What elements of the periodic table decay through electron capture?
A nucleus may decay by electron capture if the neutron-proton ratio is less than 1:1.
The graph below is a plot of the number of neutrons versus the number of protons in various stable isotopes.
The stable nuclei are in a band known as the belt of stability. They have a neutron/proton ratio between 1:1 and 1.5:1.
Nuclei below the belt of stability have low neutron-to-proton ratios. These proton-rich nuclei can increase their ratio by either positron emission or electron capture.
Both kinds of decay increase the number of neutrons and decrease the number of protons.
Positron emission is more common than electron capture among the lighter nuclei (Z < 36).
Electron capture becomes more common as nuclear charge increases, but it is still not very frequent.
Nuclei with atomic number greater than 84 tend to undergo α decay rather than electron capture.
Hope this helps.