Table of contents

With the aim of obtaining a field theory of large amplitude collective motion the author formulates the time-dependent Hartree approximation within a path-integral approach.

In order to study possible new neutral-current structures, the authors construct the most general SU(2)*U(1)*U'(1) extension of the Weinberg-Salam model and write down its effective Lagrangian. It is shown how the successful predictions of the Weinberg-Salam model in the neutrino section may be naturally maintained by restricting the representations of the Higgs scalars and the neutrinos. They also show how the effective neutral current may conserve parity in some or all channels, allowing for an absence of parity-violating transitions in bismuth and other atoms. Included in the analysis is the polarised electron-hadron asymmetry recently measured at SLAC. Tests to establish the existence of the new neutral current are considered.

Charge-dependent nuclear forces arise effectively from the coupling of the discrete states to the continuous states. They can be constructed in the framework of the continuum shell model. Numerical calculations are performed for the Coulomb energy anomaly in the ¹⁵O-¹⁵N case. The energy shift arising from the effective charge-dependent part of the Hamiltonian depends on the density dependence of the residual nuclear interaction and the method for truncation of the continuum which is used in the calculation. The calculated shift is of the order of magnitude of the Coulomb energy anomaly.

The matrix inversion method in momentum space provides a powerful tool for analysing numerically the correlation between the free scattering matrix and the Brueckner reaction matrix in nuclear matter. A study of this correlation is made for the ¹S₀ Reid soft-core and the de Tourreil-Rouben-Sprung super-soft-core potential. Reaction matrices and binding energies for all uncoupled channels with J less than two are studied. The effect of the important isobar virtual channels on these is also investigated.

Semiclassical conditions appropriate to a grazing collision have been used to study the dependence of the transfer amplitude on the distance of closest approach, d, for direct reactions. It is found to fall off exponentially with increasing d, the decay constant being a function of the initial and final binding energies of the transferred particle. The dependence on the z projections of the angular momenta of the particle separates out as a multiplicative constant. This simplified form of the transfer amplitude is used to obtain an analytic expression for angular distributions. Comparison is made with experiment for the reaction ²⁶Mg(¹¹B,¹⁰B)²⁷Mg at 114 MeV laboratory energy.

Samples of monazite from Madagascar were ground and spread on thin plastic foils giving a source of an average thickness of 1.5 mu m over an area of 100 mm². A silicon detector telescope consisting of a 12 mu m thick Delta E counter and 300 mu m thick E counter was used to measure the alpha yield. By identifying the particle type for each event and by employing pile-up protection which was effective in two ways, high-energy pulses due to pile-up were eliminated with an effectiveness of 1/10¹⁰ at counting rates of one event per second. Two runs of approximately 150 days were made in which, altogether, four alpha particles with energies between 11 and 25 MeV were observed. This rate of counts is compatible with zero events from the source when cosmic-ray-induced alpha events are taken into account. Nonetheless, assuming that all four observed high-energy events have to be accounted for by the decay of an unknown alpha-emitting element in the sample and assuming that it is of primordial nature (3*10⁸ yr<T₁2/<6*10⁹ yr), the authors conclude upper limits on its abundance in the sample. Further in this paper, a theoretical, yet semi-empirical, systematics of natural and man-made alpha emitters is presented which takes into account the mass dependence of the Geiger-Nuttal rule.

Deuteron spectra from the ¹²C( tau ,d) reaction leading to excitation energies in ¹³N of more than 4 MeV above the proton threshold have been measured at angles between 7 degrees and 20 degrees . The spectra exhibit the broad d_3/2 single-particle resonance of ¹²C+p and, interfering with it, the 120 keV wide ³/₂⁺ resonance at E_x=6.885 MeV in ¹³N. The line-shape of the ⁵/₂⁺ resonance at E_x=6.364 MeV also displays a pronounced interference pattern. An observed angle dependence of the resonance profile is interpreted as indication for contributions from the nuclear interior.

High-spin states in ⁴⁸Cr have been investigated with the ³⁶Ar(¹⁴N,pn gamma )⁴⁸Cr and ⁴⁰Ca(¹⁰B,pn gamma )⁴⁸Cr reactions. Mean lifetimes or limits have been obtained for the following levels: 0.75 MeV (10.6+or-1.1 ps), 1.86 MeV (1.9+or-0.5 ps), 3.45 MeV (<1.0 ps), 3.53 MeV (3.6+or-1.0 ns), 4.06 MeV (40+or-10 ps) and 5.19 MeV (<1.2 ps). New spin-parity assignments have been made for the last four levels: 6⁺, 5^(-), 6^(-), and (8)⁺, respectively. Comparisons are made with simple shell-model calculations.

High-spin states in ⁵⁴Mn were populated in the ⁵²Cr( alpha ,pn gamma ) reaction. Using angular distribution, linear polarisation and gamma - gamma coincidence measurements, the following unambiguous spin and parity assignments were obtained: E_x, J^pi ; 1073 keV, 6⁺; 1784 keV, 7⁺; 1925 keV, 7⁺; 2857 keV, 8⁺; and 3244, (9)⁺. In addition a new level was observed at an excitation energy of 3939 keV. The experimental data show evidence for low-lying intruder states as predicted by a recent shell-model calculation.

The level structure of ⁷⁸Br has been investigated through the ⁷⁵As( alpha ,n gamma ), ⁷⁷Se(³He,d) and ⁷⁹Br(p,d) reactions. The charged-particle reactions provided the energies of 49 levels ranging up to 2.2 MeV, and l values and spectroscopic strengths were determined for the angular distributions from neutron and proton transfer reactions to most of the states. Energies of 150 gamma rays from ⁷⁸Br were determined from singles measurements. Gamma-gamma coincidences were observed and half-lives were determined for several gamma transitions. Data from nearby nuclei were compared with the present data in order to test the validity of a weak-coupling model for ⁷⁸Br.

The (n,2n) cross sections of ⁸⁵Rb, ¹⁰⁷Ag and ¹⁸¹Ta leading to 21 min activity of ^84mRb, 24 min activity of ¹⁰⁶Ag and 8.1 h activity of ¹⁸⁰Ta were measured at a neutron energy of 14.6 MeV. Well-type NaI (Tl) crystals were used for measurement of activities by detecting X-rays, annihilation photons, and gamma rays. ⁶³Cu(n,2n)⁶²Cu and ¹²¹Sb(n,2n)¹²⁰Sb reactions were used for the measurement of neutron flux. The values of the cross sections obtained are 814+or-42, 705+or-32 and 900+or-47 mb respectively.

The neutral to charged ratio for unaccompanied high-energy cosmic-ray hadrons has been measured at a mountain altitude of 730 g cm^-2 with well-defined geometric selection and good statistical precision. The ratio is found to be independent of energy over the energy range of 100 to 3000 GeV and has an average value of 0.37+or-0.02. Using the directly measured pion to proton ratio with transition radiation detectors for hadrons of energy greater than 400 GeV, this result yields a value for the neutron to proton ratio of 0.67+or-0.08, which is significantly different from the value obtained by Pal and Peters (1964) from phenomenological considerations.