Table of contents

The spin dependence of the total cross section for pion-deuteron scattering is calculated. Relativistic effects are introduced by the P waves of the deuteron vertex. The results indicate that these P waves play an important role even at low energies.

Forward-angle ⁴⁸Ca(⁷Li,⁶He) data show the 4.49 MeV state in ⁴⁹Sc to be 2p_1/2 and not 2p_3/2 as reported in an earlier ⁴⁸Ca(¹⁵N,¹⁴C) work. The (³He,d) spectroscopic factor of 0.55 indicates that this state has the major component of the 2p_1/2 strength in ⁴⁹Sc.

A rotation-vibration model based on the molecular picture where the wide rotational resonances are fragmented by surface vibrations is proposed to account for resonances observed in heavy-ion reactions. The model is applied to the ¹²C+¹²C system; its predictions are in fair agreement with experimental data.

Recent data on the ¹²C(¹²C, alpha )²⁰Ne reaction, which are claimed to give evidence of a relatively large number of ¹²C+¹²C resonance anomalies, are re-analysed in terms of fluctuation theory. It is shown that these data provide only weak evidence for anomalies at E_CM=8.46, 9.84 and 10.63 MeV.

The properties of extensive air showers are not inconsistent, as is often claimed, with the assumption that the products of collisions above 10¹⁴ eV may be obtained by simple scaling from accelerator energies, provided that hadronic cross sections rise rapidly with energy, and a normal mixture of cosmic-ray nuclei is present.

The f' spectra of high-energy gamma-ray families are constructed from the data obtained with the Mount Fuji emulsion chambers. The shape of the spectra is almost independent of the energy of the families and is apparently contradictory to the result of the Pamir collaboration, which shows a shrinkage of the spectra as energy increases.

An on-mass-shell, parametric space renormalisation procedure for phi ³ theory in six dimensions is defined and its formal equivalence to the usual Lagrangian counter-term procedure demonstrated. Two-loop contributions to the self-energy are used as an illustration of the method.

Calculations are made of the deep inelastic electroproduction of mesons from polarised targets. Results are given for charged meson ratios ( pi ⁺/ pi ^- and K⁺/K^-) and their asymmetries, for proton, neutron and deuteron targets.

The three-nucleon force due to two-pion exchange is approximated by an effective two-nucleon potential. Its effect on the lowest-order term of the shell-model effective interaction is calculated. The effect on nuclear levels attributed to two valence particles is found to be small. This result is discussed in the context of three-nucleon force contributions to the binding energy of nuclear matter and nuclei.

Using a central-plus-tensor potential, the effective interactions are determined using the low-lying energy spectra of the nuclei in the vicinity of ²⁰⁸Pb. The effect of the second range of the potential is examined and the universal property of the potential is explored. It is found that it is possible to reproduce the energy spectra and manifest the universal features simultaneously. From the results of fittings the inclusion of the second range is favoured.

The basis of a many-phonon system is constructed in the nuclear collective model using the projection-operator method. The proof of the completeness of this basis is given and the matrices of the generators of the group SO(5) are obtained in this basis. The matrix of the additional integral of motion Omega is calculated. This matrix has a non-degenerate spectrum of eigenvalues omega _i which can be used as the missing quantum number.

Nuclear structure calculations for the low-lying states in even-N isotopes ^47,49,51V and odd-N isotopes, ^48,50V are performed in the framework of the Hartree-Fock projection formalism. All the nucleons outside the ⁴⁰Ca core are treated explicitly in the pf-shell configuration space by employing a realistic nucleon-nucleon interaction. The energy levels, static electromagnetic moments and the electromagnetic transition probabilities, are evaluated from band-mixing calculations in which the four lowest energetically-close intrinsic states of the nuclei are taken into account. The theoretical results are in fair agreement with the experimental data.

In the decay of the second excited 2⁺, T=1 state at 3160 keV in ²⁶Al a new 5+or-2% branch to the 0₁⁺, T=1 level was found. The E2 strength of this transition is compared with its analogues in the neighbouring nuclei ²⁶Mg and ²⁶Si in the light of isospin selection rules. An exceptionally large reduced isovector matrix element is obtained.

The 0⁺ to 4₁⁺ hexadecapole transitions in ⁶⁰Ni and ¹⁴⁰Ce have been investigated experimentally by means of alpha -particle scattering as well as by the spectroscopy of the electromagnetic decay of the 4₁⁺ states. In the case of ⁶⁰Ni an upper limit of 1*10^-7 was found for the branching of the E4 and E2 cascade decay of the 4₁⁺ state by conversion electron spectroscopy. It corresponds to an enhancement factor G₄<9.0 spu, while the alpha -particle scattering measurements result in G₄=(5.5+or-0.8) spu. In ¹⁴⁰Ce the 4₁⁺ to 0⁺ cross-over gamma decay has been observed with an enhancement of G₄=(11.8+or-0.7) spu, in very good agreement with the value G₄=(13+or-2) spu from the alpha -particle scattering experiments. The evaluation of the alpha -particle scattering cross sections is based on a specific reaction model (folding model). The experimental results from the direct (4₁⁺ to 0⁺) decay are considered to be an empirical test of the model dependence of the procedure for extracting L=4 transition rates from alpha -particle scattering. By comparing similar results, the consistency of the methods applied together with the evidence for and some implications of hexadecapole motion in spherical nuclei are discussed briefly.

The reaction ⁷³Ge(¹⁶O,3n) at 52.0 MeV incident energy was used to populate excited states of ⁸⁶Zr. Lifetimes of several of these states were determined with the aid of the recoil-distance Doppler-shift method. The resulting gamma ray transition probabilities are discussed in connection with the existing values in other Zr isotopes.

The observed asymmetry in the angular distribution of the ¹⁶O( gamma ,n)¹⁵O reaction above the giant resonance region is investigated. The existence of electric dipole (with T=1) and electric quadrupole (with T=0 and 1) giant resonances are considered. The particle-hole interaction in the final states is fulfilled by attributing new effective charges to the nucleons. The results of the calculation are compared with experimental data.

As an example of the theory of charged-particle transfer reactions the authors study the (d,n) and (³He,d) reactions on ¹²C. These reactions are very well suited for a detailed comparison of theory and experiment because the line-shapes of the continuum spectra have been measured carefully and, furthermore, the phase-shifts for p+¹²C elastic scattering-the input of the theory-are very well known. It is found that resonance as well as background contributions can be explained consistently with the 'model-independent' theory.

Analytic pole extrapolations are tested rigorously for a number of model amplitudes having a realistic singularity structure. Amplitude extrapolations in the energy variable using the discrepancy function method have errors of 3% in favourable cases (np scattering) and of order 30% in typical few-body reactions (nt, n alpha scattering). Cross section extrapolations in the angular variable are less reliable due to the presence of the right-hand cut. The extrapolation error is about 5% for the favourable case of nd scattering and about 50% for nt scattering. All numbers quoted are obtained using conformal mapping techniques. Results without mapping are, in general, worse. Nearby singularities, however, cannot be reliably suppressed by mapping alone. The corresponding errors in the literature are underestimated.

Simulations of the electron lateral distribution for showers of sizes between 10⁵ and 10⁷ particles at mountain altitudes have been performed. It is found that the electron distribution cannot be described by a single age parameter and that its value increases with radial distance according to s= alpha 'logr+ beta ' (10m<r<150 m). At the universal distance of 45 m (and not 70 m as has been considered previously) there exists a simple proportionality between shower size and density and here the age parameter can be considered to be equal to s_t, the theoretical value. Comparison between these calculations and the Tien-Shan experimental data shows a systematic size underestimation of 16%.