Single and double proton emissions from the ${}^{14}\mathrm{O}+{}^4\mathrm{He}$ interaction

We observed single and double proton emissions in the ${}^{14}\mathrm{O}+{}^4\mathrm{He}$ interaction by the thick target inverse kinematic (TTIK) method at initial energy for ${}^{14}\mathrm{O}$ at 32.7 MeV. We found that the protons mainly originate from the resonance excitation of states in ${}^{18}\mathrm{Ne}$. The observed states in ${}^{18}\mathrm{Ne}$ decay by protons mainly to proton unstable states in ${}^{17}\mathrm{F}$. It was found that the decay of a state in ${}^{18}\mathrm{Ne}$ at $E_{\mathrm{ex}}=8.45$ MeV demonstrates the features of a decay by a correlated proton pair. The observed properties of the ${}^{14}\mathrm{O}+{}^4\mathrm{He}$ interaction make a previous interpretation for the rate of ${}^{14}\mathrm{O}$(${}^4\mathrm{He}$, $p$)${}^{17}\mathrm{F}$ at astrophysical energies suspect. We show how the TTIK method should be modified to obtain the data of astrophysical interest.

Figure 1

The experimental setup that is described in the text.

Figure 2

Dalitz plots for the reaction ${}^{14}\mathrm{O}$($\alpha ,2p)$. (A) Conventional Dalitz plot; (B) modified Dalitz plot with the coordinates shown as excitation energies in ${}^{17}\mathrm{F}$ assuming a sequential ${}^{18}\mathrm{Ne}$${}^{*}\to p_1+$${}^{17}\mathrm{F}$${}^{*}\to p_1+$${}^{16}\mathrm{O}$$+p_2$ decay. $E_{{}^{17}\mathrm{F}}^{(1)}$${}^{*}$ is the excitation energy in ${}^{17}\mathrm{F}$ based on the assumption that one proton of the coincident proton pair is from ${}^{18}\mathrm{Ne}$${}^{*}\to p+$${}^{17}\mathrm{F}$${}^{*}$ and the other one is from ${}^{17}\mathrm{F}$${}^{*}\to p+$${}^{16}\mathrm{O}$. $E_{{}^{17}\mathrm{F}}^{(2)}$${}^{*}$ is the same with the role of the protons reversed.

Figure 3

Relevant ${}^{18}\mathrm{Ne}$ and ${}^{17}\mathrm{F}$ level scheme. Levels marked by ${}^{*}$ have not been seen before.

Figure 4

The excitation function for the ${}^{14}\mathrm{O}$$(\alpha ,2p$)${}^{16}\mathrm{O}$ reaction. Total cross section for 11.29 MeV level is estimated to be 50 mb. The energy resolution is about 0.2 MeV. Levels marked by ${}^{*}$ have not been seen before.

Figure 5

The relative energy between two protons emitted from the 8.45 MeV level in ${}^{18}\mathrm{Ne}$${}^{*}$. The lines are for calculations described in the text.

Figure 6

The TOF-E spectrum of zero degrees.

Figure 7

Yield of protons at $0^{°}$. (1) Total proton yield; (2) yield of $p_0+p_1$, see text for explanation.