• Antony Joseph

Articles written in Pramana – Journal of Physics

• Exotic decay in Ba isotopes via 12C emission

Considering Coulomb and proximity potentials as barriers, we have calculated the half lives for 12C emission from various Ba isotopes using different mass tables. The half life for 112Ba isotope calculated by us is 6.020×103 s which is comparable with the experimental value 5.620×103 s. From our study it is found that 114Ba is the good parent for 12C emission whose emission rate is favorable for measurement. The half lives predicted by us lie very close to those reported by Shanmugam et al using their cubic plus Yukawa plus exponential model. It is observed that inclusion of proximity potential does not produce significant deviation from the linear nature of the Geiger-Nuttall plots. Also it is found that the neutron excess in the parent nuclei slows down the exotic decay process.

• Exotic decay in cerium isotopes

Half life for the emission of exotic clusters like 8Be, 12C, 16O, 20Ne, 24Mg and 28Si are computed taking Coulomb and proximity potentials as interacting barrier and many of these are found well within the present upper limit of measurement. These results lie very close to those values reported by Shanmugam et al using their cubic plus Yukawa plus exponential model (CYEM). It is found that 12C and 16O emissions from 116Ce and 16O from 118Ce are most favorable for measurement (T1/2&lt;1010 s). Lowest half life time for 16O emission from 116Ce stress the role of doubly magic 100Sn daughter in exotic decay. Geiger-Nuttall plots were studied for different clusters and are found to be linear. Inclusion of proximity potential will not produce much deviation to linear nature of Geiger-Nuttall plots. It is observed that neutron excess in the parent nuclei slow down the exotic decay process. These findings support the earlier observations of Gupta and collaborators using their preformed cluster model (PCM).

• Exotic decay: Transition from cluster mode to fission mode

Exotic decay of some heavy nuclei with Z≥100 formed in heavy ion ‘cold fusion’ reaction were studied taking interacting barrier consisting of Coulomb and proximity potential. Calculated half-life time shows that some modes of decay are well within the present upper limit for measurements (T1/2&lt;1030 s). Cluster formation probabilities are calculated for different clusters within fission model. It is found that transition from cluster mode to fission mode take place at mass of the cluster, A2=20 in exotic decay which is comparable with the value A2=16 of Shanmugam et al based on cubic plus Yukawa plus exponential model (CYEM).

• Effect of parent and daughter deformation on half-life time in exotic decay

Taking Coulomb and proximity potential as interacting barrier for post-scission region we calculated half-life time for different modes of exotic decay treating parent and fragments as spheres and these values are compared with experimental data. We studied the effect of deformation of parent and daughter on half-life time treating emitted cluster as spherical. When deformations are included half-life time values are found to decrease, though slightly. It is found that parent deformation alone will not produce appreciable change in half-life time since it affects relatively small pre-scission part of the barrier.

• Cluster radioactivity in xenon isotopes

Half-life time and branching ratio for cluster decay from various xenon isotopes are studied taking Coulomb and proximity potentials as interacting barrier. Inclusion of proximity potential reduces the height of potential barrier, which closely agrees with the experiments. It is found that4He,8Be,12C and16O emissions are well within the present upper limit for measurements (T1/2 1030 s). Our predicted half-life time values lie close to those values reported by Gupta and collaborators based on preformed cluster model (PCM) and also with those values reported by Poenaruet al based on ASAFM. The calculated half-life time shows that8Be from108Xe and110Xe are most favourable for emission (T1/2 ≈ 108 s). LowestT1/2 value for8Be emission from108Xe stress the role of doubly magic100Sn daughter in cluster decay process. The logarithm of half-life time calculated for4He emission from110Xe is −0.39 s which is in good agreement with experimental value which is −0.40 s. Geiger-Nuttall plots for all clusters are studied and are found to be linear. Nuclear structure effect and shell effect are evident from the observed variation in slope and intercept of Geiger—Nuttall plots. It is found that neutron excess in the parent will slow down the cluster decay process.

• Cluster emission in superdeformed Sr isotopes in the ground state and formed in heavy-ion reaction

Cluster decay of superdeformed76, 78, 80Sr isotopes in their ground state are studied taking the Coulomb and proximity potential as the interacting barrier for the post-scission region. The predictedT1/2 values are found to be in close agreement with those values reported by the preformed cluster model (PCM). Our calculation shows that these nuclei are stable against both light and heavy cluster emissions. We studied the decay of these nuclei produced as an excited compound system in heavy-ion reaction. It is found that inclusion of excitation energy increases the decay rate (decreasesT1/2 value) considerably and these nuclei become unstable against decay. These findings support earlier observation of Guptaet al based on PCM.

• Cold valleys in the radioactive decay of 248-254Cf isotopes

Based on the concept of cold valley in cold fission and fusion, we have investigated the cluster decay process in 248-254Cf isotopes. In addition to alpha particle minima, other deep minima occur for S, Ar and Ca clusters. It is found that inclusion of proximity potential does not change the position of minima but minima become deeper. Taking Coulomb and proximity potential as interacting barrier for post-scission region, we computed half-lives and other characteristics for various clusters from these parents. Our study reveals that these parents are stable against light clusters and unstable against heavy clusters. Computed half-lives for alpha decay agree with experimental values within two orders of magnitude. The most probable clusters from these parents are predicted to be 46Ar, 48,50Ca which indicate the role of doubly or near doubly magic clusters in cluster radioactivity. Odd A clusters are found to be favorable for emission from odd A parents. Cluster decay model is extended to symmetric region and it is found that symmetric fission is also probable which stresses the role of doubly or near doubly magic 132Sn nuclei. Geiger-Nuttal plots were studied for various clusters and are found to be linear with varying slopes and intercepts.

• X-ray attenuation around $K$-edge of Zr, Nb, Mo and Pd: A comparative study using proton-induced X-ray emission and $^{241}$Am gamma rays

Mass attenuation coefficients ($\mu/\rho$) for Zr, Nb, Mo and Pd elements around their $K$-edges are measured at 14 energies in the range 15.744–28.564 keV using secondary excitation from thin Zr, Nb, Mo, Rh, Pd, Cd and Sn foils. The measurements were carried out at the $K_{\alpha} and$K_{\beta}$energy values of the target elements by two techniques: (1) Proton-induced X-ray emission (PIXE) and (2)$^{241}\$Am (300 mCi) source. In PIXE, 2 MeV proton-excited X-rays were detected by a Si(Li) detector. In the second case, X-rays excited by 59.54 keV photons from the targets were counted by an HPGe detector under a narrow beam good geometry set-up with sufficient shielding. The results are consistent with theoretical values derived from the XCOM package and indicate that the PIXE data have better statistical accuracy.

• # Pramana – Journal of Physics

Volume 95, 2021
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019