[en] The efficiency of the multicounter system (12) associated with the crystal palace was increased to improve spectrum quality and to increase double coincidence statistics by a factor of 10. Four large volume Ge, an amplifier, and an integrator were tested. The measuring chain shows good transmission performance, and allows work at very high count rates while maintaining a reasonable mid level energy resolution (2.55 keV). The time response of the detectors is excellent, and is close to that of standard Ge of smaller volume. The crystal palace will be used to study nuclear matter in rapid rotation

[en] This study presents different ballistic correction methods versus input count rate (from 3 to 50 kcounts/s) using four large Ge detectors of about 70 % relative efficiency. It turns out that the Tennelec TC245 linear amplifier in the BDC mode (Hinshaw method) is the best compromise for energy resolution throughout. All correction methods lead to narrow sum-peaks indistinguishable from single Γ lines. The full energy peak throughput is found representative of the pile-up inspection dead time of the corrector circuits. This work also presents a new and simple representation, plotting simultaneously energy resolution and throughput versus input count rate. (TEC). 12 refs., 11 figs

[en] Cross sections and γ-ray multiplicities have been measured for neutron evaporation channels in the reactions ¹⁶O + ¹⁴⁴Nd, ³⁷Cl + ¹²³Sb, ⁶⁴Ni + ⁹⁶Zr and ⁸⁰Se + ⁸⁰Se leading to the compound system ¹⁶⁰Er at common excitation energies. In the near-barrier energy regime average angular momentum transfers depend dramatically on the asymmetry of the entrance channel. The results can be interpreted in terms of barrier fluctuations induced by target and projectile ground-state vibrations

[en] The EUROGAM data-acquisition has to handle a large number of events/s. Typical in-beam experiments using heavy-ion fusion reactions assume the production of about 50 000 compound nuclei per second deexciting via particle and γ-ray emissions. The very powerful γ-ray detection of EUROGAM is expected to produce high-fold event rates as large as 10⁴ events/s. Such high count rates introduce, in a common dead time mode, large dead times for the whole system associated with the processing of the pulse, its digitization and its readout (from the preamplifier pulse up to the readout of the information). In order to minimize the dead time the shaping time constant τ, usually about 3 μs for large volume Ge detectors has to be reduced. Smaller shaping times, however, will adversely affect the energy resolution due to ballistic deficit. One possible solution is to operate the linear amplifier, with a somewhat smaller shaping time constant (in the present case we choose τ = 1.5 μs), in combination with a ballistic deficit compensator. The ballistic deficit can be corrected in different ways using a Gated Integrator, a hardware correction or even a software correction. In this paper we present a comparative study of the software and hardware corrections as well as gated integration

[en] Complete text of publication follows. The study of nuclear structure at the limits of angular momentum and isospin is only possible with very selective and powerful detection setups. The EUROBALL γ-ray spectrometer and the many associated ancillary detectors have been designed for that purpose. In its fourth phase, EUROBALL includes an inner BGO ball which works, with the Ge detectors and their suppression shields, like a multiplicity filter and a calorimeter and improves the selectivity of the device. EUROBALL IV is in operation at IReS-Strasbourg since june 1999. More than 20 experiments have already been performed with this very efficient instrument and preliminary results of some of them will be presented in this talk. (author)

[en] Ellipsoidal superdeformed nuclei (axis ratio 2/1 and β=0.6) have been experimentally observed in three mass regions: 130, 150, 190. No linking transitions are observed at present between the superdeformed and the normal deformed bands of the same nuclei. Some of the excited bands exhibit the so-called 'identical band' property. As the superdeformed structures are at the detection limit of the current devices, a France-UK collaboration between laboratories have undertaken to develop a new 4πγ array: EUROGAM. The main characteristics of this device are presented and compared to TESSA3. A new type of Ge detector, the Clover, will complete EUROGAM phase 2 leading to an improvement of its performances and allow further investigations in the field of superdeformation

[en] A short overview is presented of the status of EUROBALL IV. The new BGO inner ball and its performance is described. The main physics topics studied with this array are summarized. Three selected experiments are presented as an example. In ¹⁹⁷Pb nucleus the spin gyromagnetic factor g_s^eff was determined from M1 interband transitions between two signature partner superdeformed (SD) bands which are built on the ν[752]5/2^- neutron intruder orbital; no g-factor quenching is observed; A ΔI = 4 bifurcation was observed in the dynamical moment of inertia of the yrast SD band of ¹⁵⁰Tb; its amplitude is two times smaller than that in ¹⁴⁹Gd yrast SD band; due to the occupation in ¹⁵⁰Tb of the π6³ proton intruder orbital; Interband transitions were observed between two triaxial SD bands in ¹⁶³Lu. The excited band is a good candidate for a wobbling type of motion of the nucleus. (author)

[en] Full text of publication follows. Recent experimental discoveries have revealed that the neutron effective single-particle evolution above ⁷⁸Ni (N>50) shows peculiar or un predicted behaviours. The aim of this work is to determine the nature of the low-lying yrast or quasi yrast 7/2⁺ and 9/2⁺ states in 32 < Z < 40, odd-neutron N=51 nuclei, in order to assess their 'collective' (core-particle coupled) or u1g_7/2 and u(2d_5/2)²(1g_9/2)^-1 single-particle origin and better constrain the relative position of the neutron single-particle states above a ⁷⁸Ni core. Calculations show that there is a difference of about two orders of magnitude between core-particle coupled state and single-particle state half-lives. A Recoil distance Doppler-shift (RDDS) experiment has been performed at LNL (Italy). Neutron-rich nuclei were produced via multi-nucleon transfer with the ⁸²Se (505 MeV) + ²³⁸U system. The setup combined the AGATA demonstrator, the PRISMA fragment spectrometer and the Cologne plunger. The number of plunger distances was restricted to only two with the goal to provide the half-live domain (< 1 ps or several tens ps) of the states of interest. Half-lives of the lowest-lying 7/2 and 9/2 states of two N=51 nuclei, ⁸⁷Kr and ⁸⁵Se, as well as indications of higher lying state half-lives up to spin 19/2^- in ⁸⁷Kr have been measured. Structure analysis of these states will be discussed. A 14 days experiment combining AGATA and the VAMOS fragment spectrometer has been run last year with the aim to probe the medium spin structure of neutron-rich nuclei in the vicinity of ⁷⁸Ni, to experimentally determine the size of the N=50 gap as well as the πf_5/2-πp_3/2 spacing in ⁷⁹Cu. The fusion-fission mechanism in inverse kinematics for the ²³⁸U (6.2 MeV/A) + ⁹Be reaction at an energy around the Coulomb barrier was used as it was earlier shown to be an efficient method to populate neutron-rich nuclei at relatively large angular momentum. AGATA in a compact configuration was coupled to VAMOS++, providing an event-by-event unambiguous (A,Z) identification of one of the fission fragments, and the prompt gamma-rays emitted in coincidence. The VAMOS++ and AGATA data pre-sorting is completed. Excellent mass and atomic number resolutions have been obtained. Preliminary results on the gamma rays assigned to various neutron-rich Ge and Zn isotopes will be presented. (author)

[en] In an attempt to explain the missing cross section observed in different fusion experiments spin distribution measurements with the 4πγ multidetector system and total fusion-evaporation measurements for the ¹⁶O + ¹⁴⁴Nd and ⁸⁰Se + ⁸⁰Se near the barrier region were performed. The fission fragments produced in ¹⁶O + ¹⁴⁴Nd reaction were detected and the cross sections were measured. 6 refs., 1 tab. (M.F.W.)

[en] A new γ-tracking method based on the Compton-scattering probability of photons in a spectrometer composed of segmented Ge detectors has been developed and evaluated with the GEANT 3 simulation code. The performance of this probabilistic method, in terms of photopeak detection efficiency and peak-to-total ratio calculated for a 4π array composed of planar detectors, is comparable with the ones obtained with the previous γ-tracking methods. Furthermore, the algorithm has been tested successfully with single detection units of other crystal shapes. A simple application is also proposed as a peak-to-total ratio enhancer for bare segmented Ge crystals in replacement of the Compton-suppression shield