided by the MIR method, and inclusion of probabilities of fusion into formalism allow to essentially increase agreement between theory and experimental data. In particular, our method found new parametrization and fusion probabilities and decreased the error by 41.72 times for α+40Ca and 34.06 times for α+44Ca in a description of experimental data in comparison with existing results. Based on our proposed fusion probability formula, we explain the difference between experimental cross-sections for α+40Ca and α+44Ca, which is connected with the theory of coexistence of the spherical and deformed shapes in the ground state for nuclei near the neutron magic shell N =20. To obtain deeper insight into the physics of nuclei with the new discovered magic number N = 26, we predict new cross-section of α+46Ca for further experimental confirmation.
提出一个经验公式，预测散裂反应中同位素产生的截面值，并且利用现有GSI-FRS实验测量的300，500，750，1 000和1 500 MeV/u能量下p+56Fe散裂反应产物的实验结果进行验证。发现此经验公式预测的同位素截面值与实验值的符合度比较好，但随着质量数与能量的改变，同位素产生截面的计算值与实验值的差距也在变大。通过引入质量与能量修正可使此经验公式计算出的同位素截面值的精确度更高，与实验值的符合程度更好。
An empirical formula is proposed to predict the isotopic cross section in spallation reactions. The measured fragments in the 300, 500, 750, 1 000 and 1 500 MeV/u p+56Fe spallation reactions have been adopted to perform the analysis. The cross sections of isotopes predicted by the proposed empirical formula have been compared to the experimental results, which shows that the empirical formula can predict the results well. But with the change of the mass and incident energy, the difference between the calculated results and experimental data is larger. The proposed empirical formula is found to predict the isotopic cross sections better, by incorporating the incident energy and mass dependents of fragments.
目前处于设计阶段的哈尔滨工业大学空间辐照效应装置，其核心部件是由1台10 MeV的注入器、1台300MeV的同步加速器以及输运线构成的加速器装置。同步加速器中引出的质子束流被用于辐照研究。基于装置的概念设计，优化了其同步加速器部分的设计。设计了新的磁聚焦结构，优化了基于新的磁聚焦结构的多圈注入系统的凸轨变化模式，提高了注入效率。为了更好地优化引出束流的时间结构，慢引出系统采用了RF knock-out的方法。为了满足精准辐照的要求，研究了RF Kicker的频率调制，发现RF Kicker的双频调制能使得引出束流更均匀。
A research complex for aerospace radiation effects research is in the designing stage in Harbin Institute of Technology. Its core part is a proton accelerator complex, which consists of a 10 MeV injector, a 300 MeV synchrotron and beam transport lines. The proton beam extracted from the synchrotron is utilized for the radiation effects research. Based on the conceptual design, the design study for optimizing the synchrotron has been done. A new lattice design was worked out, and the decreasing pattern of the bump of the multi-turn injection system was optimized to increase the injection efficiency. In order to improve the time structure of the extracted beam, a RF knock-out method is employed in the slow extraction system. To meet the requirement of accurate control of dose, the frequency modulation of the RF kicker is well investigated, and the dual frequency modulation has been found to have a better performance for a uniform spill.
使用电子枪对ECR（Electron Cyclotron Resonance）等离子体注入外电子束是继铝衬弧腔、偏压盘之后，对等离子体电子的额外补充的又一种手段，通过向弧腔中注入一定能量与流强的电子束，以期提高引出束流的流强与电荷态。但由于该方法可控参数繁多，经验积累与报道资料都很少，且设计与操作远不如偏压盘等手段简便，故一直未能得到深入研究。通过以三维仿真软件CST粒子工作室对注入到弧腔电子束的运动轨迹的模拟结果为依据、以18 GHz ECR蒸发冷却源为平台，进行了ECR等离子体注入电子束的实验，结果表明：在一定实验条件下，当注入电子束能量超过1 800 eV时，会产生一种引出的离子束流的激增现象。在这个现象中，脉冲与直流的流强均比未注入电子时要高，束流电荷态向高价方向移动，且可通过控制实验条件来控制这种现象。最后对于这种电子并未通过共振面，却能起到提高电荷态与流强的作用进行了分析与讨论，并认为该现象在改善直流束与脉冲束性能的方面都有着积极的意义。
The injection of the electron beam into the ECR (Electron Cyclotron Resonance)plasma by electron gun is a new method for the additional supplementary of the plasma electron, following the aluminum chamber wall and the bias plate, we are expecting for the higher current and charge state of the ion beam with it. However, because of the controllable parameter's variety, the lack of the accumulation of experience and data, and the shortage of convenience in designing and experimental practicing compared by biased disk and other means,it has always not been intensively studied. In this article, we take the 18 GHz ECR Ion Source using evaporative cooling technique as experimental platform, do the experiment of injecting electron into ECR plasma base on the simulation result of the electron beam's path in ECR's chamber by the 3D simulation software CST the particle studio. It shows that a pulsing leap of the current of the extracting ion beam appears when the injecting electron's energy is above 1 800 eV. In the mean time, the top of the pulse and the average current of the ion beam rises, the ionization state moves to a higher level. This phenomenon can be turned on and off by controlling the experimental condition. At the last part of the article, we discuss this improvement of the current and charge state of the ion beam despite of the position's missing between the injection of electron beam and the resonance surface, and hold the opinion that this phenomenon is positive to both pulsed and direct beam.
为了提高兰州重离子加速器冷却储存环（HIRFL-CSR）的运行效率、改善加速器输出束流品质，并实现几个加速装置分时供束，提高整个重离子加速装置的利用率，特为（HIRFL-CSR）增建一台新的注入器——CSRLINAC。在108.48 MHz的RFQ之后的CSR-LINAC主加速段，主要由一台108.48 MHz和两台216.96 MHz的IH型漂移管直线加速器组成，用于加速荷质比为1/8.5~1/3之间的重离子，其最大的束流流强为3 mA，并将粒子从0.3 MeV/u加速到3.71 MeV/u。运用KONUS动力学原理，在满足设计指标的情况下，首先利用TraceWin程序进行中能束线MEBT设计，后针对高频腔体设计和束流匹配的基本参数的系列讨论，特别是对CSR-LINAC的中能束流匹配线、参数选择和IH型KONUS结构的漂移管直线加速器进行设计模拟优化。最终得出，在保证腔体设计指标和95.3%的传输效率的情况下，该紧凑型直线加速结构经过三个腔体的加速后，束流的纵向归一化均方根发射度增长仅有25%；同时发现，当流强达到3 mA时，存在空间电荷效应，导致其纵向相宽增长约25%，最大横向包络也存在16.5%的涨落。
In order to improve the operation efficiency of the Cooling Storage Ring of Heavy Ion Research Facility in Lanzhou (HIRFL-CSR), a heavy ion linac (linear accelerator) was proposed and designed as a new injector for HIRFL-CSR. Following the 108.48 MHz Radio-Frequency Quadrupole (RFQ), three tanks in total with Interdigital H-mode drift tube linac (IH-DTL) structure are installed to boost the beam energy from 0.3 to 3.71 MeV/u, and the beam current of ions with charge-to-mass ratio from 1/8.5 to 1/3 can reach to 3 mA. The first tank operatesat the same frequency as the RFQ, and the rest two operate at 216.96 MHz. The “Combined Zero-Degree Synchronous Particle Structure” (KONUS) beam dynamics was used in the beam dynamics design. The overview of the physics design on the main accelerating components, including RF design and beam dynamics design are introduced in this paper. The optimized structure design, fabrication status and simulation results are presented in this contribution. It shows that under the condition of assurance of 95.3% transmission efficiency, the normalized rms emittance is about 25%. When the beam current is up to 3 mA, owing to the space charge effect, the increase of longitudinal phase spread and transverse envelope are about 25% and 16.3%, respectively.
介绍了利用硅探测器的脉冲形状甄别进行粒子鉴别的原理。详细叙述了基于数字化方法的脉冲形状甄别的实现。采样频率和位数是数字化方法的两个重要参数。对于硅探测器信号，采用100 MS/s，12 bit的Digitizer可以满足脉冲形状甄别法对时间分辨的要求。同时对该方法粒子鉴别的特征和能量阈值做了简要的分析和对比。粒子背面入射硅探测器的所得的阈值低于正面入射的情况。例如对于氖周围的同位素，背面入射情况的阈值约为100 MeV，为正面入射情况下鉴别阈值的二分之一，相当与ΔE-E方法中ΔE探测器厚度约为60 μm情况下的阈值。最后定性讨论了硅探测器的电阻率不均匀性和沟道效应对粒子鉴别性能的影响。
In this paper Pulse Shape Discrimination(PSD) for silicon detector has been briefly introduced. The emerging digital method successfully applied to detector signal processing makes digital PSD method one of the most promising particle identification methods. Sampling frequency and the number of bits are two key parameters of digital method. For silicon detector signal, adopting 100 Ms/s, 12 bit Digitizer can satisfy the time resolution requirement of PSD method. The identification characteristic and energy threshold of this method have been discussed and compared with both front injection and rear injection cases. Energy threshold with rear injection usually is much lower than that with front injection. For example, around for Neon isotope energy threshold with rear injection is about 100 MeV which is only half of the threshold with front injection, also equivalent to thickness of about 60 μm silicon detector threshold in ΔE-E method. At the end the impact of silicon detector's resistivity nonuniformity and channel effect on the identification capacity of PSD method has been discussed in detail.
太阳极轨射电望远镜（SPORT）是一颗从事太阳活动研究的卫星。重离子探测仪是其中的高能粒子探测仪的关键组成部分。鉴于重离子探测仪对多种类离子（2 ≤ Z ≤ 26）的鉴别和大范围能段（8～300 MeV/u）的测量需求，中国科学院近代物理研究所设计并研制了一套Si-CsI（Tl）望远镜探测系统样机，这套望远镜系统由1个Si探测器、1个入射面为正六边形的CsI（Tl）晶体及其专用电子学系统构成。利用兰州重离子加速器冷却储存环系统（HIRFL-CSR）提供的高品质束流对这套望远镜探测系统样机进行了在束测试，完成了种类为2 ≤ Z ≤ 18的重离子直接测量与鉴别，利用直接测量的重离子，进行外推得到，最高测量要求的300MeV/u Fe离子也在设计要求的范围内。实验结果显示这套望远镜探测器样机满足空间中对大范围能段重离子探测的设计需求，该套方案为SPORT计划中的重离子探测仪的设计及建造奠定了很好的技术基础。
Solar Polar Orbit Radio Telescope (SPORT) project, aimed at solar activities and solar atmosphere, is a satellite-borne apparatus which is composed by many sub-payloads and is under development in China. High Energy Heavy Ion Telescope (HEHIT) is one of most key sub-payloads in this project, and the main purpose of HEHIT is to identify space heavy ions (2 ≤ Z ≤ 26) with a broad energy range (8～300 MeV/u). In this paper, a prototype telescope of HEHIT, which includes a silicon detector, a CsI(Tl) crystal with regular hexagonal incident plane and customized electronic system, has been developed in the Institute of Modern Physics, Chinese Academy of Sciences (IMP, CAS). To obtain the performance of the prototype telescope, this telescope was tested with high quality beams provided by the accelerator of Heavy Ions Facility and Cooler-Storage-Ring in Lanzhou (HIRFL-CSR). The heavy ions ranging from Z =2 to Z =18 were clearly identified and measured from the beam test and an extrapolation was also done reasonably and it showed that the prototype detector could meet the requirement of t Fe(Z =26) with energy up to 300 MeV/u. In a word, this prototype telescope could satisfy the requirements of the measured heavy ions in the future SPORT project and this scheme of telescope will provide a favorable technique in the future design and construction of HEHIT.
In this paper, the working principle of Si-APD was introduced and the dark current of Si-APD was analyzed theoretically. The intermediate energy heavy ions, which are produced on the RIBLL(Radioactive Ion Beam Line in Lanzhou), were measured with CsI(Tl)+Si-APD detector. The energy resolution of CsI(Tl)+Si-APD detector is about 3% for heavy ions with energy around 20 MeV/u. It is also found that the energy resolution of detector can be in uenced by the dark current of Si-APD and the energy of incident particles.
瞬发γ射线法测量（n，xnγ）反应截面实验中，在线的实验本底对测量结果影响显著，是影响测量结果的关键因素。为了达到降低在线实验本底一个量级的目标，通过蒙特卡罗模拟程序给出了屏蔽体和准直器的改进方案，最终选取的屏蔽方案：在原有屏蔽体上加厚30 cm（C2H4）n+9 cmPb，原屏蔽墙加厚54 cm重混凝土，再在屏蔽体和屏蔽墙上共同加厚2 cm厚的铅（Pb）；准直孔开孔形状在圆柱形、圆锥形和对称双锥形这三种方案中准直效果和能量单一性方面对称双锥形准直孔最好。在屏蔽体改造完成后，利用尺寸为φ5.08cm×5.08 cm型液体闪烁体探测器（BC501）测量了改造后距准直孔右方径向距离70 cm处透射出来的中子和γ射线的相对强度，在扣除无束流天然本底后，有束流的中子本底降低了7.75倍，γ本底降低了38.5倍，改造效果达到了测量要求。
In the experiment of measuring (n,xnγ) reaction cross section with prompt γ ray method, the experiment background has a significant influence on the result and is the key factor. In order to achieve the goal of reducing a certain amount of the experiment background, the improvement scheme of shield and collimator was given through Monte Carlo method and the shielding scheme was finally selected: add 30 cm(C2H4)n+9 cm Pb on the original shield, 54 cm heavy concrete on the original shield wall and then 2 cm thick lead(Pb) on the shield and shield wall. The collimation effect and energy uniformity of symmetrical double cone collimation hole are the best among cylindrical, conical, and symmetrical double cone. After the completion of the transformation of shield, the relative intensities of the transmitted neutron and γ rays from the 70 cm in right radial of the transformed collimation hole were measured with ϕ5.08 cm×5.08 cm type liquid scintillator detector(BC501). After deducting the natural background of no beam current, the neutron background of the beam current is reduced by 7.75 times and the γ background is reduced by 38.5 times, which meets the requirement.
For the research and design of the ADS granular-flow target concept, the Institute of Modern Physics, CAS has developed a Monte Carlo simulation software (GPU-accelerated Monte Carlo Transport program, GMT). In order to improve the computational efficiency of the GMT program, development and application of MPI in GMT were studied, to realize random distribution of the large-scale random number in the sub processes. Rapid reading and writing files were employed instead of the MPI data communication function, which greatly improves the computational efficiency. Different scale calculations were performed to study the relationship of process instance number, speedup to find the maximum acceleration process number and the number of processes when parallel efficiency is highest, which provides a scientific basis for researchers to optimize the computational program between computational resources and computation efficiency. The successful application of MPI in GMT, utilizes the computing resources fully and efficiently, improves the computational efficiency, solve the long time cost and unstable problem of Monte Carlo method in large-scale event simulations, plays an important role in the large-scale scanning calculation of the spallation target.
The Supercritical Water-cooled Reactor (SCWR) is one of the prior Generation IV advanced reactors. Irradiation damage is one of the key issues of fuel cladding materials which will suffer serious environment, such as high temperature, high pressure, high irradiation and supercritical water. The candidate materials contain zirconium alloys, austenitic stainless steels, ferritic/martensitic stainless steels, Ni-base alloys and ODS alloys. Austenitic stainless steels are the most promising materials. This paper summarized the international researches on irradiation effects in fuel cladding materials for SCWR. The group of authors also has done many researches in this field, including nickel-base alloy C-276 and 718, ferritic/martensitic steel P92 and austenitic stainless steel AL-6XN and HR3C. In AL-6XN austenitic stainless steels irradiated by hydrogen ions, dislocation loops were the dominant irradiation defects. At higher irradiation dose (5～7 dpa), the voids were found. All the dislocation loops were confirmed to be 1/3<111> interstitial type dislocation loops, and four evolution stages of dislocation loops with hydrogen retention were suggested.
低活化的铁素体/马氏体钢（RAFM）以其高导热率、低热膨胀率、高抗辐照肿胀能力成为未来核聚变堆重要的候选结构材料，在聚变堆高能中子辐照环境由于（n，α）核反应产生的高浓度He在材料中的积累对于材料微观结构和宏观性能的影响是关系这类材料服役寿命的重要问题。本工作研究了面向聚变反应堆应用的两种国产低活化钢（CLF、CNS）的辐照硬化效应，利用中国科学院近代物理研究所320 kV高压实验平台提供的4He离子束进行辐照实验，辐照剂量6×10-3，6×10-2，6×10-1 dpa （辐照损伤/原子平均离位），对应注He浓度分别为100，1 000，10 000 appm （氦离子浓度/百万分之一）。采用多能注入方法，在样品表面至1微米深度形成He浓度和离位损伤的坪区分布。利用纳米压痕仪对参比样品和注入He的样品进行了连续刚度测试。基于NIX—GAO模型对纳米硬度数据进行分析，获得了注入He的区域样品纳米硬度的数据。研究表明，注入He区域的纳米硬度与辐照损伤水平之间存在着1/2次幂函数的关系。未辐照CLF钢比CNS钢的纳米硬度略低，随着辐照剂量的增加，CLF钢呈现的辐照硬化现象更明显。
Reduced activation ferritic/martensitic steels (RAFM) are important candidate materials for future fusion nuclear reactors because of their high thermal conductivity, low thermal expansion rate and high resistance to irradiation swelling performance. The influence of high concentration helium produced by nuclear reaction (n,α) on the micro-structure and macro-properties is an important issue limiting the service lifetime of the materials. In the present work, helium implantation to three different doses (100, 1 000, 10 000 appm helium, corresponding to 6×10-3, 6×10-2, 6×10-1 dpa) was carried out to investigate irradiation hardening of two RAFM Steels. Multi-energy He ion-beams at 320 kV high-voltage platform were used to get a damage plateau from surface to 1 μm depth in specimens. The continuous-stiffness test by a Nano-indentor G2000 was carried out Data of nano-hardness were analyzed based on Nix-Gao model. It is shown that there is a 1/2-power law relationship between the hardening and the irradiation damage level. Before helium implantation, the hardness of the CLF steel is slightly lower than that of the CNS steel. However, with the increase of helium-implantation dose, the hardening is more obvious in CLF steel. Further investigation of microstructures is needed to get a deeper understanding of the hardening mechanism.
利用0.97 GeV的209Bi离子辐照二硫化钼（MoS2）晶体，辐照注量范围为1×1010～1×1012 ions/cm2，结合原子力显微镜（AFM）观测和Raman光谱分析研究了快重离子辐照对MoS2热导率的影响。实验结果显示，快重离子辐照在MoS2中产生了潜径迹，较高激光功率下的Raman测试使样品局部温度升高，导致E1/2g和A1g峰随注量增加向低波数方向移动，且峰形展宽。引入了通过改变激光功率测量Raman光谱得到MoS2热导率的计算方法，获得了不同辐照注量下MoS2的热导率的定量分析结果，随注量增加，热导率不断降低，从未辐照样品的563 W/mK下降到1×1012 ions/cm2辐照时的132 W/mK。
Molybdenum disulphide (MoS2) was irradiated by 0.97 GeV 209Bi ions with the fluence of 1×1010 to 1×1012 ions/cm2. The irradiation effect on the thermal conductivity of MoS2 was analyzed by atomic force microscope (AFM) and Raman spectroscopy. The experimental results show that hillock-like latent tracks are observed on irradiated MoS2 by AFM. The measurement of MoS2 by Raman spectrometer with high laser power results in the increase of local temperature of MoS2, which cause the downshift of peaks position and broadening of E1/2g and A1g peak. Furthermore, according to Raman spectra measured at different laser power, thermal conductivity of MoS2 before and after irradiation was calculated, which show that the thermal conductivity of MoS2 decreases with increasing fluence, from 563 to 132 W/mK for pristine and 1×1012 ions/cm2 irradiated MoS2, respectively.
Though heavy-ion therapy has demonstrated significant benefits such as well-defined range, small entrance dose and high relative biological effectiveness, the characteristics of radio-biological effects on cancer stem cells induced by heavy-ion treatment is not completely clear. In this paper, we used human glioma cancer stem cells to investigate whether heavy ions offered a biological advantage, by effectively targeting cancer stem cells, in comparison to conventional X-rays. Our results showed that the repair rate of DNA damage generated by 2 Gy of carbon ions was lower than that generated by X-rays in glioma stem cells. MTT assay showed that the viability of cancer stem cells irradiated by carbon ions was significant lower than that irradiated by X-rays. Taken together, carbon ions showed a biological advantage over X-rays by effectively targeting glioma cancer stem cells. These findings have significant importance in understanding the biological effects related to heavy-ion therapy.
The depth-dose distributions of different energy carbon ions provided by the demonstration facility of Heavy Ion Medical Machine (HIMM) in tissue-like medium water were calculated using the MCNPX Monte Carlo simulation code. The results derived from the simulation calculations were compared with those measured in the facility of HIMM and showed good agreement with the bexperimental data. Therefore, the usability of MCNPX for heavy ion transportation in tissue-like medium is verified. The present work also developed a parsed script transfer interface for MCNPX-(CSG) simulation based on ray casting technology and DCVM (Dose Calculation Viewer for MCNPX) code based on the PYDICOM code to convert the DICOM files of compensator and CT phantoms to corresponding CSG files that can be identified by MCNPX. Then modeling of the compensator and CT phantoms of HIMM in MCNPX was successfully performed. The present work provides a basis for MCNPX simulation for the dose distribution of carbon ions shaped by HIMM passive beam distribution system in patient date patient based on CT images.
The Compton profiles of the electron in the ground and excited states of H-like ions have been calculated systematically with one-electron Dirac radial orbitals by using the proper Fourier transformation. Taking the H atom and Xe53+ ion as examples, the effects of relativity and finite nuclear size on Compton profile have been discussed. Furthermore, the dependence of one-electron Compton profile on the principle quantum number n, orbital quantum number l, angular quantum number j and nuclear charge Z has also been discussed. It is found that the relativistic effect can expand the distribution of the Compton profile and split the orbital more and more obviously for given nl(l=0) as increasing Z. However, the relativistic effect can gradually weaken with the increase of the principal quantum number n and orbital quantum number l. Furthermore, the Compton profile of the orbital with quantum number nlj has certain number of platforms that is n-l. In addition, the nuclear finite size hardly affects the Compton profile for H atom and Xe53+ ion.
在中国原子能科学研究院的高压倍加器上利用中子飞行时间方法测量了2.8 MeV中子引起238U裂变的瞬发中子能谱，通过增大样品量和设计合适的屏蔽体提高了效应/本底比，使得测量数据的不确定度满足预期目标（在5.5～14 MeV能区内，能量间隔为0.5 MeV条件下能谱的不确定度小于10%）。将实验几何、中子源能量分布及角分布、探测效率、束流的时间结构等实验条件输入到MCNP程序里，模拟了出射的中子谱，模拟结果与测量结果在不确定度范围内一致，验证了在入射中子能量较低时238>U的裂变瞬发中子谱评价数据的可靠性。
The Prompt Fission Neutron Spectrum (PFNS) of 238U induced by 2.8 MeV neutron was measured using the Cockcroft-Walton accelerator in China Institute of Atomic Energy (CIAE). The signal/background ratio was improved by increasing the amount of sample mass and using an appropriate shielding system. The final uncertainty of neutron energy spectrum in 5.5～14 MeV region is less than 10% with a bin size of 0.5 MeV which has reached this project's anticipation. The experimental geometry, the angular distribution and energy distribution of neutron source, the detection efficiency and time structure of deuteron beam were inputted into the MCNP code to simulate the outgoing neutron spectrum. The simulated results agree with the experimental ones within the uncertainty. The result indicates that the evaluated PFNS for 238U at low neutron energy is reliable.
The gamma production, level production and total inelastic scattering cross sections are calculated at incident neutron energy below 20 MeV. The optical model, the intra-nuclear cascade model, the exciton model (including improved Iwamoto-Harada model), the uni ed Hauser-Feshbach theory and the distorted wave Born approximation theory are used. Theoretical calculated results are compared with the recent experimental data and other evaluated data from ENDF/B-VII, JEFF-3.1, and JENDL-4. It is found that our calculated results agree with the experimental data and the calculated results for some level cross sections are more consistent with the related experimental data than the results from ENDF/B-VII, JEFF-3.1, and JENDL-4 data base.
In an accelerator driven sub-critical (ADS) system, power control in sub-critical reactor is achieved through the control of the beam current. Excore neutron flux monitoring in an ADS system, not only provides indication of reactor power, but also provides important inputs to reactor protection system during startup and power operation, and thus plays a very important role in the control and protection of ADS system. This paper presents the excore neutron flux monitoring method which uses three fission chambers (FCs) and three uncompensated ion chambers (UICs). With three operation modes, pulse mode, current mode, and mean square voltage mode, an FC can monitor reactor power over a wide range from the source range to the intermediate and power ranges. The proposed monitoring method increases the redundancy of independent monitoring channels, improves the reliability of the protection system, and provides more information on axial power distribution. Since these neutron detectors are sensitive to the neutron energy spectrum, we propose an effective calibration method to provide the exact value of neutron flux, i.e., these neutron detectors are calibrated with a standardized neutron source, and then, a correction factor is added in the calibration by comparing the neutron energy spectrum of the neutron source with that in ADS system. Based on Geant4 simulation, the correction factors of 5 and 42 are extracted for FCs and UICs, respectively.
The physical model of the high-energy proton bombarding the tungsten pebble bed spallation target is simulated by the MCNPX program. The effect of the filling rate on the neutronic characteristics with different particle diameters is studied, by calculating the leakage neutron yield, leakage neutron spectrum axial neutron flux distribution and the energy deposition of the target. The result shows that when the diameter increases from 1 to 20 mm,the maximum deposited energy density decreases in the target, but the leakage neutron yield increases. When the filling rate reaches 74%, leakage neutron yields are almost the same value with different particle diameters. When the target is piled up with 1 mm tungsten particles, neutron leakage yield changes smaller with the variation of the filling rate than the other diameter particles which is beneficial to maintain the reactor power stability in ADS.