Table of contents

A cluster model, which previously gave a good description of ¹⁴C and ²⁴Ne emission from heavy nuclei, has been extended to take into account the effects of the different sizes of the emitted ions. The model now gives a consistent theory of the lifetimes for emission of objects ranging from alpha particles to Mg and Si ions. It generally reproduces the measured half lives (including the most recent experimental data) to within an order of magnitude using fixed set of parameters for all cases.

Angular distributions of neutrons from the ²⁰⁸Pb( pi ^+or-, pi ^+or-'n) reaction near the giant-resonance region have been measured at T_pi =180 MeV. The neutrons arising from pi ^- inelastic scattering show evidence of peaking near the quasi-free recoil direction in contrast to those arising from pi ⁺. This observation may be explained by a direct neutron-decay width for the giant resonances that is large when they are excited in ( pi ^-, pi ^-') and small in ( pi ⁺, pi ^+'). Consequences of this suggestion for the analysis of inelastic scattering to the continuum are examined.

A relationship between the Kahler potential and the superpotential is shown to exist in any N=1 spacetime supersymmetric string theory possessing target space symmetries of a specific type. The relationship is explicitly constructed for the untwisted moduli and matter scalar sectors of the (2,2) symmetric Z₃ orbifold, and is used to calculate the complete superpotential in terms of the Kahler potential. The authors demonstrate, within the context of conformal field theory, the existence and consistency of the required target space symmetries.

In the explanation given by Rossi and Testa (1984) for the removal of an apparent inconsistency in the commutation relations, and Gauss' law in the temporal gauge there is a hiatus; this paper rectifies this.

Leptonic decay widths for pseudoscalar mesons are calculated in a QCD-motivated Bethe-Salpeter formalism on a two-tier basis. This model, which is characterised by a Lorentz-invariant confining kernel that depends on the relativistic reduced mass defined in accordance with the Wightman-Garding definition of the internal 4-momenta q_mu , has already shown precision fits to the spectra of qq, qQ and qqq hadrons apart from exhibiting an explicit Regge-asymptotic behaviour (M² approximately N). The leptonic decay constants thus obtained with no free parameters, are (in MeV units), f_P=134( pi ), 166(K); 158(D); 94.9(B), 114(B_s). The decreasing trend with increasing mismatch in the constituent quark masses seems to be in accord with the latest lattice results.

The multistring model VENUS has been applied in the calculation of antiproton and antineutron yields and longitudinal momentum (Feynman X_f) spectra for p-p, p-Pb, O-Pb, and Si-Si collisions at 200A and 1000A GeV incident nuclear energies. The antiproton spectra of p-Cu collisions at an incident proton energy of 120 GeV are also analysed. The calculated antiproton spectra in the small X_f region are smaller than those calculated by Hojovat and Van-Ginneken's empirical formula used in the design of the Fermilab Tevatron antiproton source. In contrast to previous theoretical calculations, the antiproton spectra calculated by VENUS do not show asymptotic behaviour for an incident nucleon energy of 200-1000 GeV caused by the large mass of antiprotons. The yield and spectra of the antineutrons is very close to that of the antiprotons in all of the cases studied. The pion yield in a 200 GeV per nucleon energy O-Pb collision calculated by the VENUS code can explain the difference between the experimental and the calculated values for non-central collisions.

In the framework of the collective model, the general systematics of the magnetic moments of odd-odd nuclei are studied. This is done by plotting the unprojected values of the magnetic moments, i.e. mu ₀= mu (I+1)/I, against j_p for the extreme values of the projection quantum numbers Omega _p, keeping the maximum contribution of the neutron. It is noted that the experimentally observed values follow the systematics predicted on the basis of the collective model for almost all the odd-odd nuclei throughout the Periodic Table.

An effective nucleon-nucleon interaction is constructed from the extended Reid soft-core potential using the lowest order Brueckner theory of nuclear matter with the continuous choice of the single particle spectrum. A nucleus-nucleus potential is derived from the effective two-nucleon interaction using the energy-density formalism. The effect of the Delta (1236) isobar on the effective interaction and the nucleus-nucleus potential is studied. It is observed that with the inclusion of the Delta -isobar the nucleus-nucleus potential gets diluted which is quite prominent in the high-density overlap region.

The entrance channel in the ²³⁸U+²³⁸U reaction is investigated within the liquid-drop model, taking into account the effects of the nuclear proximity forces and allowing ellipsoidal deformations of the two colliding nuclei. A sudden transition occurs from strong oblate configurations to small prolate shapes when the attractive nuclear forces counterbalance the repulsive Coulomb forces. This only slightly affects the perpendicular moment of inertia and the quadrupole moment while the effective moment of inertia varies strongly. It is suggested that the angular distribution of the fragments is widely correlated with the degree of adiabaticity of the reaction and, therefore, with the relaxation time and the initial kinetic energy range.

The form factors for the inelastic electron scattering to 2⁺, 4⁺ and 6⁺ states in ^46,48,5Ti, ^50,52,54Cr and ^54,56Fe are studied in the framework of the Hartree-Fock model. The calculation is performed in the (0f₇2/, 1p₃2/, 0f₅2/, 1p₁2/) model space using a modified Kuo-Brown effective interaction. Using constant effective charges for transitions of given multipolarity, it has been possible to obtain reasonably good agreement with experiment for almost all the nuclei over a range of momentum transfer q of 0.7-3.0 fm^-1 for 0⁺ to 2⁺, 0⁺ to 4⁺ and 0⁺ to 6⁺ transitions.

The parameters which determine the decay characteristics of mixed-symmetry states are evaluated for a wide range of N and Z. Effective charges, e_pi e_nu , are obtained from B(E2;2₁⁺-O₁⁺) values for chains of isotopes and isotones, g pi g nu values are calculated from the magnetic moments of 2₁⁺ states and the behaviour of chi _pi chi _nu is considered. Regions are identified where these parameters favour strong signatures for the lowest lying 2⁺ mixed-symmetry states in vibrational-like nuclei. The influence of the parameters on B(M1) and B(E2) values in rotational nuclei is considered.

Describes the results and conclusions from an experiment set up to measure the time spread of muons in extensive air showers (EAS) detected at the Haverah Park EAS detector array, UK. The pulse risetimes (T₇₀) from 10% to 70% amplitude of the responses from 3*10 m² muon detectors are studied, and the anomalous pulse structure is investigated. The mean T₇₀ is studied as a function of shower size, zenith angle and core distance and its dependence on shower size is related to the elongation length of the EAS. Fluctuations in T₇₀ are studied as a method of yielding the mass composition of the primary particles. The measured fluctuations in T₇₀ are related to fluctuations in the depth of the electromagnetic cascade maximum. The results yield the same value for both the elongation rate and the fluctuation in the depth of maximum sigma (X_m) of 58(+or-23) g cm^-2. The results are consistent with simulation studies that assume protons are still the dominant component of cosmic rays in the energy range 10¹⁷ to 10¹⁸ eV.

A double correlation of the age parameter with the primary energy/electron size ratio, E₀/N_e, and with the muon-electron abundance ratio is observed in a sample of 10000 showers (10⁴<or=N_e<or=10⁷) simulated under various conditions. It implies that the primary energy may be determined according to the empirical formula E₀=(a1n(N_mu /N_e)+b)N_e, which is valid for any primary (small and medium showers at high altitude). Good agreement with the total primary energy spectrum measured with satellites is obtained. At energies higher than 1-2*10⁶ GeV, consistency between the muon size spectrum and the electron size spectrum requires the occurrence of new mechanisms such as photoproduction or quark gluon plasma.