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Coupling of valence particles/holes to 68,70Ni studied via measurements of the B(E2) strength in 67,69,70Ni and 71Cu.

High-spin states have been studied in neutron-rich nuclei produced in deep-inelastic collisions between a pulsed beam of Pb ions and a U target. The structure of nuclei such as Hg, Pb and Bi has revealed new information on the couplings of single-particle states to each other and to the octupole-vibrational phonon, essential input to the nuclear shell model. In addition, the first observations of high-spin states in U, U and U are compared to recent results for neighbouring plutonium nuclei.

The GT beta decay of 150 Ho has been studied with a Total Absorption Spectrometer (TAS), with an array of 6 Euroball CLUSTER Ge detectors (the CLUSTER CUBE), and with an alpha detector. The three techniques complement each other. The results provide the first observation of an extremely sharp resonance in GT beta decay.

Measurements of γ-ray, γγ-coincidence and internal conversion electron spectra from the 106 Cd( α , nγ ) 109 Sn reaction were carried out at 15–20 MeV α-particle bombarding energies with Ge(HP) γ-ray and superconducting magnetic lens plus Si(Li) electron spectrometers. The energies, relative intensities, internal conversion coefficients and coincidence relations of the 109 Sn transitions were determined, and a more complete, consistent level scheme has been deduced. Spin and parity values have been determined from the internal conversion coefficients, the bombarding-energy dependence of the side-feeding intensities of the states and the available γ-ray angular distribution data. The level scheme was interpreted in the framework of the quasi-particle shell model.

The differential coincident pion electroproduction cross section in the 3 He(e,e π + ) 3 H reaction has been measured with high resolution with the three-spectrometer set-up at the Mainz Microtron (MAMI) electron accelerator. Measurements were performed at the four incident energies E 0 = 855, 675, 600, and 555 MeV at fixed four-momentum transfer Q 2 = 0.045 GeV 2 , with the pions detected in parallel kinematics. This enables a separation of the measured cross section into the transverse and longitudinal structure functions by means of the Rosenbluth method. The experimental data are compared to model calculations, in which the elementary pion production amplitude includes the standard Born-amplitudes and also delta and higher resonance terms. Three-body Fadeev wave functions are used and the final state interaction of the outgoing pion is taken into account. The calculation describes the data only after medium modifications of the delta and of the pion are included.

Neutron deficient nuclei close to 100Sn have been studied using the NORDBALL Ge-detector array together with ancillary particle detectors. Evaporation residues from the compound nucleus 108Te were identified with charged particle and neutron detectors. In this paper a considerable extension of the level scheme of the nucleus 102Cd is presented. The strongest cascade of the new level scheme reveals an irregular sequence of dipole transitions above Iπ = 10+ extending up to spin 17. A strongly populated rather regular side band consisting of four quadrupole transitions ranging from spin 9 to spin 17 was also discovered. This band was tentatively assigned negative parity. Shell model calculations were performed and a very good agreement with the experimental results was found. The excited states could successfully be interpreted as neutron particle and proton hole excitations with respect to the doubly closed core 50100Sn50.

Excited states of Co-56 were studied in the reaction Al-27(S-32,2p1n) Co-56. The NORDBALL array with a Neutron Wall and a Silicon Ball was employed. The excited states were interpreted in terms of ...

Excited states of Cd-103 were studied in the reaction Ni-58(Cr-50,4pn)Cd-103. The NORDBALL array with neutron and charged particle detectors was employed for the detection of gamma rays and light evaporated particles. The level scheme of Cd-103 was significantly extended. A strong cascade of E2 transitions connecting negative parity states was found, Shell model calculations were performed and positive parity excited states were interpreted in terms of neutron-particle and proton-hole excitations with respect to the doubly magic N = Z = 50 core. The negative parity band was well reproduced by the total routhian surface calculations. (C) 1997 Elsevier Science B.V.

New levels in the neutron deficient nuclei 106Sn and 108Sn have been investigated by using the NORDBALL detector array combined with charged particle and neutron detectors. The excited structures are discussed in terms of collectivity and the shell model. The excitations are interpreted to be based on d52, g72 and h112 both for protons and neutrons and g92 for protons. The systematical behaviour of the specific states in the Sn isotopes is studied in the mass range of A = 106–118.

Excited states of Cd-101 were studied in the reaction Ni-58(Cr-50,2p alpha n)Cd-101. The NORDBALL array with a Neutron Wall and a Silicon Ball was employed for the detection of gamma-rays and evaporated particles, The level scheme of Cd-101 was significantly extended, Shell-model calculations were performed and the excited states were interpreted in terms of neutron particle and proton hole excitations with respect to the doubly magic N = Z = 50 core.

Proton-rich odd-odd In isotopes have been investigated by in-beam spectroscopic methods using the NORDBALL detector array. A Ni-58 beam with an energy of 270 MeV was used to bombard a Fe-54 target. ...

Experimental studies at the OSIRIS fission-product mass separator have yielded a wealth of new results on the doubly-magic region near 132 Sn. In the following we focus on two aspects of the new results: on the evidence for octupole collectivity of the 3 1 − state in 132 Sn and on the similarity of the 208 Pb and 132 Sn regions as evidenced from the modelling of the low excitations in 132 Sb. The Stage-I of the PIAFE facility recently proposed at Grenoble will offer exciting possibilities for even more detailed studies of the doubly magic regions near 132 Sn and 78 Ni (the latter for the first time).

The 6 Li(γ,p) reaction was measured at average tagged photon energies of 〈 E γ 〉 = 59 and 75 MeV. Protons were detected at 5 different angles between 30° and 150°. Most of the observed strength is apparently due to the three-body breakup channels. In particular the semi-inclusive (γ,p(n)) and (γ,p(t)) channels are discussed.

The quasiparticle multistep shell model method is applied to calculate the spectra of light Sn isotopes. A simple interpretation of the main excitations is given. The calculated quantities agree reasonable well with the sparse experimental data which are available.

A spectroscopic study of Sb-108 has been carried out as a part of a larger experiment where in total twenty-nine different residual nuclei were identified. This study gives the first information on excited levels in this nucleus. A low-lying two-quasi-particle multiplet together with some of the higher lying levels are discussed within the framework of the nuclear shell model. A rotational, strongly coupled, band is identified as, most likely, being built on the deformed pig9/2(-1) nuh11/2 configuration in accordance with total routhian surface calculations. Tentative spins and parities are presented as well as B(M1)/B(E2) ratios for some of the transitions in the strongly coupled band.

The results of a study of the 6 Li (γ, cc) (c, c : charged particle ) reaction with the tagged-photon technique are presented. It is shown that the (γ, pt) reaction can be understood within the framework of a semi-phenomenological quasi-alpha reaction model. The total (γ, pt) cross section is found to be larger than the 6Li(γ, pn)α cross section at the same photon energy. No evidence is found for a three-body absorption mechanism, but the possible role of final-state interactions in the (γ, pd) reaction is outlined.

Two positive-parity and two negative-parity groups of states of non-collective character with excitation energies ranging from 3 to 7 MeV and spins as high as 21 ħ have been established in 192 Pb. The main features of each group are described phenomenologically as four-quasiparticle configurations, arising from coupling of the 2 + 1 , 4 + 1 and 6 + 1 states to a specific aligned neutron two-quasiparticle configuration. Supporting evidence for this interpretation and the importance of proton excitations in this singly closed-shell nucleus is obtained from the predictions of the quasiparticle multi-step shell model (QMSM). In addition, a four-quasiparticle structure of predominant neutron character is proposed on the basis of comparisons with the experimental data on 194 Pb and with the results of the QMSM calculations.

Excited states in 206 Pb have been populated in the 204 Hg(α, 2n) reaction using a 35 MeV α-beam. In-beam measurements have been performed to obtain γ-ray angular distributions, time spectra and γγ-coincidences. The level scheme has been extended to a spin value of 16kh and an excitation energy of 6.8 MeV. The present measurements confirm the previously reported half-life of the 12 + state and identify nine new high-spin states above the 12 + isomer in 206 Pb. The new high-spin states are expected to have a one-particle three-hole character and they are interpreted within the nuclear shell model using known two-hole and particle-hole states.

Odd and even Sn isotopes are studied within the framework of a multistep shell-model BCS formalism. In each step one calculates a nucleus in terms of quantities corresponding to previously calculated nuclei. Good agreement with available experimental data is obtained.

Using 58 and 73 MeV tagged photons and scattering angles from 60° to 150°, it is shown that it is possible to observe Compton scattering by “mesons in nuclei” through an incomplete cancellation of the mesonic (exchange-current) seagull amplitude by parts of the nuclear resonance amplitude related to the giant-dipole resonance of 208 Pb. This phenomenon is a property of an extended nucleus and, therefore, cannot be studied on the deuteron. Predictions of the exchange from factor which determines the angular distribution of the exchange seagull amplitude are compared with experimental data.

The quadrupole interaction frequencies of the 8+, 11−, 13− and 16+ isomers in 210Po have been measured in a Bi single crystal by the DPAD method with the 209Bi(t, 2n) 210Po reaction. The results for the quadrupole moments, normalized to Q(8+1) = −55.2 (20)fm2, are |Q(11−)| = 86 (11)fm2, |Q(13−)| = 90(7)fm2 and |Q(16+)| = 129.7 (20) fm2. The quadrupole moment of the 0 i 13 2 proton orbital was deduced, and found to be surprisingly small. The results are compared with shell model calculations using the surface delta interaction as residual interaction.

In the framework of a quasiparticle multistep shell model method we study four-quasiparticle states in lead isotopes. For this we first calculate single-quasiparticle quantities within the BCS formalism and two-quasiparticle states within a QRPA. Finally the four-quasiparticle basis set of states is formed as the tensorial product of two-quasiparticle states previously evaluated. The resulting spectra agree reasonable well with available experimental data. A number of as yet undetected states are predicted.

Empirical interaction matrix elements, fitted to the nuclei 206Pb, 206Tl and 206Hg, are used to make shell-model calculations of the wave functions and energies of 205Tl, 205Hg and 204Hg. The proton 2s1/2 spectroscopic factor for the ground state of 205Tl is calculated to 0.78 and the log ft value of the neutrino capture reaction 205Tl(ν,e−)205Pb is predicted to be 5.8. The collectivity of the ground-state band in 204Hg is explained within the framework of the shell model.