新同位素235Am的产生与鉴别

一种缺中子新同位素２３５Ａｍ通过２３８Ｐｕ（ｐ,４ｎ）２３５Ａｍ反应而产生．产物借助Ｈｅ－ｊｅｔ系统的传输,快化学分离以及γ、Ｘ射线和γ－Ｘ（γ）符合测量等得到鉴别,测得其半衰期为１５±５ｍｉｎ． A new neutron deficient isotope 235 Am was produced via 238 Pu(p,4n) 235 Am reaction. The products were identified by means of the transporting of He jet system, separating of rapid radiochemical method and measuring of γ and X rays as well as X γ coincidence. The measured half life of 235 Am is 15±5min.     

并合不变中子质子产额比值角分布各向异性与对称能关系的研究

采用ImQMD05模型分析了非对称反应体系40Ar+197Au,124Sn在中低能区（E_beam=35~100 MeV/u）的半擦边反应的条件下的反应机制,并进一步探索了不同模型参数,如对称能斜率、碰撞参数等,对轻粒子并合不变中子质子产额之比角分布各向异性的影响。通过研究发现:对于出射动能大于每核子10 MeV的动力学出射的轻粒子而言,其并合不变的中子质子产额比值角分布各向异性与对称能的软硬具有明显的关联;碰撞参数对轻粒子动力学发射各向异性的影响最弱。By using the ImQMD05 code,we simulate the 40Ar+197Au,+124Sn at beam energy of 35,50 and 100 MeV/u and semi-peripheral collisions.The reaction mechanism,symmetry potential and Coulomb potential competition around the overlapped neck region and impact parameters effects are investigated for understanding the angular distribution of isospin contents of dynamical emitted light particles.Our results show that the angular anisotropy of the coalescence invariant neutron to proton yield ratios is sensitive to the stiffness of symmetry energy,especially for the dynamical emitted light particles with E_k>10 MeV.     

The influence of Isospin Dependence of In-Medium NN Cross Sections on the Ratio of Emitted Neutrons to Protons in HICs

The influence of isospin dependence of in-medium nucleon-nucleon cross sections on the nip ratios for emitted nucleons in reactions 96Zr-j-96Zr and 96Ru-j-96RH at Eb z 400 AMeV is investigated by means of an improved quantum molecular dynamics model. Our results show that the high energy part of the spectra of the n//p ratios for emitted nucleons is sensitive to the isospin dependence of in-medium nucleon-nucleon cross sections for neutron-rich reaction systems. Therefore, we propose that the nip ratio of emitted high energy nucleons in a very neutron-rich reaction system at several hundreds of AMeV can be taken as sensitive observables to constrain the isospindependence of in-medium nucleon-nucleon cross sections.     

替代反应法测量锕系核(n,f)和(n,xn)截面

对于某些中子反应截面,在直接测量上存在困难。为了获得那些对核能发展极其重要的核数据,人们提出替代反应法,即利用带电粒子代替中子进行反应,从而实现中子反应截面间接测量的方法。现有替代反应一般采用非弹激发、转移等周边反应,涉及的角动量远比中子反应的大,需要理论修正,这造成了一定的困难。有鉴于此,提出利用轻带电离子的俘获反应作为替代反应,其复合核自旋与中子反应的相当,有效避免了自旋修正的困难。根据这个思路,采用236U的（α,f）和（α,2n）反应作为替代反应,成功提取了239Pu的（n,f）和（n,2n）反应截面,与ENDFB7评价库数据在误差范围内符合较好,表明了替代反应法的优越性,可以在核数据测量中推广应用。There are always difficulties in the direct measurement of reactions induced by neutron, in order to obtain the neutron induced nuclear reaction data which are extremely important for nuclear power development, the surrogate reaction method, which uses charged particles instead of neutron, was proposed. The existing surrogate reaction method generally chooses peripheral reaction as the surrogate reaction, such as inelastic scattering excitation or transfer reaction. As a result, the angular momentum involved is always far larger than the neutron induced reaction, which causes difficulties in the theoretical calculation. Because of this, we proposed to use light-ion capture reaction as the surrogate reaction, the compound nuclei spin is similar with that of the neutron induced reaction, so that the difficulties in spin correction can be effectively avoided. Based on this idea, the 239Pu(n, f) and (n, 2n) reaction cross sections were successfully extracted using 236U(α,f) and (α,2n) reactions as the surrogate reaction. The results coincide well with the data of ENDFB7 within the error range, which shows that the surrogate reaction method has its own superiority, and it can be applied in the measurement of nuclear data.     

中子注量率波动修正因子及其应用

在中子核反应研究中,尤其是在利用活化法进行中子核反应截面测量研究时,需要准确测量样品辐照的中子注量。监督反应标准截面法简便可行,在一些核反应截面测量研究中经常用来定量样品辐照的中子注量。在利用监督片核反应剩余核的放射性活度计算平均中子注量率时,中子注量率波动修正因子是一个很重要的参数。对中子注量率波动修正因子进行了详细阐述,通过理论推导给出了中子注量率波动修正因子的定义,从实际应用出发讨论了中子注量率波动修正因子的使用条件和监督反应的选择原则。Incident neutron flux has to be measured accurately in the neutron reaction study especially in the neutron reaction cross-section measurement with activation method. Average neutron flux in the irradiated sample is usually determined by the monitor reaction with reference cross-section values. However, the average incident neutron flux, based on the radioactivity of the residual nuclei produced in the monitor reaction, is dependent upon the neutron flux fluctuation. In the procedure of the average neutron flux calculation, the correction factor for the neutron flux fluctuation plays a key role. In this paper, definition of the neutron flux fluctuation correction factor is inferred heoretically. The selection principles of the monitor reaction and the utilization of the correction factor have been discussed.     

Multiplicities of forward-backward particles in ^16O-emulsion interactions at 4.5 AGeV/c

An exclusive study of the characteristics of interactions accompanied by backward emission（θlab 90°） of shower and grey particles in collisions of a 4.5 AGeV/c ^16O beam with emulsion nuclei is carried out. The experimental multiplicity distributions of different particles emitted in the forward（θlab 〈 90°） and backward hemispheres due to the interactions with the two emulsion components（CNO,AgBr） are presented and analyzed. The correlations between the different emitted particles are also investigated. The results indicate that there are signatures for a collective mechanism,which plays a role in the production of particles in the backward hemisphere. Hence,the backward multiplicity distribution of the emitted shower and grey particles at 4.5 AGeV/c incident momentum can be represented by a decay exponential law formula independent of the projectile size. The exponent of the power was found to increase with decreasing target size. The experimental data favor the idea that the backward particles were emitted due to the decay of the system in the latter stages of the reactions.     

Hyperon Dynamics in Heavy-Ion Collisions near Threshold Energy

Within the framework of quantum molecular dynamics transport model,the isospin and in-medium effects on the hyperon production in the reaction of ~(197)Au+~(197)Au are investigated thoroughly.A repulsive hyperon-nucleon potential from the chiral effective field theory is implemented into the model,which is related to the hyperon momentum and baryon density.The correction on threshold energy of the elementary hyperon cross section is taken into account.It is found that the Σ yields are suppressed in the domain of midrapidity and kinetic energy spectra with the potential.The hyperons are emitted in the reaction plane because of the strangeness exchange reaction and reabsorption process in the nuclear medium.The Σ~-/Σ~+ ratio depends on the stiffness of nuclear symmetry energy,in particular in the high-energy region(above 500 MeV).     

Angular Distribution of the 12C（6He, 7Li）nB Reaction

Angular distribution of the 12C（6He, 7Li）llB transfer reaction is measured with a secondary 6He beam of 36.4 MeV for the first time. The experimental angular distribution is well reproduced by the distorted-wave Born approxima- tion （DWBA） calculation. The success of the present experiment shows that it is feasible to measure one-nucleon transfer reaction on a light nucleus target with the secondary beam facility of the 1-11-13 tandem accelerator at China Institute of Atomic Energy （CIAE）, Beijing.     

Investigation of KTiOPO4 nanocrystals by means of second-harmonic light emission

The finding of nonlinear nanometric-sized probes is of key importance for the development of nonlinear microscopy in physical as well as biological sciences. We isolate nonlinear KTiOPO4 nanocrystals and study them by second-harmonic generation microscopy （SHGM） and atomic force microscopy （AFM） independently. With both polarization analysis and defocused imaging of the emitted second harmonic field, we extract the Euler angles of the crystalline axes of a single nanocrystal. A balanced coherent optical homodyne detection shows the coherent nature of the nanocrystal nonlinear emission and allows a phase measurement of the emitted second-harmonic field. These features make the KTiOPO4 nanocrystal a good candidate for a vectorial probe of electromagnetic near fields.     

Study of the H＋HS reaction on a newly built potential energy surface using the quasi-classical trajectory method

<正>The quasi-classical trajectory（QCT） method is used to study the H+HS reaction on a newly built potential energy surface（PES） of the triplet state of H₂S（³A″） in a collision energy range of 0-60 kcal/mol.Both scalar properties, such as the reaction probability and the integral cross section（ICS）,and the vector properties,such as the angular distribution between the relative velocity vector of the reactant and that of the product,etc.,are investigated using the QCT method.It is found that the ICSs obtained by the QCT method and the quantum mechanical（QM） method accord well with each other.In addition,the distribution for the product vibrational states is cold,while that for the product rotational states is hot for both reaction channels in the whole energy range studied here.     

相对论下二体反应出射粒子的能量

利用洛伦兹变换，画出了相对论下二体反应实验室系和动心系出射粒子动量的关系图，并利用关系图，对不同情况下的出射粒子能量分布作了讨论，最后导出相对论下的Ｑ方程出出射粒子动能表达式。     

Effect of radiative transfer of heat released from combustion reaction on temperature distribution: A numerical study for a 2-D system

Both light and heat are produced during a chemical reaction in a combustion process, but traditionally all the energy released is taken as to be transformed into the internal energy of the combustion medium. So the temperature of the medium increases, and then the thermal radiation emitted from it increases too. Chemiluminescence is generated during a chemical reaction and independent of the temperature, and has been used widely for combustion diagnostics. It was assumed in this paper that the total energy released in a combustion reaction is divided into two parts, one part is a self-absorbed heat, and the other is a directly emitted heat. The former is absorbed immediately by the products, becomes the internal energy and then increases the temperature of the products as treated in the traditional way. The latter is emitted directly as radiation into the combustion domain and should be included in the radiation transfer equation (RTE) as a part of radiation source. For a simple, 2-D, gray, emitting-absorbing, rectangular system, the numerical study showed that the temperatures in reaction zones depended on the fraction of the directly emitted energy, and the smaller the gas absorption coefficient was, the more strong the dependence appeared. Because the effect of the fraction of the directly emitted heat on the temperature distribution in the reacting zones for gas combustion is significant, it is required to conduct experimental measurements to determine the fraction of self-absorbed heat for different combustion processes.     

中高能质子与核碰撞反应机制的研究

用量子分子动力学模型,在质子能量为200MeV、585MeV和1000MeV的情况下,对P+⁵⁶Fe的碰撞反应机制进行了研究,并计算了核子能谱、碎块质量分布随时间的演化以及中子发射的双微分截面等,得到了合理的结果.     

Excited state production and temperature measurement in a heavy ion reaction

An effective temperature inferred from the slope of kinetic energy spectra of the emitted fragments is not reflected in the relative populations of excited states of the emitted nuclei. We found that the excited state populations of ⁶Li, ⁷Li and ⁷Be emitted near 90° in the lab from the reaction of 490 MeV ¹⁴N with Ag are significantly lower than those expected on the basis of their effective temperature.     

Study of the Reaction Mechanisms Induced by 16O on 64Ni at 96MeV

The angular distributions and Wilczynski plots of emitted fragments from He to O in reaction of ¹⁶O+⁶⁴Ni at 96MeV have been measured.The DIC cross section and intereaction time were obtained.DIC character of the reaction was discussed.The trace which shows that the emitted fragments of He and Li mainly come from the evaporation process of compound nuclei emerged.     

α PARTICLES EMITTED IN THE REACTION OF 12C ON 209Bi

The energy spectra and angular distributions of alpha particles emitted in the reaction of 12C on 209Bi in the energy range 61.1—73.0 MeV were observed.The △E— E detector system was used to separate alpha particles and other particles emitted in this reaction.The results can be interpreted in terms of the reaction mechanism,in which a 8Be cluster is transfered from the projectile to the target.Good agreement has been obtained between the cross section for the production of the direct alpha particles and that of the heavy residue 217*Fr which,left in the ground state after evaporation of 2 neutron's,decays into 211At by alpha emission.The experimental energy spectra and angular distributions have been fitted by a semi-classical formula for the differential cross section per unit solid angle and energy interval.     

Analysis of some Elements in Fuel Oil by using Neutron Capture Gamma Ray Spectroscopy

The analysis of some elements in fuel oil was done by using neutron capture gamma ray spectroscopy. The gamma rays emitted after the reaction of (n, γ) from the fuel oil atoms bombarded with the thermal neutrons emitted from a ²⁵²Cf source were investigated in the energy interval 0 … 10 MeV. The impurity elements in the sample were determined.     

致密双星后牛顿偏心轨道的引力波研究

本文主要研究非保守的后牛顿哈密顿自旋致密双星偏心轨道的引力辐射,数值比较保守的和非保守的自旋致密双星系统轨道参量偏心率大小与 引力波形的关系及引力辐射耗散效应项对轨道动力特性的影响. 数值研究表明：由于系统能量积分被保持,保守的双星轨道偏心率值改变对时域引力波形变化影响不是很明显,但辐射的引力波频率分布范围随着偏心率的增大而扩大. 而当运动方程中包含2.5PN引力耗散效应项时,由于引力辐射时伴随着能量和角动量损失,导致双星两体之间的距离和轨道偏心率逐渐衰减,轨道动力特性变得更加复杂. 双星旋进合并过程中辐射的引力波受到轨道偏心率的调制,引力辐射的强度随着偏心率的增大而增强,而引力辐射持续的时间缩短,且自旋与自旋耦合效应项对引力的贡献增大了. 关键词： 非保守的 引力辐射 耗散 偏心率     

The angular distribution of the 12C(γ,pn) reaction for Eγ=120−150 MeV

The angular distribution of nucleons emitted in the ¹²C(γ,pn) reaction has been measured using tagged photons at the Mainz microtron MAMI. The variation of the reaction strength with the polar angles of the two emitted nucleons is reported for E_γ=120−150 MeV. The proton angular distribution peaks at more backward angles than the ²H(γ,p) differential cross section indicating a departure from the simple quasi-deuteron model of 2N photo-emission. The distribution shape is in reasonable agreement with microscopic theoretical models which include both π- and ρ-exchange. Received: 3 September 1997 / Revised version: 17 December 1997