Low-spin states of odd-mass xenon isotopes

In this work, we analyse the positive parity of states of odd-mass nucleus within the framework of interacting boson-fermion model. The result of an IBFM-1 multilevel calculation with the 2d_5/2, 1g_7/2, 3s_1/2, 2d_3/2 and 1h_11/2, single particle orbits is reported for the positive parity states of the odd-mass nucleus ^125–129Xe. Also, an IBM-1 calculation is presented for the low-lying states in the even-even ^124–128Xe core nucleus. The energy levels and B(E2) transition probabilities were calculated and compared with the experimental data. It was found that the calculated positive parity low-spin state energy spectra of the odd-mass ^125–129Xe isotopes agree quite well with the experimental data.      

壳模型对13N Gamow-Teller跃迁的研究

最近的研究表明¹³N的beta衰变对于Ia型超新星爆炸前的电子丰度有着重要的影响.本文在壳模型的基础上,首先计算¹³N基态到基态以及基态到不同激发态的Gamow-Teller(GT)跃迁强度,并将其与实验数据进行了比较.在理论计算的GT强度基础上,对不同温度和密度天体环境下¹³N的电子俘获率进行了细致的计算,并重点讨论基态到激发态的GT跃迁对电子俘获率变化的影响.结果表明,考虑基态到激发态的跃迁后,超新星的电子丰度下降,中微子能量损失增大.基态到激发态跃迁对电子俘获率的影响主要由低激发能级贡献. 关键词： Gamow-Teller跃迁 壳模型 电子俘获 激发态     

Structure analysis of ~(159)Sm and properties of odd-mass neutron-rich nuclei in mass-160 region

Recent fission experiment data provide interesting structure information for neutron-rich nuclei in the mass A ～ 160 region. We apply the projected shell model to study the strongly-deformed, neutron-rich Sm isotopes. We perform calculations for rotational bands up to spin I = 20 (29/2) for even-even (odd-neutron) Sm isotopes, and analyze the band structure of low-lying states with quasiparticle excitations. Emphasis is given to rotational bands based on one-quasiparticle (1-qp) configurations in the odd-ma...     

Muonic atoms of odd-mass nuclei

The effect of the single particle excitations on the spectra of muonic atoms with odd-mass nuclei is studied in the frame work of the unified model. The theoretical spectra are compared with the experimental ones and the excitation strengths of the nuclear states as well as the nuclear polarization due to the muon are calculated.     

Application of Dyson mapping to odd-mass nuclei

The Dyson mapping is applied to the analysis of low-lying collective states in odd-mass nuclei. The original fermion (quasiparticle) space is truncated to a collective subspace which consists of products of collective phonons and a single fermion (quasiparticle). This subspace is mapped on an ideal boson-fermion space by the Dyson mapping and a simple but non-hermitian hamiltonian is obtained. The eigenvalue equations for the hamiltonian are numerically solved for the cases of the unique-parity states in the odd-mass Rh isotopes. The results show that the Dyson mapping is quite useful for analyses of phonon-particle coupling in odd-mass nuclei.     

Exchange magnetic moments of some odd-mass nuclei

The exchange magnetic moment has been calculated for the nuclei ⁹¹Zr, ⁸⁹Sr and ⁸⁷Kr in the ground state. By adding the core polarization contribution to the magnetic moments computed earlier, an improved value is obtained for the magnetic moments of these nuclei.     

Ab Initio MRD-CI Investigation of the Electronic Spectrum of Dichloromethanol Cl2CHOH

Multireference configuration interaction calculations (MRD-CI) are performed to compute excited states of dichloromethanol Cl₂CHOH, a species relevant to atmospheric chemistry. Oscillator strengths f are also calculated to predict the electronic spectrum. Four strong transitions calculated at 7.12 eV (1¹A″←X¹A′), 7.50 eV (2¹A″←X¹A′), 8.38 eV (3¹A″←X¹A′), and 8.8 eV (5¹A″←X¹A′) can serve as a guideline for experimental search. The corresponding triplet states are also given.     

Quantum Logic Gates and Cluster States with Four-level Atoms in Cavity QED

We propose a model to implement the two-qubit quantum logic gates, i.e., the quantum phase gate and the Controlled-NOT gate, and generate the atomic qubits cluster states with a large detuned interaction between four-level atoms and a single-mode cavity field. In the presented protocol, the quantum information is encoded on the stable ground states of the atoms, and the effect of decoherence from atomic spontaneous emission is negligible. In addition, the interaction between atoms and the cavity is large detuned, and the cavity is only virtually excited. Therefore, the scheme is insensitive to the cavity decay. The experimental feasibility of our proposal is also discussed.     

Half-life measurements of intrinsic states in deformed odd-mass nuclei

The half-lives of the following intrinsic states in deformed odd-mass nuclei has been measured by delayed coincidences with a time-to-amplitude converter:

1. 5/2 5/2⁺[642] at 86.5 keV in¹⁵⁵Gd:T _1/2=6.7±0.3 ns, which results in the determination of theE1,ΔK=1 transition probability to the ground state 3/2 3/2^?[521] and first rotational state 5/2 3/2^?[521], yielding hindrance factors ofF _N ≈5.5 and ≈1.8 (F _W =3.1×10⁴ and 2.3×10⁴) respectively.
2. (3) 5/2 5/2^?[512] at 191.4 keV in¹⁶⁹Yb:T _1/2=3.35±0.15 ns and at 122.39 keV in¹⁷¹Yb:T _1/2=265±20 ns which results in the determination of the transition probabilities of theE1,ΔK=1 transitions to the ground states 7/2 7/2⁺[633], of theK-forbiddenM1 transitions to the 5/2 and 3/2 1/2^?[521] and of theE2 transitions to the 5/2, 3/2 and 1/2 1/2^?[521] states in both nuclei.

TheE1 transition probabilities are compared to the transitions between the same Nilsson states in¹⁷³Yb and¹⁷⁵Hf discussing the influence of the position of the Fermi surface — obtained from recent stripping and pick-up reactions — on these transition probabilities. Additional information on the decay scheme of¹⁷¹Lu→¹⁷¹Yb is obtained by delayed coincidence measurements. For testing the used time-to-amplitude converter the well known half-lives of the 482 keV level in¹⁸¹Ta (T _1/2=10.4±0.3 ns) and of the 279 keV level in²⁰³Tl (T _1/2=0.285 ±0.015 ns) were measured, in good agreement with other measurements.     

Fission times of excited nuclei: An experimental overview

An overview of selected recent experimental results on fission times is presented. Evidences for over-damped motion up to saddle point during the fission process of highly excited nuclei have been obtained independently through fission probability, pre-scission multiplicity and direct time measurements. In addition, strong clues have been found for a temperature dependency of friction. Experiments probing transient effects through fission probabilities are presented and the counterbalanced effects of friction and level density parameters are discussed. Promising perspectives for super-heavy stability studies, based on fission time measurements, are presented.     

Cluster decay of the high-lying excited states in 14C

A cluster-transfer experiment of ⁹Be(⁹Be,¹⁴C→α+¹⁰Be)α at an incident energy of 45 MeV was carried out in order to investigate the molecular structure in high-lying resonant states in ¹⁴C. This reaction is of extremely large Q-value, making it an excellent case to select the reaction mechanism and the final states in outgoing nuclei. The high-lying resonances in ¹⁴C are reconstructed for three sets of well discriminated final states in ¹⁰Be. The results confirm the previous decay measurements with clearly improved decay-channel selections and also show a new state at 23.5(1) MeV. The resonant states at 22.4(3) and 24.0(3) MeV decay primarily into the typical molecular states at about 6 MeV in ¹⁰Be, indicating a well developed cluster structure in these high-lying states in ¹⁴C. Further measurements of more states of this kind are suggested.     

Singlet excited states of anions with higher main group elements

Previous studies have shown that dipole-bound excited states exist for certain small anions. However, valence excited states have been reported for some closed-shell anions, but those with singlet valence excited states have, thus far, contained a single silicon atom. This work uses high-level coupled cluster theory previously shown to reproduce excited state energies to better than 0.1 eV compared with experiment in order to examine the electronic excited state properties of anions containing silicon and other higher main group atoms as well as their first row analogues. Of the 14 anions involved in this study, 9 possess bound excited states of some kind: CH₂SN^?, C₃H^?, CCSiH^?, CCSH^?, CCNH^?₂, CCPH^?₂, BH₃PH^?₂, AlH₃NH^?₂ and AlH₃PH^?₂. Two possess clear valence states: CCSiH^? and its first row analogue C₃H^?. Substantial mixing appears to be present in the valence and dipole-bound characters for the first excited state wavefunctions of many of the systems reporting excited states, but the mixing is most pronounced with the ammonia borane-like AlH₃NH^?₂, and AlH₃PH^?₂ anions. Inclusion of second row atoms in anions whose corresponding radical is strongly dipolar increases the likelihood for the existence of excited states of any kind, but among the systems considered to date with this methodology, only the nature of group 14 atoms in small, closed-shell anions has yet been shown to allow valence singlet excited states.     

外电场下Ti2O4团簇分子的激发与光谱性质研究

采用密度泛函(DFT) B3LYP方法在6-31+G基组水平上优化得到了分子轴方向不同电场作用下,Ti2O4团簇分子的基态稳定构型,电偶极矩μ,分子的总能量等,并且分析了Ti2O4团簇分子从HOMO-2到LUMO+2轨道能量的变化.在优化的构型下,用同样的基组利用CIS-DFT方法计算了外电场下Ti2O4纳米团簇分子的前9个激发态的激发能、波长和振子强度.结果表明,在有外电场的作用下,分子总能量随着外电场的增加不断减小,偶极矩随外电场的增加逐渐增大.其前线轨道的能量也随着外电场的增加逐渐减小.另外,Ti2O4团簇分子的激发能,激发波长和振子强度也受到了外电场的影响.     

Radiative decay from doubly to singly excited states of He via generalization of Laguerre-type orbitals： A non-orthogonal formalism

By taking full account of the non-orthogonality of the orbitals between the low-lying doubly excited states ¹P^o and the singly excited states ¹S^e and ¹²D^e of He, the corresponding radiative decay rates have been investigated theoretically via analytic generalized Laguerre-type atomic orbitals at a nearly numerical multi-configuration self-consistent field accuracy in a general non-orthogonal configuration interaction scheme. From these rates, we calculate the VUV photon emission and metastable atom spectra, and both are found to be in good qualitative agreement with recent excellent measurements. We obtain, successfully, the enhancement of the VUV photon spectrum, experimentally observed at the energy of (2s4p-4s2p)/(2p,3d) ¹P^o as compared with other nearby lying states. The mechanism proposed by Odling-Smee et al is verified, implying that taking appropriate account of the overlap existing between orbitals of the low-lying doubly excited and singly excited states (especially important for the compact orbitals) can reveal basic physical dominant mechanism and is crucial in understanding these spectra.     

电子碰撞诱导原子从低激态向高激态弛豫

本文根据空心阴极放电中电子能量分布的物理图象,分析了原子从低激态向高激态弛豫的可能途径。建立高低激态集居数密度增量的关系。讨论高激态集居数密度增量获得可观量的条件。根据此条件分别选取钠原子的基态3s~2S_(1/2)和铜原子的亚稳态4s~2D_(3/2)为与激光共振的下能级,并激发具有较大自发发射几率的3s~2S_(1/2)→3p~2P°_(1/2)(和3p~2P°_(3/2))和4s~2D_(3/2)→4p~2P°_(1/2)跃迁,在远离上能级的高激态上观测到敏化荧光,并精确测得这些态的自发发射系数比值,而在更高激态上没有观测到敏化荧光,表明讨论中提出的条件是合理的。     

Solution of Bohr's collective Hamiltonian for transitional odd-mass nuclei

A numerically feasible method, based on the use of deformed phonons, is developed for the diagonalization of the collective quadrupole Hamiltonian for a system with an odd particle coupled to an anharmonic even core. Examples: the transition from prolate to oblate via γ-unstable shapes and furthermore the $\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ spectra of the nuclei ¹⁸⁷Ir and ¹⁹⁷Tl.     

Cold events in thermal-neutron-induced fission of heavy nuclei

An interpretation of the cold fission events in thermal-neutron-induced fission of heavy nuclei is given. The descent from the saddle point is considered as a dynamical process with reversible coupling between collective and intrinsic degrees of freedom. The distribution function for the collective variables is expressed as a product of two terms: the adiabatical and the dynamical factors. A simple model for symmetric fission to study the mass distribution is presented. As example, the calculations are performed for the nucleus ²⁶⁴Fm. Gross features of the cold fission are discussed as well as the dependence of the theoretical mass distribution on the parameters of the model. Received: 29 April 1998 / Revised version: 11 September 1998     

杂质对硬球系统团簇成核临界条件的影响

通过CS状态方程及熵极大原理在多元胶体系统研究了杂质对硬球系统团簇成核临界条件的影响. 极少量元素或杂质的小胶球对系统成核的临界条件的影响也是不可忽略的: 成核的临界体积分量显著地降低;此外,研究还发现杂质对成核的临界尺寸影响较少.     

Multiphoton ionization of iodine atoms and CF<Subscript> 3</Subscript>I molecules by XeCl laser radiation

We report about effective ionization of iodine atoms and CF₃I molecules under the action of intense XeCl laser radiation (308 nm). The only ion fragment resulting from the irradiation of the CF₃I molecules is the I⁺ ion. We have studied the influence of the intensity, spectral composition, and polarization of the laser radiation used on the intensity of the ion signal and the shape of its time-of-flight peak. Based on the analysis of the results obtained, we have suggested the mechanism of this effect. The conclusion drawn is that the ionization of the iodine atoms by the ordinary XeCl laser with a nonselective cavity results from a three- (2 + 1)-photon REMPI process. This process is in turn due to the presence of accidental two-photon resonances between various spectral components of the laser radiation and the corresponding intermediate excited states of the iodine atom. The probability of ionization of the atoms from their ground state I(²P_3/2) by the radiation of the ordinary XeCl laser is more than two orders of magnitude higher than the probability of their ionization from the metastable state I^*(²P_1/2). The ionization of the CF₃I molecules by the XeCl laser radiation occurs as a result of a four-photon process involving the preliminary one-photon dissociation of these molecules and the subsequent (2 + 1)-photon REMPI of the resultant neutral iodine atoms.