In electron capture, which change occurs to the atomic number?

• A. Z decreases by 1
• B. Z increases by 1
• C. A decreases by 1
• D. A increases by 1

Answer: (A)

In electron capture, a proton in the nucleus captures an inner-shell electron and converts into a neutron, releasing a neutrino. Because a proton becomes a neutron, the number of protons decreases by one, so the atomic number decreases by one. The mass number stays the same since a proton and a neutron have nearly the same mass. After the capture, the electron shell reorganizes to fill the vacancy, which can emit X-rays or Auger electrons.