7Be

7Be is a radioactive isotope of beryllium with four protons and three neutrons. It decays exclusively by electron capture to 7Li and has a half-life of about 53.22 days. Because the decay proceeds via capture of an inner-shell electron, the rate can be influenced by the ionization state of the atom; in highly ionized environments the decay is strongly suppressed, while in neutral atoms the 53-day half-life applies.

In neutral atoms, the decay of 7Be to 7Li proceeds primarily to the ground state of 7Li, emitting a neutrino with an energy of about 0.862 MeV. A smaller fraction (around 10%) decays to the first excited state of 7Li, which then emits a gamma ray of 0.477 MeV as it relaxes to the ground state, producing a second, lower-energy neutrino line of about 0.386 MeV.

Production and occurrence: 7Be is produced in the atmosphere by spallation reactions of cosmic rays with nitrogen and oxygen. In stars, it is formed in the solar pp-chain via the reaction 3He + 4He → 7Be + γ, and its subsequent electron capture contributes to the solar neutrino flux, including monoenergetic lines at 0.862 MeV and 0.386 MeV. In the early solar system, 7Be was a short-lived radionuclide (t1/2 ≈ 53 days) that contributed to the inventory of short-lived nuclides in meteoritic materials through in situ irradiation.

Applications and significance: 7Be is used as a tracer in chemical and environmental studies due to its convenient half-life and gamma emissions. It has played a role in solar neutrino research, notably in experiments investigating the flux of 7Be neutrinos from the Sun, and in cosmochemical investigations of irradiation processes in the early solar system.