Shape changes in189Au at high spins

The level scheme of¹⁸⁹Au has been extended to high spins. Decoupled, strongly coupled as well as vibrational bands have been found indicating shape coexistence in this nucleus.     

Development of magnetic rotation in light Gd nuclei; study of 142Gd

High-spin states in ¹⁴²Gd have been populated by means of the ⁹⁹Ru(⁴⁸Ti, 2p3n) reaction at 240 MeV and investigated with the γ-spectrometer EUROBALL III and the charged-particle detector array ISIS. The features of four dipole bands have been determined and compared with tilted-axis cranking model calculations indicating that they are magnetic rotational bands. A transition from regular to irregular bands has been found approaching N = 82 demonstrating that this is a general phenomenon in nuclei near a double-shell closure. Received: 9 December 2001 / Accepted: 9 January 2002     

Pseudo-spin band in the odd-odd nucleus 172Lu

High-spin states in the odd-odd nucleus ¹⁷²Lu have been populated in a ¹⁷⁰Er(⁷Li, 5n) reaction and the emitted -radiation was detected with the GASP array. Two sequences of a new identical band have been observed with the transition energies in the favoured and unfavoured sequences being identical within keV at low spins and keV at high spins over the whole observed spin range. Aninterpretation as a pseudo-spin singlet band of configuration is proposed. It represents the best example of a pseudo-spin singlet band in normal deformed nuclei known until now.Received: 19 February 2003, Revised: 27 March 2003, Published online: 12 August 2003PACS: 21.10.-k Properties of nuclei; nuclear energy levels - 21.10.Re Collective levels - 23.20.Lv transitions and level energies - 27.70.+q      

Observation and interpretation of a side band in the deformed nucleus162Er

A side band in¹⁶²Er was observed in (¹²C, 4n) and (α, 4n) reactions usingγ-γ coincidence and angular distribution measurements. The excitation energies and branching ratios were compared with the predictions of recent theoretical calculations.     

Study of band crossings in 182Os

High-spin states in ¹⁸²Os have been populated by the (¹⁸O, 4n) reaction and studied using in-beam spectroscopy methods. Seven side bands have been established for the first time. Three of the side bands show a band crossing. The features of the bands have been interpreted in the framework of the cranking model considering the motion of independent particles in a rotating deformed potential. The band crossings of the yrast band and of these three side bands can be explained by the rotation-alignment of a pair of $\text{i}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ quasineutrons.     

Interaction strength and shape difference for the h9/2 and h11/2 configurations in163Tm

The strongly shape driving πh_9/2[541]l/2^? configuration with α=+1/2 exhibits some anomalous, and so far unexplained, features concerning the crossing frequency, ?ω_c, the aligned angular momentum, i_x, and interaction strength, at the alignment of the first pair of i_13/2 quasineutrons in several odd-Z rare earth-nuclei. The h_9/2[541]1/2^? and h_11/2[523]7/2^? bands have been studied in the stably deformed rare-earth nucleus¹⁶³Tm to investigate these features. A difference in band crossing frequency of ～ 80 keV between the two bands is found. Rotational bands built on these two configurations have been found to cross in the spin range I=25/2–29/2 ?. Theγ-decay pattern between the two bands is established in the crossing region and analysed in terms of a moderate shape difference between them. A theoretical estimate of the size of the interaction strength between the two bands is presented and compared to the experimental value. The observed band structure in¹⁶³Tm is very similar to that of¹⁶⁷Lu which has 2 protons and 2 neutrons in addition. This observation is discussed in relation to the similarity of the yrast bands of the two even-even “core” nuclei¹⁶²Er and¹⁶⁶Yb, for which theγ-transition energies are identical within ～0.2 keV below the vi_13/2 crossing.     

Superdeformed band in Gd. First observation of band crossing

A discrete superdeformed band is found in ¹⁴⁶Gd. Lifetime measurements yield an average quadrupole moment of 12±2 e b. A band crossing corresponding to an alignment of ≈2 is observed at a rotational frequency of 0.65 MeV. A theoretical analysis suggests that the band has a π6²v7¹ configuration with odd spins and odd parity. Arguments are given that the [651 1/2] and [642 5/2] single-particle states are involved in the band crossing.     

Investigations of the level scheme of 144Gd and lifetimes in the quadrupole bands

For a level scheme investigation of ¹⁴⁴Gd an experiment with the -spectrometer EUROBALL III has been carried out and lifetimes have been measured with the -spectrometer GASP using the Doppler-shift attenuation method. The high-spin states have been populated in these experiments by means of the ¹⁰⁰Mo(⁴⁸Ti,4n) reaction at 215 MeV and the ¹¹⁴Cd(³⁶S,6n) reaction at E = 182 MeV, respectively. The known quadrupole band has been modified and a new one has been established. Reduced E2 transition probabilities B(E2) were determined for seven members of these quadrupole bands. They show values between and 130 W.u. and this considerable enhancement gives evidence for a significant nuclear deformation. A configuration may be assigned to one of the quadrupole bands according to total Routhian surface calculations. The spin dependence of the B(E2) values has been explained by IBM calculations involving high-spin quasiparticle excitations.Received: 5 June 2003, Revised: 10 December 2003, Published online: 23 July 2004PACS: 21.10.Re Collective levels - 21.10.Tg Lifetimes - 21.60.Fw Models based on group theory - 27.60. + j      

Study of Coriolis-decoupled bands in 155, 157, 159Dy and 155, 157, 159Er using (α, xnγ) reactions

Levels in ^{155, 157, 159}Dy and in ^{155, 157, 159}Er have been populated using (α, xnγ) reactions where x = 5, 7 or 9. The resulting γ-rays have been investigated using in-beam y-spectroscopic techniques. Mixed positive-parity bands were predominantly populated and are identified with the Coriolis-deeoupled bands described in the framework of the rotation-alignment model of Stephens and coworkers. In the case of ¹⁵⁷Dy the band was observed up to the $\text{49}\text{2}$⁺ state. The absence of the backbending effect in these nuclei can be explained by the blocking of certain $\text{13}\text{2}$ neutron orbitals near the Fermi surface which are essential for the development of the baekbending mechanism.