T. Härtlein

Observation of a harmonic two-phonon vibration in a deformed nucleus

Abstract We report on the observation of a rotational band in 232Th built on a 4+ state at 1414 KeV, which shows all characteristics expected for the band head of a pure Kπ=4+ two-phonon γγ-vibrational band: The excitation energy is about twice that of the γ-band head, all observed decays lead to the γ-band, and the B(E2) values between the two bands have the appropriate strength expected for a harmonic surface vibration.

γ Spectroscopy in the superdeformed minimum of 240Pu

Abstract The γ decay of excited states built on the superdeformed shape isomer 240 f Pu was measured for the first time with an array of EUROBALL CLUSTER detectors in coincidence with delayed fission decays using the 238 U( α ,2n) reaction. The strongest γ transitions can be assigned to the out-of-band decays of three excited superdeformed rotational sequences: A K π =2 − and K π =1 − (2 − ) band with respective bandhead energies of 806.2 keV and 836.0 (846.8) keV decaying to the ground state band of 240 f Pu, and a K π =2(1) band at 1360.9 (1344) keV populating mainly the K π =2 − (806.2 keV) band.

Two-phonon γ-vibrational states in 166Er

Abstract The nucleus 166Er has been Coulomb excited using a beam of 58Ni. In addition to the ground-and γ-vibrational bands three states were observed, a new state at 1943 keV, a previously known 4+ state at 1978 keV and a new state at 2029 keV suggested to have also spin and parity 4+. The two 4+ states decay to the 2+ and 3+ states of the one-phonon γ-vibrational band, and their B(E2) values to the 2γ+ state are measured to 49−25+20 and 267−100+100 e2 fm4, respectively. It is suggested that the 1978 keV state has a small and the 2029 keV state a large component of the Kπ = 4+ two-phonon γ vibrational configuration in their wave functions.

Potential and limitations of nucleon transfer experiments with radioactive beams at REX-ISOLDE

Abstract:As a tool for studying the structure of nuclei far off stability the technique of γ-ray spectroscopy after low-energy single-nucleon transfer reactions with radioactive nuclear beams in inverse kinematics was investigated. Modules of the MINIBALL germanium array and a thin position-sensitive parallel plate avalanche counter (PPAC) to be employed in future experiments at REX-ISOLDE were used in a test experiment performed with a stable 36S beam on deuteron and 9Be targets. It is demonstrated that the Doppler broadening of γ lines detected by the MINIBALL modules is considerably reduced by exploiting their segmentation, and that for beam intensities up to 106 particles/s the PPAC positioned around zero degrees with respect to the beam axis allows not only to significantly reduce the γ background by requiring coincidences with the transfer products but also to control the beam and its intensity by single particle counting. The predicted large neutron pickup cross-sections of neutron-rich light nuclei on 2H and 9Be targets at REX-ISOLDE energies of 2.2 MeV . A are confirmed.

Large oblate deformation of69Se proven by measured transition probability

SummaryThe large oblate deformation of the69Seg9=2 band was proven by the DSA analysis of the 13/2+ →11/2+ 403 keV transition measured via32S(40Ca, 2pn)69Se at 125 MeV beam energy with six escape suppressed EUROBALL Cluster detectors at ±44°. Applying the model of a rigid axial-symmetric rotor the determined lifetime resulted in ∣β2∣ ɛ [0.24,0.85].

New insights in the first backbending region of heavy Dy isotopes

SummaryThe7Li-induced incomplete fusion reaction158/160Gd(7Li,p(d,t)xn) (beam energy 56 MeV) has been used to investigate in detail the first backbending region of the heavy stable Dy nuclei160/162Dy. In162Dy, the measured low interaction strength between the ground band and the Stockholm band of |Vgs| ≈ 17 keV confirms the predicted existence of a node in the interaction strength for nuclei with neutron number betweenN = 96 andN = 98, which has not been accessed earlier. The crossing frequency between the ground band and the Stockholm band in162Dy was measured to be hwc = 320 keV, which is about 40 keV higher than the expected value of hwc = 280 keV known from other nuclei in this mass region. In160Dy, an yrare band could be established for the first time in a nucleus with a very large interaction strength. From fits to level energies as well as from branching ratios, an interaction strength of |Vgs| ≈ 220 keV was extracted.

Rotational bands in neutron-rich 160-162Ho

We have studied the high spin states in 160–162Ho in order to investigate the properties of the rotational bands and their dependence on the single particle orbits involved. The reaction 158,160Gd(7Li,xn) at 56 MeV were used to produce the Ho isotopes of interest. In all three Ho isotopes the known rotational bands have been significantly extended. New band‐crossings have been observed for the first time in this work.

Fragmentation of the two-phonon γ-vibration in166Er

Two-phonon γ-vibrational states in166Er have been populated using Coulomb excitation. The Kπ=4+ component of the vibration appears to be fragmented over several states, whereas only one Kπ=0+ state is observed.