- Radioactivity
Spontaneous emission of active rays by certain unstable elements.
- Three types of radiations are:
(i) Alpha particles He2+ ion (Helium nuclei).
(ii) Beta - rays - consist of electrons.(iii) Gamma - rays - High energy electromagnetic rays.
- Emission of alpha particle reduces the atomic number by 2 and the mass number by 4. b- emission advances the atomic number by one unit without changing the mass number. Emission of a - rays affects neither the mass nor the atomic number.
- N/P Ratio - Stable nuclei has N/P ratio in the range 1 - 1.6.
- For a particular radioactive decay process, the number of nuclei decaying in a short period of time is proportional to the number present and is independent of physical and chemical conditions surrounding the atom. Decay process follows First order kinetics.
- Half-life period of a nuclide
The time taken to reduce the number of nuclei to one half the original.
- 3 natural decay series - decay by emission of and emission
2nd series starts with 238U end with 206Pb
3rd series starts with 235U ends with 207Pb4th artificial series starts with 237Np ends in 209Bi.
- Artificial radioactivity
Nuclear changes can be brought about by bombardment of nuclei with accelerated particles like neutrons, deuterons and protons.
- A particularly important process for the production of artificial radioactive isotope is the (n, g) reaction, which is applied to synthesize new elements.
- Units of Activity - 1 Becqueral (Bq) = 1 disintegration per second
= 3.7 x 1010 Bq.
- Nuclear Fission
Heavy nuclei can break up into two fragments of intermediate size and a few neutrons, the loss in mass occurs which releases vast amount of energy.
- Nuclear Fusion
Light nuclei fuse together with mass losses, which produce large quantities of energy. Fusion reactions require high temperatures to be initiated. Hence they are called thermonuclear reactions.
- Radioisotopes find applications as tracers in analytical uses, for dating the age of minerals, rocks etc. and in the field of medicines.
