Table of contents

Relativistic heavy ion reactions are reviewed in terms of our present understanding of some selected experimental results from the LBL Bevalac and the CERN ISR. The Lund Model for nucleus-nucleus collisions is presented and its power of predictivity is illustrated.

Heavy ion collisions at intermediate energies are reviewed in terms of the present understanding of some selected experimental results from the CERN synchrocyclotron.

Charged particle spectra were obtained in coincidence with gamma rays characteristic of target-like products in reactions of 118 MeV ¹²C with ¹¹⁸Sn. The alpha-energy spectra clearly indicate the presence of non-equilibrium particle emission. The multiplicities of gamma cascades observed in coincidence with charged particles were measured. Predictions by the sum-rule model for incomplete and complete fusion combined with a statistical evaporation code are in good agreement with the experimental average gamma-ray multiplicities.

The yields, angular distributions and differential range spectra have been measured for individual target residues from the interaction of 8.5 MeV/A ¹⁶O, 19 MeV/A ¹⁶O, 35 MeV/A ¹²C and 85 MeV/A ¹²C with ¹⁵⁴Sm. From the measured data, fragment isobaric yields and velocity spectra were deduced. The results are compared to the predictions of a modified Boltzmann master equation model of precompound particle emission.

In Deep Inelastic Scattering, DIS, a lepton interacts directly with a target quark, provided that the energy and momentum transfers are sufficient. This direct interaction hypothesis is tested in shadowing experiments where nuclear media are used to detect departures from a point-like lepton-quark interaction. The struck quark may interact with nuclear constituents before it forms a hadron. Thus hadron production in different target nuclei provides information on quark-quark and quark-nucleon interactions.

The EMC effect, discovered a few years ago by the European Muon Collaboration, indicates that the quark structure in bound nucleons is different from that in free nucleons. Hence DIS may become a valuable tool for studies of nuclear structure based on constituent quarks.

In this paper we develop a recently suggested approach to account for nucleon off-shell effects in deep-inelastic lepton scattering from nuclei. We pay special attention to achieve a consistent description of the deep-inelastic scattering and information from nucleon knock-out reactions in more conventional nuclear physics.

Two new Uppsala accelerators, a sector-focusing synchrocyclotron and a cooler storage ring will soon be in operation. The synchrocyclotron will be used in many areas of natural science and medicine. The cooler storage ring receives beam from the synchrocyclotron and will be used for high precision physics experiments both with light and heavy ions.

The nucleon-nucleon interaction is derived in the Skyrme model for the baryons. The full time dependence of the rotating soliton fields is taken into account and shown to lead to interaction components that do not appear in the static approximation as well as to small corrections to those that do. The spin-independent interaction is shown to be attractive at long range although the attraction for reasonable choices of the parameter values in the model is too weak to explain nuclear binding.

Differential cross sections (mainly of p, n processes) for spin-isospin excitations in nuclei are reviewed and compared with theoretical predictions, particularly as obtained from the theory of finite Fermi systems.

Short range repulsions suggested by skyrmion-antiskyrmion models of the N potential are shown not to improve significantly predicted annihilation cross sections based on quark-antiquark rearrangement.

The rates of the main weak processes involving strange quarks in degenerate quark matter are calculated numerically. The calculations are performed for temperatures up to 100 MeV. Pauli-blocking turns out to be very important. The rates obtained differ by three orders of magnitude from simple estimates in the literature. The results are briefly applied to cosmologically produced quark nuggets, and may also be of interest in connection with supernova core collapse and quark-hadron phase transitions in general.

Nuclei moving through magnetized materials at high velocities are subject to very intense transient magnetic fields, resulting from the ion-solid interaction in the polarized material. The transient field has been used for g-factor measurements of short-lived nuclear states for more than a decade. Still the origin of the field is not fully explained. The present paper presents a detailed discussion of the inherent assumptions of a model based on polarized bound electrons (PBE). The contact fields from unpaired s electrons are calculated for all ions, and a number of possible polarization mechanisms are discussed in detail. Extensive studies of K-shell populations of light ions, from O through S, penetrating ferromagnetic solids are summarized, referring to a separate paper for details. Based on these known K-shell populations the PBE model, including a contribution from scattered polarized electrons, is compared with all available data for ions of C through S in magetized iron, cobalt, nickel, and gadolinium. The quantative agreement with the data is found to be very good if all ionic electrons are assumed to be polarized to a degree of 0.14 and 0.20 in iron and gadolinium, respectively. Furthermore, simple estimates based on the PBE model are found to reproduce the gross features of the transient field for heavier ions in iron as well as gadolinium. The processes responsible for the polarization of the deeply bound electrons are, however, still not understood in detail.

An overview of progress in the target and ion source techniques at the ISOLDE on-line mass separator is given. The production of high intensity beams of mass-separated radioactive nuclei by bombardment of targets with 600 MeV protons and 910 MeV ³He from the CERN synchro-cyclotron is discussed. Off-line tests performed in order to clarify the release properties of different target materials are described. The targets are metal powders or foils, alloys, carbides, oxides, intermetallic compounds or molten metals. The influence of reactive gases on the release rates and progress in ion-source techniques are also discussed. Recent on-line tests are described in details, and systems are suggested for the production of elements which are not yet available as primary products in on-line mass separators.

The massive antineutrino recently reported by Simpson in an experiment on tritium decay has not been confirmed by experiments on ³⁵S decay. As an independent check, we report here the negative result of a search for the corresponding antiparticle (a massive neutrino) using the decay of ¹²⁵I. As a by-product, we give accurate data on internal-bremsstrahlung spectra which we have followed over close to four decades in intensity, and we report a new way of measuring its E1/M1 ratio. The experiment provides a new and very accurate value for the ¹²⁵I-¹²⁵Te mass difference of 186.1 ± 0.3 keV.

A survey is given on the development of the Z-separator SISAK, which continuously isolates nuclides with half-life down to ∼ 1 s according to their atomic number. The separation equipment is described, as well as the connection to gas jet recoil transportation systems and the data acquisition and evaluation systems used. The use of the SISAK technique is exemplified by results obtained for neutron-rich nuclei in the mass regions A ∼ 150, A ∼ 110 and A ∼ 245. Other applications of the technique are also briefly discussed.

Some weak beta-delayed particle emitters in the T_z = -3/2, -1, -1/2, +1/2 and +5/2 series are reviewed. Selected features of the delayed particle emission are discussed in terms of experimental delayed particle data and (p, γ), (p, p') and (p, n) reaction data. Experimental beta transition strengths are compared with the existing complete shell-model calculations for the sd-shell nuclei. The effect of the Gamow-Teller giant resonance on the structure of the delayed particle spectra is considered. The correlation between the widths of two decay channels, protons and alpha particles, and the preceeding beta decay is studied in the case of the ⁴⁰Sc decay.

The decays of strongly neutron rich isotopes of Zn have been studied with the primary aim of nuclear mass determinations. The work has also resulted in considerable information on the previously practically unknown level structure of ^{75,76,77,79,80}Ga. Improved Q_β-values are obtained for ^75,76,77,78Zn and ^76,78,80Ga. The Q_β-values of ^79,80Zn are reported for the first time. The experimental results are compared with predicted values of nuclear masses.

The nuclear and electronic magnetic dipole moments of ²¹Fr and the nuclear ground-state spin of ²⁰⁷Fr have been measured directly by on-line atomic-beam magnetic resonance techniques at the ISOLDE facility at CERN. The following results have been obtained: μ_I(²¹¹Fr) = 4.00(8) nm, g_J(Fr, 7s²S_1/2) = 2.00497(9) and I(²⁰⁷Fr) = 9/2. A large deviation of the electronic magnetic moment from the free electron value was found. Using the measured nuclear magnetic moment μ_I(²¹¹Fr), a comparison is made between different theoretical calculations of the magnetic dipole hyperfine constants and with the available experimental data in ²¹¹Fr. An analysis of the electric quadrupole interaction is also given. Nuclear magnetic dipole and electric quadrupole moments are deduced for the sequences ^207-213Fr and ^220-228Fr, using the data on ²¹¹Fr as reference values. The nuclear quantities are discussed within the framework of the shell model and the core-quasiparticle model, giving information on the nuclear single-particle structure and on the variation in deformation along the sequences of francium isotopes.

Recent experimental developments in in-beam internal-pair spectroscopy are reviewed. They concern methods based on the use of magnetic transporters and cooled Si(Li) detectors. Some results obtained with the aid of these new techniques are also described.

The structure and decay properties of levels between 1 and 40 MeV of excitation energy in rare earth nuclei have been studied. In particular, coupling phenomena and signatures of non-statistical cooling are discussed.

General properties of terminating bands are briefly reviewed and exemplified on the observed high-spin properties of ¹⁵⁸Er and ¹⁵⁶Er. The very similar features of the positive parity high-spin spectra of the N = 88 isotones of Dy, Er and Yb are pointed out and discussed. The possibility to estimate B(E2)-values in terminating bands from measured feeding times is explored. The spin contribution from different orbitals is calculated in terminating bands as well as more collective bands. One aim is to get some idea of the interaction between different configurations and to this end we also consider a single-j shell model. The limits of terminating bands in the yrast region when the number of valence nucleons increases is discussed. The usefulness of these results when planning future experimental studies is considered.

Excited states in the N = 28 isotones ⁵⁴Fe and ⁵⁵Co were populated in the bombardment of ⁵⁴Fe with ³He ions. The subsequent de-excitation was studied using experimental in-beam techniques including γ-γ coincidences and γ-ray angular distributions. A number of previously unobserved levels were discovered in ⁵⁴Fe and a new high-spin complex was assigned to ⁵⁵Co. Self-consistent Hartree-Fock calculations were performed to elucidate the underlying nuclear structures. It was found that the ground-state shapes of ⁵⁴Fe and ⁵⁵Co correspond to deformation parameters β₂ = +0.03 and +0.02, respectively. Shell-model arguments and calculations were used to assign configurations to the excited states.

We investigate the origin of the broad structure present in the continuum region of the nuclear spectrum excited in (p, t) and (p, d) reactions leading to ¹¹⁸Sn. We find that the incoherent excitation of mainly pure configurations of the type 1 valence + 1 deep hole with different angular momenta dominates the observed structure, while the giant pairing resonance lies at higher excitation energy and only affects its upper tail.

Excited states in ^114-117Te were populated in the bombardment of ^114,116Sn targets with ³He ions at energies E_lab = 20.9-27.5 MeV. The subsequent de-excitation was studied using in-beam spectroscopic methods, including measurements of γ-ray excitation, γ-γ coincidences, γ-RF timing, γ-ray angular distributions and conversion electrons. States with angular momenta up to J ≲ 12 h were observed, but no isomers with T_1/2 ≳ 1 ns were located. The excited structures are discussed in terms of vibrational bands coupled to one- and two-quasiparticle shell-model structures. The systematical behaviour of the excited states in Te isotopes is studied in the mass range A = 115-123 for the odd, and A = 112-134 for the even isotopes.

Angular distributions from the ^158,160Gd (t, p) ^160,162Gd reactions were studied, with 17 MeV tritons from the McMaster University tandem Van de Graaff accelerator. The reaction products were analyzed with a magnetic spectrograph and detected with photographic emulsions. Members of the ground state bands were populated up to 6⁺, and γ-vibrational bands were populated up to spin 4⁺ in both nuclides. Compared to the L = 0 strengths to the ground states, the excited strengths are as different as 20% and 50% for ¹⁶⁰Gd and ¹⁶²Gd. The considerable excited L = 0 strength found for ¹⁶²Gd is interesting as there are no sudden changes of deformation or prominent shell structures in this region.

The differential cross-section of inelastic electron scattering for the excitation of the K^π = 1⁺ mode in ¹⁵⁶Gd is calculated in DWBA by using microscopically calculated transition-densities. Discussions are given in comparison with experimental data, isovector rotational mode and the q_eff quasi-DWBA technique.

An explanation of anomalous L = 0 transfer in (t, p) reactions on the high-spin targets ¹⁶¹Dy(5/2_g⁺), ¹⁶⁷Er(7/2_g⁺) and ¹⁷⁹Hf(9/2_g⁺) is suggested, based on the interplay between intrinsic parentage amplitudes derived from pair-excited intrinsic states and the variation in transfer probability carried by individual deformed orbits.

High-spin states in ¹⁷⁷Re have been populated in the ¹⁶⁵Ho (¹⁶O, 4n)¹⁷⁷Re reaction. A level scheme is constructed from the studies of γγ-coincidences, the relative excitation function, and γ-ray angular distribution measurements. Three decay sequences identified with 5/2⁺[402], 1/2^-[541] and 9/2^-[514] Nilsson orbitals have been extended up to spin 29/2⁺, 49/2^- and 33/2^-, respectively, and a newly observed sequence based on the 1/2⁺[660] Nilsson orbital is established. The experimental data are discussed within the Woods-Saxon cranking model. Observed shifts in the band crossing frequencies are interpreted theoretically as being caused by different deformation driving forces of quasiparticle orbitals. B(M1)/Q₀² ratios are discussed in connection with quasineutron alignment.

The g-factor of the 21/2⁺ state at 1921.9 keV in ²⁰³Pb has been measured through the time differential perturbed angular distribution technique in an external magnetic field B = 2.028 T. The measured g-factor g = -0.063(2) indicates a predominantly three neutron hole configuration described by the wave function 0.68|i_13/2^-1f_5/2^-2⟩ ± 0.73|i_13/2^-1f_5/2^-1p_3/2^-1⟩.

Excited states in ²⁰⁶Po with spins up to 16 ℏ were identified through reactions with ³He- and α-particles on targets of ²⁰⁶Pb. Level and transition properties were studied using conventional in-beam γ-ray and conversion electron spectroscopy. The half-life of the yrast 9^- state, identified as the neutron two-quasiparticle state ν(f_5/2^-1i_13/2^-1)_9-, was determined as 1.0 μs. No other isomers, besides the previously known isomeric 8⁺ state, were observed. The excited states are classified within the shell-model description. Transition probabilities are discussed.