(a) A radioactive transformation in which an aparticle is emitted is called α-decay. In an α-decay, the atomic number of the nucleus decreases by 2 and the mass number decreases by 4.

Example : \(^{38}_{92}U\) → \(^{234}_{90}Th\) + \(^4_2α\)

Q = [m_U – m_Th – m_α]c²

(b) A radioactive transformation in which a βparticle is emitted is called β-decay. In a β -decay, the atomic number of the nucleus increases by 1 and the mass number remains unchanged.

Example : \(^{23}_{90}Th\) → \(^{234}_{91}Pa\) + \(^0_{-1}e\) + \(\bar v_e\)

where \(\bar v_e\) is the antineutrino emitted to conserve the momentum, energy and spin. Q = [m_Th – m_pa – m_e]c²

In a β⁺ -decay, the atomic number of the nucleus decreases by 1 and the mass number remains unchanged.

Example : \(^{30}_{15}P\) → \(^{30}_{14}Si\) + \(^0_{+1}e\) + v_e

where v_e is the neutrino emitted to conserve the momentum, energy and spin.

Q = [m_p – m_Si – m_e]c²

[Note : The term f_i particle refers to the electron (or positron) emitted by a nucleus.]