J. N. Scheurer

Improvements in the in-beam γ-ray spectroscopy provided by an ancillary detector coupled to a Ge γ-spectrometer: the DIAMANT-EUROGAM II example

For the first time the 4π γ-ray spectrometer EUROGAM II has been coupled to a 4π light charged particle detector array, DIAMANT, during a test experiment on the reaction 32S + 58Ni at 120 MeV beam energy. A very large improvement in the peak-to-background ratio of the γ-spectra has been found when EUROGAM II is triggered by DIAMANT to select an exit channel. A simple algebra has been developed which provides theoretical estimates in good agreement with these experimental results. It is demonstrated that, depending on both the γ-spectrometer and ancillary detector performances, much better peak-to-background can be obtained by such a coupling. For the same peak-to-background ratio, the use of an ancillary detector allows for a lower γ-ray coincidence level and therefore improves the statistics. Ways to select the most appropriate ancillary detector are given. The ability of the ancillary detector to provide a total Doppler shift correction is crucial for the improvement of the peak-to-background ratio.

γ -ray linear polarization measurements and (g9/2) −3 neutron alignment in 91Ru

The authors would like to thank the operators of the GANIL cyclotrons for providing the 36Ar beam. We would also like to thank the EXOGAM Collaboration for use of the clover Ge detector array, the DIAMANT Collaboration for use of the charged particle detector system, and the European gamma-ray Spectroscopy Pool for use of the neutron detector system. We acknowledge funding support from the French-Polish LEA COPIGAL and the IN2P3-Polish laboratories COPIN Agreement No. 06-122, from the UK STFC, from the Swedish Research Council (Contracts No. 2007-4067 and No. 2008-5793), from the Goran Gustafsson Foundation, from the OTKA under Contract No. K100835, and from the Bolyai Janos Foundation. AG has been supported by the Generalitat Valenciana, Spain, under Grant No. PROMETEO/2010/101 and by MINECO, Spain, under Grants No. AIC-D-2011-0746 and No. FPA2011-29854. AJ acknowledge financial support from the Spanish Ministerio de Ciencia e Innovacion under Contract No. FPA2011-29854-C04. ZY acknowledges the support from the Chinese Academy of Sciences, China.

The DIAMANT electronics and data acquisition system

Abstract We describe the electronics and data acquisition system of the 4π light particle multidetector array DIAMANT. This system has been conceived to be very modular with regard to both the kind and number of detectors. The whole system is designed to run either with a few additional ancillary detectors (Ge) or linked to 4π γ arrays such as EUROGAM. Part of the electronics has been designed using SMD devices; the acquisition is based on CAMAC ADCs and VME units for data acquisition, data transfer is handled via a 32 bit ECL bus (DT32) used for EUROGAM. The data acquisition, distributed on a network, is based on the VxWorks Real Time kernel and the UNIX Operating System.

γ‐ray Spectroscopy of Proton Drip‐Line Nuclei in the A∼130 Region using SPIRAL beams

A fusion‐evaporation experiment has been performed with a SPIRAL 76Kr radioactive beam in order to study the deformation of rare‐earth nuclei near the proton drip‐line. The experimental setup consisted in the EXOGAM γ‐array, coupled to the light‐charged particles (LCP) DIAMANT detector and to the VAMOS heavy‐ion spectrometer. The difficulties inherent to such measurements are enlightened. The coupling between EXOGAM and DIAMANT has been used to decrease the huge background caused by the radioactivity of the beam. It further permits assigning new γ‐ray transitions to specific residual nuclei. A γ‐ray belonging to the 130Pm level scheme has thus been observed for the first time.

Charged particle feeding of hyperdeformed nuclei in the A=118?126 region

A breakthrough was recently obtained in the analysis of the so-called Hyper-Long-HyperDeformed (HLHD) experiment made at the EUROBALL-IV γ-detector array (EB). The 64Ni + 64Ni ⇒ 128Ba* fusion reaction was studied at Ebeam = 255 and 261 MeV, reaching the highest angular momentum that the compound nuclei can accommodate. To date no discrete HD rotational bands have been identified. However, rotational patterns in the form of ridge-structures in three-dimensional (3D) rotational mapped spectra are identified with dynamic moments of inertia J(2) ranging from 71 to 1112 MeV-1 in 12 different nuclei selected by charged particle- and/or γ-gating. The four nuclei, 118Te, 124Cs, 125Cs and 124Xe found with moment of inertia J(2)≥100 2 MeV-1, are most likely hyperdeformed, the remaining nuclei with smaller values of J(2), are considered to be superdeformed, in qualitative agreement with recent theoretical calculations.

{gamma}-Spectroscopy and Radioactive Beams: How To Perform Channel Selection ?

An experiment has been performed using a SPIRAL 76Kr radioactive beam at GANIL to investigate rare‐earth nuclei near the proton drip‐line. The EXOGAM gamma array was coupled with the DIAMANT light charged‐particle detector and the VAMOS spectrometer. We report here on the powerful of this setup to extract fusion‐evaporation γ‐rays from a large beam contamination.

Hyperdeformed Shapes and Jacobi Transitions in 126Ba

Systematic searches for exotic shapes, hyperdeformation (HD) and Jacobi transitions, have been made in Hf, Nd, Ba, Xe, Sn and Cd nuclei during the last 4 years, guided by theoretical predictions. The most promising results showing patterns of rotational correlations (e.g. 2. order ridges of multiple rotational bands) are found for 126Xe and 126Ba when the very highest multiplicity cascades are selected by various techniques. In particular, the results on 126Ba obtained in 3 different experiments, using both Gammasphere in Berkeley and Euroball IV in Strasbourg are discussed and compared to theoretical predictions and to simulations by a double‐potential statistical model for population and γ‐decay. A very surprising result was obtained in the last experiment at Euroball, in a full month running time, namely that the observed ridge structure depends very sensitively on the bombarding energy, which points to entrance channel effects. The analysis shows that a discrete HD yrast band intensity will be signifi...

Correction method for Doppler broadened γ-ray lines using the linear momentum of the evaporated charged particles in heavy-ion induced fusion–evaporation reactions

Abstract A method based on the conservation of linear momentum is used to correct the position and the width of the γ-ray lines of the residual nucleus produced in heavy-ion induced fusion–evaporation reactions. This method implies the measurement of the total number of the emitted particles, their masses, energies and directions of emission in coincidence with the prompt γ-rays. It has been applied to the 120 MeV 32 S + 58 Ni reaction whose data have been collected using the high efficiency and large granularity 4 π light charged particle detector DIAMANT, coupled to the 4 π γ-ray spectrometer EUROGAM II.

Half-life of the first excited state of {sup 201}Hg

The lifetime of the first excited state of {sup 201}Hg, populated by the {sup 201}Tl electron capture decay and subsequent {gamma}-ray transitions, has been measured for the first time. This measurement has been carried out using a coincidence between an internal conversion electron and a {gamma}-ray. The half-life of 81{+-}5 ns has been obtained and B(E2) and B(M1) values were deduced and compared to previous estimates. With these reduced matrix elements, the excitation rate of the first excited state of {sup 201}Hg in plasma have been calculated in the frame of a Nuclear excitation by electronic transition (NEET) process.

High-spin structure of Ru102

High-spin states in the nucleus 102Ru have been investigated via the 96Zr(13}C,alpha3n) reaction at beam energies of 51 and 58 MeV, using the EUROBALL IV gamma-ray spectrometer and the DIAMANT charged particle array. Several new high-spin bands have been established. The ground state band has been extended up to E_x \sim 12 MeV with Ipi = (26+), while the previously published negative-parity bands have been extended up to E_x \sim 11 and sim 9 MeV with I pi = (23-) and (20-), respectively. The deduced high-spin structure has been compared with Woods-Saxon TRS calculations and, on the basis of the measured Routhians, aligned angular momenta, and B(M1)/B(E2) ratios, nu h_11/2(g_{7/2},d_{5/2} configurations are suggested for the negative-parity structures.