The reaction 57Ni 28 + e- → 57Co 27 + ν is an example of which process?

• A. Electron capture
• B. Alpha decay
• C. Beta minus decay
• D. Positron emission

Answer: (A)

Electron capture occurs when a proton in the nucleus captures one of the atom’s inner-shell electrons, turning into a neutron and emitting a neutrino. In this reaction, nickel-57 (with 28 protons) captures an electron and becomes cobalt-57 (27 protons) while releasing a neutrino. The mass number stays the same (57), but the atomic number decreases by one, which is exactly what electron capture does. Other processes would involve different changes: beta minus decay would convert a neutron to a proton and emit an electron, alpha decay would reduce the mass and alter both Z and A more dramatically, and positron emission would reduce Z by one but emits a positron rather than involving a captured electron. This alignment with a captured electron and neutrino emission is why this is electron capture.