Table of contents

Nuclear photoabsorption around the pion threshold is schematised as photoproduction of a pion which undergoes final-state interaction with the nucleus, accounted for by the pion optical potential. It is shown that the real pion photoproduction and exchange effects are naturally described by the same mechanism with a non-static pion. The complementarity of photoabsorption to pion physics and its usefulness in gaining new information about pion-nucleus dynamics are stressed.

The authors present some characteristics of the observables A_xz and A_y0 of the pp to pi d reaction deduced from the world-available data. Emphasis is given to their extrema and to their trajectories as a function of the centre-of-mass (CM) angle.

The (¹⁴C, ¹⁶O) reaction on even Ru and Pd isotopes has been investigated at 60 MeV bombarding energy. Relative spectroscopic strengths for transitions to the ground states are found to decrease suddenly at N=60. Evidence is presented which suggests that a significant contribution to the reaction mechanism for transfers to the ground states could be due to the sequential transfer of the protons. Large two-proton hole components are found in the first excited 0⁺ states of the light Mo isotopes.

Using Schwinger's proper time formalism, the author constructs the one-loop effective potential for a supersymmetric non-Abelian gauge theory in a background constant magnetic field and study supersymmetry breaking in the strong-field approximation. The problem of symmetry restoration in non-supersymmetric gauge theory is also discussed.

The author investigated the grand canonical partition function for pure SU(N) Yang-Mills theory in the context of perturbation theory. The presence of a chemical potential is equivalent to having a constant imaginary term in the A₀ field. Perturbation theory is found to be softened in the infrared region. The free energy of two loops is computed in the presence of a chemical potential and a logarithmic divergence in the charge fluctuation operator is noticed. This divergence can be understood as being due to plasmon effects being accounted for improperly. The author encounters collinear divergences in higher-order terms of the full propagators and possible cures have been discussed. Finally, the theory in (2+1) dimensions is discussed.

The author considers a statistical ensemble of gluons constrained to be colour singlet at high temperatures. This naturally leads us to consider the grand canonical partition function with an imaginary chemical potential. It is demonstrated that up to two loops the constrained colour singlet ensemble is thermodynamically equivalent to the unconstrained one, neglecting surface effects. The author also evaluates the free energy of heavy quarks or the thermal Wilson loop up to two loops. It is realised that in the confinement phase charged gluons behave as fermions.

A search for slowly moving superheavy magnetic monopoles has been performed using a combination of scintillation counters and proportional chambers which are situated on the ground near sea level. The minimum threshold threshold of the energy loss is set at ¹/₂₀ of the minimum ionisation. An upper flux limit of 1.8*10^-12 cm^-2 sr^-1 s^-1 for magnetic monopoles was obtained over a wide velocity range from 2.5*10^-4 c to 1.0*10^-1 c at the 90% confidence level. The velocity range for the trigger system was set from 10^-4 c to 10^-1 c.

The analysis of space-like data on the isovector part of the electric nucleon form factor G_E^V(t) is carried out by means of a new analytic parametrisation of G_E^V(t). The analysis confirms the importance of the short logarithmic cut on the second sheet just below the pi pi threshold coming from nucleon exchange in the pi N scattering amplitude. It also favours the existence of a rho -meson pole on the second Riemann sheet and of rho '- and rho "-meson poles on the third Riemann sheet in the variable t. The analysis gives R_E^V=0.87 fm for the isovector electric nucleon radius and estimates the corresponding coupling constants.

The author calculates, the dependence of the energy-differential inclusive cross sections for the (e,e' pi ) reaction on the mass number A for N=Z nuclei up to A approximately 60. The author also calculates the variations of the exclusive cross section near threshold, where the outgoing pion has very low energy. The author finds a strong A dependence resulting from the increase in number of neutrons (and in the effective nuclear density). The threshold behaviour is very different for the (e,e' pi ^+or-) cases and also depends on the exact level (J^P) treated. It is also different from an inclusive threshold behaviour. The relative importance of Coulomb distortions and optical and true absorptions is studied at threshold. All cases are studied as a function of g', the Migdal spin-isospin parameter; a very strong dependence on the value of this parameter is found for A>or approximately=50.

The conditions for the validity of an 'adiabatic' symmetry property of the inelastic scattering amplitude are studied in some detail. It is shown that these conditions include some restrictions on the potentials but that the symmetry property holds more generally than within the DWBA. The corresponding property of the T-matrix elements is derived and some consequences of this property are noted.

Using a 'turning-wave' decomposition of the inelastic scattering amplitude, analogous to that employed in the elastic scattering of spin-zero nuclei, the authors give a qualitative interpretation of various properties of inelastic reactions. As in the elastic case, amplitudes of various dynamical origins exist, though they do not discuss here the effect of internal waves or of Coulomb excitation. Many of the arguments are based on the form of the DWBA radial integral and show how the concept of an angular momentum mismatch, due to the nonadiabaticity of the reaction, may be applied directly at the level of the entrance- and exit-channel wavefunctions. The authors discuss particularly a 'quasiclassical' limit in which the populations of the various magnetic substates are related in a simple way to one basic amplitude. At a given scattering angle these populations are essentially proportional to the angular part of the excited state's wavefunction evaluated at the points of closest approach for the corresponding nearside and farside 'trajectories'. It is shown that it is the relative sign of these wavefunctions for points on opposite sides of the nucleus which gives rise to the Blair phase rule. In this quasiclassical limit the spin of the excited state is left precessing about the recoil direction. In order to quantify some of the results the authors derive an analytic expression based on the Hahne prescription for the inelastic radial integrals in which they employ the McIntyre parametrisation of the elastic S matrix. The consequences of an angular momentum mismatch on the polarisation of the excited state and on the symmetry angle for its subsequent gamma decay are discussed in terms of nearside and farside components and they study in particular the phenomenon of the rapid reverse rotation of this symmetry angle.

The fragmentation of the neutron-hole 1f_7/2 and 1f_5/2 states in the nuclei ⁸⁹Zr and ⁹¹Mo is calculated within the quasiparticle-phonon model. The interaction of the hole subshells with the 'quasiparticle-plus-phonon' and 'quasiparticle-plus-two-phonon' states is taken into account. The results of the calculation are compared with experimental data for one-nucleon transfer reactions.

Dynamic deformation theory based on the pairing plus-quadrupole model is employed for a detailed study of the N=88 transitional nucleus ¹⁵²Gd. Comparisons with experiment and with other models are presented for the potential minimum and related properties, B(E2) values, rho (E0), X(EO/E2) and delta (E2/M1) values for transitions from seven 2⁺ states and a number of other states below 2 MeV. Brief comparisons with two N=88 isotones (¹⁴⁸Nd and ¹⁵⁰Sm) and with five Z=64 isotopes (^{150,154,156,158,160}Gd) are also given.

A connection is established between the parameters of two widely used realisations of the deformed axially symmetric Woods-Saxon potential-the spherical coordinates Dubna version and the cylindrical coordinates Copenhagen version. The parameters of the latter version are determined for the mass zones A=155, 165, 173 and 181 by a fit to the single-particle levels of the former version but a larger nuclear radius (r₀ⁿ=1.30 fm, r₀^p=1.26 fm) is introduced in order to better reproduce the experimental RMS radii.

Root-mean-square radii of 2d_5/2, 2d_3/2 and 3s_1/2 neutron orbits in ⁸⁹Sr have been determined from a DWBA analysis of angular distributions and absolute cross sections of the reaction ⁸⁸Sr(d,p). The data were taken at sub-Coulomb deuteron energies of 3.4, 3.8 and 4.0 MeV. With spectroscopic factors obtained from a sum-rule analysis of existing ⁸⁸Sr(d,p) and ⁸⁸Sr(p,d) data it was possible to determine the RMS radii for the 2d_5/2, 2d_3/2 and 3s_1/2 states.

Inner bremsstrahlung (IB) accompanying first-forbidden beta decay of ¹¹¹Ag has been measured using the magnetic deflection technique with a 4.5 cm*5.1 cm NaI(Tl) scintillation spectrometer in the energy region 100-1000 keV. The contribution to the IB pulse-height distribution from the two prominent monoenergetic gamma-ray lines emitted by the source was subtracted by constructing their spectra using peak-to-total ratios, peak-to-valley ratios and peak-to-valley separations. The raw spectrum is unfolded following the method of Liden and Starfelt and compared with the theories of KUB, Lewis and Ford (LF) and Ford and Martin (FM). The measured pulse-height distribution is found to show agreement with LF theory in the lower energy region up to 450 keV; it is found to be lower than KUB and FM theories up to 550 keV and thereafter deviates positively from all three theories.

The authors have measured the angular distributions of 68 gamma rays in ¹⁴⁶Sm following the decay of ¹⁴⁶Eu polarised at low temperature in an iron host. Multipole mixing ratios have been evaluated for 52 gamma rays, 32 of them uniquely. The mixing ratio chi (E0/E2) has been evaluated for four transitions. Spin and parity assignments have been made or confirmed for 27 levels in ¹⁴⁶Sm. Energy levels and B(E2), X(E0/2) and delta (E2/M1) values are examined in terms of the TBA-1 model. The calculated delta values agree with experiment in sign and, to within a factor of two, in magnitude.