A. Fleury

Influence of shell structure and pairing correlations on the nuclear state density

A microscopic calculation of nuclear state densities was performed starting from realistic single-particle levels. Within this concept, a correspondence between microscopic ground state energy corrections and microscopic effects on state densities was deduced. It is shown that the approximations introduced by a simple analytical expression for the nuclear state density are comparable to the uncertainties of microscopically calculated state densities for nuclei in their ground state configuration. Guidelines for the determination of the parameters of this analytical expression were deduced from the microscopic computations.

Two-proton radioactivity studies with 45Fe and 48Ni

In an experiment at the SISSI/LISE3 facility of GANIL, we have studied the decay of the two proton-rich nuclei 45Fe and 48Ni. We identified 30 implantations of 45Fe and observed for the second time four implantation events of 48Ni. In 17 cases, 45Fe decays by two-proton emission with a decay energy of 1.154(16) MeV and a half-life of T_1/2 = 1.6+0.5_-0.3 ms. The observation of 48Ni and of its decay allows us to deduce a half-life of T_1/2 = 2.1+2.1_-0.7 ms. One out of four decay events is completely compatible with two-proton radioactivity and may therefore indicate that 48Ni has a two-proton radioactivity branch. We discuss all information now available on two-proton radioactivity for 45Fe and 48Ni and compare it to theoretical models.

Two-proton radioactivity studies withFe45andNi48

In an experiment at the SISSI/LISE3 facility of GANIL, we have studied the decay of the two proton-rich nuclei 45Fe and 48Ni. We identified 30 implantations of 45Fe and observed for the second time four implantation events of 48Ni. In 17 cases, 45Fe decays by two-proton emission with a decay energy of 1.154(16) MeV and a half-life of T_1/2 = 1.6+0.5_-0.3 ms. The observation of 48Ni and of its decay allows us to deduce a half-life of T_1/2 = 2.1+2.1_-0.7 ms. One out of four decay events is completely compatible with two-proton radioactivity and may therefore indicate that 48Ni has a two-proton radioactivity branch. We discuss all information now available on two-proton radioactivity for 45Fe and 48Ni and compare it to theoretical models.

Two-proton decay of 45Fe: a new type of radioactivity

Abstract According to most mass models, several of the best candidates for two-proton radioactivity lie in the A = 50 mass region, at the proton drip-line. Recent experiments using the fragmentation of a 58Ni beam allowed us to reach this region and observe some of these candidates, like 45Fe and 48Ni. During an experiment at the GANIL/LISE3 facility, devay events correlated to the implantation of 22 ions of 45Fe could be assigned to the direct emission of two protons from the ground state. This decay mode appears through a (1.14 ± 0.04) MeV peak observed in the decay energy spectrum with a half-life of (4.7−1.4+3.4) ms.In an experiment at the SISSI-LISE3 facility of GANIL, the decay of the proton drip-line nucleus Fe45 has been studied after projectile fragmentation of a Ni58 primary beam at 75 MeV/nucleon impinging on a natural nickel target. Fragment-implantation events have been correlated with radioactive decay events in a 16x16 pixel silicon strip detector on an event-by-event basis. The decay-energy spectrum of Fe45 implants shows a distinct peak at (1.06+/-0.04)MeV with a half-life of T1/2 = (4.7+3.4-1.4)ms. None of the events in this peak is in coincidence with beta particles which were searched for in a detector next to the implantation detector. For a longer correlation interval, daughter decays of the two-proton daughter Cr43 can be observed after Fe45 implantation. The decay energy for Fe45 agrees nicely with several theoretical predictions for two-proton emission. Barrier-penetration calculations slightly favour a di-proton emission picture over an emission of two individual protons and point thus to a He2 emission mode.

Two-proton radioactivity studies with {sup 45}Fe and {sup 48}Ni

In an experiment at the SISSI/LISE3 facility of GANIL, we have studied the decay of the two proton-rich nuclei 45Fe and 48Ni. We identified 30 implantations of 45Fe and observed for the second time four implantation events of 48Ni. In 17 cases, 45Fe decays by two-proton emission with a decay energy of 1.154(16) MeV and a half-life of T_1/2 = 1.6+0.5_-0.3 ms. The observation of 48Ni and of its decay allows us to deduce a half-life of T_1/2 = 2.1+2.1_-0.7 ms. One out of four decay events is completely compatible with two-proton radioactivity and may therefore indicate that 48Ni has a two-proton radioactivity branch. We discuss all information now available on two-proton radioactivity for 45Fe and 48Ni and compare it to theoretical models.

Two‐proton radioactivity: the case of 45Fe

According to most mass models, several of the best candidates for two‐proton radioactivity lie in the A = 50 mass region, at the proton drip‐line. Recent experiments using the fragmentation of a 58Ni beam allowed us to reach this region and observe some of these candidates, like 45Fe and 48Ni. During an experiment at the GANIL / LISE3 facility helded in 2000, we could identify 22 events of implantation of 45Fe nuclei. The energy distribution of the corresponding decay events shows a clear peak at (1.14 ± 0.04) MeV that could be assigned to the direct 2‐proton emission from the ground state. This energy is in very good agreement with several theoretical predictions, and no coincident β particle has been observed experimentally. A half‐life of (4.7−1.4+3.4)u2009ms has been measured for the decay of 45Fe.

First Observation Of Two‐Proton Radioactivity Of 45Fe

In experiments at the FRS of GSI and at the SISSI‐LISE3 facility of GANIL, the decay of the proton drip‐line nucleus 45Fe has been studied after projectile fragmentation of a 58Ni primary beam. Fragment‐implantation events have been correlated with radioactive decay events in silicon telescopes on an event‐by‐event basis. The decay‐energy spectrum of 45Fe implants shows a distinct peak consistent with a two‐proton ground‐state decay of 45Fe. None of the events in the peak were found to be in coincidence with γ radiation or with β particles which were searched for in the telescope‐surrounding detectors. The decay energy for 45Fe agrees nicely with several theoretical predictions for two‐proton emission. These predictions strongly support the observed decay to be a simultaneous two‐proton ground‐state decay.

Indication for superallowed Fermi decay from the N=Z nuclei {sup 78}Y,{sup 82}Nb,{sup 86}Tc

The heavy odd-odd N=Z nuclei {sup 78}Y,{sup 82}Nb,{sup 86}Tc have been produced at GANIL by fragmentation of a 60 MeV/u {sup 92}Mo beam on a natural nickel target. Their lifetime have been measured for the first time, using the identification-implantation and subsequent time correlated {beta} counting technique at the LISE spectrometer. The obtained half-lives for {sup 78}Y,{sup 82}Nb,{sup 86}Tc are consistent with the microscopic predictions. These nuclei are good candidates to extend the mass range for the V{sub ud} matrix element evaluation and our experimental results highlight the interest of further investigation of their excited states and {beta} decay schemes as a function of isospin. {copyright} {ital 1998 American Institute of Physics.}