Figure 1

Sketch of the experimental setup. The ${}^{20}\mathrm{Mg}$ secondary beam was tracked by a silicon strip detector, DSSD, and a multiwire chamber, MW. ${}^{19}\mathrm{Mg}$ nuclei were formed in the reaction $({}^{20}\mathrm{Mg},{}^{19}\mathrm{Mg})X$ and products of the decays ${}^{19}\mathrm{Mg}\to {}^{17}\mathrm{Ne}+p+p$ were tracked by three planes of silicon microstrip detectors (D1–D3). ${}^{17}\mathrm{Ne}$ ions were identified at foci F2 and F3 as described in the text.Reuse & Permissions

Figure 2

(a) Illustration of the kinematical enhancement of angular correlations of decay products at the maximum possible angles between the decay products. (b) Angular $p-{}^{17}\mathrm{Ne}$ correlations obtained from the measured ${}^{17}\mathrm{Ne}+p+p$ events by selecting their vertex position inside the target (full circles).Reuse & Permissions

Figure 3

Profiles of the reaction vertices along the beam direction with respect to the closest microstrip detector. (a) Ideal profiles of prompt (gray curve) and delayed (black curve) decays expected in a thick target. (b) Vertex distribution of ${}^{17}\mathrm{Ne}+p+p$ events gated by large $p-{}^{17}\mathrm{Ne}$ angles (and thus large $p-{}^{17}\mathrm{Ne}$ relative energies), which corresponds to short-lived excited states in ${}^{19}\mathrm{Mg}$ (full circles with statistical uncertainties). The dashed curve shows the Monte Carlo simulations of the detector response for the $2p$-decay ${}^{19}\mathrm{Mg}^{*}\to {}^{17}\mathrm{Ne}+p+p$ with $T_{1/2}=0$. (c) The same as (b) but gated by small $p-{}^{17}\mathrm{Ne}$ angles corresponding to the “ground state” group in Fig. 2b. The dashed curve depicts a simulation of the $2p$-decay component with $T_{1/2}=0$. The solid and dash-dotted curves are fits to the data assuming a mixture of 25% of the $T_{1/2}=0$ component and 75% of the radioactivity component with $T_{1/2}$ values of 4 and 8 ps, respectively. The inset shows the probability (as a function of the assumed half-lives) that the simulations match the data.Reuse & Permissions

Figure 4

Angular $p-{}^{17}\mathrm{Ne}$ correlations obtained from the measured ${}^{17}\mathrm{Ne}+p+p$ events (histograms with statistical uncertainties) with three different gates: (a) events with vertex positions between the target and the first detector. The solid and dashed curves show the simulations for the model calculations [8] of the ${}^{19}\mathrm{Mg}$ $2p$ decay with decay energies of 0.75 and 0.60 MeV, respectively. The upper axis shows the transverse proton momentum relative to ${}^{17}\mathrm{Ne}$. (b) Same as (a) but gated on a vertex inside the target. The solid curve is the same as in (a). The dashed and dash-dotted curves illustrate the sequential proton emission of a suggested excited state in ${}^{19}\mathrm{Mg}$ via a narrow and a broad ($\Gamma =0.5\mathrm{MeV}$) ground state of ${}^{18}\mathrm{Na}$, respectively. The vertical solid and dashed lines indicate the gates used for selecting vertex distributions for the “ground state” and “excited state” of ${}^{19}\mathrm{Mg}$, respectively (see text). (c) Angular $p_1-{}^{17}\mathrm{Ne}$ correlations selected in the same way as in (b) but additionally gated by a small angle in another $p_2-{}^{17}\mathrm{Ne}$ pair matching the ground state gate defined in (b). The solid curve is the same as in (a); the dotted curve is the fit of the broad distribution extrapolated into the ground state area. The inset shows the probability (as a function of $2p$-decay energy) that the simulations match the data.Reuse & Permissions