Representation mixing of meson states is considered with particular reference to the 1 ←→ 15 mixing in SU(4). The 16 meson states are assigned to the representation (4*, 4) of a non-chiral group SU(4) ⊗ SU(4), whose factors are related by charge-conjugation. Mass formula, mixing angles and electromagnetic mass shifts are rigorously derived. Connection of the present formalism with conventional quark model is pointed out and generalisations to higher groups SU(n) ⊗ SU(n) as well as to higher representations, are indicated.

Accidental degeneracy seems to be the rule rather than an exception amongst thed orbital energies of substituted octahedral complexes ofd¹ configuration. By using symmetry and physical arguments, in conjunction with first-order and second-order degenerate perturbation theory, it is shown that such accidental degeneracies arise in crystal-field theory due to the choice of an inflexible basis set of metal orbitals which neglects the polarisation of metal orbitals by the ligand charges.

We construct here the coherent states (annihilation operator eigenstates) of a damped harmonic oscillator. These coherent states, which are normalizable, have the desired behaviour in the classical limit (ℏ→0).

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.

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.