Multi-step processes in the interpretation of the 28Si(d, 3He)27Al reaction

Results from a CCBA analysis of the ²⁸Si(d, ³He)²⁷Al reaction are reported. The transfers are assumed to occur between dominant components of (λμ) symmetry (0, 12) and (2, 10) in the initial and final nuclear eigenstates respectively. The results show that cross sections to four of the six levels observed below 3 MeV can be fairly well reproduced within a pure K_(J) band framework. However, consistent with electromagnetic results, all six levels can be fit if the K_(J) band purity of the analysis, SU(3) model. $\text{5}\text{2}{}^{\mathrm{+}}\text{(}\text{ground and}\text{2.73}\text{MeV}\text{)}$ states and $\text{9}\text{2}{}^{\mathrm{+}}\text{(3.00}\text{MeV}\text{)}$ state is abandoned.     

Structure calculations for 25Mg-25Al

The results of a shell model calculation for ²⁵Mg-²⁵Al are presented in which the Hamiltonian for the system was taken to be that of an inert ¹⁶O core plus nine s-d shell particles interacting through the usual one-body l² and l · s terms plus general two-body residual interactions of the Kuo-Brown type. The basis was truncated to include nine favored representations of SU(3) in each of the two leading spatial symmetries ([441]: (66), (93), (74), (82)², (55)², (28), (90); [432]: (10,1), (74), (82)², (55)², (28), (47), (90)). It is found that a (λμ)-dependent renormalization of the type proposed by Harvey but empirically modified for axially asymmetric shape distributions is required to reproduce the experimentally observed ordering of the three lowest rotational bands. The goodness of K_J as a band label for the calculated eigenstates is investigated by comparing calculated quadrupole moments with simple rotational model predictions. Calculated B(E2) and B (M1) rates are compared with the available data. Results for relative spectroscopic factors from (d, p) stripping on the ground state of ²⁴Mg are also presented.     

A close look at the competition of isovector and isoscalar pairing in A=18 and 20 even-even N≈Z nuclei

competition of isovector and isoscalar pairing in A=18 and 20 even-even N≈Z nuclei is analyzed in the framework of the mean-field plus the dynamic quadurpole-quadurpole, pairing and particle-hole interactions, whose Hamiltonian is diagonalized in the basis U(24) ?(U(6) ? S U(3) ? S O(3))■(U(4) ? S US(2)■ S UT(2)) in the L = 0 configuration subspace. Besides the pairing interaction, it is observed that the quadurpole-quadurpole and particlehole interactions also play a significant role in determining the relative positions of low-lying excited 0~+ and 1~+ levels and their energy gaps, which can result in the ground state first-order quantum phase transition from J = 0 to J = 1.The strengths of the isovector and isoscalar pairing interactions in these even-even nuclei are estimated with respect to the energy gap and the total contribution to the binding energy. Most importantly, it is shown that although the mechanism of the particle-hole contribution to the binding energy is different, it is indirectly related to the Wigner term in the binding energy.     

Algebraic realization of the quantum rotor — odd-A nuclei

An algebraic realization of the quantum rotor for non-zero spin values (integer as well as half-integer) is established by constructing a model Hamiltonian out of rotationally invariant functions of the generators ofSU(3). The eigenvalues of this Hamiltonian in the leading normal-SU(3) symmetry for²⁵Mg and the so-called leading pseudo-SU(3) symmetries for¹⁵⁹Dy and¹⁶⁵Er are compared with the corresponding rotor results. For spinfree systems the internal symmetry group of the rotor and itsSU(3) realization are known to be D₂, the Vierergruppe. This symmetry extends to integral spin values, while for half-integer spins the rotor and itsSU (3) realization are shown to display an internal quaternion group symmetry. The theory points to a microscopic (many-particle shell-model) picture of nuclear rotational motion with spin degrees of freedom taken fully into account. An algebraic realization of the many-particle Nilsson model for odd-A nuclei, with the orbit-orbit and spin-orbit terms included, is given and applied to²³Na.     

一种推广对力模型及在大形变核中的应用

总结了可描述大形变原子核运动的Nilsson平均场加推广的对力相互作用的可解模型.该模型在对力强度较弱的区域仍然以单体和两体相互作用为主.但随着对力强度的增加,高阶相互作用的修正将逐渐变得重要.通过对同位素154—171Yb奇偶质量差的数值拟合显示,该新模型可说明大形变核的运动规律.     

A New Expression for Nuclear Rotational Spectra

A new formula, which is derived from a deformed rotor model for describing nuclear rotational spectra, is analyzed. The ground band of most even-even rare-earth and actinide nuclei are accurately reproduced using a damped nonlinear least-square fitting procedure for determining parameters of the theory. The results show that energy spectra obtained from a deformed rotor model are more accurate than those from a three-parameter formula based on perturbation theory.