In alpha decay, what is emitted and how do Z and A change?

In alpha decay, what is emitted and how do Z and A change?

• A. A neutron is emitted; Z decreases by 1 and A decreases by 1
• B. A gamma photon is emitted; Z and A unchanged
• C. A beta particle is emitted; Z increases by 1
• D. An alpha particle is emitted; Z decreases by 2 and A decreases by 4

Answer: (D)

In alpha decay, the nucleus throws out an alpha particle, which is two protons and two neutrons (a helium-4 nucleus). This removal reduces the total count of nucleons by 4 and the number of protons by 2, so the mass number drops by 4 and the atomic number drops by 2 (Z → Z−2, A → A−4). The emitted alpha particle carries away charge and energy, leaving behind a lighter nucleus with fewer protons. The other scenarios don’t match alpha decay: neutron emission lowers A by 1 but leaves Z unchanged; gamma emission carries energy with no change to Z or A; beta emission changes Z by ±1 without changing A.

In alpha decay, the nucleus throws out an alpha particle, which is two protons and two neutrons (a helium-4 nucleus). This removal reduces the total count of nucleons by 4 and the number of protons by 2, so the mass number drops by 4 and the atomic number drops by 2 (Z → Z−2, A → A−4). The emitted alpha particle carries away charge and energy, leaving behind a lighter nucleus with fewer protons. The other scenarios don’t match alpha decay: neutron emission lowers A by 1 but leaves Z unchanged; gamma emission carries energy with no change to Z or A; beta emission changes Z by ±1 without changing A.