# Answer in brief. What are alpha, beta and gamma decays? - Physics

What are alpha, beta and gamma decays?

#### Solution

1. A radioactive transformation in which an α-particle 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: $\ce{_92^238U->_90^234Th + _2^4\alpha}$
Q = [mU - mTh - mα]c2
2. A radioactive transformation in which a β-particle 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: $\ce{_90^234Th->_91^234Pa + _-1^0e +\bar{v}_e}$
where bar"v"_"e" is the antineutrino emitted to conserve the momentum, energy and spin.
Q = [mTh - mpa - me]c2
In a β+ -decay, the atomic number of the nucleus decreases by 1 and the mass number remains unchanged.
Example: $\ce{_15^30P->_14^30Si +_+1^0e +v_e}$
where ve is the neutrino emitted to conserve the momentum, energy and spin.
Q = [mP - mSi - me]c
3. A given nucleus does not emit α- and -β particles simultaneously. However, on emission of α or β-particles, most nuclei are left in an excited state. A nucleus in an excited state emits a γ-ray photon in a transition to the lower energy state. Hence, α- and β-particle emissions are often accompanied by γ-rays.
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#### APPEARS IN

Balbharati Physics 12th Standard HSC Maharashtra State Board
Chapter 15 Structure of Atoms and Nuclei
Exercises | Q 2.3 | Page 342