No abstract

Abstract. The angular motion of a few-body system is described with global vectors which depend on the positions of the particles. The previous study using a single global vector is extended to make it possible to describe both natural and unnatural parity states. Numerical examples include three-and four-nucleon systems interacting via nucleon-nucleon potentials of AV8 type and a 3α system with a nonlocal αα potential. The results using the explicitly correlated Gaussian basis with the global vectors are shown to be in good agreement with those of other methods. A unique role of the unnatural parity component, caused by the tensor force, is clarified in the 0 − 1 state of 4 He. Twoparticle correlation function is calculated in the coordinate and momentum spaces to show different characteristics of the interactions employed.

No abstract

t+t clustering in He isotopes is investigated by using two theoretical approaches. A role of the t+t cluster component in the ground state is examined with AMD triple-S, allowing the wider configuration space containing simultaneously the "t+t+valence neutrons" structure and "4 He +valence neutrons" structure. We understand the importance of the t + t component even for the ground state. Further, t + t resonances are investigated with RGM type approach. We obtained many t + t states as resonances near to t + t threshold.

The structure of the mirror nuclei 9 Be and 9 B is studied in a microscopic ␣ϩ␣ϩn and ␣ϩ␣ϩp threecluster model using a fully antisymmetrized nine-nucleon wave function. The two-nucleon interaction includes central and spin-orbit components together with the Coulomb potential. The ground state of 9 Be is obtained accurately with the stochastic variational method, while several particle-unbound states of both 9 Be and 9 B are investigated with the complex scaling method. The calculation for 9 Be supports the recent identification for the existence of two broad states around 6.5 MeV, and predicts the 3/2 2 Ϫ and 5/2 2 Ϫ states at about 4.5 MeV and 8MeV, respectively. The similarity of the calculated spectra of 9 Be and 9 B enables one to identify unknown spins and parities of the 9 B states. Available data on electromagnetic moments and elastic electron scatterings are reproduced very well. The enhancement of the E1 transition of the first excited state in 9 Be is well accounted for. The calculated density of 9 Be is found to reproduce the reaction cross section on a carbon target. The analysis of the beta decay of 9 Li to 9 Be clearly shows that the wave function of 9 Be must contain a small component that cannot be described by the simple ␣ϩ␣ϩn model. This small component can be well accounted for by extending a configuration space to include the distortion of the ␣ particle to tϩ p and hϩn partitions. ͓S0556-2813͑96͒02607-6͔

No abstract

No abstract

The structure of certain bound excited states in 10 Be have been shown to have exotic features because of their weak binding and cluster-like configurations. In this article, we investigate E1 and E2 transitions between these states and compare the findings with recent experimental results. We compare the predictions of two types of structure calculations: a microscopic multicluster model and an ab initio no-core shell model. Both predict very similar transition strengths. By considering the relative contributions from the various matrix elements contributing to the transitions arising from the coupling of different 9 Be×n configurations in the wave functions making up the states, we conclude that the very weak B(E1; 2 − → 2 + 1 ) can only be understood if the 2 − state (with a separation energy of its predominantly 1s 1/2 neutron of just 0.548 MeV) is a clear halo state. Other nearby states, such as the 2 + 2 , do not exhibit a clear halo signature because of the less than clean decoupling into the well-defined 9 Be core plus halo neutron.