粒子–转子模型与奇奇核的能谱统计分析

用轴对称粒子–转子理论模型计算奇奇核⁸⁴Y低自旋下的能谱,研究了能谱的最近邻能级间距分布和能谱刚性度随自旋的变化规律,并对该模型中特定形式的质子–中子相互作用和科氏力作用对能谱统计特征的影响作了分析.     

A=100区奇奇核旋称反转

利用两准粒子加轴对称转子模型,对A=100质量区两个奇奇核¹⁰²Rh和^{9 8}Rh的旋称反转进行了研究.结果表明,在A=160,130,80三个质量区奇奇核的计算中 已得到证实的、可能的旋称反转机制(即低K空间n-p相互作用和科氏力的相互竞争),对 于A=100质量区奇奇核也是适用的.这暗示在不同质量区奇奇核可能存在一种普遍的旋称 反转机制. 关键词： 奇奇核 旋称反转 两准粒子加轴对称转子模型     

A=80区奇奇核的晕带能谱计算

采用二准粒子加轴对称转子模型,研究了A=80区部分奇奇核的晕带能谱,理论计算结果准确地再现了每个核的signature反转,并与实验值符合相当好- 关键词：     

IBFM模型U(6/4)超对称SO(6)极限的能谱统计

用相互作用玻色子费米子模型(IBFM)计算了奇A核U(6/4)超对称SO(6)极限的理论能谱，对不确定核的最近邻能级间距分布和能谱刚性度进行了研究，并对影响能谱统计特征的因素进行了讨论. 结果表明，有限的玻色子数N的大小显著地影响能谱统计. 当N接近于真实核的玻色子数时，子群SOBF(5)的作用强度和自旋对能谱统计起重要作用. 然而，当N趋于无穷大时，能谱统计总是趋于Poisson分布.     

A=160号区部分奇奇核的晕带能谱计算

将奇核轴对称转子加准粒子模型推广到奇奇核的情况,考虑了在奇奇核的基矢空间中计及模型的质子—中子相互作用项,方法用于A=160号区多个实际核的计算,所得结果均与实验值定性相符.文中还对奇奇核Signature反转的一种可能的机制进行了讨论.     

准单能中子单粒子效应研究现状

对国际上用于单粒子效应(SEE)研究的准单能中子源进行了相关调研,对产生准单能中子源的⁷Li(p, n)⁷Be核反应、装置布局以及表征中子场性质的中子注量率、中子能谱、中子束流轮廓及其均匀性、热中子本底等参数的理论计算及实验测量进行了系统的介绍。进行准单能中子SEE实验要求中子源有较高的中子注量率水平、较大的束流轮廓、较好的束流均匀性以及较低的热中子本底,并且能测量出精确的中子能谱。对准单能中子SEE实验过程以及三种中子SEE截面的尾部修正方法进行了介绍。     

同位旋效应对中能重离子反应中轻粒子产物的影响

利用同位旋相关的量子分子动力学模型,研究了¹¹²Sn+¹¹²Sn和¹²⁴Sn+¹²⁴Sn两反应系统在不同入射能量、不同碰撞参数、不同势场和不同核子-核子碰撞截面下的粒子发射特征.阐述了发射体系的同位旋对轻粒子产额比的影响.发现轻粒子产额比是同位旋的敏感观测量.另外,还发现中快度区发射的粒子有更高的丰中子程度.同时,轻粒子的比不敏感于核子核子碰撞截面,而敏感于核态方程,这使得从轻粒子比提取同位旋相关的核态方程变成一种可能. 关键词： 同位旋相关的量子分子动力学 同位旋效应 轻粒子产额比     

采用超薄双层靶提高质子束的单能性

利用1维粒子模拟程序,研究了超短超强激光脉冲与超薄双层靶（基底层和加速层厚度均为nm量级）相互作用产生准单能质子束的过程。研究表明,基底层厚度及加速层厚度对质子能谱的影响至关重要。减小基底层厚度,靶后静电场增强,质子的最大能量显著增大;减小加速层厚度,靶后静电场分布变得更加均匀,质子能谱中心能量变化不大,单能性变好。通过优化参数,获得了能散度为7%的准单能质子束。     

采用超薄双层靶提高质子束的单能性

利用1维粒子模拟程序,研究了超短超强激光脉冲与超薄双层靶(基底层和加速层厚度均为nm量级)相互作用产生准单能质子束的过程。研究表明,基底层厚度及加速层厚度对质子能谱的影响至关重要。减小基底层厚度,靶后静电场增强,质子的最大能量显著增大;减小加速层厚度,靶后静电场分布变得更加均匀,质子能谱中心能量变化不大,单能性变好。通过优化参数,获得了能散度为7%的准单能质子束。     

稀土区奇奇核πh_(11/2)νi_(13/2)带B(M1)/B(E2)比值增强特性

在稀土区奇奇核πh11/2νi13/2转动带中,系统地观测到随转动频率或角动量增加,B(M1)/B(E2)曲线表现出所谓parabola like形状,即在增加到某一转动频率或自旋后,B(M1)/B(E2)比值快速增强。基于推转模型和粒子转子模型关于奇奇核二准粒子转动带磁偶极约化跃迁几率的描述,对稀土区双奇核的这一行为进行了讨论。指出该现象的发生与νi13/2准中子转动顺排特性密切相关。B(M1)/B(E2)比值在接近第二带交叉(即BC准中子对顺排)的较高频率处的增强效果,可以理解为主要来源于带交叉引起的波函数中混合四准粒子成分的结果。通过对B(M1)/B(E2)比值的增强效果发生在较低频率处的分析,对稀土区奇奇核πh11/2νi13/2带角动量耦合图像有了进一步认识。     

192Tl高自旋态能级结构研究

通过熔合蒸发反应181Ta（16O,5n）192Tl,在入射束流为97 MeV能量下,布居192Tl的高自旋态,更新了192Tl的能级纲图。共增加8条新能级,尝试性地指定了能级自旋,将负宇称晕带的能级推高到23-?。讨论了192Tl与相邻同位素奇奇核194,196,198Tl负宇称晕带的旋称劈裂与反转现象,发现随着中子数增加,196,198Tl在高自旋处出现了旋称反转,其原因可能是由于中子质子相互作用与科里奥利力相互竞争所致。High spin states of 192Tl were populated by the 181Ta(16O, 5n)192Tl heavy ion fusion evaporation reaction at 97 MeV beam energy. A new level scheme with 8 new levels was constructed and the level spins were tentatively assigned. The negative yrast band was extended up to 23-?. Systematics of signature of inversion were also discussed for the negative yrast band of odd-odd Tl istopes. Signature inversion has been found in 196,198Tl with neutron number increasing in these four Tl isotopes, and it is explained by the competition between the strength of n-p interaction and Coriolis force.     

Low-lying states of ~(92,93)Nb excited in the reactions induced by the weakly-bound nucleus ~6Li near the Coulomb barrier

Excited states of odd-odd nucleus ~(92)Nb and odd-A nucleus ~(93)Nb were populated in the 6 Li+ 89 Y reaction with an incident energy of 34 MeV. The processes that produce 92,~(93)Nb and can be measured by a combination of light charged particle and gamma ray measurements are discussed. Twenty new transitions are observed and eight new levels are constructed in ~(92)Nb, and in addition two new transitions are added to the level scheme of ~(93)Nb. Using shell2 model calculations, the low-lying structure of 9 Nb is investigated and compared with the experimental results.     

IBFFM description of energy levels and electromagnetic properties of 134Cs

The first calculation in IBFFM for both energy levels and electromagnetic properties is performed for the odd-odd nucleus ¹³⁴Cs and compared to recent experimental data.     

Structure of high spin states in83Y

We report on the first in-beam study of high spin levels in⁸³Y which were established up to 9.0 MeV excitation energy and probable spin of 41/2⁺ resp. 27/2^? by means of the reaction⁵⁸Ni(²⁸Si, 3p). Ten lifetimes and six lifetime limits in the 10^?12–10^?9 s range were determined in two recoil distance Doppler shift experiments. The positive parity yrast states form ag _9/2 Coriolis decoupled band with partial alignment, near-rigid rotor moment of inertia and deformationβ ₂=0.29. The negative parity yrast band has very similar collective properties; it shows a pronounced band crossing at rotational frequency ?ω≈0.40 MeV which we associate with twoquasiparticleg _9/2 proton alignment. At 2.56 MeV excitation, a second ΔI=1 band starting with 17/2^? was found. On the basis of the similarity to⁸⁵Y and the very weakE2 decay of this state, we suggest that this band has (3qp) configuration with an alignedg _9/2 neutron pair. The lifetimes of the lowest 2⁺ and 4⁺ state in⁸⁴Zr populated in the reaction⁵⁸Ni (²⁸Si, 2p) were determined to be τ(2)=17.8(11) ps resp. τ(4)=3.5(4) ps.     

丰中子核91Y 的高自旋能级结构(英文)

丰中子核91Y 的高自旋能级结构通过82Se(13C, p3n)91Y 反应被再次研究了。新建立的包含几条关键能级的能级纲图澄清了以前研究中的几点不确定的地方。这几条能级具有Z=38 和N=56 子闭壳打破的特征,这涉及到张量力和自旋-同位旋依赖的中心力。High-spin level structure of the neutron-rich nucleus 91Y has been reinvestigated via the 82Se(13C, p3n)91Y reaction. A newly constructed level scheme including several key levels clarifies the uncertainties in the earlier studies. These levels are characterized by the breaking of the Z = 38 and N =56 subshell closures, which involves in tensor force and the spin-isospin dependent central force.     

Level structures in the odd-odd nucleus180Re

Experimental data on energy levels of the odd-odd deformed nucleus¹⁸⁰Re obtained from radioactive-decay and heavy-ion reaction studies are analysed to deduce spin-parity and configuration assignments for the six observed rotational bands based on the selection rules for fast beta transitions, criteria for the relative-energy ordering of the triplet and singlet bandheads, two-particle-plus-rotor model calculations including Coriolis mixing, rotational energy systematics involving staggering features, and considerations of gyromagnetic ratios, signature splittings and rotational band alignments.     

Isomeric and two-quasiparticle states in the neutron-excess odd-odd nucleus <Superscript>134</Superscript>Sb

Detailed theoretical calculations of the properties of the neutron-excess odd-odd nucleus ¹³⁴Sb are performed by using different theoretical approaches. A comprehensive comparison with the recent experimental data is performed; this comparison suggests the presence of isomeric states among the low-lying levels of this nucleus. These states are the twins of the corresponding levels of the odd-odd nucleus ²¹⁰Bi that is situated near the stability line. The obtained results manifest the similarity of nuclear structure in the region of the “remote” doubly magic nucleus ¹³²Sn and in the region of the classical stable doubly magic nucleus ²⁰⁸Pb. The text was submitted by the authors in English.     

Statistical Treatment of Low-Energy Nuclear Level Schemes

The level density parameter and the back shift energy E1 are determined for nuclei with A-values across the whole periodic table from fits to complete level schemes at low excitation energy near the neutron binding energies.We find that the energy back shift E1 shows complicated behavior and depends on the type of the nucleus,even-even,odd mass,and odd-odd.The spin cut-off factor has also been investigated for nuclei mentioned above.The results arecompared with the previous results and different experimental data on level densities.     

IBFFM predictions for low-lying spherical states in the shape-coexisting odd-odd nucleus98Y

Extrapolating the Interacting Boson-Model treatment from lighter neighbours to⁹⁸Y we predict the properties of low-lying states of spherical nature in IBFFM. This odd-odd nucleus which presents one of the rare cases of coexisting spherical and deformed shapes is of fundamental importance for understanding nuclear phase transitions.