• K P Santhosh

Articles written in Pramana – Journal of Physics

• 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.

• Neutron and proton shell closure in the superheavy region via cluster radioactivity in 280−314 116 isotopes

Based on the concept of cold valley in fission and fusion, the radioactive decay of superheavy280−314116 nuclei was studied taking Coulomb and proximity potentials as the interacting barrier. It is found that the inclusion of proximity potential does not change the position of minima but minima become deeper which agrees with the earlier findings of Gupta and co-workers. In addition to alpha particle minima, the other deepest minima occur for 8Be, 12,14C clusters. In the fission region two deep regions are found each consisting of several comparable minima, the first region centred on 208Pb and the second is around 132Sn. The cluster decay half-lives and other characteristics are computed for various clusters ranging from alpha particle to 70Ni. The computed half-lives for alpha decay match with the experimental values and with the values calculated using Viola–Seaborg–Sobiczewski (VSS) systematic. The plots connecting computed 𝑄 values and half-lives against neutron number of daughter nuclei were studied for different clusters and it is found that the next neutron shell closures occur at $N$ = 162, 172 and 184. Isotopic and isobaric mass parabolas are studied for various cluster emissions and minima of parabola indicate neutron shell closure at $N$ = 162, 184 and proton shell closure at $Z$ = 114. Our study shows that $^{276}_{162}$114 is the deformed doubly magic and $^{298}_{184}$114 is the spherical doubly magic nuclei.

• Stability of 244-260Fm isotopes against alpha and cluster radioactivity

Taking Coulomb and proximity potentials as the interacting barrier we have studied the cold valley in the radioactive decay of 244-260Fm isotopes. It is found that in addition to alpha particle minima, other minima occur at S, Ar and Ca clusters. We have computed the half-lives and other characteristics of different clusters emitted from these parents treating parent, daughter and emitted cluster as spheres. Our study reveals that most of these parents are unstable against alpha and heavy cluster (46Ar, 48,50Ca) emissions and stable against light cluster emission, except 8Be from 244-248Fm isotopes. 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 ($Z = 20$, $N = 28$) and also stress the role of doubly magic 208Pb daughter. The computed half-lives for alpha decay are in good agreement with the experimental data. It is found that the presence of neutron excess in the parent nuclei slows down the cluster decay process. The effect of quadrupole $(\beta_{2})$ and hexadecapole $(\beta_{4})$ deformations of parent and fragments on half-lives are also studied. It is found that inclusion of $\beta_{2}$ and $\beta_{4}$ reduces the height and shape of the barrier (increases barrier penetrability) and hence the half-life decreases.

Decay of neutron-deﬁcient 128−137Gd parents emitting 4He to 32S clusters are studied within the Coulomb and proximity potential model. The predicted half-lives are compared with other models and most of the values are well within the present experimental limit for measurements ($T_{1/2}$ &lt; $10^{30} s$). The lowest $T_{1/2}$ value for 28Si emission from 128Gd indicates the role of doubly magic 100Sn daughter in cluster decay process. It is also found that neutron excess in the parent nuclei slows down the cluster decay process. Geiger–Nuttal plots for all clusters are found to be linear with different slopes and intercepts. The 𝛼-decay half-lives of ${}^{148−152}$Gd parents are computed and are in agreement with experimental data. The role of doubly magic 132Sn daughter in cluster decay process is also examined for various neutron-rich Ba, Ce, Nd, Sm and Gd parents emitting clusters ranging from 4He to 32Si. Alpha-like structures are most probable in the decays leading to 100Sn, while non-𝛼-like structures are probable in the decays leading to 132Sn. The neutron–proton asymmetry in parent and daughter nuclei is responsible for the reduced decay rate in the decay leading to 132Sn.

• Sensitivity in the trajectory of long-range 𝛼-particle

The factors influencing the trajectory of long-range 𝛼-particle in the cold ternary fission of 252Cf are discussed. The trajectory of the 𝛼-particle is studied by considering the influence of the force on the 𝛼-particle due to Coulomb and proximity potentials and is found to have sensitive dependence on the initial position and initial energy of the 𝛼-particle. The sensitivity to initial conditions signifies the presence of deterministic chaos which is characterized by Lyapunov exponent (LE). The LE is calculated using Wolf’s algorithm and found positive which implies that the objectives of trajectory calculations are restricted.

• Role of energy cost in the yield of cold ternary fission of 252Cf

The energy costs in the cold ternary fission of 252Cf for various light charged particle emission are calculated by includingWong's correction for Coulomb potential. Energy cost is found to be higher in cold fission than in normal fission. It is found that energy cost always increases with decrease in experimental yield in all the light charged particle emissions. The higher ground state deformation of the fragments, the odd–even effect and the enhanced yield in the octupole region observed in cold fission are found to be consistent with the concept of energy cost.

• Decay of heavy and superheavy nuclei

We present here, an overview and progress of the theoretical works on the isomeric state 𝛼 decay, 𝛼 decay fine structure of even–even, even–odd, odd–even and odd–odd nuclei, a study on the feasibility of observing 𝛼 decay chains from the isotopes of the superheavy nuclei $Z = 115$ in the range $271 \leq A \leq 294$ and the isotopes of $Z = 117$ in the range $270 \leq A \leq 301$, within the Coulomb and proximity potential model for deformed nuclei (CPPMDN). The computed half-lives of the favoured and unfavoured 𝛼 decay of nuclei in the range $67 \leq Z \leq 91$ from both the ground state and isomeric state, are in good agreement with the experimental data and the standard deviation of half-life is found to be 0.44. From the 𝛼 fine structure studies done on various ranges of nuclei, it is evident that, for nearly all the transitions, the theoretical values show good match with the experimental values. This reveals that CPPMDN is successful in explaining the fine structure of even–even, even–odd, odd–even and odd–odd nuclei. Our studies on the 𝛼 decay of the superheavy nuclei ${}^{271−294}$115 and ${}^{270−301}$117 predict 4𝛼 chains consistently from ${}^{284,285,286}$115 nuclei and 5𝛼 chains and 3𝛼 chains consistently from ${}^{288−291}$117 and ${}^{292}$117, respectively. We thus hope that these studies on ${}^{284−286}$115 and ${}^{288−292}$117 will be a guide to future experiments.

• Superheavy elements and decay properties

The 𝛼 decay properties of the isotopes of 𝑍 = 115, 117, 118 and 119 have been extensively investigated, focussing on the newly synthesized isotopes within the Coulomb and proximity potential model for deformed nuclei (CPPMDN). The 𝛼 half-lives have also been evaluated using the Viola–Seaborg systematic (VSS) and the analytical formulae of Royer and it can be seen that our calculated values match well with these theoretical values. The mode of decay of these isotopes has also been studied by calculating the spontaneous fission half-lives. Thus, we have predicted 4𝛼 chains from 287115, 3𝛼 chains from 288115, 3𝛼 chains from 293117, 4𝛼 chains from 294117 and 3𝛼 chains from 294118 and, it can be seen that our predictions on the 𝛼 decay chains also match well with the experimental observations. The study on 𝑍 = 119 has predicted six consistent 𝛼 chains from 292−295119, 5𝛼 chains from 296119, 4𝛼 chains from 297119 and 3𝛼 chains from 298,299119. Thus, through our study on isotopes of 𝑍 = 115, 117, 118 and 119 superheavy nuclei, we could predict the range of isotopes that may be detectable using 𝛼 decay and we hope that the findings on the isotopes of 𝑍 = 119 will provide a new guide for future experiments.

• # Pramana – Journal of Physics

Volume 96, 2022
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Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019