Divergence in the Relativistic Mean Field Formalism: A Case Study of the Ground State Properties of the Decay Chain of 214,216,218U Isotopes

A new α-emitting has been observed experimentally for neutron deficient 214U which opens the window to theoretically investigate the ground state properties of 214,216,218U isotopes and to examine α-particle clustering around the shell closure. The decay half-lives are calculated within the preformed cluster-decay model (PCM). To obtain the α-daughter interaction potential, the RMF densities are folded with the newly developed R3Y and the well-known M3Y NN potentials for comparison. The alpha preformation probability (Pα) is calculated from the analytic formula of Deng and Zhang. The WKB approximation is employed for the calculation of the transmission probability. The individual binding energies (BE) for the participating nuclei are estimated from the relativistic mean-field (RMF) formalism and those from the finite range droplet model (FRDM) as well as WS3 mass tables. In addition to Z=84, the so-called abnormal enhancement region, i.e., 84≤Z≤90 and N<126, is normalised by an appropriately fitted neck-parameter ΔR. On the other hand, the discrepancy sets in due to the shell effect at (and around) the proton magic number Z=82 and 84, and thus a higher scaling factor ranging from 10−5–10−8 is required. Additionally, in contrast with the experimental binding energy data, large deviations of about 5–10 MeV are evident in the RMF formalism despite the use of different parameter sets. An accurate prediction of α-decay half-lives requires a Q-value that is in proximity with the experimental data. In addition, other microscopic frameworks besides RMF could be more reliable for the mass region under study. α-particle clustering is largely influenced by the shell effect.

Cluster decay half-lives using asymmetry dependent densities

Adopting different neutron and proton density distributions the cluster decay half-lives have been investigated using double-folding potentials with constant and nuclear asymmetry dependent sets of the parameters of nuclear densities. Two adopted asymmetry dependent sets of the parameters are fitted based on the microscopic calculations and calculated based on the neutron skin/halo-type nuclei assumption and employing experimental rms charge radii. The bulk agreement between theory and experiment has been obtained for entire sets of parameters using calculated cluster preformation probability. The very little differences between skin and halo-type assumption have been observed. However, the notable role of the asymmetry parameter has been seen in relatively large differences between the skin and skin-type with zero thickness.

Cluster decay half-lives in trans-tin and transition metal region using RMF theory

In the present work, we have studied the alpha-like clusters (8Be, 12C, 16O, 20Ne, and 24Mg) decay half-lives in the trans-tin region for (106-116Xe, 108-122Ba, 114-124Ce, and 118-128Nd) and in transition metal region for (156-166Hf, 158-172W, 160-174Os, 166-180Pt, and 170-182Hg) nuclei. These half-lives have been calculated using the shape parametrization model of cluster decay in conjunction with the relativistic mean-field (RMF) model with the NL3* parameter set. Thus calculated cluster decay half-lives are also compared with the half-lives computed using the latest empirical relations, namely Universal decay law (UDL) and the Scaling Law given by Horoi et al.. From the calculated results, it has been observed that in the trans-tin region, the minimum cluster decay half-lives are found at nearly doubly magic or doubly magic daughter 100Sn (Nd = 50, Nd is the neutron number of the daughter nuclei) shell effect at Nd = 50 and in transition metal region, half-lives are minimum at Nd = 82, which is a magic number. Further, the Geiger-Nuttal plots of half-lives showing Q dependence for different alpha-like clusters from various CR emitters that have been plotted are found to vary linearly.

Decay Analysis of 197Tl* Compound Nucleus Formed in 16O + 181Ta Reaction at above Barrier Energy Ec.m.~100 MeV

The decay dynamics of 197Tl* compound nucleus has been studied within the framework of the dynamical cluster-decay model (DCM) at above barrier energy Ec.m. ≈ 100 MeV using quadrupole deformed configuration of decay fragments. The influence of various nuclear radius parameters on the decay path and mass distributions has been investigated by analysing the fragmentation potential and preformation probability. It is observed that 197Tl* nucleus exhibits the triple-humped mass distribution, independent of nuclear radius choice. The most preferred fission fragments of both fission modes (symmetric and asymmetric) are identified, which lie in the neighborhood of spherical and deformed magic shell closures. Moreover, the modification in the barrier characteristics, such as interaction barrier and interaction radius, is observed with the variation in the radius parameter of decaying fragments and influences the penetrability and fission cross-sections. Finally, the fission cross-sections are calculated for considered choices of nuclear radii, and the results are compared with the available experimental data.

Role of Polar vs Non-polar Configurations in the Decay of 268Sg* Compound Nucleus Within the Skyrme Energy Density Formalism

The effect of polar and non-polar configurations is investigated in the decay of 268Sg* compound nucleus formed via spherical projectile (30Si) and prolate deformed target (238U) using the dynamical cluster decay model. The SSK and GSkI skyrme forces are used to investigate the impact of polar and nonpolar (equatorial) configurations on the preformation probability P0 and consequently on the fission cross-sections of 268Sg* nucleus. For non-polar configuration some secondary peaks corresponding to magic shells Z=28 and N=50 are observed, whose magnitude is significantly suppressed for the polar counterpart. The effect of polar and non-polar configurations is further analyzed in reference to barrier lowering parameter ΔVB. The calculated fission cross-section find adequate agreement with experimental data for chosen set of skyrme forces.

Effect of Oriented Nuclei on the Competing Modes of α and One-Proton Radioactivities in the Vicinity of Z = 82 Shell Closure

The purpose of the present work is to investigate the alpha (α) emission as competing mode of one proton emission using the preformed cluster decay model (PCM). PCM is based on the quantummechanical tunneling mechanism of penetration of the preformed fragments through a potential barrier, calculated within WKB approximation. To explore the competing aspects of α and one proton radioactivity, we have chosen emitters present immediately above and below the Z = 82 shell closure i.e. 177Tl and 185Bi by taking into account the effects of deformations (β2) and orientations of outgoing nuclei. The minimized values of fragmentation potential and maximized values of preformation probability (P0) for proton and alpha fragment demonstrated the crucial role played by even Z - even N daughter and shell closure effect of Z = 82 daughter, in 177Tl and 185Bi, respectively. The higher values of P0 of the one proton further reveal significance of nuclear structure in the proton radioactivity. From the comparison of proton and α decay, we see that the former is heavily dominating with larger values of P0 in comparison to the later. Theoretically calculated half-lives of one proton and α emission for spherical and deformed considerations have also been compared with available experimental data.

Enhanced Fission Probability of Even-Z Fragments in the Decay of Hot and Rotating 210Rn* Compound System

Mass and charge distribution of the cross-section for the fission fragments obtained in the decay of hot and rotating compound system formed in the reaction 48Ca + 162Dy → 210Rn* at an incident energy 139.6 MeV has been calculated using the dynamical cluster-decay model. Isotopic composition for each element belonging to the symmetric mass region has been obtained. The shell closure at N=50 for light and at Z=50 for heavy mass binary fragments gives a deep minima in the fragmentation potential at touching configuration and governs the fission partition of the compound system. The fission fragments of the symmetric mass region have their dominating presence along with strong odd-even staggering i.e., even-Z fission fragments are more probable than the odd ones, similar to the observed trends of the yield.