The nucleus of 40K (of spin-parity 4+ in the ground state) is unstable and decays to 40Ar. The mass difference between these two nuclei is ΔMc2 = 1504.4 keV. The nucleus 40Ar has an excited state at 1460.8 keV with spin- parity 2+. The most probable decay mode of 40K is by
1
a β+-decay to the 2+ state of 40Ar
2
an electron capture to the 2+ state of 40Ar
3
an electron capture to the ground state of 40Ar
4
a β+ -decay to the ground state of 40Ar