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Articles written in Pramana – Journal of Physics

• Heavy ion fusion with lead and bismuth targets

The cold fusion reactions with lead and bismuth as targets were used in the synthesis of superheavy elements (SHE) with mass number up to 113. Researchers ignored the cold fusion reactions in the synthesis of SHE>113. This may be due to the improper choice of projectiles. The present study focusses on cold fusion reactions leading to the formation of SHE from Z = 112 to 126. Suitable projectiles for the fusion reaction using $^{208}$Pb and $^{209}$Bi targets were identified. The fusion and evaporation residue cross-sections are evaluated usingadvance statistical model. The produced cross-sections were compared with the available experiments. Suitable projectiles for synthesising the superheavy elementswith Z = 104–126 using lead and bismuth targets are predicted.The predicted production cross-sections vary from nanobarn (nb) to picobarn (pb). The use of spherical–spherical projectile and target yields larger cross-sections than spherical–deformed or deformed–spherical projectile andtarget combination.

• On the time-scale of quasifission and Coulomb fission

The Coulomb fission may take place in a reaction if the maximum Coulomb excitation energy transfer exceeds the fission barrier of either the projectile or the target nucleus. This condition is satisfied in all the reactions used for the earlier blocking measurements of fission time-scale except for the reaction $^{208}$Pb + natural Ge crystal, where the time-scale is below the measurement limit of the blocking technique $\les$ 1 as. Inclusion of Coulomb fission in the data analysis of the blocking experiments leads us to interpret the measured time-scales longer than a few attoseconds (as) (about 1–2.2 as) due to slow Coulomb fission and those shorter than 1 as, as due to quasifission and fast Coulomb fission. Consequently, this finding resolves the critical discrepancies between the fission time-scales measured using the nuclear and blocking techniques. This, in turn, validates the fact that the quasifission and fast Coulomb fission time-scales are indeed of the order of zeptosecond (zs) in accordance with the nuclear experiment sand theories. The present results thus provide an essential input to the understanding of the fusion evaporation reaction during the formation of heavy elements.

• An accurate empirical formula for the average total kinetic energy released in fission

The empirical formulae for an average total kinetic energy released during the symmetric and asymmetric fission has been estimated by considering the recently available experimental data. An empirical formulae is deduced by the systematic variation of $\langle$E$_K$$\rangle with Z^2/A^{1/3}. The least-square analysis of symmetricfission yields \langleE_K$$\rangle$ = 0.12014(Z$^2$/A$^{1/3}$) + 5.99 MeV in the atomic number range 23 ≤ Z ≤ 120 and mass number range 46 ≤ A ≤ 302, whereas asymmetric fission yields $\langle$E$_K$$\rangle$ = 0.1367(Z$^2$/A$^{1/3}$) − 18.94 MeV in the atomic number range 78 ≤ Z ≤ 102 and mass number range 178 ≤ A ≤ 258. The root mean square error (RMSE) values are smaller than the previous systematics. The covariance of matrix and its parameters are evaluated both in symmetric and asymmetric fission of the nuclei along with the error band.

• # Pramana – Journal of Physics

Volume 97, 2023
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