Characterization of a new generation of silicon detector: The SIRIUS side “Strippy-Pad” detector

International audienceSIRIUS (Spectroscopy & Identification of Rare Isotopes Using S3) is a detection system designed for the focal plane of S3 (the Super Separator Spectrometer), which is part of the SPIRAL2 (Système de Production d’Ions RAdioactifs en Ligne de 2e génération) facility at GANIL (France). This study presents the characterization of the Side silicon detector of SIRIUS. This new “Strippy-pad” detector design benefits from an ultra-high resistivity and the windowless technique from Micron Semiconductor Ltd. These detectors were tested at the IPHC Strasbourg on a dedicated test bench with custom fast preamplifiers coupled to digital electronics cards. Combining all these elements, we obtained resolutions as good as 13.6 keV for certain pixels of this detector for 8.8 MeV alpha particles, with an average resolution measured at 14.7 keV over the whole detector

Investigation of the Spontaneous Fission Properties of Neutron-Deficient Nobelium Isotopes

International audienceIn the last years we carried out several experiments aimed to investigate properties of short-lived SF isotopes. The neutron-deficient isotopes of nobelium were produced in fusion-evaporation reactions using 206,208Pb targets and an intense 48Ca-beam. Fusionevaporation residues were separated by the SHELS separator and implanted into a largearea double-sided 48×48 strip silicon detector surrounded by 3He-based neutron counters. Half-lives and decay branching ratios for 252,254No isotopes were measured. The average number of neutrons per spontaneous fission of 254No determined for the first time

Comparative Study of Spontaneous-Fission Characteristics of 252^{252}No and 254^{254}No Isotopes

International audienceSpontaneous fissions of the $^{252}$No and $^{254}$No nobelium isotopes have been studied in a series of experiments with the SHELS separator. These isotopes are produced by colliding a beam of $^{48}$Ca ions from the U-400 cyclotron with the $^{206}$Pb and $^{208}$Pb targets. The measured characteristics of the $^{252}$No and $^{254}$No spontaneous fissions include their half-lives, total kinetic energies of fission fragments, and prompt-neutron multiplicities. The average number of neutrons per $^{254}$No spontaneous-fission act is measured for the first time as 4.88 ± 0.53

Measurement of proton-evaporation rates in fusion reactions leading to transfermium nuclei

International audienceThe analysis of fission events following the implantation of evaporation residues produced in the fusion reaction of 50 Ti and 209 Bi at different bombarding energies has revealed 5 millisecond decays, which are attributed to the spontaneous fission of proton-evaporation channels. The average cross sections for proton evaporation are found to be ∼100 and 10 times smaller than the largest neutron-evaporation channel cross section at the same excitation energy. These results suggest that the proton evaporation channel, albeit weak, may represent a realistic alternative to synthesize new, more neutron rich super heavy nuclei

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

The SFiNx Detector System

International audienceA new detector system for investigating the properties of spontaneous fission of short-lived transuranium nuclei has been created. This system consists of an assembly of double-sided silicon strip detectors surrounded by 116 proportional neutrons counters filled with $^{3}$He. The neutron registration efficiency is 54.7 ± 0.1%. The detector system is tested in an experiment investigating the characteristics of spontaneous fission of the $^{252}$No isotope. The experimental data on neutron yields are compared with previously published results. The average number of neutrons per fission act ($\bar {\nu }$ = 4.25 $\pm$ 0.09) and the multiplicity distribution of prompt neutrons are obtained. The true form of the neutron distribution is reconstructed via a statistical regularization

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

© 2018 American Physical Society. The 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.status: Published onlin