Optical studies for the super separator spectrometer S3

International audienceS3 (Super Separator Spectrometer) [1] is a future device designed for experiments with the high intensity heavy ion stable beams of SPIRAL2 [2] at GANIL (Caen, France). It will include a target resistant to these very high intensities, a first stage momentum achromat for primary beam extraction and suppression, a second stage mass spectrometer and a dedicated detection system. This spectrometer includes large aperture quadrupole triplets with embedded multipolar corrections. To enable the primary beam extraction one triplet has to be opened on one side, which requires an appropriate design of such a multipolar magnet. The final mass separation power required for S3 needs a careful design of the optics with a high level of aberration correction. Multiple symmetric lattices were studied for this purpose. A 4-fold symmetric lattice and the achieved results are described in this paper

Nuclear astrophysics with radioactive ions at FAIR

The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process, β-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes

The Super Separator Spectrometer S3 and the associated focal plane detection systems SIRIUS and REGLIS3

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Toward the drip lines and the superheavy island of stability with the Super Separator Spectrometer S3

International audienceThe Super Separator Spectrometer S3 is a major experimental system developed for SPIRAL2.It has been designed for physics experiments with very low cross sections by taking full advantage of the veryhigh intensity stable beams to be produced by LINAG, the superconducting linear accelerator at GANIL.These intensities will open new opportunities in several physics domains using fusion evaporation reactions,principally: super-heavy and very heavy element properties, spectroscopy at and beyond the dripline,and isomer and ground-state properties. The common feature of these experiments is the requirementto separate very rare events from intense backgrounds. S3 accomplishes this with a large acceptance, ahigh background rejection efficiency, and a physical mass separation. This article will present the technicalspecifications and optical constraints needed to achieve these physical goals. The optical layout of thespectrometer will be presented, focusing on technical elements of the target system, the superconductingmultipole magnets used to correct high-order optical aberrations, the electric and magnetic dipoles, andthe open multipole triplet used for primary beam rejection. The expected system performance will bepresented for three experimental cases using 3 specific optical modes of the spectrometer

First experimental tests of shels: A new heavy ion separator at the JINR

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Fine structure in the alpha decay of 224^{224}U

224U nuclei were populated in fusion-evaporation reactions using a 206Pb target and an intense 22Ne beam. Fusion-evaporation residues were separated by the new separator SHELS at the FLNR, Dubna and implanted into a large-area double-sided silicon strip detector. Position- and time-correlated alpha decays were used to identify evaporation residues. A new α -decay line at 8095(11) keV was observed in this work and assigned as the decay from 224U to the first excited 2+ in the daughter nucleus 220Th. Coincident photons were also observed allowing to unambiguously determine the excitation energy of the first excited 2+ state in 220Th to be 386.5(1) keV and not 373.3(1)keV as previously reported. The half-life of 224U was measured to be 396(17)μs

Influence of octupole vibration on the low-lying structure of 251^{251}Fm and other heavy N=151N=151 isotones

International audienceThe structure of low-lying excited states in Fm251, populated by the α decay of No255, has been investigated by means of combined γ and internal conversion electron spectroscopy. The values for the internal conversion coefficients for the 1/2+→5/2+ and 5/2+→9/2− transitions have been measured. The determined M2/E3 mixing ratio and lifetime for the 5/2+ decay to the ground state allowed to determine the corresponding reduced transitions strengths of B(E3)=18(6) W.u. and B(M2)=3.0(6)×10−3 W.u. These results, as well as the results of previous studies in N=151 isotopes, are compared to theoretical calculations beyond the mean-field approach, including the first QRPA calculations using the Gogny D1M parametrization for such heavy odd-N nuclei. The comparison points to the importance of accounting for the octupole vibrations for a proper understanding of the low-lying nuclear structure of some of the heaviest elements