Document of Radioactivity - Inorganic Chemistry

Points to be Remembered

12. Definitions of some nuclides:

• Isotopes: Species with same no. of protons but different mass no. Example - 'H, and 2H|.
• Isotones: Species with same no. of neutrons but different no. of protons. Example - l4C6 and l5N7.
• Isobars: Species with same mass no. but different no. of protons. Example - MC,5 and l5N7.
• Mirror Nuclei: Species in which the difference between the no. of protons and neutrons are unity. Example - ³H₁ and ³He₂.

13. Nuclear stability:

• Even-odd nature of nucleons (Harkin's Rule): Nuclei having even no. of protons and neutrons are more stable and most abundant.
• Neutron to Proton ratio (n/p): Nuclei having n/p ratio close to unity is more stable.
• Packing Fraction (PF): Negative value in packing fraction indicates the stability of nuclei. Greater is the negative packing fraction value of a nuclei, higher will be its stability.
• Nuclear Binding Energy (NBE): Positive value in nuclear binding energy indicates the stability of nuclei. Greater is the positive nuclear binding energy value of a nuclei, higher will be its stability.
• Magic no.: Nuclei having 2, 8, 20, 50, 82 or, 126 no. of protons or, neutrons are more stable. These nos. are called magic nos.

14. Soddy-Fajan group displacement law:

• When an ∝-particle is emitted by an element, it mass and atomic no. will be decreased by four and two units respectively.
• When an β-particle is emitted by an element, it mass no. will remain same but atomic no. will be increased by one unit.

15. Some important mathematical relations:
A. kt = 2.3031og(N₀/N);
B. t_1/2 = 0.693/k;
C. t_av ----- 1/k
where, N₀ = no. of radioactive atoms present initially,
N = no. of radioactive atoms present after time t,
k = rate constant,
t_{1/2 =} Half-life period and t_av = Average life period.

16. There are four disintegration series.
These are:
1. Thorium series (4n),
2. Uranium series (4n+2),
3. Actinium series (4n+3) and
4. Neptunium series (4n+1).
The first three of them are naturally occurring while the last one is artificially made.