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I have a follow-up question to this one:

Solar neutrino Spectrum - Why are there discrete energies for Be and pep?

I understand why the lines for $^{7}\text{Be}$ and $pep$ are discrete, but why do we have $\textit{two}$ of them in the case of $^{7}\text{Be}$?

Igor Valuev
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1 Answers1

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If the final state contains three particles, solar neutrinos exhibit a continuous spectrum; if it's only two products, the solar neutrino spectrum is a discrete line. That's just energy and momentum conservation. The reaction you point out is

$e^-+{}^7\mathrm{Be}\rightarrow {}^7\mathrm{Li}+\nu_e$

But the ${}^7\mathrm{Li}$ has an energy state that is accessible in this decay; from the iaea.org Live Chart of Nuclides:

enter image description here

The lowest 477keV energy state is accessible, so the de-excitation gamma from that may carry those 477keV away. Hence, two discrete neutrino energies are possible with either 0.86MeV or 0.38MeV.

rfl
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