Double electron capture

Double electron capture is a decay mode of an atomic nucleus.[1] For a nuclide (A, Z) with a number of nucleons A and atomic number Z, double electron capture is only possible if the mass of the nuclide (A, Z−2) is lower.

In this mode of decay, two of the orbital electrons are captured via the weak interaction by two protons in the nucleus, forming two neutrons (Two neutrinos are emitted in the process). Since the protons are changed to neutrons, the number of neutrons increases by two, while the number of protons Z decreases by two, and the atomic mass number A remains unchanged. As a result, by reducing the atomic number by two, double electron capture transforms the nuclide into a different element.[2]

Example:

130
56
Ba
 

e
 
→  130
54
Xe
 

ν
e
  1. ^ Hirsch, M.; et al. (1994). "Nuclear structure calculation of β+β+, β+/EC and EC/EC decay matrix elements". Zeitschrift für Physik A. 347 (3): 151–160. Bibcode:1994ZPhyA.347..151H. doi:10.1007/BF01292371. S2CID 120191487.
  2. ^ Abe, K.; Hiraide, K.; Ichimura, K.; Kishimoto, Y.; Kobayashi, K.; Kobayashi, M.; Moriyama, S.; Nakahata, M.; Norita, T.; Ogawa, H.; Sato, K. (2018-05-01). "Improved search for two-neutrino double electron capture on 124Xe and 126Xe using particle identification in XMASS-I". Progress of Theoretical and Experimental Physics. 2018 (5). arXiv:1801.03251. doi:10.1093/ptep/pty053.