I've heard of $\beta^-$ decay,
$$n \rightarrow p^+ + e^- + \bar \nu_e$$
$\beta^+$ decay,
$$p^+ \rightarrow n + e^+ + \nu_e$$
and electron capture,
$$p^+ + e^- \rightarrow n + \nu_e$$
but every time I've googled "positron capture," which I assume would probably happen as
$$n + e^+ \rightarrow p^+ + \bar \nu_e$$
I've never found any reliable results that mention anything about it other than a footnote on some website that mentions that a positron would annihilate with an electron in the cloud surrounding a nucleus before it even came close to the nucleus. However, if all of the electrons surrounding the nucleus were removed, then I see no reason why this reaction would not be possible at least in theory.
Is positron capture theoretically possible? If not, why not? If so, what nuclei could allow for this process to occur?
Best Answer
Positron capture is not possible, and here is why: The "capture" part refers to the fact that the electron is taken from its atomic orbit around the nucleus containing the proton with which it reacts. Since a positron cannot for a bound state with a nucleus--it can't be captured.
Nevertheless, $e^+p(n, \bar{\nu}_e)$, is a perfectly good scattering reaction.