~(19)F+~(27)Al耗散反应产物激发函数的长程关联

在中国原子能科学研究院的HI-13串列静电加速器上完成了19F+27Al耗散反应产物的激发函数测量。束流19F的入射能量从110.25MeV到118.75MeV,步长250keV,测量了实验室系+57°,+31°,-15°和-29°出射的类弹产物B,C,N,O,F和Ne的激发函数。观测到激发函数具有耗散反应的特征涨落结构,分析了激发函数之间的长程角度关联以及强烈的电荷数关联。

~(19)F+~(27)Al耗散反应中双核系统的转动与形变

测量了19F+27Al耗散反应产物B,C,N,O,F和Ne的激发函数,入射束流的能量从110．25MeV 到118．75MeV,能量步长为250keV．从产物的能量自关联函数中提取了反应中所形成的中间双核系统的转动惯量,与相粘模型计算的刚体转动惯量相比较,结果表明形成的双核系统有大的形变．

(19)~F+(27)~Al耗散反应中双核系统的转动与衰变

测量了19F+27Al耗散反应产物B,C,N,O,F和Ne的激发函数,入射束流的能量从110.25MeV 到118.75MeV,能量步长为250keV.用能量自关联函数方法从激发函数中提取了各反应产物的平均衰变宽度,利用同时考虑反应中所形成的中间双核系统的转动特性和衰变特性而发展了的Ericson核反应统计理论,讨论了19F+27Al耗散反应中双核系统随时间的演化过程.

Influence of in-medium nucleon-nucleon cross section on the isoscaling parameter alpha

The influence of in-medium nucleon-nucleon cross section on the isoscaling parameter a is investigated for two couples of central nuclear reactions Ca-40 + Ca-40 and Ca-60 + Ca-40; Sn-112 + Sn-112 and Sn-124 + Sn-124 within the isospin dependent quantum molecular dynamics. The calculated result shows that the influence of the in-medium nucleon-nucleon cross section on the isoscaling parameter a is mainly determined by the corresponding number of collisions, both for isospin dependent and isospin independent parameterizations. The mechanisms behind the effects of the in-medium nucleon-nucleon cross sections on the alpha are investigated in more details.

Isoscaling parameter a as a possible probe of medium effect of nucleon-nucleon cross section

The medium effect of nucleon-nucleon cross section sigma(med)(NN) (alpha(m)) on the isoscaling parameter a is investigated for two central nuclear reactions Ca-40+Ca-40, Ca-60+Ca-60. within isospin-dependent quantum molecular dynamics at beam energies from 40 to 50 MeV/nucleon. It is found that there is the very obvious medium effects of nucleon-nucleon cross section sigma(med)(NN)(alpha(m)) on the isoscaling parameters a. In this case the isoscaling parameter a is a possible probe of the medium effect of nucleon-nucleon cross section sigma(med)(NN)(alpha(m)) in the heavy ion collisions. The mechanism of the above-mentioned properties is studied and discussed.

beta-delayed proton decays of Sm-133 and Yb-149

Sm-133 was produced via fusion evaporation in the reaction Ca-40+Ru-96. Its P-delayed proton decay was studied by means of "p-gamma" coincidence in combination with a He-jet tape transport system, including half-lives, proton energy spectra, gamma-transitions following the proton emissions, and the branching ratios to the low-lying states in the grand-daughter nuclei. The possible spins and parities of 133Sm were extracted by fitting the experimental data with a statistical model calculation. The configuration-constrained nuclear potential energy surfaces of Sm-133 were calculated by using the Woods-Saxon Strutinsky method. Comparing the experimental and calculated results, the spins and parities Of Sm-133 were assigned to be 5/2(+) and 1/2(-), which is reconciled with our published simple (EC+beta(+)) decay scheme Of Sm-113 in 2001. In addition, our experimental data on the beta-delayed proton decay of Yb-149 reported in Eur. Phys. J., 2001, A12: 1-4 was also analyzed by using the same method. The spin and parity of Yb-149 was assigned to be 1/2-.

Rotation and deformation of the dinuclear system formed in dissipative reaction of F-19+Al-27

Excitation functions of the reaction products B, C, N, O, F and Ne emitted from the dissipative reaction of (19) F+(27) Al have been measured at incident energies from 110.25MeV to 118.75MeV in steps of 250keV. The moments of inertia of the intermediate dinuclear system formed in the reaction are extracted from the energy autocorrelation functions of the products. Comparing the moment of inertia extracted from the experimental data with the calculated one by using the sticking limit, it indicates that the formed dinuclear system has a large deformation in the reaction process.

beta-delayed proton decays of Tb-140 and Dy-140 as well as the spin and parity of Dy-143

Tb-140 and Dy-141 were produced via fusion evaporation in the reaction Ca-40+Cd-106. Their beta-delayed proton decays were studied by means of "p-gamma" coincidence in combination with a He-jet tape transport system, including half-lives, proton energy spectra, gamma-transitions following the proton emissions, and the branching ratios to the low-lying states in the grand-daughter nuclei. The ground-state spins and parities of Tb-140 and Dy-141 were extracted as 7(+/-) and 9/2(+/-), respectively, by fitting the experimental data with a statistical model calculation. The configuration-constrained nuclear potential energy surfaces (NPES) of Tb-140 and Dy-141 were calculated by using the Woods-Saxon Strutinsky method, which indicate the ground-state spins and parities of Tb-140 and Dy-147 to be 7(+) and 9/2(-), respectively. In addition, the configuration-constrained NPES of Dy-143 was also calculated by using the same method. From the NPES a 1/2(+) ground state and a 11/2(-) isomer with the excitation energy of 198keV were found. The calculated results are consistent with our experimental data on the decay of Dy-143 reported in Eur. Phys. J., 2003, A16: 347-351.

beta-delayed proton decays and spin assignments for Tb-140, Dy-141 and Dy-143

The proton-rich isotopes Tb-140 and Dy-141 were produced via the fusion evaporation reaction Ca-40+ Cd-106. Their beta-delayed proton decays were studied by p-gamma coincidence in combination with a He-jet tape transport system, and half-lives, proton energy spectra, gamma-transitions following the proton emission, as well as beta-delayed proton branching ratios to the low-lying states in the grand-daughter nuclei were determined. Comparing the experimental data with statistical model calculations, the ground-state spins of Tb-140 and Dy-141 were found to be consistent with 7 and 9/2, respectively. The configuration-constrained nuclear potential energy surfaces (NPES) of Tb-140 and Dy-141 were calculated using the Woods-Saxon-Strutinsky method, which suggest the ground-state spins and parities of Tb-140 and Dy-141 to be 7(+) and 9/2(-), respectively. In addition, the configuration-constrained NPES of Dy-143 were calculated, which predict a 1/2(+) ground state and a 11/2(-) isomer with excitation energy of 198 keV. These findings are consistent with our previous experimental data on Dy-143 reported in Eur. Phys. J. A 16, 347 (2003).

Medium effect of nucleon-nucleon cross section on the isoscaling parameter alpha

The medium effect of in-medium nucleon-nucleon cross section sigma(med)(NN) (alpha(m)) on the isoscaling parameter a is investigated for two couples of central nuclear reactions Ca-40 + Ca-48 and Ca-60 + Ca-48; Sn-112 + Sn-112 and Sn-124 + Sn-124 at beam energy region from 40 to 60 MeV/nucleon with isospin dependent quantum molecular dynamics. It is found that there is the obvious medium effect of sigma(med)(NN) (alpha(m)) on the isoscaling parameters alpha. The mechanism for the medium effect of sigma(med)(NN) (alpha(m)) on a is investigated.

Influences of the isospin-dependence of in-medium nucleon nucleon cross-section and momentum dependent interaction on isoscaling parameter

Influences of the isospin-dependent in-medium nucleon nucleon cross-section (sigma(iso)(NN) and momentum-dependent interaction (MDI) on the isoscaling parameter a are investigated for two central collisions Ca-40 +Ca-40 and Ca-60+ Ca-60. These collisions are with isospin dependent quantum molecular dynamics in the beam energy region from 40 to 60 MeV/nucleon. The isotope yield ratio R-21 (N, Z) for the above two central collisions depends exponentially on the neutron number N and proton number Z of isotopes, with an isoscaling. In particular, the isospin-dependent (sigma(iso)(NN) and MDI induce an obvious de crease of the isoscaling parameter a. The mechanism of the decreases of a by both sigma(iso)(NN) and MDI are studied respectively.

Development of multi-channel gated integrator and PXI-DAQ system for nuclear detector arrays

A multi-channel gated integrator and PXI based data acquisition system have been developed for nuclear detector arrays with hundreds of detector units. The multi-channel gated integrator can be controlled by a programmable Cl controller. The PXI-DAQ system consists of NI PXI-1033 chassis with several PXI-DAQ cards. The system software has a user-friendly GUI which is written in C language using LabWindows/CVI under Windows XP operating system. The performance of the PXI-DAQ system is very reliable and capable of handling event rate up to 40 kHz. (C) 2010 Elsevier B.V. All rights reserved.

同中子素核9C、8B、7Be和6Li在中能区与28Si反应总截面的测量

放射性束流(RIB)装置拓广了实验核物理在同位旋(T_z)自由度上从稳定核直到滴线核的广袤空间。通常，位于β-稳定线及其附近的核，N／Z在1－1.5范围变化，其分离能E_s无论对于质子还是中子，总是在6-8 MeV之间；对于远离稳定线的非稳定核，N／Z可在0.5-4范围变化，如~9C的N／Z = 0.5，~(10)He的N／Z = 4，而且分离能E_s是在0-40 MeV之间变化的，开展对这些远离β-稳定线非稳定核性质、结构的研究是目前核物理的前沿之一。核反应总截面σ_R是表征原子核性质特征的一个基本物理量，从实验测得的核反应总截面中可以得到有关核结构和核内核子分布的信息。在由放射性束流所产生奇异核的结构与各种反应机制研究中，反应总截面的测量更是有其特殊的重要性，具有奇异核结构如晕核的一个典型的物理特征就是其反应总截面要比稳定核大得多，Tanihata等人最早就是通过对放射性束流的相互作用截面的测量发现了具有奇异结构的核，即中子晕核。由于反应总截面的测量对探测器的要求不高，而且数据分析过程相对较为简单，因而反应总截面的测量已经成为放射性束核物理的研究的一个非常重要实验手段。中子晕核以及中子皮核的发现促使人们去寻找质子晕核和质子皮核，由于最后一个质子的结合能非常小只有136，keV，并且有较大的电四极矩，因而使得~8B成为质子晕的最大热门候选核，有关~8B是否具有质子晕核结构的问题，许多实验科学家得出了相互矛盾的回答；而目前有关另外一个质子晕候选核~9C的实验数据非常少，目前还没有人从实验上对~9C是否为质子晕核这一问题进行肯定或否定的回答。因此非常有必要测量~9C和~8B的反应总截面。对反应总截面进行研究的一个非常有用理论就是Glauber模型，该模型考虑了库伦效应的多次散射理论。它是一种基于自由核子-核子(N-N)碰撞的与核物质密度相关的理论，因而能够从实验测量到的反应总截面中提取核物质分布的信息。该理论对中低能区的反应总截面描述却有一个缺憾：理论值比实验值都要小。本论文主要描述了利用透射法测量了中能区同中子素核~9C、~8B、~7Be及~6Li与~(28)Si的反应总截面，并介绍了重离子碰撞以及描述重离子性质的几种常用理论。在论文里对实验测量得到的结果进行了理论分析，这些理论包括半经验的Shen公式、Glauber模型、BUU模型以及SHF理论。如果将~9C和~8B当成具有正常核结构来处理，半经验的Shen公式和Glauber模型(HO密度分布)的理论计算值总是比实验值要小得多；对于Glauber模型的理论计算值和实验值的差异，Ozawa等定义了一个差值因子d，方德清等人对轻核系统的d值进行了详细的分析。一般认为，正常核的d值在20％以内，而对于具有晕或皮奇异结构的核，其d值则超过30％，甚至可达50％，因此可根据一个核的d值是否超过30％而且比相邻核的d值明显大这种半经验的方法来判断一个核是否具有奇异结构；利用d值的分析结果，我们认为：~9C和~8B都具有奇异核结构；对于BUU模型用同样的方法引进差值因子d值，对于~9C和~8B有相同的结论。用SHF理论计算得到B和C同位素的密度分布结果显示，~9C和~8B的密度分布比相邻的同位素扩展都要大得多。为减小Glauber模型计算的反应截面与实验值的差别，本论文还对Glauber模型的输入密度形式进行了修改，在原单一HO分布基础上加一个高斯分布的尾巴，并对丰质子的同中子素核~9C、~8B、~7Be及~6Li与~(28)Si靶以及~(12)C和丰中子的C同位素核~(13-16)C与~(12)C靶的反应截面重新进行了计算，结果显示在中能区的计算值比原来单一密度分布的计算结构有明显改善。

10～100 MeV/u能区重离子反应机制的研究

把QMD模型扩展至10～100MeV/A能区，研究了该能区的重离子碰撞，并仔细检验了初始核在基态时传播的稳定性条件。~(40)Ca+~(40)Ca���统，在10 ～ 100MeV/A能区范围内研究了重离子反应机制随入射能量及碰撞参数的演化情况。我们发现，反应机制随能量的变化并不是突然的跃迁，而是一个连续的变化过程，不同的反应机制可以同时存在并发生竞争。在中心碰撞时，反应机制从全融合发展至非全融合，最后演化至碎裂机制。在周连碰撞时，随着入射能量的增加，根据我们提出的关于深部非弹碰撞和参加者－旁观者质量分布的判据，反应机制的可能变化趋势为从非完全融合或深部非弹碰撞到参加者－旁观者，最后发展至碎裂反应。我们知道，目前还没有人用QMD模型来研究过渡能区DIC机制的基本特征，我们还对~(20)(25Mev/A)+~(20)Ne系统周边碰撞时DIC机制的基本特征作了研究，计算结果表明：在中能区，DIC机制仍然存在，同时，在质量分布、旋转效应及能量损失方面具有低能时相同的特征，但与低能DIC的明显差别在于，出射的中间质量碎片已成为质量分布的主要部分，出射的轻粒子数目也相对增多。当碰撞参数小于7fm时，这里存在着不同反应机制的共存及竞争。根据质量分布随时间的演化情况，我们发现，中间质量碎片主要是由动力学过程中平均场涨落引起的动力学不稳定性造成的，统计衰变也贡献较小的一部分。由粗糙估计可以看出，25MeV/A时~(20)Ne+~(20)Ne系统的DIC机制仍然是一个趋向于平衡过程。相又于低能区，中能区的周边碰撞显得相当复杂

中能重离子碰撞中的涨落和中间质量碎片发射的机制

在QMD模型的基础上，系统研究了~(40)Ca+~(40)Ca���心碰撞系统能量从10MeV/A～120MeV/A变化时，碎块形成的几何结构、密度分布的二矩随时间的演化，平均中间质量碎片、相对涨落与能量的关系以及反应机制的跃迁，并由此确定了碎裂的时间尺度。对~(197)Au+~(197)Au系统在200MeV/A的入射能量下的阶乘矩的计算，清楚地观察一了阵发混沌的存在，并对临界现象做了初步的讨论。