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In the EXILL campaign a highly efficient array of high purity germanium (HPGe) detectors was operated at the cold neutron beam facility PF1B of the Institut Laue-Langevin (ILL) to carry out nuclear structure studies, via measurements of γ-rays following neutron-induced capture and fission reactions. The setup consisted of a collimation system producing a pencil beam with a thermal capture equivalent flux of about 108 n s−1cm−2 at the target position and negligible neutron halo. The target was surrounded by an array of eight to ten anti-Compton shielded EXOGAM Clover detectors, four to six anti-Compton shielded large coaxial GASP detectors and two standard Clover detectors. For a part of the campaign the array was combined with 16 LaBr3:(Ce) detectors from the FATIMA collaboration. The detectors were arranged in an array of rhombicuboctahedron geometry, providing the possibility to carry out very precise angular correlation and directional-polarization correlation measurements. The triggerless acquisition system allowed a signal collection rate of up to 6 × 105 Hz. The data allowed to set multi-fold coincidences to obtain decay schemes and in combination with the FATIMA array of LaBr3:(Ce) detectors to analyze half-lives of excited levels in the pico- to microsecond range. Precise energy and efficiency calibrations of EXILL were performed using standard calibration sources of 133Ba, 60Co and 152Eu as well as data from the reactions 27Al(n,γ)28Al and 35Cl(n,γ)36Cl in the energy range from 30 keV up to 10 MeV.

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The collective wobbling mode, the strongest signature for the rotation of a triaxial nucleus, has previously been seen only in a few Lu isotopes in spite of extensive searches in nearby isotopes. A sequence of transitions in the N = 94 167 Ta nucleus exhibiting features similar to those attributed to the wobbling bands in the Lu nuclei has now been found. This band feeds into the πi 13/2 band at a relative energy similar to that seen in the established wobbling bands and its dynamic moment of inertia and alignment properties are nearly identical to the i 13/2 structure over a significant frequency range. Given these characteristics, it is likely that the wobbling mode has been observed for the first time in a nucleus other than Lu, making this collective motion a more general phenomenon. PACS number(s): 21.10. Re, 23.20.Lv, 27.70.+q Our understanding of the wobbling mode in nuclei (and the associated stable triaxial deformation) has evolved quickly over the past decade. Bohr and Mottelson [1] first proposed that the rotation of a stable triaxially deformed nucleus would result in the presence of wobbling excitations. These excitations occur because the rotational angular momentum is not aligned with any of the body-fixed axes; rather it precesses and wobbles around one of these axes in a manner similar to that of an asymmetric top.In 1995, Schnack-Petersen et al.[2] first suggested that rotational bands based on proton i 13/2 excitations in 163,165 Lu are associated with a triaxial strongly deformed (TSD) potential well. The large deformation is mainly due to the occupation of the intruder i 13/2 orbital, and the triaxial deformation (γ = 20 • ) results from an N = 94 shell gap that develops with enhanced quadrupole deformation ( 2 ≈ 0.37). No direct experimental evidence for triaxiality was observed until the wobbling mode was confirmed in 163 Lu by Ødegård et al.[3]. This seminal work established the existence of a band feeding into the πi 13/2 structure where the two sequences have nearly identical moments of inertia and alignments over a large frequency range. The similarities of the moments of * Present address: inertia and alignments are a predicted feature for a wobbling band as the intrinsic structure for both bands should be the same; the only difference between the two is the degree to which the rotational angular momentum vector lies off axis. The collective wobbling behavior can thus be described within a phonon model, where the energy of each band is equal to E =¯h 2 2J I (I + 1) +hω w (n w + 1/2), wherehω w = hω rot (J x − J y )(J x − J z )/(J y J z ) [1]. The n w = 0 phonon number is assigned to the energetically lowest band in the family, as its angular momentum vector lies closest to a body axis, and in the case of the Lu isotopes, this is associated with the πi 13/2 band. Wobbling excitations with n w = 1, 2, 3, etc. then follow, each lying successively higher in energy as the rotational angular momentum vector progressively lies farther from the body axis with increasing n w . Indeed, Jense...

The nucleus '~Sm has been studied with the (n, n'y) reaction and lifetimes of many states have been extracted from the observed Doppler shifts of the deexciting y rays. A large number of fast E1 transitions have been observed and have led to the identification of possible members of the octupole-octupole and the quadrupole-octupole multiplets.Substantial fragmentation of the twophonon octupole strength is indicated.