Two-Proton Correlations in the Decay of ${}^{45}\mathrm{Fe}$

The decay of extremely neutron-deficient ${}^{45}\mathrm{Fe}$ has been studied in detail by means of a novel type of a gaseous detector employing digital imaging to record tracks of charged particles. The two-proton radioactivity channel was clearly identified. For the first time, the angular and energy correlations between two protons emitted from the nuclear ground state were determined, indicating the genuine three-body character of this decay. The half-life of ${}^{45}\mathrm{Fe}$ was found to be $2.6\pm 0.2\mathrm{ms}$ and the observed $2p$ decay branching ratio is $70\pm 4\%$.

Figure 1

An example of a registered two-proton decay event of ${}^{45}\mathrm{Fe}$. Top: an image recorded by the CCD camera in a 25 ms exposure. A track of a ${}^{45}\mathrm{Fe}$ ion entering the chamber from left is seen. The two bright, short tracks are protons of approximately 0.6 MeV, emitted $535\mu \mathrm{s}$ after the implantation. Bottom: a part of the time profile of the total light intensity measured by the PMT (histogram) showing in detail the $2p$ emission. Lines show results of the reconstruction procedure yielding the emission angles $\vartheta$ with respect to the axis normal to the image.

Figure 2

The partial $2p$ half-life of ${}^{45}\mathrm{Fe}$ as a function of the $2p$ decay energy. The experimental result is shown superimposed on predictions of the 3-body model [13, 21]. The decay width is taken from this work; the energy is taken from Ref. 11. The numerical labels indicate the relative weights of the $p^2$ and $f^2$ configurations, respectively.

Figure 3

The measured distribution of the opening angle between two protons emitted in the decay of ${}^{45}\mathrm{Fe}$ (histogram). Lines show the predictions of the 3-body model for the same mixtures of $p^2$ and $f^2$ configurations as shown in Fig. 2 with the dashed lines.

Figure 4

The energy distribution of individual protons emitted in the $2p$ decay of ${}^{45}\mathrm{Fe}$ (histogram). The energy is given in units of the total decay energy $Q_{2p}=1.15\mathrm{MeV}$. The solid line indicates the prediction of the 3-body model [13] while the dotted line shows this theoretical prediction folded with a Gaussian function representing the detector energy resolution of 20%.