Radiochemistry Programme at Pelletron

The Radiochemistry programme at Pelletron facility consists of radiochemical studies on heavy ion induced fission, complete and incomplete fusion in heavy ion reactions, synthesis of heavy elements and development of radiochemical separation procedures for radioisotopes of special importance.

In the field of nuclear fission, mass and charge distribution studies have been carried out in the fission of ²³²Th by ¹²C, ¹⁶O and ¹⁹F at beam energies around 5-6 MeV/ nucleon by recoil catcher technique followed by off-line gamma-ray spectroscopy of fission products. The results show significant amount of transfer induced fission events apart from fusion-fission. Using the measured charge distribution parameters, the transfer fission cross section was delineated from the fusion-fission cross section. The fraction of transfer fission cross section was found to decrease with the increasing beam energy. Mass resolved angular distribution studies were aimed at investigating the dependance of angular anisotropy on the mass asymmetry, which in turn gives information about the correlation between the mode of mass division and saddle point shapes. Mass resolved angular distribution studies in ¹⁰B, ¹²C and ¹⁶O induced fission of ²³²Th were carried out using the recoil catcher technique and direct off-line gamma-ray spectrometry of fission products. The results showed that the angular anisotropy is independent of mass asymmetry in the case of ¹⁰B and ¹²C, while the same was higher for symmetric mass products than asymmetric products in the case of ¹⁶O. This was explained in terms of the difference in rotational energy for the symmetric and asymmetric modes for large spin of the compound nucleus.

The studies on complete and incomplete fusion reactions in light heavy ion induced reactions on medium mass target nuclei were aimed at investigating the entrance channel mass asymmetry dependence as well as the angular momenta involved in incomplete fusion (ICF) reactions. The experiments included measurement of excitation functions and recoil range distributions of evaporation residues formed in complete and incomplete fusion reactions by recoil catcher technique followed by off-line gamma-ray spectroscopy. The systems studied involved projectiles like ¹²C, ¹⁶O and ¹⁹F and the targets such as ⁸⁹Y, ⁹³Nb and ¹⁰³Rh, The energy spectra and angular distribution of projectile like fragments were also measured in some cases by silicon based telescopes.. The general results of these investigations are that ICF reactions start competing with complete fusion (CF) reactions just above the Coulomb barrier and the probability of ICF depends upon the entrance channel mass asymmetry. Analysis of the relative yields of evaporation residues formed in ICF reaction showed that these reactions are associated with peripheral collisions.

With an aim to study the chemical and nuclear properties of heavy elements, experiments were carried out to synthesize these elements using reactions such as, ¹⁶O + ²³⁸U. The cross sections for the evaporation residues are in the region of microbarns and very careful radiochemical separation procedures are needed to separate these products. In one such study ²⁵⁰Fm was produced and separated from the bulk uranium target and its cross section was measured. The development of radiochemical separation procedures for radioisotopes of special interest is important for production of these isotopes for practical purposes. Many such studies have been carried out on separation of carrier free rare earth radioisotopes from irradiated rare earth targets.

Want to know more? Contact Dr. B. S. Tomar.

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