L. Hildingsson

In-beam study of 80Kr; Quasiparticle excitations in nuclei around mass 80

Abstract The excited states in 80 Kr have been studied in the reactions 77 Se(α, n), 78 Se(α, 2n), 80 Se(α, 4n) and 65 Cu( 18 O, p2n) by using in-beam γ-ray spectroscopy. In addition to γγ-coincidences, excitation functions and angular distributions, linear polarization of γ-rays and conversion electrons were also measured. All together, 32 levels have been identified up to spin 14 at an excitation energy of 6.7 MeV in 80 Kr. For 21 of these levels the mean lifetime could be determined by Doppler shift methods and by the pulsed-beam γ-timing method. The B (E2) values of 30–60 W.u., derived for many transitions, indicate strong collectivity and the existence of several band structures is suggested. Above 2.5 MeV 2-quasiparticle (qp) excitations become important. The excitation energies of 80 Kr and its neighbours 77, 78, 79 Kr, 77 Br and 81 Rb have been analysed in terms of the cranked shell model. In 78,80 Kr two-proton excitations have been found to be responsible for the observed band crossing. Quasiparticle excitations strongly influence the pairing and stabilize the deformation. The anomalies in the negative-parity bands of 81 Rb and 77 Br are interpreted as a crossing of a 3qp and a 1qp band and the relatively low frequency of the crossing point is ascribed to the blocking effect.

Shape change and fast M1 transitions in 81Kr

Abstract A shape transition from a probably asymmetric shape at low excitation to a more axial-symmetric shape above 21 2 + has been found in 81 Kr. This shape change and the drastic increase of the M1 transition probabilities above spin 21 2 are attributed to the alignment of two g 9 2 protons.

Signature inversion in 120Cs: Evidence for a residual pn interaction

Abstract High-spin states have been observed in the odd-odd isotope 120Cs in 32S-induced reactions. The previously known band is extended to higher spin and several new bands are identified. Band-head configurations have been inferred by comparing the band properties with known bands in the odd nuclei 121Cs and 121Ba. A remarkable signature inversion is observed in the π h 11 2 ⊗ν h 11 2

Transverse BGO Compton suppression shield

The performance of a Compton suppressed Ge spectrometer, that utilizes a transverse BGO suppression shield, is presented. A comparison of the experimental measurements and Monte Carlo calculations is made.

Evidence for shape coexistence from few-quasiparticle excitations in 83Kr

Excited states in 83Kr were studied in the 82Se(α, 3n) reaction using in-beam γ-ray spectroscopy. Measurements of γγ coincidences, excitation functions, angular distributions and linear polarization of the γ-rays were carried out and levels were established up to I = 292. Most of the levels above 2.5 MeV could be grouped into 3 band-like sequences. Lifetimes or limits of lifetimes were determined for 8 members of these bands using the DSA method. The positive-parity 3qp band, I = 212 to 292, indicates a prolate deformation similar to the corresponding band in 81Kr. In contrast, only low collectivity was found for a ΔI = 2 sequence built on the 172− yrast state and reaching up to I = (292). From similarities of the level spacings with the ground state bands and 2qp bands of the even-mass neighbours, the 3qp configuration ν(g92)−2νp12 is proposed for this sequence. Another band, comprising levels with Iπ = 132− to (272−) in a ΔI = 1 sequence, displays a sharp decrease of the intraband M1 transition rates with increasing spin.

Gamma-gamma energy correlations and moment of inertia in 130Ce

Abstract High-spin properties of 130Ce have been studied by using the reaction (12C, 6n). The γ-rays following this reaction were detected by six NaI(Tl) detectors in a two-dimensional coincidence arrangement. An experimental γ-ray energy-energy correlation spectrum was extracted from the original coincidence matrix. The matrix of the correlated spectrum shows a valley along the 45° diagonal extending up to Eγ ≈ 1.2 MeV, thus indicating a collective behaviour beyond the region of known discrete lines. From the width of the valley a collective moment of inertia is deduced.

Collective excitations in 106Cd

High Spin states in 106Cd were populated by the reactions Zr-94(O-17, 5n) and Ge(S-32, 4n) at 80 MeV and at 148 MeV, respectively. The gamma-decay was studied by gamma-spectroscopic methods using t ...

High-spin properties of 173Re

Abstract The high-spin structure of 173 Re has been investigated by in-beam γ-ray spectroscopy. Strongly coupled bands based on the 5 2 + [402] and 9 2 − [514] Nilsson proton states and decoupled bands based on the h 11 2 and i 13 2 intruder proton orbitals have been established. The alignment of an i 13 2 neutron pair has been identified at h ω c = 0.25–0.29 MeV . The detailed behaviour of the neutron crossing shows a marked dependence on the proton configuration. Ratios of the reduced transition rates B (M1)/ B (E2) have been extracted for the ΔI = 1 bands and have been used to confirm the neutron origin of the alignment. The results are interpreted within the total routhian surface (TRS) approach.

Collective bands in 106Ag and 107Ag

Abstract The nuclei 106 Ag and 107 Ag have been studied using 80 MeV 17 O ions impinging on 94 Zr. The γ- rays were detected with the NORDBALL array and light charged particles with a charged-particle detector system. Rotational bands have been established using γ-ray yields, γγ coincidences and angular correlation information. Calculations of spin diabatic surfaces have been done and are used for assigning quasiparticle configurations to the bands. Deformation effects are observed in almost all bands.

High-spin phenomena in 174Os☆☆☆

High-spin states of 174Os have been investigated by means of the (Nd(S, 4n)Os)-Nd-146-S-32-Os-174 reaction using the ESSA30 multidetector system. The decay is dominated by the ground-state positive ...