[en] Using the nuclear proximity approach and the two center nuclear shape parametrization, the interaction potential between two deformed and pole-to-pole oriented nuclei forming a necked configuration in the overlap region is calculated and its role is studied for the cluster decay half-lives. The barrier is found to move to a larger relative separation, with its proximity minimum lying in the neighborhood of the Q value of decay and its height and width reduced considerably. For cluster decay calculations in the preformed cluster model of Malik and Gupta, due to deformations and orientations of nuclei, the (empirical) preformation factor is found to get reduced considerably and agrees nicely with other model calculations known to be successful for their predictions of cluster decay half-lives. Comparison with the earlier case of nuclei treated as spheres suggests that the effects of both deformations and neck formation get compensated by choosing the position of cluster preformation and the inner classical turning point for penetrability calculations at the touching configuration of spherical nuclei. copyright 1997 The American Physical Society

[en] We propose a description of cluster states in nuclei in terms of representations of unitary algebras U(ν+1), where ν is the number of space degrees of freedom. Within this framework, a variety of situations including both vibrational and rotational spectra, soft and rigid configurations, identical and nonidentical constituents can be described. As an example, we show how the method can be used to study α clustering configurations in ¹²C with point group symmetry D_3h. (c) 2000 The American Physical Society

[en] Bond percolation model predictions for the behavior of scaled factorial moments (SFM close-quote s) of cluster size distributions do not show intermittency for open-quotes near-criticalclose quotes events. An intermittentlike signal is observed only for open-quotes overcriticalclose quotes events, independent of the size of the lattice. SFM analysis of ALADIN experimental data (600, 800, and 1000 MeV/nucleon Au + Au reactions) is in qualitative agreement with the percolation predictions. copyright 1997 The American Physical Society

[en] We study the low-energy 3/2^- and 1/2^- states of ⁵He and ⁵Li in a microscopic cluster model. The scattering phase shifts of Bond (α+n) and of Schwandt (α+p), respectively, are well reproduced. We determine the resonance parameters by localizing the poles of the analytically continued S matrix at complex energies. Our results differ from conventional R-matrix resonance parameters, that were extracted from experimental data using the definition of a resonance based on the positions and widths of reaction cross section peaks. However, they nicely agree with the results of an extended R-matrix method that works at complex energies. copyright 1997 The American Physical Society

[en] We present an algorithm for Monte-Carlo selection of exciton energies for reactions induced by clusters. Reaction mechanisms are addressed that involve a dissolution of the cluster into its constituent nucleons followed by the initiation of a preequilibrium cascade. Calculated single differential spectra and excitation functions for ⁹³Nb(α,xn) reactions are compared with experimental results to illustrate use of this method. Some advantages of exclusive computational techniques over analytic inclusive methods are summarized. (c) 2000 The American Physical Society

[en] We report quantum Monte Carlo calculations of ground and low-lying excited states for A=8 nuclei using a realistic Hamiltonian containing the Argonne v₁₈ two-nucleon and Urbana IX three-nucleon potentials. The calculations begin with correlated eight-body wave functions that have a filled α-like core and four p-shell nucleons LS coupled to the appropriate (J^π;T) quantum numbers for the state of interest. After optimization, these variational wave functions are used as input to a Green's function Monte Carlo calculation made with a new constrained path algorithm. We find that the Hamiltonian produces a ⁸Be ground state that is within 2 MeV of the experimental resonance, but the other eight-body energies are progressively worse as the neutron-proton asymmetry increases. The ⁸Li ground state is stable against breakup into subclusters, but the ⁸He ground state is not. The excited state spectra are in fair agreement with experiment, with both the single-particle behavior of ⁸He and ⁸Li and the collective rotational behavior of ⁸Be being reproduced. We also examine energy differences in the T=1,2 isomultiplets and isospin-mixing matrix elements in the excited states of ⁸Be. Finally, we present densities, momentum distributions, and studies of the intrinsic shapes of these nuclei, with ⁸Be exhibiting a definite 2α cluster structure. (c) 2000 The American Physical Society

[en] The proton momentum and density distributions of closed shell nuclei are calculated with a model treating short-range correlations up to first order in the cluster expansion. The validity of the model is verified by comparing the results obtained using purely scalar correlations with those produced by finite nuclei Fermi hypernetted chain calculations. State dependent correlations are used to calculate momentum and density distributions of ¹²C, ¹⁶O, ⁴⁰Ca, and ⁴⁸Ca, and the effects of their tensor components are studied. copyright 1997 The American Physical Society

[en] The long-standing problem of experimental signatures for clustering effects in light nuclei is discussed for the conditions corresponding to a recent experiment. The specific reaction ¹²C(p,p^'α)⁸Be at incident proton energy 300 MeV and fixed proton and alpha-particle angles near the quasielastic peak is discussed. The Glauber approximation with a simple parametrization of the elementary nucleon-nucleon amplitude is used for calculating the cross section. The main emphasis is on the existence of virtually excited cluster configurations and their manifestation in experimental observables. The shell model wave function of the ¹²C ground state is used to extract the weights of excited cluster components and to calculate their contributions to the cross section. The presence of several excited components and their complicated interference influence the shape and the height of the quasielastic peak; the change can reach an order of magnitude. It is shown that the cross section for cluster emission with the excitation of ⁸Be into the first excited 2⁺ state is small as compared to the process leaving ⁸>Be in its ground state. copyright 1997 The American Physical Society