Characterization of segmented HPGe detectors using Pulse Shape Comparison methods

In this work we present the first results of a detector characterization technique named Pulse Shape Comparison Scan (PSCS), applied to a large volume segmented HPGe detector of the AGATA array. The experimental data were collected with the Liverpool University scanning system. Processing two sets of singles scan data acquired with a 137Cs (662 keV) gamma collimated source (with the collimation lines perpendicular one in respect to the other), it has been possible to extract the position response of 4 detector segments. \ua9 2010 IEEE

Quadrupole moments of coexisting collective shapes at high spin in 154Er

Four high-spin collective bands have been populated in 68154Er86 via the 110Pd(48Ti,4nγ)154Er reaction. Average transition quadrupole moments Qt have been measured for three of the bands by using the Doppler-shift attenuation method. The strongest band has a value of Q t=11.0±1.0eb, similar to values found recently for four triaxial strongly deformed (TSD) bands in 157,158Er. The second band has a value of Qt=19.5±3.2eb, consistent with a predicted axially symmetric superdeformed (SD) shape, similar in deformation to the 152Dy isotone, and is used as a calibration point. The third, new band has a value of Qt=9.9±2.2eb. The results confirm the unexpectedly large Qt moments for the favored TSD bands in light erbium isotopes

Relative quadrupole moments of exotic shapes at ultrahigh spin in 154Er: Calibrating the TSD/SD puzzle

Transition quadrupole moments, Qt, of two ultrahigh-spin, collective structures in 154Er have been measured for the first time using the Doppler Shift Attenuation Method (DSAM). Data were acquired at the ATLAS accelerator facility of Argonne National Laboratory, using the Gammasphere detector array. A thick, gold-backed 110Pd foil was bombarded by a beam of 48Ti ions at 215 MeV. The Qt for each band was determined from the Doppler shift of gamma rays emitted by the resulting recoil nuclei. The extracted transition quadrupole moments are significantly different in magnitude, suggesting the two structures in 154Er represent distinct exotic nuclear shapes, namely axial superdeformed (SD) with Q t 20 eb, and triaxial strongly deformed (TSD) with Qt ≈ 11 eb. Indeed, the results calibrate the quadrupole moments of TSD bands recently measured in light erbium nuclei, 157,158Er

Core-excited smoothly terminating band in 114Xe

High-spin states have been studied in neutron-deficient 54114Xe, populated through the 58Ni(58Ni,2p) fusion-evaporation reaction at 230 MeV. The Gammasphere γ-ray spectrometer has been used in conjunction with the Microball charged-particle detector in order to select evaporation residues of interest. The yrast band has been greatly extended to a tentative spin of 52hℏ and shows features consistent with smooth band termination. This band represents the first evidence for a core-excited (six-particle, two-hole) proton configuration above Z = 53

Quadrupole moments of collective structures up to spin ̃65h in 157Er and 158Er: A challenge for understanding triaxiality in nuclei

The transition quadrupole moments, Qt, of four weakly populated collective bands up to spin ̃65h in 157,158Er have been measured to be ̃11 eb demonstrating that these sequences are associated with large deformations. However, the data are inconsistent with calculated values from cranked Nilsson-Strutinsky calculations that predict the lowest energy triaxial shape to be associated with rotation about the short principal axis. The data appear to favor either a stable triaxial shape rotating about the intermediate axis or, alternatively, a triaxial shape with larger deformation rotating about the short axis. These new results challenge the present understanding of triaxiality in nuclei

Non-yrast positive-parity structures in the γ-soft nucleus Er156

Weakly populated band structures have been established in Er156 at low to medium spins, following the Cd114(Ca48,6nγ) reaction at 215 MeV. High-fold γ-ray coincidence data were recorded in a high-statistics experiment with the Gammasphere spectrometer. Bands built on the second 0+ and 2+ (γ-vibrational) states have been established. A large energy staggering between the even- and odd-spin members of the γ-vibrational band suggests a γ-soft nature of this nucleus. An additional band is discussed as being based on a rotationally aligned (νh9/2,f 7/2)2 structure, coexisting with the systematically observed, more favorable (νi13/2)2 aligned structure seen in this mass region

Collective structures up to spin ∼ 65h in the N 90 isotones 158Er and 157Ho

A new collective band with high dynamic moment of inertia in 158Er at spins beyond band termination has been found in addition to the two previously reported ones. The measured transition quadrupole moments (Qt) of these three bands are very similar. These three bands have been suggested to possess a triaxial strongly deformed shape, based on comparisons with calculations using the cranked Nilsson-Strutinsky model and with tilted axis cranking calculations using the Skyrme-Hartree-Fock model. In addition, three collective bands with similar high dynamic moments of inertia, tentatively assigned to 157Ho, have been observed. Thus, it is suggested that all these structures share a common underlying character and that they are most likely associated with triaxial strongly deformed minima which are predicted to be close to the yrast line at spin 50 - 70h