Talk:Double electron capture

Conditions

Double electron capture is a decay mode of atomic nucleus. For a nuclide (A, Z) with number of nucleons A and atomic number Z, double electron capture is only possible if the mass of the nuclide of (A, Z-2) is lower. How is this ever possible? If you count the mass of a neutron and proton as equal, the mass would remain the same. If you use the real mass then the proton has a slightly smaller mass then (A, Z-2) would have a somewhat higher mass. Can someone explain this to me? --84.246.55.33 12:22, 6 February 2007 (UTC)

The mass of a nucleus is the mass of the protons, plus the mass of the neutrons, minus the mass defect. The whole is less than the sum of its parts. This mass defect is just the binding energy (divided by -c^2) that it would take to pull the nucleus apart. Since selenium-78 has higher binding energy than krypton-78, it has less mass. You can look up the binding energy (or, for that matter, the primary decay modes) of any nuclide at Wikipedia, or various other sources. --69.107.81.199 17:59, 17 March 2007 (UTC)

It is not clear in this article if this has been proven to occur, or whether it is only theoretical. For example have decay products been found in old minerals? Also this would be one way to make neutrinos with a fixed known energy, forming a line spectrum, is this significant? Graeme Bartlett (talk) 21:25, 17 February 2011 (UTC)

It is proven only for two cases where periodicity helps: Ba-130 (with excesses of Xe-130 found in old minerals; Xe being an inert gas, this is hard to explain otherwise), and Kr-78 (which is itself an inert gas). Double sharp (talk) 06:58, 8 September 2017 (UTC)

Double positron emission

Why is the decay mode of ⁷⁸
₃₆Kr, ¹²⁴
₅₄Xe, and ¹³⁰
₅₆Ba listed as εε everywhere (in the main page, the pages of corresponding isotopes, double beta decay and list of nuclides) instead of β+β+, if they can all decay via double positron emission? Is it that their double positron emission is not observed?

By the way, a decay energy exceeding 2.044 MeV is seemingly high, but none of ⁷⁸Kr, ⁹⁶Ru, ¹⁰⁶Cd, ¹²⁴Xe, ¹³⁰Ba, ¹³⁶Ce, ¹⁴⁸Gd and ¹⁵⁴Dy has higher decay energy than the double beta minus decay energy of ⁴⁸Ca (4.2736 MeV), ⁹⁶Zr (3.3477 MeV) or ¹⁵⁰Nd (3.36768 MeV). 129.104.241.214 (talk) 21:54, 1 February 2024 (UTC)