M. Chartier

Direct mass measurements of {sup 68}Se and {sup 80}Y

The masses of neutron-deficient nuclides near the N=Z line with A=64-80 have been determined using a direct time-of-flight technique which employed a cyclotron as a high-resolution spectrometer. The measured atomic masses for {sup 68}Se and {sup 80}Y were 67.9421(3) u and 79.9344(2) u, respectively. The new values agree with the 2003 Atomic Mass Evaluation. The result for {sup 68}Se confirms that this nucleus is a waiting point of the rp-process, and that for {sup 80}Y resolves the conflict between earlier measurements. Using the present results and the 2003 Atomic Mass Evaluation compilation, the empirical interaction between the last proton and the last neutron in N=Z nuclei has been revisited and extended.

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.

The Masses of A ≈ 60–70 Nuclei Close To The N = Z Line

The masses of very neutron‐deficient 66As, 68,70,71Se and 71Br were measured for the first time and those of 64,65Ge and 67As remeasured, with total uncertainties ranging from 200 to 1000 keV, including systematic, extrapolation and statistical errors, using the SPEG direct time‐of‐flight method at GANIL. These new results are discussed and compared to other recent experimental data and mass predictions.

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.