In beta decay, what happens to the atomic number Z?

• A. Increases by 1
• B. Increases by 2
• C. Decreases by 1
• D. Remains the same

Answer: (A)

In beta minus decay, a neutron in the nucleus converts into a proton, emitting an electron (the beta particle) and an antineutrino. This increases the number of protons by one, so the atomic number Z goes up by 1. The total number of nucleons stays the same, so the mass number A remains unchanged. The emitted electron carries away negative charge, but the net effect is that the nucleus gains a proton, shifting to the next higher element. (In beta plus decay, Z would decrease by 1 instead.)