B. S. Tomar

Complete and incomplete fusion reactions in the 12 C +169 Tm

Abstract Excitation functions of evaporation residues produced in 12 C + 169 Tm reaction have been measured at several beam energies in the range of 60–84 MeV using recoil catcher technique followed by off-line gamma-ray spectrometry. Comparison of the experimental excitation functions with those calculated using the statistical model code PACE2 revealed dominance of incomplete fusion in the cross section of alpha-emission products. Measurement of recoil-range distributions of evaporation residues at 84 MeV beam energy corroborated these observations. Analysis of the cross sections of incomplete fusion products showed that these reactions are associated with peripheral collisions. Comparison of the present data with similar data on 16 O + 165 Ho system revealed that incomplete fusion probability is more in a mass asymmetric system than in a mass symmetric system.

Effect of projectile structure on evaporation residue yields in incomplete fusion reactions

The excitation functions of heavy residues, representing complete and incomplete fusion products, produced in the reaction of 12C and 13C on 181Ta have been measured over the projectile energy range of 5 to 6.5 MeV/nucleon by the recoil catcher method and off-line γ-ray spectrometry. Comparison of the measured excitation functions with those calculated using the PACE2 code based on the statistical model revealed the occurrence of incomplete fusion reactions in the formation of α emission products. The fraction of incomplete fusion cross sections in the 12C + 181Ta reaction was found to be higher, by a factor of ~2, than that in the 13C + 181Ta reaction. The results have been discussed in terms of the effect of alpha cluster structure of the projectile on incomplete fusion reactions.

Fusion of 19F with 188, 192Os

Fission fragment angular distributions and evaporation residue excitation functions have been measured in the bombarding energy range from 80 to 105 MeV for the 19F+188, 192Os systems. The measured fission and evaporation residue excitation functions are compared with the predictions of the statistical model code PACE. The fission and the evaporation residue excitation functions alone are not sufficient to constrain the statistical model parameters. Hence, the pre-fission neutron multiplicity, multi-chance behaviour of fission and the fission fragment angular distribution, which are very sensitive to statistical model parameters, have also been considered in carrying out a comprehensive statistical model analysis. Fission fragment anisotropies calculated in the statistical saddle point model (SSPM) framework using rotating finite range model (RFRM) effective moment of inertia values were found to over-predict the experimental data. Using scaled up values of RFRM effective moment of inertia, a good agreement between the fission anisotropy data and the SSPM calculations has been obtained over the entire energy range except at the highest energy.

INCOMPLETE FUSION IN THE EXCITATION FUNCTIONS OF 12C + 115In REACTIONS AT 4–7 MeV/NUCLEON

We measured the excitation functions for nine evaporation residues for the 12C + 115In system in the energy range well beyond the Coulomb barrier. The experimental results are compared with the theoretical values calculated using the Monte Carlo simulation code PACE2. Several complete and incomplete fusion products are observed in the present study. It is observed that a definite amount of incomplete fusion contribution is present, even at the lowest energy. The results clearly show the incomplete fusion contributions in the iodine and antimony products.

Nondestructive assay of the fissile content in FBTR fuel pins

A rapid method for nondestructive assay of Fast Breeder Test Reactor (FBTR) fuel pins has been demonstrated using the two-step process of high-resolution gamma-ray spectrometry for isotopic composition measurement followed by neutron well coincidence counting for total plutonium content. The data have been compared with those obtained from Thermal Ionization Mass Spectrometry (TIMS) and potentiometry. The fissile isotopic ratio 239Pu/241Pu measured by gamma-ray spectrometry was found to be close to the TIMS values within 1%. The total plutonium content of FBTR fuel pins measured by neutron counting was found to be in agreement with the estimated values obtained using potentiometry within 1%.

Incomplete fusion mechanism in 16O + 93Nb reaction at 6 MeV/nucleon : Recoil range measurements

Summary Recoil range distribution of evaporation residues formed in complete and incomplete fusion of 96 MeV 16O with 93Nb has been measured by recoil catcher technique followed by off-line gamma-ray spectrometry. The cross sections for complete and incomplete fusion were delineated from the earlier measured excitation function data at the same beam energy. The results show that incomplete fusion is associated with angular momentum values close to the critical angular momentum for complete fusion of the projectile and target.

Fragment angular momenta in low and medium energy fission of242Pu

Independent isomeric yield ratios of128Sb were determined radiochemically in the thermal neutron induced fission of241Pu and 34 MeV alpha particle induced fission of238U, both involving the same compound nucleus (242Pu). Fragment angular momenta estimated from the measured isomer ratios using the statistical model analysis showed significantly larger fragment angular momenta in the medium energy fissioning system compared to the low energy fissioning system. This has been attributed to the effect of higher excitation energy and angular momentum in the entrance channel leading to increased fragment temperature, moments of inertia and angular velocity. An attempt was made to calculate the fragment angular momentum in the medium energy fission using the Fermi gas model for the fissioning nucleus, taking into account the multichance fission, saddle shapes of the fissioning nuclei and the angular velocity components of the fissioning nuclei both along and orthogonal to the fission axis. The calculated angular momenta agree well with the experimental results.

Yields of rare earth fission products in the spontaneous fission of californium-252

Cumulative fission yields of rare earth isotopes have been determined in the spontaneous fission of252Cf by fast radiochemical separation and gamma-ray spectrometry. The determined yield values are compared with the available literature data. The yield values for147Nd,151Nd and151Pm differ from the reported values. The yield for145Ce is determined for the first time.