12. Definitions of some nuclides:
Isotopes: Species with same no. of protons but different mass no. Example - 1H1, and 2H1.
Isotones: Species with same no. of neutrons but different no. of protons. Example - 14C6 and 15N7.
Isobars: Species with same mass no. but different no. of protons. Example - MC,5 and 15N7.
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 a-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. t1/2 = 0.693/k ; C. tav----- 1/k where, N0 = no. of radioactive atoms present initially, N = no. of radioactive atoms present after time t, k = rate constant, t1/2 - Half-life period and tav = 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.