No abstract

No abstract

In an experiment at the SISSI/LISE3 facility of GANIL, we have studied the decay of the two proton-rich nuclei 45 Fe and 48 Ni. We identified 30 implantations of 45 Fe and observed for the second time four implantation events of 48 Ni. In 17 cases, 45 Fe 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 48 Ni 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 48 Ni has a two-proton radioactivity branch. We discuss all information now available on two-proton radioactivity for 45 Fe and 48 Ni and compare it to theoretical models.

The nucleus54 Zn has been observed for the first time in an experiment at the SISSI/LISE3 facility of GANIL in the quasi-fragmentation of a 58 Ni beam at 74.5 MeV/nucleon in a nat Ni target. The fragments were analysed by means of the ALPHA-LISE3 separator and implanted in a silicon-strip detector where correlations in space and time between implantation and subsequent decay events allowed us to generate almost background free decay spectra for about 25 different nuclei at the same time. Eight 54 Zn implantation events were observed. From the correlated decay events, the half-life of 54 Zn is determined to be 3.2 +1.8 −0.8 ms. Seven of the eight implantations are followed by two-proton emission with a decay energy of 1.48(2) MeV. The decay energy and the partial halflife are compared to model predictions and allow for a test of these two-proton decay models.PACS numbers: 23.50.+z, 23.90.+w, 21.10.-k, 27.40.+z Our understanding of nuclear structure is mainly based on results obtained with nuclei close to the line of stability. These studies allowed for understanding of the basic structure of the strong interaction which governs the interplay between neutrons and protons in an atomic nucleus. However, these nuclei close to stability cover only a very small range in isospin, i.e. their proton-toneutron ratio is rather similar. With the advent of machines to produce radioactive nuclei, these basic concepts can now be tested with more and more exotic nuclei having a strong imbalance of neutrons and protons.With these exotic nuclei being much further away from stability, also new phenomena appeared. For nuclei beyond the proton drip line, where the strong force can no longer bind all protons, one-and two-proton (2p) radioactivity was predicted more than 40 years ago by Goldanskii [1]. For odd-Z nuclei, one-proton radioactivity was proposed to occur, whereas for medium-and heavy-mass even-Z nuclei the nuclear pairing energy renders one-proton emission impossible. In this case, twoproton emission is to be expected.One-proton radioactivity was observed for the first time about 20 years ago by Hofmann et al. [2]. Twoproton radioactivity was sought for many years without success. This research field experienced a strong boost with the advent of high-intensity projectilefragmentation facilities. At these facilities, experimentalists could for the first time reach the most promising candidates for two-proton radioactivity. According to recent theoretical predictions, proton drip-line nuclei in the A=40-55 region were identified as the most promising candidates [3][4][5]. Zn were regarded as possible candidates to exhibit two-proton radioactivity. In the present letter, we report on the first observation of 54 Zn and its decay by two-proton radioactivity. 54 Zn was produced by quasi-fragmentation reactions of a primary 58 Ni 26+ beam, accelerated to 74.5 MeV/nucleon by the GANIL cyclotrons, which impinged with an average intensity of 4µA on a nat Ni target of thickness 250mg/cm 2 installed in the SISSI device. The fragment...

The two protons emitted in the decay of 54Zn have been individually observed for the first time in a time projection chamber. The total decay energy and the half-life measured in this work agree with the results obtained in a previous experiment. Angular and energy correlations between the two protons are determined and compared to theoretical distributions of a three-body model. Within the shell model framework, the relative decay probabilities show a strong contribution of the p2 configuration for the two-proton emission. After 45Fe, the present result on 54Zn constitutes only the second case of a direct observation of the ground state two-proton decay of a long-lived isotope.

No abstract

Masses of the radioactive isotopes 62 Ga, 62 Zn and 62 Cu have been measured at the JYFLTRAP facility with a relative precision of better than 1.8 × 10 −8 . A Q EC value of (9181.07 ± 0.54) keV for the superallowed decay of 62 Ga is obtained from the measured cyclotron frequency ratios of 62 Ga-62 Zn, 62 Ga-62 Ni and 62 Zn-62 Ni ions. The resulting Ft-value supports the validity of the conserved vector current hypothesis (CVC). The mass excess values measured were (−51986.5 ± 1.0) keV for 62 Ga, (−61167.9 ± 0.9) keV for 62 Zn and (−62787.2 ± 0.9) keV for 62 Cu.

The proton-rich nucleus 33 Ar has been studied by detailed proton and γ-ray spectroscopy at the low-energy facility of SPIRAL at GANIL. Proton and γ-ray singles and coincidence measurements allowed to establish a quasi complete decay scheme of this nucleus. By comparing the proton intensity to different daughter states, tentative spin assignments have been made for some of the states of 33 Cl. The Gamow-Teller strength distribution is deduced and compared to shell-model calculations and a quenching factor is determined. States close to the isobaric analogue state are searched for with respect to isospin mixing.PACS numbers: 21.10.-k Properties of nuclei, 23.50.+z Decay by proton emission, 29.30.Ep Charged-particle spectroscopy