实验验证激发能在3MeV/u的热核级联通过断点进行裂变

用相对库仑速度的最小化过程来分析热核三块大质量碎片出射的衰变过程,用它处理Ar(25MeV/u)+Au、Bi、Tb反应,对中心碰撞形成的激发能为3MeV/u热核出射的三重裂变碎片进行运动学分析,数据处理的结果显示了关联的三大质量碎片是来源于级联的二体分裂,同时质心系三裂变碎片平面的法线角分布与级联通过断点的裂变假设下的角分布相符.     

40Ar+197Au(25MeV/u)产生的热核激发能与核温度的关系

对25MeV/u ⁴⁰Ar+¹⁹⁷Au反应系统裂变与后角轻粒子发射进行了符合测量,用裂变碎片折叠角和裂变碎片的飞行时间再构转移到类熔合核的线性动量.通过对线性动量转移和轻带电粒子能谱测量,给出从中心碰撞到周边碰撞产生的类熔合核的初始激发能、角动量和核温度,讨论它们的关系.发现了中心碰撞形成的类复合核的核温度已经接近饱和状态,接近多重碎裂的“准相变区”.     

中能区86Kr+197Au反应中的能量耗散、π介子阈下产生和流角

用扩展BUU模型计算了中能区⁸⁶Kr+¹⁹⁷Au重系统的能量耗散、π介子阈下产生和流角,定量地拟合了43MeV/u ⁸⁶Kr+¹⁹⁷Au实验的能量耗散和类弹碎片核电荷数的关系及类弹类靶碎片核电荷数的关联.     

中能区40Ar+197Au反应中轻粒子的发射时间测量

本文报道了25MeV/u ⁴⁰Ar+¹⁹⁷Au反应中粒子-粒子关联函数的实验结果.利用三体弹道模型从关联函数提取了轻粒子发射时间.轻粒子的平均发射时间随粒子能量而变化,从低能时的约300fm/c下降至高能时的约100fm/c.     

25MeV/u 40Ar+natAg、209Bi反应中热核的温度和激发能测量

在25MeV/u ⁴⁰Ar+^natAg、²⁰⁹Bi反应中,用4个PPAC和11组望远镜完成了关联裂变碎片与发射轻粒子的符合测量,角关联描绘为两个被探测到碎片折叠角θ_ff的函数,线性动量转移〈LMT〉由测量到的角关联推出.将符合测量得到的对应于不同窗的后角轻带电粒子能谱用Maxwell分布来拟合其谱的后沿,经过一些修正,由能谱得到热核的初始温度T_int,在考虑反应Q值和预平衡发射的修正之后,可以得到不同窗所对应的激发能.实验结果表明,在⁴⁰Ar+^natAg、²⁰⁹Bi反应的中心碰撞中激发能分别为4.2、2.4MeV/u,而温度达6.1、5.5MeV,在半中心碰撞中激发能为3.5、1.9MeV/u,温度可达5.8、4.8MeV.     

轻粒子发射时间随测量角的变化

利用小相对角关联方法测量了25MeV/u⁴⁰Ar+⁹³Nb反应中关联出射的轻粒子.通过与三体弹道模型的比较,从关联函数提取了轻粒子的发射时间.结果表明,轻粒子的发射时间随粒子能量的升高而降低,从低能的约600fm/c下降至高能的约50fm/c.将此数据与⁴⁰Ar+¹⁹⁷Au反应中的发射时间进行了比较,发现随着实验室系角度的增加,提取的轻粒子的发射时间变长,并认为其原因在于随发射角度的增加,前平衡发射成份越来越少,平衡发射成份增加.     

25MeV/u 40Ar引起的反应中碎片同位素分布的研究

本文描述了25MeV/u ⁴⁰Ar+²⁷Al、⁵⁸Ni、¹¹⁵In反应中在小角区方向测得的出射碎片同位素分布及其产额,给出了出射碎片的中子数与质子数之比(N/Z)和靶核的关系. 并对出射碎片的来源进行了分析.     

35MeV/u 40Ar+197Au反应中热核的统计发射研究

利用硅半导体+CsI(T1)闪烁体望远镜测量35MeV/u ⁴⁰Ar+¹⁹⁷Au中发射的轻带电粒子,用能谱斜率方法和双同位素产额比方法提取了核温度参量.研究了热核发射过程中的统计发射规律.     

25MeV/u 40Ar+209Bi裂变反应的断点激发能和裂变时标测量

对25MeV/u ⁴⁰Ar+²⁰⁹Bi非完全熔合反应中形成的热核,测量了与裂变碎片相符合的α粒子能谱,用运动源模型分解α粒子能谱得到了裂变断前和断后发射α粒子多重性.由断后碎片发射α粒子多重性得到断点激发能约为172.5MeV.由断前α粒子多重性得到激发能在470—600MeV范围内的热核的裂变时标约为4×10^－21S.     

25MeV/u 40)Ar+209Bi裂变反应研究

实验对25MeV/u ⁴⁰Ar+²⁰⁹Bi体系的裂变反应,利用线性动量转移的分窗选择不同的激发能,研究裂变动能分布和质量分布与热核初始激发能的关系.实验证实激发能小于380MeV时裂变总动能分布与低激发能复合核相似.激发能大于380MeV时,最可几动能呈现出随激发增加而增加,并出现高能非对称性,而且质量分布宽度随激发能增加而迅速增大.     

Studies of light-charged particle emission in fission at Trombay

Studies of prompt radiations emitted in fission were started at Trombay in the late 1950’s by Dr R Ramanna and over the years extensive investigations on the emission of prompt neutrons, gamma ray and K x-rays in fission were carried out with neutron beams fromapsara andcirus reactors. In the early 1960’s studies on the emission of light-charged particles in fission, which is a rare mode of fission, were also started. This paper reviews some of the recent studies on the emission of light-charged particles (lcp) in fission which were carried out with a view to investigate the mechanism oflcp emission, the scission configuration and the dynamics of the last stages of the fission process.     

Unified fission model for proton emission

The unified fission model (UFM) combining with the phenomenological assault frequency has been carried out to investigate the proton-radioactivity half-lives of spherical proton emitters. The results are in good agreement with the experimental data and other theoretical values, and newly observed spherical proton emitters have been analyzed. Finally, the effect of angular momentum transfer on half-life of proton emission has been discussed in detail and a formula can be used to describe this relationship.     

超重复合核的存活概率

考虑角动量相关性的情况下计算了超重核259Db的裂变位垒Bf.计算了258Rf,259Db,266Hs和267Mt 4个超重核单中子蒸发的存活概率Wsur及其随角动量分波的变化关系.给出了中子蒸发宽度、裂变宽度和超重核蒸发一个中子的概率对激发能与角动量分波的依赖关系. Considering the dependence on angular momentum， the fission barriers of super heavy nuclei 259Db have been calculated. The survival probability for 258Rf， 259Db，266Hs，267Mt compound and its relation with angular momentum have been estimated. The neutron emission width， the fission width and the realization probability for one neutron emission and their relation with excitation energy and angular momentum are also presented.     

Unified fission model for proton emission

The unified fission model （UFM） combining with the phenomenological assault frequency has been carried out to investigate the proton-radioactivity half-lives of spherical proton emitters. The results are in good agreement with the experimental data and other theoretical values, and newly observed spherical proton emitters have been analyzed. Finally, the effect of angular momentum transfer on half-life of proton emission has been discussed in detail and a formula can be used to describe this relationship.     

Possible reference method of total excitation energy partition between complementary fission fragments

A method of total excitation energy (TXE) partition between fully-accelerated fission fragments based exclusively on the systematic behaviour of experimental ν(A) (νH/νpair as a function of AH being parameterized) is proposed. This TXE partition method has the advantage to be not dependent on models and assumptions made at scission and in this sense it can be taken as a possible reference method. From this TXE partition applied on many fissioning systems a general parameterization of the fragment residual temperature ratio RT=TL/TH as a function of AH is obtained, giving the possibility to predict prompt fission quantities as a function of fragment. Other TXE partition methods (based on models and assumptions at scission or on equal residual temperatures of complementary fragments at full acceleration) are compared to this one, revealing limits of applicability as well as the sensibility of prompt neutron emission models to the TXE partition. The behaviour of experimental ν(A) with the increase of incident energy consisting in the multiplicity increase for heavy fragments only, is argued and entirely supported by the quantitative Point-by-Point model results of ν(A) describing very well the experimental ν(A) of ²³⁷Np(n, f) at 0.8 and 5.5 MeV incident energies.     

Systematic study of survival probability of excited superheavy nuclei

The stability of excited superheavy nuclei (SHN) with 100 Z 134 against neutron emission and fission is investigated by using a statistical model. In particular, a systematic study of the survival probability against fission in the 1n-channel of these SHN is made. The present calculations consistently take the neutron separation energies and shell correction energies from the calculated results of the finite range droplet model which predicts an island of stability of SHN around Z = 115 and N = 179. It turn...     

Light-charged particle emission in fission

The emission of light charged particles in the fission process is of interest as they are believed to emerge from the neck region of the deformed fissioning nucleus at a time close to the scission point and may thus prove a useful probe to investigate the last stages of fission close to the rupture point. Experimental results on light charged particle emission and the efforts made to obtain information about the scission point parameters therefrom are reviewed.     

Study of Survival Probability of Super Heavy Nuclei

The survival probability of super heavy nuclei produced in cold fusion reactions is studied by using thestandard Fermi gas level density formula and analyzed with fission and neutron evaporation characteristics predicted indifferent theoretical models. The level density formula used in this letter suppresses the ratio of neutron emission widthalso investigated.     

Study of Survival Probability of Super Heavy Nuclei

The survival probability of super heavy nuclei produced in cold fusion reactions is studied by using the standard Fermi gas level density formula and analyzed with fission and neutron evaporation characteristics predicted in different theoretical models. The level density formula used in this letter suppresses the ratio of neutron emission width to fission width, Гn/Гf. The dependence of Гn/Гf on the saddle point level density parameter and excitation energy is also investigated.