date : June 2000
Several experiments have been conducted in the last 10 years to study proton-rich nuclei close to the limits of stability with respect to proton emission (proton drip line) in the region of Z = 30 -38. They reported the discovery of new isotopes and have allowed to reach the drip line for odd-Z elements.
The aim of the present experiment was the spectroscopic study of very exotic nuclei in this mass region and had five main topics:
• Study of the decay by and emission of odd-odd nuclei (62Ga, 66As, 70Br and 74Rb) to determine the half-life and thus the ft value of these super-allowed Fermi transitions
• Study of the decay of the Tz = -1/2 nuclei 67Se, 71Kr and 75Sr by -delayed proton emission to improve the knowledge of their half-life and their branching ratios
• First determination of the half-lives and the decay properties of 60Ga and 64As in order to investigate whether these nuclei are proton emitters (they would be the lightest proton emitter ever observed) or whether the decay by emission which would open new branches for the astrophysical rp process.
• Improvement of the knowledge of the properties of 61Ga and 65As
• Study the decay of 69Kr and 73Sr by -delayed proton emission to study the structure of 69Br and 73Rb.
Figure 1 : Region of the experiemnt in the chart of nuclei
The detection system comprised a silicon telescope including a double-sided silicon strip detector in which the nuclei of interest were implanted. This allowed to correlate implantation and decay in the same pixel of this detector. This setup was mounted at the end of the LISE3 beam line of GANIL surrounded by four high-efficiency germanium detectors.
Figure 2 : Experimental setup
The figure presented here are online screen copies from data taking. The isotopes produced and separated are clearly identified on the two-dimensional spectra representing the energy loss of the isotopes as a function of their time-of-flight. The energy loss is measured in the silicon detectors and the time-of-flight is determined between a micro-channel-plate detector in the first LISE focal plane and the silicon detectors at the end of the LISE beam line as well as between the radio-frequency of the cyclotrons and the same silicon detectors.
The primary beam in the present experiment was 78Kr with an energy of 73 MeV/nucleon and an intensity of 2-3 A. This primary beam was fragmented in a beryllium target. The LISE beam line was set on 69Kr and 70Br.
Figure 4 : Identification Tz = -1/2 nuclei
Figure 5 : Identification Tz = -1 nuclei
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