Fission product mass distribution studies in 35Cl + 176Yb and 35Cl + 165Ho reactions

Many studies on the fission fragment mass distribution in the sub-lead and pre-actinide region have proposed the presence of asymmetric components in this mass region, primarily due to proton shells corresponding to Z ≈ 36, 38. Present studies have been carried out to investigate the mass distributions in the ³⁵Cl + ¹⁷⁶Yb → ²¹¹Fr and ³⁵Cl + ¹⁶⁵Ho → ²⁰⁰Po reactions in the mass region around ~ 200, a transition between the sub-lead and actinide region. Mass distribution studies have been carried out near the entrance channel Coulomb barrier using the recoil catcher technique, followed by off-line γ-ray spectrometry of the fission products. The broad Gaussian nature of the mass distribution in the ³⁵Cl + ¹⁷⁶Yb reaction indicates a dominant symmetric fission contribution. The mass distributions for the ³⁵Cl + ¹⁷⁶Yb and ³⁵Cl + ¹⁶⁵Ho reactions were found to be in gross agreement with GEF (Schmidt et al. in Nucl Data Sheets 131:107, 2016; Schmidt and Jurado in Rep Prog Phys 81:106301, 2018). The GEF model predicts a dominant symmetric fission contribution along with the contribution from the asymmetric fission mode corresponding to Z ≈ 38. The most probable charge, Z_P was varied within a range of ± 1.5 units with respect to that obtained using the unchanged charge density hypothesis to obtain the best agreement with GEF. However, a few experimental mass yields in the mass regions corresponding to Z ≈ 50–52 and Z ≈ 54–56 were observed to be still higher (more than ~ 50%) compared to the GEF predictions. A similar enhancement observed in the corresponding fission product yields indicates possible contributions from the conventional asymmetric fission modes, in addition to the shell corresponding to Z ≈ 38.