What change in atomic number occurs when a nucleus emits an alpha particle? a beta particle? a gamma ray?

1. Alpha decay

Alpha particle is a ₂⁴He nucleus. When a parent atom emits an alpha particle, the atomic number reduces by 2 in the formed daughter atom while reducing the mass number by 4. Since atomic number = proton number, due to the decreasing of atomic number, proton number also reduces by 2 in daughter nucleus.

2. Beta emission.

There are two types of beta decay. One is β⁻ and other one is β⁺ emission.

β⁻ emission

β⁻ emission is an emission of an electron by converting a neutron to a proton. Hence, in β⁻ decay, the atomic number increases by 1 and mass number is not changed in the formed daughter nucleus.

β⁺ emission

β⁺ emission is an emission of an positron while converting a neutron to a proton. Hence, in β⁺ decay, the atomic number decreases by 1 and mass number is not changed in the formed daughter nucleus.

3. Gamma decay

In Gamma decay there is no any particle decay from the parent nucleus. Unstable nucleus emits energy photon and becomes as stable by undergoing a gamma decay. Hence, there is no change in atomic number or mass number of the daughter atom.