SIRIUS is a state-of-the-art detector system for nuclear decay spectroscopy that will be mounted at the focalplane of S3 (Super Separator Spectrometer), which is part of the new SPIRAL2 facility at GANIL, Caen in France. Such a systemrequires high performance as it is dedicated to the study of very exotic nuclei. It is the result of collaboration between GANILCSNSM, IRFU, and IPHC It is composed of a succession of detectors (Trackers, Silicon detector DSSD and Tunnel plus anarray of five clover Germanium detectors). This set-up is mounted in a compact geometry. The energy measurement variesfrom 50 keV to over 500 MeV with high precision (2 x 10-3) at low energies and 1 % for the detection of heavy ions. A majorchallenge has been the development of new electronics with a very large dynamic range maintaining an adequate energyresolution for the measured particles (with energies from a few hundred keV up to 500 MeV).

International audienceSIRIUS is a state-of-the-art detector system for nuclear decay spectroscopy that will be mounted at the focal plane of S$^3$ (Super Separator Spectrometer), which is part of the new SPIRAL2 facility at GANIL, Caen in France. Such a systemrequires high performance as it is dedicated to the study of very exotic nuclei. It is the result of collaboration between GANILCSNSM, IRFU, and IPHC It is composed of a succession of detectors (Trackers, Silicon detector DSSD and Tunnel plus anarray of five clover Germanium detectors). This set-up is mounted in a compact geometry. The energy measurement variesfrom 50 keV to over 500 MeV with high precision (2 x 10$^{-3}$) at low energies and 1 % for the detection of heavy ions. A majorchallenge has been the development of new electronics with a very large dynamic range maintaining an adequate energyresolution for the measured particles (with energies from a few hundred keV up to 500 MeV)

Reinterpretation of excited states in 212^{212}Po: Shell-model multiplets rather than α\alpha-cluster states

International audienceA $\gamma$ -ray spectroscopic study of $^{212}$Po was performed at the Grand Accélérateur National d’Ions Lourds, using the inverse kinematics α-transfer reaction $^{12}$C($^{208}$Pb, $^{212}$Po) $^8$Be and the AGATA spectrometer. A careful analysis based on $\gamma \gamma$ coincidence relations allowed us to establish 14 new excited states in the energy range between 1.9 and 3.3 MeV. None of these states, however, can be considered as candidates for the levels with spins and parities of $1^-$ and $2^-$ and excitation energies below 2.1 MeV, which have been predicted by recent αcluster model calculations. A systematic comparison of the experimentally established excitation scheme of $^{212}$Po with shell-model calculations was performed. This comparison suggests that the six states with excitation energies (spins and parities) of 1744 (4$^-$), 1751 (8$^-$), 1787 (6$^-$), 1946 (4$^-$), 1986 (8$^-$), and 2016 (6$^-$) keV, which previously were interpreted as α-cluster states, may in fact be of positive parity and belong to low-lying shell-model multiplets. This reinterpretation of the structure of $^{212}$Po is supported by experimental information with respect to the linear polarization of $\gamma$ rays, which suggests a magnetic character of the 432-keV $\gamma$ ray decaying from the state at an excitation energy of 1787 keV to the $6^+_1$ yrast state, and exclusive reaction cross sections

Conceptual design of the AGATA 1 pi array at GANIL

The Advanced GAmma Tracking Array (AGATA) has been installed at the GANIL facility, Caen-France. This setup exploits the stable and radioactive heavy-ions beams delivered by the cyclotron accelerator complex of GANIL. Additionally, it benefits from a large palette of ancillary detectors and spectrometers to address in-beam gamma-ray spectroscopy of exotic nuclei. The set-up has been designed to couple AGATA with a magnetic spectrometer, charged-particle and neutron detectors, scintillators for the detection of high-energy gamma rays and other devices such as a plunger to measure nuclear lifetimes. In this paper, the design and the mechanical characteristics of the set-up are described. Based on simulations, expected performances of the AGATA l pi array are presented

Lifetime measurements in Ti-52,Ti-54 to study shell evolution toward N=32

Lifetimes of the excited states in the neutron-rich Ti-52,Ti-54 nuclei, produced in a multinucleon-transfer reaction, were measured by employing the Cologne plunger device and the recoil-distance Doppler-shift method. The experiment was performed at the Grand Accelerateur National d'Ions Lourds facility by using the Advanced Gamma Tracking Array for the gamma-ray detection, coupled to the large-acceptance variable mode spectrometer for an event-by-event particle identification. A comparison between the transition probabilities obtained from the measured lifetimes of the 2(1)(+) to 8(1)(+) yrast states in Ti-52,Ti-54 and that from the shell-model calculations based on the well-established GXPF1A, GXPF1B, and KB3G fp shell interactions support the N = 32 subshell closure. The B(E2) values for Ti-52 determined in this work are in disagreement with the known data, but are consistent with the predictions of the shell-model calculations and reduce the previously observed pronounced staggering across the even-even titanium isotopes

Lifetime measurements in 52,54^{52,54}Ti to study shell evolution toward N=32N=32

International audienceLifetimes of the excited states in the neutron-rich Ti52,54 nuclei, produced in a multinucleon-transfer reaction, were measured by employing the Cologne plunger device and the recoil-distance Doppler-shift method. The experiment was performed at the Grand Accélérateur National d'Ions Lourds facility by using the Advanced Gamma Tracking Array for the γ-ray detection, coupled to the large-acceptance variable mode spectrometer for an event-by-event particle identification. A comparison between the transition probabilities obtained from the measured lifetimes of the 21+ to 81+ yrast states in Ti52,54 and that from the shell-model calculations based on the well-established GXPF1A, GXPF1B, and KB3G fp shell interactions support the N=32 subshell closure. The B(E2) values for Ti52 determined in this work are in disagreement with the known data, but are consistent with the predictions of the shell-model calculations and reduce the previously observed pronounced staggering across the even-even titanium isotopes