Several characteristics of fission accompanied by long range alpha particles (LRA) have been studied in the thermal neutron induced fission of²³⁵U. The kinetic energies of fission fragments and the LRA were measured with a back-to-back ionization chamber and semiconductor detectors respectively. The kinetic energies of the two fragments and the LRA in LRA fission, along with the energies of pair fragments in the normal binary fissions, were recorded event by event on a magnetic tape by means of a four-parameter data acquisition system. The data were analysed to study the dependence of different quantities in LRA fission on the fragment mass ratio, LRA energy and the total kinetic energy of the fission fragments. It is seen that the most probable energy of LRA increases significantly for near symmetric mass divisions. The total kinetic energy for all mass ratios in LRA fission is found to be (2.6±0.7) MeV larger than that in binary fission. The difference in the total kinetic energies in LRA and binary fissions is seen to be dependent on mass ratio. This result may suggest that the scission configuration in LRA fission is different for different mass ratios. Correlations between the fission fragment and LRA energies have been studied for several mass ratios. It is seen that the most probable fragment kinetic energyĒ_k varies nearly linearly with the LRA energyE_a for various mass divisions but the variation of the most probable LRA energyĒ_a with fragment kinetic energyE_k is found to deviate from linearity for several mass ratios. From a least square fit to the variation ofĒ_k withE_a it is found that the slope (dĒ_k/dE_a) increases with the increase in mass ratio. The present results are discussed to arrive at a better understanding of the scission configuration in the fission accompanied by LRA emission.

The yields and energy spectra of light charged particles emitted in the fission of²³⁵U have been measured in the neutron energy range of 100 keV to 1 MeV. The yield of long range alpha particles is found to increase around 200 keV neutron energy compared to thermal fission. A low energy component observed in the energy spectrum was assigned to the tritons emitted in fission. The yield of this triton component is seen to have a marked increase around 500 keV. These results indicate that LCP yield is influenced by the transition state level characteristics.

Studies of prompt radiations emitted in fission were started at Trombay in the late 1950’s by Dr R Ramanna and over the years extensive investigations on the emission of prompt neutrons, gamma ray and K x-rays in fission were carried out with neutron beams fromapsara andcirus reactors. In the early 1960’s studies on the emission of light-charged particles in fission, which is a rare mode of fission, were also started. This paper reviews some of the recent studies on the emission of light-charged particles (lcp) in fission which were carried out with a view to investigate the mechanism oflcp emission, the scission configuration and the dynamics of the last stages of the fission process.

The emission of light charged particles in the fission process is of interest as they are believed to emerge from the neck region of the deformed fissioning nucleus at a time close to the scission point and may thus prove a useful probe to investigate the last stages of fission close to the rupture point. Experimental results on light charged particle emission and the efforts made to obtain information about the scission point parameters therefrom are reviewed.

The emission spectra of prompt fission neutrons from mass and kinetic energy selected fission fragments have been measured in²³⁵U(n_th,f). Neutron energies were determined from the measurement of the neutron time of flight using a NE213 scintillation detector. The fragment energies were measured by a pair of surface barrier detectors in one set of measurements and by a back-to-back gridded ionization chamber in the second set of measurements. The data were analysed event by event to deduce neutron energy in the rest frame of the emitting fragment for the determination of neutron emission spectra and multiplicities as a function of the fragment mass and total kinetic energy. The results are compared with statistical model calculations using shell and excitation energy dependent level density formulations to deduce the level density parameters of the neutron rich fragment nuclei over a large range of fragment masses.

The measurements of fission fragment angular distributions for the system¹⁹F+²³²Th have been extended to the sub-barrier energies of 89.3, 91.5 and 93.6 MeV. The measured anisotropies, within errors are nearly the same over this energy region. However, the deviation of the experimental values of anisotropies from that of standard statistical model predictions increases as the bombarding energy is lowered.

The³²S +²⁷Al reaction was studied to investigate the deep inelastic collisions at a bombarding energy of 130 MeV which is well above the Coulomb barrier. The energy distributions of the binary decay products of 6⩽Z⩽10 were determined using a large area position sensitive ionization chamber. The average kinetic energies of the reaction products indicate that the exit shapes correspond to highly stretched scission configurations in the deep-inelastic processes.

Study of heavy ion induced fusion-fission reactions at near and below barrier energies has attracted a great deal of attention in recent years, due to the observations of anomalous features in the fragment angular distributions for many target-projectile systems. Additionally there are also measurements of the fragment spin distributions and time-scales of the fusion-fission reactions, which have provided important information on the dynamics of these processes. In the present paper, the emphasis would be to highlight some of the recent experimental findings and their implications on the dynamics of the fusion-fission reactions in heavy ion collisions at near and above barrier energies.