S. Elfström

Evidence for rotational band structures in the N = 88 nuclide 153Tb

Excited states in 15365Tb88 have been studied in the reactions 151Eu(α, 2n) and153Eu(α,4n) using in-beam γ-ray spectroscopy. Levels of positive parity are identified up to spin 272. Most of these states are interpreted as members of rotational bands characterized by the Nilsson configurations 32+[411], 52+[402] and 72+[404]. Furthermore, a sequence of negative-parity states is observed up to spin 312 (352). The negative-parity band is remarkably well described in a Coriolis coupling calculation including all configurations of the h112 Nilsson multiplet. In this calculation the moment of inertia parameter varies with collective angular momentum in the same way as in the ground-state band of 152Gd. Using the same prescription for calculating rotational energies, the irregular level spacings within the 52+[402] and 72+[404] bands are also well explained.

In-beam study of high-spin few-particle states and the decay of an 112 isomer in 151Tb

Abstract Levels in 151Tb have been populated in (α, 4n) and (τ, 3n) reactions on an 151Eu target and the decay of these levels has been studied in-beam. Excitation functions, angular distributions and γγ coincidences are measured using Ge(Li) spectrometers. Also, conversion electrons and delayed γ-rays have been recorded. The measurements have revealed a 25 s isomeric 11 2 − level decaying via levels with spin and parity 5 2 + and 3 2 + to the 1 2 + ground state. The isomer and a 15 2 + state are fed through two similar level sequences, which have been established up to levels with spin and parity Equal to 31 2 − ( 35 2 − and 35 2 + ( 39 2 + ) , respectively. Another level sequence ranges from 33 2 (+) to ( 45 2 + ) . The levels with spin below 11 2 are interpreted as shell-model excitations of the odd proton. The high-spin states are ascribed to excitations of the five valence nucleons outside the magic 64146Gd82 core. In particular, a reasonable interpretation of the high-spin level sequences is obtained if the three-particle clusters (π h 11 2 vf 7 2 vh 9 2 ) 27 2 ) − and (π h 11 2 vh 9 2 vi 13 2 ) 33 2 + are assumed topersist as stable components within the sequences. The stability of these clusters is explained as a result of the maximization of the overlap of nucleonic wave functions that is obtained by alignment of angular momentum (MONA).

The effective moment of inertia in 124Xe, 126–128Ba, 129,131Ce and 162Er isotopes

Abstract The γ-rays produced in the reactions of 118 MeV 12 C on 120 Sn, 122 Sn, 124 Te and 39.5 MeV 4 He on 161 Dy are investigated by using a sum spectrometer, a single NaI(Tl) detector and Ge(Li):s. Different nuclei were selected by setting gates on known transitions in the Ge(Li) spectra. The second effective moment of inertia I (2) eff is extracted and compared with values from known discrete γ-rays as well as with the results from cranked shell model and cranked Nilsson-Strutinsky calculations. The systematics of the i 13 2 neutron orbital is investigated.

The Effective Moment of Inertia in 130Ce and 129La

The moments of inertia Jeff(2) are measured for 130Ce and 129La, which were produced in the reaction (118 MeV) 12C on 124Te and identified by means of Ge(Li)-gates. Comparison with other measurements of discrete gamma transitions and of Jband(2) are made.

A multi-purpose NaI(Tl) detector system

A multi-purpose detector system consisting of six hexagonal NaI(Tl) detectors is described. The detectors can be arranged as a total energy spectrometer or together with a Ge(Li) detector as a Compton suppression device. The detectors can also be used individually for detection of γ-ray energies in, e.g., Eγ − Eγ correlation measurements.

Isomeric states and rotational structure in the doubly-odd nucleus176Ta

The doubly-odd nucleus176Ta is investigated by means of in-beamγ-ray spectroscopy techniques using the reactions (α, 3n), (d, 2n) and (p, n). Life-time measurements in thens-region yield low-lying isomeric states withT1/2=13±1 ns and 30.5±1 ns, while measurements in the ms-region show the existence of a 1.1±0.1 ms isomeric state. A rotational sequence, withK=5 or 6 for the band-head, is also observed.

Quantitative study of EγEγ correlations in the 122Sn + 106 MeV 12C compound system

Abstract The EγEγ correlations in the 122Sn + 106 MeV 12C compound system have been measured by using the techniques of time of flight to reject events due to neutrons and of unfolding to remove events due to Compton escape. The rotational correlations in the measured matrix can be followed up to Eγ = 1.2 MeV which is shown to correspond to a collective spin of 15. An attempt to estimate the amount of aligned angular momentum by utilizing the intensities in the unfolded matrix failed mainly because at least half of all E2 γ-rays showed no rotational correlations. An independent evidence for this background of uncorrelated events is obtained by comparing the rotational correlations in the data with the rotational correlations obtained by simulating the decay of the known discrete levels in 127, 128Ba on a computer. The comparison indicates that the observed rotational correlations are mainly due to the known discrete transitions. While the moment of inertia obtained from the correlation pattern is less than 80 % of the rigid-body value the high-energy end of the spectrum of E2 radiation can only be explained if γ-ray energy and spin are related by the rigid-body moment of inertia. The area of positive correlations that occurs in most published correlation plots at E1 = E2 and at the high-energy end of the E2 radiation is understood from the unfolding to be an artifact of the subtraction procedure.

Effective moment of inertia in132Ce,134Nd and136Nd

The effective moment of inertiaIeff(2) of132Ce,134Nd and136Nd produced in40Ar induced reactions has been deduced from continuumγ-ray spectra measured by sum spectrometer methods. Results concerning the deformation of these nuclei are obtained by comparison of the experimental data and calculations in the frame of a cranking Nilsson — Strutinsky model.