Radioactive Disintegration Series
The phenomenon of natural radioactivity continues till stable nuclei are formed. All the nuclei from the initial element to the final stable element constitute a series known as disintegration series. Further we know that mass numbers change only when a-particles are emitted (and not when b-particles are emitted) causing the change in mass of 4 units at each step. Hence the mass numbers of all elements in a series will fit into one of the formulae. 4n, 
, 
and 
, hence there can be only four disintegration series.
| 4n | 4n + 1 | 4n + 2 | 4n + 3 | |
 |
58 | 59 | 59 | 58 |
| Parent element |  |
 |
 |
 |
| Half life (yrs) |  |
10 |  |
 |
| Half life (yrs) | |
 |
|
13.5 |
| Name of series | Thorium (Natural) | Neptunium (Artificial) | Uranium (Natural) | Actinium (Natural) |
| End product |  |
 |
 |
 |
|
52 | 52 | 51 | 51 |
| Number of lost particles |
|
|
|
|
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