Question

When a nucleus in an atom undergoes a radioactive decay, the electronic energy levels of the atom ______.

विकल्प

• do not change for any type of radioactivity.

• change for α and β radioactivity but not for γ-radioactivity.

• change for α-radioactivity but not for others.

• change for β-radioactivity but not for others.

Answer 1

When a nucleus in an atom undergoes a radioactive decay, the electronic energy levels of the atom change for α and β radioactivity but not for γ-radioactivity.

Explanation:

Features		α- particles	β- particles	γ-rays
1.	Identity	Helium nucleus or doubly ionised helium atom (2He4)	Fast moving electron (–β0 or B–)	Photons (E.M. waves)
2.	Charge	+ 2e	– e	Zero
3.	Mass	4 mp (mp = mass of proton) = 1.87 × 10–27	me	Massless
4.	Equation of decay	\[\ce{_{Z}X^A ->[α-decay]}\] \[\ce{_{z-2}Y^{A-4} + _{2}He^4}\] \[\ce{n_α = A - A^{'}/4}\]	\[\ce{_{z}X^A -> _{z + 1} Y^A + _{-1}e^0 + {v}}\] \[\ce{_{z}y^A ->[n_{β}] z^' X^A}\] ⇒ nβ = (2nα = – Z + Z')	\[\ce{_{Z}X^A -> _{Z}X^α + γ}\]

A /3-particle carries one unit of negative charge (– e), an α-particle carries 2 units of positive charge (+ 2e) and γ (particle) carries no charge. Hence electronic energy levels of the atom charge for α and β decay, but not for γ-decay.