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.

The shape parameters of the multiplicity distribution of prompt gamma rays emitted in spontaneous fission of²⁵²Cf were obtained using the multiple coincidence technique. The multiplicity distribution is well represented by a Gaussian distribution. Assuming the average number of prompt gamma rays emitted per fission to be 10.3, the standard deviation of the multiplicity distribution was estimated to be 4.2±0.4. The variation of the standard deviation of the multiplicity distribution has also been obtained as a function of kinetic energy of one of the fragments and was found to exhibit a strong zigzag dependence on the single fragment kinetic energy. The results have been discussed on the basis of the emission mechanism of prompt gamma rays in fission.

The first and the second moments of the multiplicity distribution of prompt gamma rays in spontaneous ternary fission of²⁵²Cf have been measured by the multiple coincidence technique. While both these moments were found to be nearly independent of the energy of the light charged particle accompanying the fission fragments, the width of the multiplicity distribution was larger than that in the case of normal binary fission by about 20%.

Application of energy dispersive X-ray fluorescence (EDXRF) and proton induced X-ray emission (PIXE) methods has been demonstrated for determining the elemental composition of thin film superconducting materials. The results of analysis carried out by EDXRF method have been compared with those obtained by PIXE method. Thin films of YBa₂Cu₃O₇ superconducting material were deposited on various substrates such as thin mylar sheet and thick substrates of SrTiO₃, MgO and Al₂O₃. In thin backing the minimum detection limits obtained for Cu, Y, Ba by the PIXE method are 20 ng, 70 ng and 800 ng respectively and the corresponding values by the EDXRF method are 3000 ng, 600 ng and 1000 ng. Detection limits for samples on thick backings deteriorated to a large extent by both methods.

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.

Dynamical trajectory calculations were carried out for the reactions of¹¹B+²³⁷Np and¹²C,¹⁶O and¹⁹F+²³²Th, having mass asymmetries on either side of the Businaro-Gallone critical mass asymmetry α_BG, in order to examine the mass asymmetry dependence of fusion reactions in these systems. The compound nucleus formation times were calculated as a function of the partial wave of the reaction for all the systems. This study brings out that for systems with α<α_BG, the formation times are significantly larger than for α>α_BG, which is caused by the dynamical effects involved in the large scale shape changes taking place in the fusion process as well as due to the interplay between the thermal and the collective motion during the collision process. The calculated time scales are comparable to the experimental values derived from the pre-fission neutron multiplicity measurements.

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.

The PHENIX experiment consists of a large detector system located at the newly commissioned relativistic heavy ion collider (RHIC) at the Brookhaven National Laboratory. The primary goal of the PHENIX experiment is to look for signatures of the QCD prediction of a deconfined high-energy-density phase of nuclear matter quark gluon plasma. PHENIX started data taking for Au+Au collisions at √sNN=130 GeV in June 2000. The signals from the beam-beam counter (BBC) and zero degree calorimeter (ZDC) are used to determine the centrality of the collision. A Glauber model reproduces the ZDC spectrum reasonably well to determine the participants in a collision. Charged particle multiplicity distribution from the first PHENIX paper is compared with the other RHIC experiment and the CERN, SPS results. Transverse momentum of photons are measured in the electro-magnetic calorimeter (EMCal) and preliminary results are presented. Particle identification is made by a time of flight (TOF) detector and the results show clear separation of the charged hadrons from each other.