[en] The neutron deficient rare-earth nuclei of the A∼130 region are of particular interest since highly deformed prolate ground states are expected. Indeed these nuclei are predicted to show maximal ground-state deformations of β₂ ∼ 0.40 (axis ratio of 3:2), comparable to the deformation deduced for superdeformed cerium isotopes at high spin. A fusion-evaporation experiment was performed with radioactive ion beams at GANIL in October 2004 which had the goal to reach very proton-rich exotic nuclei located near the proton drip-line. A radioactive ⁷⁶Kr beam, delivered by the SPIRAL facility, was used to bombard a thin ⁵⁸Ni target. Emitted γ-rays were detected by the EXOGAM γ-ray spectrometer which was, for the first time, coupled with both the DIAMANT charged-particle array and the VAMOS spectrometer

[en] In 1974 Aage Bohr and Ben Mottelson predicted the different ‘phases’ that may be expected in deformed nuclei as a function of increasing angular momentum and excitation energy all the way up to the fission limit. While admitting their picture was highly conjectural they confidently stated ‘...with the ingenious experimental approaches that are being developed, we may look forward with excitement to the detailed spectroscopic studies that will illuminate the behaviour of the spinning quantised nucleus’ . High resolution gamma-ray spectroscopy has indeed been a major tool in studying the structure of atomic nuclei and has witnessed numerous significant advances over the last four decades. This article will select highlights from investigations at the Niels Bohr Institute, Denmark, and Daresbury Laboratory, UK, in the late 1970s and early 1980s, some of which have continued at other national laboratories in Europe and the USA to the present day. These studies illustrate the remarkable diversity of phenomena and symmetries exhibited by nuclei in the angular momentum–excitation energy plane that continue to surprise and fascinate scientists. (invited comment)

[en] Detailed band structures of three chiral-candidate nuclei, ¹³⁴Pr, ¹³²La and ¹⁰³Rh have been studied. The aim of the study was twofold. First, to try to explore the reasons behind the contradiction between the theoretically predicted chirality in these nuclei and the recently observed fingerprints that suggest non-chiral interpretation for the previous chiral candidate band doublets. Second, to search for multiple chiral bands of different types in these nuclei. In ¹³⁴Pr a new πh_11/2vh_11/2 band has been observed besides the previously known chiral-candidate πh_11/2vh_11/2 doublet. This new band and the yrare πh_11/2vh_11/2 band show the expected features of a chiral doublet structure. This fact combined with the observed similarity between the band structures of ¹³⁴Pr and ¹³²La suggests that chirality might exist in these nuclei. The detailed study of the ¹⁰³Rh band structure resulted in the observation of two new chiral-doublet looking structures besides the previously known one. This is indicative of possible existence of multiple chiral doublet structure in this nucleus.

[en] Excited states in the neutron-deficient nuclide ¹⁶³W were investigated using the ¹⁰⁶Cd(⁶⁰Ni,2pn)¹⁶³W reaction at a beam energy of 270 MeV. The level scheme for ¹⁶³W was extended significantly with the observation of five new band structures. The yrast band based on a 13/2⁺ isomeric state is extended up to (57/2⁺). Two band structures were established on the 7/2^- ground state. Quasiparticle configuration assignments for the new band structures were made on the basis of cranked Woods-Saxon shell-model calculations. The results reported in this article suggest that the negative-parity ν(f_7/2,h_9/2) orbitals are responsible for the first rotational alignment in the yrast band.

[en] Selective tagging techniques have been used to establish new band structures in the transitional isobars ¹⁶³Re and ¹⁶³W. These nuclei were produced in the ¹⁰⁶Cd(⁶⁰Ni, xp yn γ) reaction at a bombarding energy of 270 MeV. Prompt γ rays were detected at the target position using the JUROGAM spectrometer while recoiling ions were separated by the RITU separator and implanted into the GREAT spectrometer. At low spin, the yrast band of ¹⁶³Re is shown to be a strongly coupled collective band based on a proton h_11/2 configuration. In ¹⁶³W, the decay path of the 13/2⁺ isomeric state to the ground state has been identified and negative parity structures based on the ground state established.

[en] New high-spin bands have been established in ^98,99,100Ru. Some are interpreted as terminating configurations using the Nilsson-Strutinsky cranking formalism. They are observed up to the predicted terminating states which are built from g_9/2 protons and N=3 proton holes combined with d_5/2, g_7/2 and h_11/2 neutrons relative to a ⁹⁰Zr core. The observed high-spin states assigned as terminating show systematic behavior and provide new information on the energy spacing between the 2d_5/2 and 1g_7/2 neutron subshells

[en] A level scheme has been constructed for the proton-unbound, T_z=3/2 nuclide ₅₃¹⁰⁹I₅₆ following a recoil-decay-tagging experiment using the ⁵⁸Ni(⁵⁴Fe, p2nγ) reaction at a beam energy of 195 MeV. The experiment was performed using the highly efficient JUROGAM γ-ray spectrometer in conjunction with the RITU gas-filled recoil separator and the GREAT focal-plane spectrometer. Cranking calculations are used to interpret band structures built on πg_7/2 and πh_11/2 states in a weakly deformed, triaxial nucleus

[en] A fusion-evaporation experiment has been performed with a SPIRAL ⁷⁶Kr radioactive beam in order to study the deformation of rare-earth nuclei near the proton drip-line. The experimental setup consisted in the EXOGAM γ-array, coupled to the light-charged particles (LCP) DIAMANT detector and to the VAMOS heavy-ion spectrometer. The difficulties inherent to such measurements are enlightened. The coupling between EXOGAM and DIAMANT has been used to decrease the huge background caused by the radioactivity of the beam. It further permits assigning new γ-ray transitions to specific residual nuclei. A γ-ray belonging to the ¹³⁰Pm level scheme has thus been observed for the first time.

[en] An experiment has been performed using a SPIRAL 76Kr radioactive beam at GANIL to investigate rare-earth nuclei near the proton drip-line. The EXOGAM gamma array was coupled with the DIAMANT light charged-particle detector and the VAMOS spectrometer. We report here on the powerful of this setup to extract fusion-evaporation γ-rays from a large beam contamination

[en] Excited states of the nucleus ¹⁶⁷Os have been populated by the reaction ⁹²Mo(⁷⁸Kr,2pn). The JUROGAM γ-ray detector array has been used in conjunction with the RITU gas-filled separator and the GREAT spectrometer to observe prompt γ rays in coincidence with recoiling fusion-evaporation residues and their subsequent decay by α particle emission. By correlating prompt γ radiation with the characteristic α radioactivity of ¹⁶⁷Os, it has been possible to extend the level scheme for this nucleus significantly. In particular, an extension of the yrast band and four previously unobserved bands are reported. In addition, the recoil distance Doppler-shift method was used to determine a lifetime of τ=20(4) ps for The I^π=17/2⁺ state in ¹⁶⁷Os. Hence, the level of collectivity and magnitude of deformation of the low spin yrast band of this nucleus is established.