F. A. Beck

The Clover: a new generation of composite Ge detectors

This paper presents the characteristics of a new generation of composite germanium detectors: the Clover detector. Its development was based on simulation calculations performed with the code GEANT3. An extensive study of its main characteristics involving the photopeak detection e

Measurements on prototype Ge and BGO detectors for the Eurogam array

ciency, the energy resolution and the timing performed with sources and in-beam experiments have been measured. A simple Doppler broadening correction procedure is proposed to improve the in-beam energy resolution of the Clover detector. An other important property, the sensitivity to the linear polarisation of c-rays has been measured. The performances obtained with the associated BGO suppression shield are also reported. All these results compare very well with the initial simulation calculations. ( 1999 Elsevier Science B.V. All rights reserved.

Calibration of the new composite “clover” detector as a Compton polarimeter for the EUROGAM array

Abstract This paper presents the results of tests, both with sources and in-beam experiments, on prototype Ge and BGO detectors of the Eurogam array. Timing and energy resolution data are reported along with results for various methods of ballistic deficit correction. The first measurements with the new “shared suppression” technique are presented.

Superdeformed bands in 150Gd and 151Tb: Evidence for the influence of high-N intruder states at large deformations

Abstract The application of a composite Ge detector to the measurement of the linear polarisation of γ-rays has been investigated. The polarisation sensitivity of this device has been determined over the energy range 197–1368 keV. Comparison to a previous design of a similar detector has been made.

High-spin excitations of 187, 188Hg

Abstract Rotational bands, characteristic of a superdeformed prolate shape ( e ≈0.6) and extending to above spin 60 h , have been observed in both 150 Gd and 151 Tb. The magnitudes of the moments of inertia I (2) were found to vary with frequency and the variation greatly exceeded that seen in 148,149 Gd and 151,152 Dy. The differences in the I (2) s are attributed to the occupation of particular high- N orbitals. Moreover, contrary to the previous examples the bands in both 150 Gd and 151 Tb de-excited at a much higher rotational frequency of h ω≈0.4 MeV and this may indicate that the pair gap extends to higher frequencies in 150 Gd and 151 Tb.

γ rays in the 2–18 MeV range from the reaction 120Sn(28Si, 4n)144Gd

Abstract High-spin states in 187, 188 Hg have been investigated via the 163, 164 Dy ( 28 Si , x n ) reactions by in-beam γ-ray spectroscopic techniques using the “Chateau de Cristal” 4π-multidetector array. Level schemes have been established. Spins and parities of the states have been deduced from transition multipolarities obtained from measurements of the angular distribution and linear polarization of the γ-rays. The shape coexistence of both prolate and oblate band structures has been observed for the first time in 187 Hg. In 188 Hg negative-parity bands are well developed. The band structure is interpreted within the frame of the Strutinsky method with the deformed Woods-Saxon average field. Pairing behaviour with increasing spin and general features of shape coexistence in mercury nuclei are illustrated.

Excited bands in the doubly-magic superdeformed 152Dy nucleus: evidence for the first N = 7 proton hyper-intruder orbital

Abstract Unresolved γ radiation preceding the decay of the I π = 10 + isomer in 144 Gd has been studied via the 120 Sn + 28 Si reaction using a large NaI detector. The γ-ray multiplicity and anisotropy have been measured for 2 ⩽E⩽ 18MeV . At energies above 8 MeV a broad shoulder, presumably arising from the giant dipole resonance, is observed on top of the statistical tail. These high-energy γ rays are shown to deexcite high spin states and have a nearly isotropic angular distribution.

A comparative study of superdeformation in 146,147,148Gd. Possible manifestations of the pseudo-SU3 symmetry, octupole shape susceptibility and superdeformed deep-hole excitations

Abstract Five excited superdeformed bands have been observed in the doubly closed-shell superdeformed nucleus 152 Dy. Three of the new bands are interpreted in terms of single neutron excitations across the N = 86 shell gap. One of these bands appears to partly decay into the yrast superdeformed band. Another band involves a single proton excitation across the Z = 66 shell gap into the N = 7 hyper-intruder orbital. This is the first evidence of the influence of this deformation driving orbital on superdeformed structures in any mass region.

Multi-particle excitations in the superdeformed 149Gd nucleus

Abstract Two discrete superdeformed (SD) bands have been identified in the nucleus 147Gd and the twin-band mechanism studied by comparison with SD results for 146,148Gd. Theoretical interpretation in terms of nucleonic orbitals with the Woods-Saxon potential is consistent with the pseudo-spin symmetry picture and the octupole susceptibility mechanism predicted by theory.

The TMR network project "Development of γ-ray tracking detectors"

Abstract Six rotational bands built on superdeformed intrinsic configurations have been observed in the 149 Gd nucleus with the Eurogam spectrometer. Orbital configuration assignments have been suggested on the basis of their effective alignments calculated with the Nilsson-Strutinsky cranking model. Most of the excited bands have identical partners in neighboring nuclei including one case differing by four mass units. Measurements of feeding patterns indicate that the 149 Gd yrast superdeformed band is fed over a wider range of angular momentum than other yrast superdeformed bands in this mass region whereas weaker excited bands in the same nucleus are populated in narrower spin windows.