Table of contents

Several observed properties of the T=2 states of the A=12 nuclei favour a model in which only small components of the states belong to the lowest shell-model configuration.

The distribution of angular momentum states in ground-state bands of axially symmetric even-even nuclei with large intrinsic deformation is analysed in the framework of the SU(3) nuclear model and compared with the relevant expression obtained by Bhaduri and Das Gupta (see Nucl. Phys., vol.A212, p.18 of 1973) with a statistical approach.

Excitation functions at two angles for the reaction ¹²C(¹⁶O,²⁰Ne_GS)⁸Be_GS exhibit sharp minima at E_CM=12.9 MeV, 13.7 MeV and 14.7 MeV. Angular distributions show that the behaviour of the cross section is anomalous at 13.7 MeV but not at 12.9 MeV. A simple diffraction model of direct transfer can account for the data, except for the anomalous behaviour. If the model is modified to incorporate approximately the effects of intermediate, perhaps quasimolecular, structure the trend of the anomalous behaviour is obtained.

The validity of previous comparisons between model results and observations of the neutral to charged ratio of hadrons in the atmosphere is re-examined. The authors then select the most appropriate published data plus data taken by the authors at Chacaltaya and compare them with model results.

A partially unitarized model for scattering amplitudes is constructed starting from the impact-parameter representation. In this model, in which the singularity at the origin of the impact-parameter plane is explicitly taken into account, a dominating peripheral trajectory generates an effective trajectory of the same kind in the t-channel. Thus it is demonstrated that there exists a model in which the peripheral trajectory comes out as a bootstrap solution.

The pi-meson rescattering contribution to the pi ⁺ photoproduction from ³He is evaluated for photon energies and momentum transfers of a recent experiment (see Phys. Lett., vol.44B, p.44 of 1973) using the multiple scattering formalism and the full spin and isospin dependence of the scattering amplitudes. It is pointed out that the inclusion of the rescattering term can improve the agreement between experiment and previous impulse approximation calculations.

The properties of the negative parity states of ^65,67,69Zn are investigated in the framework of the unified vibrational model. In the model a quasi-neutron is coupled to anharmonic vibrations of the core. Anharmonicities in the vibrations of neighbouring even-even cores are estimated through the observed properties of the core. Energy levels, spectroscopic factors and electromagnetic properties have been calculated. The results of the present calculations are compared with available experimental results and other theoretical results. The model accounts very well for the variations in the systematics of the low-lying states.

From the accurately measured gamma ray intensities following the decay of ¹⁶⁰Tb (72.4 d), the properties of the gamma vibrational band in ¹⁶⁰Dy have been critically examined. No unique value of the band-mixing parameter, Z_gamma , could be obtained from the B(E2) ratios corresponding to different interband transitions. This inconsistency is also observed in the values of Z_{beta gamma} parameter arising from the mixing of the gamma vibrational band with a possible beta vibrational band. A comparison of the properties of ¹⁶⁰Dy with those of the nuclei in the strongly deformed region and those in the beginning of this region indicates that the nucleus resembles transitional nuclei and hence a microscopic approach may be essential to understand its properties.

The 680 keV and 1620 keV betas in the decay of ^115mCd have been investigated with a thoroughly tested intermediate-image magnetic spectrometer. The outer beta (¹¹/₂^- to ⁹/₂⁺) transition has been subjected to shape analysis and the experimental shape has been fitted to a shape factor of the form. C(W)=k(1+aW+b/W) with a=(-0.180+or-0.008) and b=(0.185+or-0.005). The inner beta (¹¹/₂^- to ⁷/₂⁺) first-forbidden unique transition exhibited an ideal unique shape within statistical error.

Excitation energies, mean lifetimes, mixing ratios, branching ratios, angular distributions and linear polarizations have been measured for levels in ³⁶Ar and ³⁶Cl. The states were populated using the reactions ³³S( alpha ,n gamma )³⁶Ar and ³³S( alpha ,p gamma )³⁶Cl at beam energies up to 14 MeV. The decay schemes were determined with the help of a gamma-gamma coincidence experiment carried out at a beam energy of 14 MeV. New spin assignments were made for four levels in ³⁶Cl: 2518 keV, 5^-; 2810 keV, 4^-; 3102 keV, 4^-; 3723 keV, 4^-. Mean lifetimes were measured for four levels in the two nuclei using the recoil distance method. Two new levels were found in ³⁶Cl at excitation energies of 4291 keV and 5311 keV, both being candidates for high spin. The results are discussed in terms of recent shell-model calculations which reproduce very well the three new 4^- states in ³⁶Cl.

An apparently significant result in an experiment to search for tachyons in the interval of time immediately preceding the arrival of air showers of energy greater than 10¹⁵ eV has been reported by Clay and Crouch (see Nature, vol.248, p.28 of 1974). Several similar experiments have been completed, all of which have yielded null results. The original data of Clay and Crouch have been re-examined and it is shown that an artifact of the apparatus was contributing to the original, apparently significant, result. An upper limit estimate shows that the number of tachyons is less than the number of hadrons of energy greater than 100 GeV in showers of average size N=6*10⁵ particles.