Experimental Evidence of ${}^2\mathrm{He}$ Decay from ${}^{18}\mathrm{Ne}$ Excited States

Two-proton decay from ${}^{18}\mathrm{Ne}$ excited states has been studied by complete kinematical reconstruction of the decay products. The ${}^{18}\mathrm{Ne}$ nucleus has been produced as a radioactive beam by ${}^{20}\mathrm{Ne}$ primary projectile fragmentation at $45A\mathrm{MeV}$ incident energy on a Be target. The ${}^{18}\mathrm{Ne}$ at $33A\mathrm{MeV}$ incident energy has been excited via Coulomb excitation on a ${}^{\mathrm{nat}}\mathrm{Pb}$ target. The obtained results unambiguously show that the 6.15 MeV ${}^{18}\mathrm{Ne}$ state two-proton decay proceeds through a ${}^2\mathrm{He}$ diproton resonance (31%) and democratic or virtual sequential decay (69%). The quoted branching ratio has been deduced from relative angle and momentum correlations of the emitted proton pairs.

Figure 1

Top panel: Level scheme of ${}^{18}\mathrm{Ne}$ from Ref. 10. Bottom panel: Energy loss in the DSSD versus ToF.

Figure 2

Left panel: Excitation-energy spectrum of ${}^{16}\mathrm{O}$ from ${}^{12}\mathrm{C}+\alpha$ events. Right panel: Excitation-energy spectrum of ${}^{18}\mathrm{Ne}$ from ${}^{16}\mathrm{O}+2p$ events and from ${}^{17}\mathrm{F}+p$ channel (scaled $1/4$). The levels values are from Ref 20.

Figure 3

Relative-momentum $|{\overrightarrow{q}}_{\mathrm{rel}}|$ (top panel) and relative-angle (bottom panel) spectra, in the ${}^{16}\mathrm{O}+2p$ CM system, of the two protons emitted from the 6.15 MeV level, compared with Monte Carlo simulations.

Figure 4

Left panel: Two protons $|{\overrightarrow{q}}_{\mathrm{rel}}|$ spectrum for ${}^{16}\mathrm{O}+2p$ events with $E^{*}>6.5\mathrm{MeV}$. Right panel: Excitation-energy spectrum from inclusive ${}^{16}\mathrm{O}+2p$ events compared with those gated in the $|{\overrightarrow{q}}_{\mathrm{rel}}|$ spectra of the left panel and of Fig. 3.