Two-proton radioactivity studies with ${}^{45}\mathrm{Fe}$ and ${}^{48}\mathrm{Ni}$

In an experiment at the SISSI/LISE3 facility of GANIL, we have studied the decay of the two proton-rich nuclei ${}^{45}\mathrm{Fe}$ and ${}^{48}\mathrm{Ni}$. We identified 30 implantations of ${}^{45}\mathrm{Fe}$ and observed for the second time four implantation events of ${}^{48}\mathrm{Ni}$. In 17 cases, ${}^{45}\mathrm{Fe}$ decays by two-proton emission with a decay energy of 1.154(16) MeV and a half-life of $T_{1/2}={1.6}_{-0.3}^{+0.5}$ ms. The observation of ${}^{48}\mathrm{Ni}$ and of its decay allows us to deduce a half-life of $T_{1/2}={2.1}_{-0.7}^{+2.1}$ ms. One out of four decay events is completely compatible with two-proton radioactivity and may therefore indicate that ${}^{48}\mathrm{Ni}$ has a two-proton radioactivity branch. We discuss all information now available on two-proton radioactivity for ${}^{45}\mathrm{Fe}$ and ${}^{48}\mathrm{Ni}$ and compare it to theoretical models.

Figure 1

(Color online) Two-dimensional identification plot for the present experiment. The implantation events are plotted as a function of their time-of-flight between the target and the first silicon detector and their energy loss in the first silicon detector. 30 ${}^{45}\mathrm{Fe}$ and four ${}^{48}\mathrm{Ni}$ events are unambigously identified.

Figure 2

(Color online) Decay energy spectrum for the first decay event in the same pixel after an implantation of ${}^{45}\mathrm{Fe}$. A decay energy of 1.154(16) MeV is determined from the seventeen events in the peak. Events with an energy release above 6 MeV are cut in the figure.

Figure 3

(a) Energy spectrum from the last silicon detector obtained in coincidence with events in the peak at 1.154 MeV (see Fig. 2) from the decay of ${}^{45}\mathrm{Fe}$. No β signal beyond the detector noise is observed. For this plot, we excluded the event discussed in detail in the text. (b) Same spectrum in coincidence with a signal between 1.1 and 1.2 MeV for ${}^{43}\mathrm{Cr}$. Similar spectra were obtained also with the detector in front of the DSSSD.

Figure 4

(Color online) Decay time spectrum for the first decay event after ${}^{45}\mathrm{Fe}$ implantation with a decay energy in the 1.154 MeV peak. A maximum likelihood fit yields a half-life of ${1.6}_{-0.3}^{+0.5}$ms.

Figure 5

(Color online) Decay energy spectrum for the first decay event after a ${}^{48}\mathrm{Ni}$ implantation. The count at 1.35(2) MeV may be of two-proton origin.

Figure 6

(Color online) Decay time spectrum for ${}^{48}\mathrm{Ni}$. The spectrum shows the time for the first decay event after the implantation of an identified ${}^{48}\mathrm{Ni}$ nucleus. A half-life of $T_{1/2}={2.1}_{-0.7}^{+2.1}$ ms is determined.

Figure 7

(Color online) Comparison of our experimental data point for ${}^{45}\mathrm{Fe}$ with the three-body model of Grigorenko and co-workers [21, 22] for p-wave and f-wave emission and with the diproton model for two different channel radii in the R-matrix sense. In addition, we present also the results from the R-matrix approach of Brown and Barker [16] with and without the $p\text{−}p$ resonance.