Table of contents

The authors have searched the data-set of the Buckland Park air-shower array for showers arriving from the direction of Scorpius X-1 during March-May 1986, a time reported by Tonwar et al. (1991) as a period of source activity above 2.5*10¹⁴ eV. They confirm their result at a confidence level of 99.89% by examining their data for evidence of a DC excess and burst activity. The implied source flux is estimated to be (1.3+or-0.7)*10^-11 cm^-2 s^-1 above 10¹⁴ eV.

The authors review the decay modes of nuclear compound states formed after heavy-ion fusion reactions. Temperature-dependent mean-field theory is used as a basis for a statistical description of the hot nuclear system. After a short resume of traditional cascade calculations for the emission of light particles, statistical gamma -rays and the fission process, much emphasis is put on the discussion of recent work on the giant resonance decay. It allows a detailed investigation of these collective excitations and their damping mechanisms both as a function of temperature and angular momentum. Temperature-dependent linear response theory in connection with a classical treatment of thermal fluctuations provide a relatively simple framework for a microscopic description not only of these collective transitions but also for the first microscopic calculations of the statistical gamma -decay properties.

The authors study the O(3)-nonlinear sigma model soliton coupled with an isospin-¹/₂ fermion doublet by the Yukawa-type interaction. Describing the Q=1 bosonic sector by a collective coordinate they present a diagrammatic computation for its effective Lagrangian induced by the interaction with the fermionic fields. They show that in lowest order this induced Lagrangian can be identified with the Hopf term for the bosonic sector. They also present the induced (topological) fermionic current and some commutation relations between the fermionic charge operator with the total Hamiltonian and mass term using the Bjorken-Johnson-Low analysis.

On the basis of the QCD model at large distances, the author analyses the qq-sea contribution to the spin effects in the s to infinity , t-fixed limit. It is shown that such effects lead to the spin-flip amplitude increasing as s. The magnitude of spin-flip and spin-nonflip amplitudes is estimated within simple nonperturbative models for quark and gluon propagators. The relative role of spin effects from the wavefunction and the elementary quark subprocess is also discussed. It is shown that the quark-sea effects in the scattering amplitude can reach 30-40% of the contribution of the simple two-gluon exchange at small momenta transfer.

The temperature effects of the three-line vertices graph on the one-pion exchange potential (OPEP) with the pseudoscalar and pseudovector couplings is investigated using the method of Matsubara imaginary-time Green function. It is found that the effective coupling of nucleon-nucleon-pion (NN pi ) decreases with temperature and drops rapidly at high temperature. At a critical temperature T_c, the effective NN pi coupling diminishes to zero and the one-pion exchange potential vanishes. T_c is determined to be 215 MeV. OPEP with both mass and vertices corrections are obtained.

In view of recent interest in the use of the Duffin-Kemmer-Petiau (DKP) relativistic equation, the authors consider some of its properties which are needed for practical calculations. They also address the unresolved problem of the spinless DKP boson in a central field and derive the system of first-order coupled differential radial equations which enable the energy eigenvalues as well as the full wavefunctions to be evaluated. As an example they calculate the free DKP spherical waves and then solve the problem of a pionic atom with a point Coulomb interaction only.

The magnetic excited states of ⁴⁸Ca below particle emission threshold (i.e. up to approximately 10 MeV) are studied in the framework of the random-phase approximation. The results of the calculation are compared with the available experimental data. The obtained wavefunctions are analysed by calculating the form factors corresponding to the excitation of the different states by means of inelastic electron scattering. In particular, the role of the nondominant one-particle-one-hole components of the RPA wavefunctions is investigated. Special attention is paid to the excitation energy region between 6 and 8 MeV because of its particular characteristics regarding the details of the residual nucleon-nucleon interaction.

The authors present the results of an analysis of the positive-parity states of the odd-mass nucleus ¹²⁵Te within the framework of the interacting boson-fermion model. The predictions of the simple single j-orbit calculation for the neutron hole in the 3s_1/2 orbital are compared with those of the multilevel approach taking into account other higher-lying single particle orbits, 2d_3/2, 2d_5/2 and 1g_7/2. The calculated energy spectra, transition probabilities and electromagnetic moments and compared with experimental data.

The authors analyse the properties of the Sp(1,R) model states using a basis obtained from the deformed harmonic oscillator wavefunctions. They make an Sp(1,R) calculation for ¹²C and consider bases obtained from oblate, triaxial and prolate intrinsic states. The model states are given by angular momentum projection of vibrational phonons, which are associated with giant monopole and quadrupole resonances.

The double beta decay ( beta beta ) of ⁴⁸Ca to the ground state of ⁴⁸Ti is analysed using the quasiparticle random phase approximation with (PQRPA) and without (QRPA) particle-number projection. The pairing interaction strength and the strength of other multipole channels of the renormalized G matrix interaction are adjusted to yield optimal beta ^- and beta ⁺ decay properties of ⁴⁸Ca and ⁴⁸Ti and to comply with the experimental limits of the 2 nu beta beta decay half-life. Nuclear matrix elements of the 0 nu beta beta decay transition are then calculated using the QRPA and PQRPA parameter-free to yield an estimate of the Majorana neutrino mass. In addition, the contribution of the right-handed weak currents is studied. The number projection is found to be important for light nuclei near magic numbers. The g_A/g_V ratio of the weak axial vector and vector coupling coefficients is found to be renormalized by the dynamics of the effective weak transition operators derived from a relativistic quark-confinement model.

The secondary collisions of the pi mesons produced in nucleon-nucleon collisions with surrounding nucleons in the nucleus can change the K⁺/ pi ⁺ ratio. The authors calculate this effect in proton-nucleus and nucleus-nucleus collisions by an eikonal approximation and find that the final-state interactions are important.

The reaction p+d to ³He+ gamma is analysed within a relativistic framework. Radiation from the external legs only is considered, i.e. the matrix element is calculated in the relativistic impulse approximation. The pd to ³He and pd* to ³He vertex functions are approximated by sums of pole terms. The restrictions imposed by gauge invariance are discussed. A comparison with experimental data and other theoretical models is made.

Three recoil studies of the system 120 MeV ¹²C+²³⁸U have been performed, one measuring the cross section of 49 fission products, the second, the angular distribution of 33 of them, and the third, the differential range distribution of the same 33. Using the recoil velocity of the intermediate nucleus as a signature of the projectile-target interaction, the cross section, angular anisotropy, and kinetic energy measurements have been divided into complete and incomplete fusion contributions. About 30% of the cross section may be accounted for by incomplete fusion, most probably of an alpha -particle. Angular anisotropies are calculated for both complete and incomplete fusion components for each of the individual products. A method is introduced for the reconstruction of fission events based on the measured energies of individual products and is used to determine kinetic energy distributions in the two types of processes.

It is shown that reported coincidence relations which were used to establish the levels at 1624.07 and 1654.64 keV do not belong to the decay of ¹⁸²Ta and thus these levels are not populated in the decay of ¹⁸²Ta.