Systematic and consistent microscopic description of measured reaction cross sections at low projectile en-ergies is presented. Finite-range Glauber model (GM-F) along with the Coulomb modification is used. The required inputs, namely the neutron and proton density distributions of the relevant projectiles and the targets, are calculated in the relativistic mean field framework. The GM-F reproduces the experiment well. At high projectile energies both the GM-F and the zero-range Glauber model in the optical limit (GM-Z) yield almost identical results; however, the GM-F in general is superior at low projectile energies, as expected.

The reaction cross sections for neutron-rich nuclei with 7 <= Z <= 18 on a Si-28 target at intermediate energies (30-65A MeV) are calculated and are compared with the corresponding recently reported new measurements. A finite-range Glauber model along with a Coulomb modification is used. The required nucleon density distributions of the relevant projectiles and the targets are obtained in the relativistic mean field framework. The calculations reproduce the experiment well. A simple phenomenological modification of the zero-range Glauber model is proposed to incorporate the finite-range effects. This one-parameter expression is found to reproduce the experimental reaction cross sections quite well.

The finite range Glauber model along with the Coulomb modification is used to analyze recently measured reaction cross sections with neutron-deficient Ga, Ge, As, Se, and Br isotopes as low-energy projectiles incident on Si-28 target. The required input, namely the neutron and proton density distributions of the relevant projectiles and the target, are calculated in the relativistic mean-field framework. Though the calculations qualitatively agree with the experiment, on the average, slightly overestimate the cross sections. A phenomenological expression with a single parameter is proposed that consistently improves the agreement with the experiment.

Based on the detailed analysis of the reaction cross sections obtained using the finite range Glauber model, a systematic study of strong absorption radii is carried out. A simple phenomenological expression is proposed to calculate reaction cross sections directly using the average nucleon-nucleon cross section for a given target-projectile combination at given energy. Reliability of the model expression is demonstrated through a variety of illustrative examples.

KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.

Gambhir, Y. K.

The alpha-nucleus potential for fusion and decay2008In: Journal of Physics G: Nuclear and Particle Physics, ISSN 0954-3899, E-ISSN 1361-6471, Vol. 35, no 6, p. 065109-Article in journal (Refereed)

Abstract [en]

The alpha-nucleus fusion cross sections at energies around and below the barrier and the alpha-decay half lives are calculated in the semi-classical WKB approach using the same microscopic as well as empirical alpha-nucleus potentials. The microscopic potential is generated within the double-folding framework using M3Y nucleon-nucleon interaction along with the required neutron and proton density distributions calculated in the relativistic mean field theory. It is found that in spite of the excellent results for the half lives the fusion cross sections are underestimated by almost a factor of 3. However, the experimental fusion cross sections can be reproduced by introducing a norm factor (overall multiplicative factor to the potential) 1.3 but this then worsens the agreement for half lives. To verify this observation and for comparison the calculations are repeated using some of the representative empirical potentials available in the literature. The same conclusion emerged. The present study thus indicates that the same alpha-nucleus potential may yield accurate description for both the alpha-nucleus fusion cross sections and alpha-decay half lives only with the introduction of additional parameter(s).

The semiclassical Wigner-Kirkwood h expansion method is used to calculate shell corrections for spherical and deformed nuclei. The expansion is carried out up to fourth order in h. A systematic study of Wigner-Kirkwood averaged energies is presented as a function of the deformation degrees of freedom. The shell corrections, along with the pairing energies obtained by using the Lipkin-Nogami scheme, are used in the microscopic-macroscopic approach to calculate binding energies. The macroscopic part is obtained from a liquid drop formula with six adjustable parameters. Considering a set of 367 spherical nuclei, the liquid drop parameters are adjusted to reproduce the experimental binding energies, which yields a root mean square (rms) deviation of 630 keV. It is shown that the proposed approach is indeed promising for the prediction of nuclear masses.

KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.

Gupta, M.

The superheavy elements: overview2009In: INDIAN JOURNAL OF PHYSICS AND PROCEEDINGS OF THE INDIAN ASSOCIATION FOR THE CULTIVATION OF SCIENCE, ISSN 0973-1458, Vol. 83, no 5, p. 661-669Article in journal (Refereed)

Abstract [en]

Superheavy Elements (SHE) up to Z = 118 have been produced and studied. The Relativistic Mean Field (RMF) theory provides a reasonably good description of the ground state properties (binding energies, Q-values, deformation, radii, densities etc.) of these elements. Shell closures revealed by the vanishing/minimum pairing energy, are predicted for specific combination of neutron number N and proton number Z, specifically at N = 38, 164, 172, 184 and 198. Some of these have been confirmed experimentally. Future experiments are expected to validate the remaining predictions. Microscopic alpha-nucleus potential generated in the frame work of double folding model, employing the RMF densities for the daughter nucleus and the experimental densities for the alpha, along with the density dependent M3Y nucleon - nucleon interaction, qualitatively reproduce the experimental half lives for alpha - decay, calculated in the WKB approximation.

A comparative study of the S-matrix and the WKB methods for the calculation of the half widths of alpha decay of super heavy elements is presented. The extent of the reliability of the WKB methods is demonstrated through simple illustrative examples. Detailed calculations have been carried out using the microscopic alpha-daughter potentials generated in the framework of the double-folding model using densities obtained in the relativistic mean field theories. We consider alpha-nucleus systems appearing in the decay chains of super heavy parent elements having A = 277, Z = 112 and A = 269, Z = 110. For negative and small positive log T-1/2 values the results from both methods are similar even though the S-matrix results should be considered to be more accurate. However, when log inverted perpendicular(1/2) values are large and positive, the width associated with such state is infinitesimally small and hence calculation of such width by the S-matrix pole search method becomes a numerically difficult problem. We find that overall, the WKB method is reliable for the calculation of half lives of alpha decay from heavy nuclei.