Question

In which of the following decays the element does not change?
(a) α-decay
(b) β⁺-decay
(c) β⁻-decay
(d) γ-decay

Answer 1

(d) γ-decay

​In alpha particle decay, the unstable nucleus emits an alpha particle reducing its proton number Z by 4 and neutron number N by 2 such that the element gets changed.
${}_Z{}^{A}X\to {}_{Z-2}{}^{A-4}Y+{}_2{}^{4}He$
During β⁻-decay​, a neutron is converted to a proton​, an electron and an antineutrino, i.e. an active nucleus gets converted to one of its isobars and hence the element gets changed.
${}_Z{}^{A}X\to {}_{Z+1}{}^{A}Y+e+\overline{\nu }$
During β⁺-decay​, a proton in the nucleus is converted to a neutron​, a positron and a neutrino in order to maintain the stability of the nucleus, i.e. an active nucleus gets converted to one of its isobars and hence the element gets changed.
${}_Z{}^{A}X\to {}_{Z-1}{}^{A}Y+{\beta }^{+}+\nu$
When a nucleus is in higher excited state or has excess of energy, it comes to the ground state in order to become stable and release energy in the form of electromagnetic radiation called gamma ray. Hence, the element in gamma decay doesn't change.