International Journal of Modern Physics E

This is a review of the principal motivations behind, and the status of, color transparency physics, with particular emphasis on the effects of a large coherence length at high energies.

A long-standing issue in nuclear structure is whether double giant resonances do exist. Exotic excitations like the double giant-dipole were predicted for many years but not observed experimentally until recently. Several experiments have been carried out at Los Alamos National Laboratory and other laboratories to search for these new collective modes of the nucleus. The results discover the existence of two previously unobserved types of double giant resonances. This work presents a review of the pion double charge exchange data and the analysis which support the existence of two such exotic vibrational nuclear modes: the giant dipole resonance built on the isobaric analog state and the double isovector giant-dipole resonance. Excitation of multiphonon states also becomes a very likely process in relativistic heavy-ion reactions where a direct identification of the double giant-dipole resonance has been reported recently.

This is a review of the current status of theoretical treatments of neutrino-nucleus reactions that are relevant to the detection of astrophysical neutrinos. Various nuclear physics aspects involved in the evaluation of the neutrino-nucleus reaction cross-sections are critically surveyed.

The deuteron-nucleus interaction has been studied in the approximation where the deuteron radius and the nuclear surface diffuseness are small compared with the nuclear radius. The closed formulae have been derived for the integrated cross-sections of different deuteron-nucleus interaction processes and for differential cross-sections of the deuteron elastic scattering and the deuteron inelastic scattering with excitation of the low lying vibrational states of nuclei. It is shown that the allowance for nuclear surface diffuseness substantially influences the values of the different deuteron-nucleus reaction cross-sections.

We examine the prediction of supersymmetric quantum mechanics that bands with identical gamma-ray energies occur in quartets. The experimental data suggest that this scenario is actually realized in nature. In the A=150 mass region, four known pairs of isospectral bands can be grouped in two quartets, while there are indications of such patterns around A=190. We introduce a small supersymmetry breaking, necessary to describe the details of the data. We derive relations among the transition rates that can be used to test our predictions.

Pairing vibrations in strongly rotating nuclei are treated using the variational approach. The residual interaction is assumed to be due to monopole pairing. A simple generalization of the standard BCS plus RPA enables us to obtain the set of mutually dependent equations describing the quasi-particles and the pairing vibrational phonons.

Cold fission of radioactive nuclei is studied in the super-asymmetric mass region of exotic cluster radioactivity, using the quantum-mechanical fragmentation theory (QMFT) based saddle-point fission (SPF) model for calculating the decay half-life times. The calculations show that cold fission also prefers light fragments like ^24–26Ne, ^28,30Mg, ^32,34,36Si, ³⁷P ³⁸S, ⁴⁶Ar and ^48,50Ca, some of which are observed in exotic cluster radioactivity. The predictions of the SPF model calculations are compared with the available exotic cluster-decay experimental data and the calculations based on the preformed-cluster model (PCM). The SPF model calculations show large disagreements with both the PCM and cluster-decay experimental data. For clusters of mass A₂<46, the predicted half-lives for the SPF model are much smaller than for the PCM, which apparently means predicting the cold fission as a more probable process than the cluster-decay. The cold fission predicts some new decay modes which are far more probable (smaller log₁₀ T_1/2-values) as cold fission fragments than as cluster-decay products. For heavier clusters (A₂≥46), the two models (SPF and PCM) make nearly identical predictions, which means predicting an overlap of two processes (cold fission and cluster-decay) for A₂>46. Also, cold fission is found to be more probable than hot fission and a new fission mode (known as bimodel fission) is identified in the neighbourhood of the doubly magic fragment. Our calculations are made for ²³⁴U, ²³⁸Pu, ²⁴¹Am and ²⁵²Cf.

The theory of heavy ion reactions with particle transfer is considered in the framework of the exact finite-range distorted wave Born approximation (EFR-DWBA). Modified Woods-Saxon potentials which include a parity dependent interaction and an angular momentum absorptive term have been used as the ion-ion interactions in the initial and final channels. The bound state interactions are represented by nucleus-nucleus inter-actions which include repulsive and attractive Yukawa type components. The present numerical calculations of the differential cross-sections are in good agreement with the experimental measurements. The distorting parity dependent potentials are found very important in reproducing the cross-sections at backward as well as at intermediate angles. The obtained extracted values of the spectroscopic factors are reasonable.

The excitation function of α-induced reactions on ¹²¹Sb and ¹²³Sb has been measured. The α-beam energy ranges from 55.0±0.5 MeV to 21.9±1.2 MeV. In these experiments, the stacked foil activation technique was used. The reaction yield was measured by counting the gamma ray activity produced by the alpha-induced reactions. Results so obtained were compared with the calculations from the geometry-dependent hybrid (GDH) model. The assumption of initial exciton number n₀=4 with n=2, p=2 and h=0 best satisfies the results measured in the present work. The model calculations were done using the ALICE/LIVERMORE-82 computer code. The pre-equilibrium fraction has also been calculated.