Browsing by Author "K. Mahata"

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Asymmetric fission around lead: The case of Po 198
(American Physical Society, 2019) Shilpi Gupta; C. Schmitt; K. Mahata; A. Shrivastava; P. Sugathan; A. Jhingan; K.S. Golda; N. Saneesh; M. Kumar; G. Kaur; L. Stuttgé; D. Arora; H. Arora; A. Chatterjee; K. Chauhan; S.K. Duggi; D.P. Kaur; V. Mishra; Prashant N. Patil; K. Rani
Asymmetric low-energy fission of neutron-deficient nuclei around lead is addressed with the measurement of fragment mass and total kinetic energy properties for the fissioning system Po198 produced in heavy-ion fusion. Interpretation of the measurement for such a transitional nucleus at finite excitation energy is challenging. The presence of asymmetric partitions is suggested by the observed weak dependence of the total kinetic energy on mass and by the nonmonotonic evolution of the fragment-mass distribution width with excitation energy. The interpretation is supported by microscopic model calculations as well as by the results of an advanced semiempirical code. Combined with previous experiments in the region, the present measurement contributes to establish the evolution of the fragment-mass distribution as a function of the fissioning system. The connection between the "new" and the "old" islands of asymmetric fission is discussed. © 2019 American Physical Society.
Collective enhancement in nuclear level density
(American Physical Society, 2019) G. Mohanto; A. Parihari; P.C. Rout; S. De; E.T. Mirgule; B. Srinivasan; K. Mahata; S.P. Behera; M. Kushwaha; D. Sarkar; B.K. Nayak; A. Saxena; A. K. Rhine Kumar; A. Gandhi; Sangeeta; Nabendu K. Deb; P. Arumugam
Several experimental investigations have reported evidence of collective enhancement of the nuclear level density and its fadeout. However, a suitable method is needed for experimental determination of the enhancement factor as a function of excitation energy. In this study, neutron spectra were measured in coincidence with evaporated α particles produced in the reactions B11+Ta181,Au197. The nuclear level density parameter has been extracted for the Os(A≈188) and Pb(A≈204) isotopes by comparing neutron spectra with statistical model prediction. Evidence for collective enhancement has been found for Os nuclei whereas no such enhancement has been seen for Pb nuclei. The energy-dependent enhancement factor has been extracted by simultaneous fitting of the neutron spectra at various excitation energies. Near a temperature of 0.8 MeV, the enhancement starts to fadeout which is lower than the theoretically predicted temperature of 1.4 MeV for Os187. Also, free energy surface calculation shows that the Os187 nucleus undergoes a transition from collective prolate to noncollective oblate shape close to the temperature of 0.8 MeV, corroborating the early fadeout. No such shape transition is seen for Pb203. © 2019 American Physical Society.
Experimental study of the transfer-induced fission fragment angular distribution in the Li 6 + U 238 reaction
(American Physical Society, 2017) A. Parihari; G. Mohanto; Gurpreet Kaur; A. Jhingan; K. Mahata; R.G. Thomas; P.C. Rout; E.T. Mirgule; V.V. Desai; B. Srinivasan; C. Joshi; V. Mishra; M. Kushwaha; Shilpi Gupta; D. Sarkar; S.V. Suryanarayana; A. Shrivastava; N.L. Singh; A. Misra; B.K. Nayak; A. Saxena
Transfer-induced fission fragment angular distribution measurements have been carried out in Li6+U238 reaction at beam energies of 36 and 40 MeV in coincidence with projectile-like fragments. The fission fragment anisotropies for α- and deuteron-transfer-induced fission reactions are obtained with respect to the recoil direction. The anisotropy values for transfer-induced fissions are observed to be either similar or lower than the inclusive measurement. In order to quantitatively understand the present experimental data on transfer-induced fission, anisotropy values have been compared with the preequilibrium fission model considering ground-state spin of the projectile and/or target. It is found that the model predicts the inclusive and exclusive anisotropy data reasonably well. © 2017 American Physical Society.
Fusion of O 16 + Ho 165 at deep sub-barrier energies
(American Physical Society, 2021) Saikat Bhattacharjee; A. Mukherjee; Ashish Gupta; Rajkumar Santra; D. Chattopadhyay; N. Deshmukh; Sangeeta Dhuri; Shilpi Gupta; V.V. Parkar; S.K. Pandit; K. Ramachandran; K. Mahata; A. Shrivastava; Rebecca Pachuau; S. Rathi
Fusion cross sections have been measured for the asymmetric system O16+Ho165 at energies near and deep below the Coulomb barrier with an aim to investigate the occurrence of fusion hindrance for the system. Cross sections down to ≈700 nb have been measured using the off-beam γ-ray technique. The fusion cross sections have been compared with the coupled channel calculations. The energy onset of fusion hindrance appears to occur at Ec.m.=57±0.85 MeV, where a deviation in the slope of the experimental logarithmic derivative compared to that of coupled channel calculations has been observed. This is in agreement with the value obtained from the touching point configuration of the adiabatic model. © 2021 American Physical Society.