Triafol-TN plastic detector foils have been irradiated with²³⁸U ions of energy 16.34 MeV/u and the tracks produced have been observed using the chemical etching technique. The bulk etch rate and track etch rate are determined under successive chemical etching. In our case, the validity of Arrhenius’s law is confirmed by the fact that the same value ofE_a obtained for these different concentrations, within experimental errors. The results show a linear correlation between the measured track etch rate along the track and the corresponding total energy loss rate and a threshold value of ∼ 5.0 MeV/(mg/cm²) for track registration was obtained. The maximum etched track length of²³⁸U-ion in triafol-TN has been compared with the theoretically computed range.

The angular distribution of fission fragments in alpha induced fission has been studied at an incident energy of 55 MeV in¹⁹⁷Au target. The relative differential fission cross sections were measured at different angles between 10° and 170° and the resulting angular distributions fitted by least squares method with Legendre polynomials. In the present work, a correction for the self-scattering and self-absorption of fission fragments in the target itself was applied and a target of 3 mg/cm² was used to get good statistics. The anisotropy for 55 MeV alpha induced fission of gold was 2·83±0·43 and the fission cross section calculated by integrating the measured angular distributions over all the solid angles was 5·2±1.0 mb, confirming the value of 4·0±0·05 mb reported by Burnettet al but contrary to the high value of 10±3 mb reported by Ralarosyet al.

Isomeric yield ratios have been measured for⁹³Nb(α, 2n)^95m,gTc reaction in the energy range 25–60 MeV. The ratios were compared with theoretical values obtained by means of two models one based on compound nucleus mechanism only and the other including pre-equilibrium effects. The trend of experimental ratios is better reproduced by the latter model, although there remains some discrepancy as to the magnitude at higher energies.

Using Lexan polycarbonate plastic as the fission fragment track detectors, the fragment angular distributions have been measured in the cases of fission of²³²Th and²³⁸U induced by alpha particles of various energies ranging from 40 to 70MeV obtained from the 88″ variable energy cyclotron at Calcutta. The center-of-mass angular distributions have been calculated and fitted by a series of Legendre polynomials. TheW(10°)/W(90°) ratios (defined as anisotropy) were measured at several energies for both the targets. These data are utilized in calculation of the energy dependence ofK₀², the standard deviation of the distribution in the angular momentum projection on the nuclear symmetry axis at the saddle point. Values of Γ_f/Γ_η, i.e. the ratio of the fission width to neutron emission width have been determined for²³²Th and²³⁸U nuclei. The integral cross-section for alpha induced fission in each target was determined by numerical integration of the respective center-of-mass angular differential cross-sections. The results were compared with similar data available in the literature which served to resolve some of the discrepancies observed in earlier measurements. The results were also compared with theoretical cross-sections.

Fission-track registration characteristics of Lexan solid state nuclear track detectors have been used to measure the fast neutron induced fission cross section of²³²Th. The fast neutrons (≅14.2MeV) were produced with the help of an AN-400 model Van-de-Graaff accelerator at Banaras Hindu University laboratory using³H(²H,n)⁴He reaction and were used to irradiate the fissile target deposited on the plastic detector. The track densityT, registered on the plastic detector is related to the fission cross sectionσ_f, through the relationT=knσ_føt wheren is the number of fissile atoms per cm² in the deposit, ø is the neutron flux,k is fission track registration efficiency andt is the time of irradiation. The fission cross sectionσ_f of²³²Th, relative to the well measured fission cross section of²³⁸U, was found to be 0.36±0.04 barn.

An investigation has been made relating the effect of UV radiations on etching parameters and activation energy of CR-39 (solid-state nuclear track detectors, (SSNTDs)). Corresponding changes in bulk etch rate (BER) (V$_B$), track etch rate (TER) (V$_T$), sensitivity (S), critical angle (θ$_C$) and efficiency (η) due to pre-irradiation and post-irradiation on CR-39 polycarbonate plastic detector have been reported and discussed in detail. Both bulk activation energy (BAE) (E$_B$) and track activation energy (TAE) (E$_T$) are reported to decrease with post-irradiationand are explained based on chain degradation, free radical formation, cross-linkage, chain scission and softening of the detector material. Further unusual decrease in BAE (E$_B$) and TAE (E$_T$) was observed for pre-irradiated CR-39 polycarbonate detectors, possibly due to the nature and density of the detector material.