D. C. Biswas

Specific energy-loss behaviour of fission fragments along their range in P-10 gas

Abstract Energy loss of 252 Cf fission fragments in P-10 gas (90% Ar + 10% CH 4 ) at different pressures has been measured using a hybrid ΔE − E R detector telescope. The data were fitted to a polynomial function and the differential or specific energy loss (d E /d x ) along the range of the fission fragments was determined for different fragment kinetic energies. The experimentally measured energy-loss data for most probable light and heavy fragments are compared with calculations using different available energy-loss expressions based on the Bethe energy-loss formula.

A position sensitive ionisation chamber for measurement of fission fragments and medium mass heavy ions

A position sensitive ionisation chamber telescope is described with ΔEgasEgas sections which can measure simultaneously the specific energy loss ΔE, energy E and the position of heavy ion reaction products in the median plane. The position information is derived by having a split ΔE structure and by adopting the pulse division method for the signals collected by the two ΔE sections. For on-line angle calibration, the E-part of the anode structure is also split into five segments. The detector was tested with fission fragments from a 252Cf spontaneous fission source and with heavy ions from the pelletron tandem accelerator. Simultaneous measurement of ΔE and E gives good separation for heavy and light fission fragment groups. The position resolution is found to be 1.1 mm for fission fragments. The detector has been used in heavy ion reaction studies for measuring fission fragments, providing good separation from projectile-like particles.

A large area position-sensitive ionization chamber for heavy-ion-induced reaction studies

Abstract A large area position-sensitive ionization chamber with a wide dynamic range has been developed to measure the mass, charge and energy of the heavy ions and the fission fragments produced in heavy-ion-induced reactions. The split anode geometry of the detector makes it suitable for both particle identification and energy measurements for heavy ions and fission fragments. The detector has been tested with α particles from 241 Am– 239 Pu source, fission fragments from 252 Cf and the heavy-ion beams from the 14UD Mumbai Pelletron accelerator facility. Using this detector, measurements on mass and total kinetic energy distributions in heavy-ion-induced fusion–fission reactions have been carried out for a wide range of excitation energies. Results on deep inelastic collisions and mass–energy correlations on different systems using this detector setup are discussed.

Charge determination of fission fragments via energy loss and X-ray measurements

Abstract Energy loss of fission fragments of specified charges and kinetic energies have been measured with a gas detector telescope. The singles data from the telescope (DE-E R ) and coincidence data with a HP Ge X-ray detector (DE-E R -X) were taken using a 252 Cf fission source. An empirical expression for the dependence of Z eff on charge and energy of fragments has been determined by fitting the observed energy loss behaviour of the fission fragments. The resolution in the measurement of charge from event by event analysis of DE-E R data for the light fragment mass group was found to be about 1.8 charge units (FWHM). The present data were analysed to determine the fragment charge distribution as well as the X-ray yield per fragment in 252 Cf fission.

Deep inelastic collisions of32S +27Al reaction at 130 MeV bombarding energy

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.

Evidence of massive cluster transfers in {sup 19}F+{sup 232}Th reaction at near barrier energies

Yields and angular distributions of the transfer reaction products have been measured in the {sup 19}F+{sup 232}Th reaction at bombarding energies near the Coulomb barrier. The transfer probabilities were calculated ({ital P}{sub tr}) from the measured differential cross sections at the grazing angle, for the most dominant channels for given ({Delta}{ital N}) transfers. The values of {ital P}{sub tr} show, in general, an exponential dependence on the ground state {ital Q} value ({ital Q}{sub 0}) of the reaction and the large cross sections observed for 1{alpha} and 2{alpha} transfer channels are largely accounted by the {ital Q}-value variations. However, the transfer channels of {Delta}{ital N}=5, 9, and 12 leading to {sup 14}C, {sup 10}Be, and {sup 7}Li products, respectively, show strong enhancements in the transfer probabilities. The large cross sections in these channels may imply simultaneous correlated transfers of ({alpha}{ital p}), ({alpha}{ital p},{alpha}), and (3{alpha}) clusters from the {sup 19}F projectile to the target.

Influence of breakup on fusion barrier distributions

Fusion barrier distributions have been extracted from the quasi-elastic scattering excitation functions, measured at backward angle θlab = 160° in reactions of 6,7Li+209Bi. The present results have been compared with the barrier distributions obtained from the fusion excitation function measurements for the above mentioned systems. The fusion barrier distributions from the quasi-elastic scattering excitation functions have been analyzed with simplified Coupled Channels calculations using Fresco. Inclusions of resonant states for both 6,7Li projectiles improve the predictions to describe the measured quasi-elastic scattering excitation functions and barrier distributions. For both the reactions peak positions of fusion barrier distributions are shifted towards a lower energy side in comparison to that obtained from the fusion excitation function measurements. The observed discrepancy in peak positions of barrier distributions obtained from quasi-elastic scattering and fusion excitation function measurement...

Angular momentum dependence of the nuclear level-density parameter around Z ~ 50

{alpha}-particle evaporation spectra and {gamma}-ray multiplicities were measured for various target-projectile systems corresponding to residual nuclei in the range of Z{sub R}=48-55 and with excitation energy in the range of 30-40 MeV. The high-energy part of the evaporation spectra were analyzed using the statistical model code PACE2 to derive values of the inverse level-density parameter (K). The K values were found to be in the range of 9.0-10.5 for all systems. Angular momentum dependence of the inverse level-density parameter was investigated using the {gamma}-ray multiplicity data. It is seen that there are strong variations in K as a function of angular momentum for many systems. Present results provide important input information for a systematic understanding of the statistical properties of nuclei at moderate excitation energies and angular momenta.

Determination of the {sup 233}Pa(n,f) reaction cross section from 11.5 to 16.5 MeV neutron energy by the hybrid surrogate ratio approach

A new hybrid surrogate ratio approach has been employed to determine neutron-induced fission cross sections of {sup 233}Pa in the energy range of 11.5 to 16.5 MeV for the first time. The fission probability of {sup 234}Pa and {sup 236}U compound nuclei produced in {sup 232}Th({sup 6}Li, {alpha}){sup 234}Pa and {sup 232}Th({sup 6}Li, d){sup 236}U transfer reaction channels has been measured at E{sub lab}=38.0 MeV in the excitation energy range of 17.0 to 22.0 MeV within the framework of the absolute surrogate method. The {sup 233}Pa(n,f) cross sections are then deduced from the measured fission decay probability ratios of {sup 234}Pa and {sup 236}U compound nuclei using the surrogate ratio method. The {sup 233}Pa(n,f) cross section data from the present experiment along with the data from the literature, covering the neutron energy range of 1.0 to 16.5 MeV have been compared with the predictions of statistical model code EMPIRE-2.19. While the present data are consistent with the model predictions, there is a discrepancy between the earlier experimental data and EMPIRE-2.19 predictions in the neutron energy range of 7.0 to 10.0 MeV.

An annular ionization detector for quasi-elastic and transfer reaction studies

An annular ionization chamber detector has been developed to study quasi-elastic and transfer reactions in heavy-ion collisions at near-barrier and sub-barrier energies. The important feature of the detector is that it has a near 2π coverage in the azimuthal angle φ for the particles entering in the detector at a given θ direction. This feature makes the detector very useful for measurement of the differential cross-sections at backward angles with respect to the beam direction, involving low cross-section reaction channels. The split anode configuration of the detector makes it capable of both particle identification and energy measurement for heavy ions and fission fragments. The detector has been tested using heavy-ion beams from the 14 MV-pelletron accelerator at Mumbai. Results on quasi-elastic excitation function measurements and barrier distribution studies in many heavy-ion reactions using this detector setup are discussed.