By Sunil Bhardwaj

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Rutherford and Soddy have shown that when radioactive substance emits ? or ? -particles, the new product is obtained if it is radioactive it will again emit the particles. It is found that chemical and physical properties of new elements are entirely different than the parent. It was proved that each radioactive nuclide is member of one of the known series. These series are

i) Uranium series,

In Uranium series, the mass no. of each member of the series can be expressed in the form of (4n + 2) where n is integer. In this case. n =59.

The 4n+2 chain of U-238 is called the "uranium series" or "radium series". Beginning with naturally occurring uranium-238, this series includes the following elements: astatine, bismuth, lead, polonium, protactinium, radium, radon, thallium, and thorium. All are present, at least transiently, in any natural uranium-containing sample, whether metal, compound, or mineral. The series terminates with lead-206.

ii) Actinium series,

In the Actinium series, the mass no. of each member can be determined by using the formula(4n + 3). Here the n is 56.

The 4n+3 chain of uranium-235 is commonly called the "actinium series" or "plutonium cascade". Beginning with the naturally-occurring isotope U-235, this decay series includes the following elements: actinium, astatine, bismuth, francium, lead, polonium, protactinium, radium, radon, thallium, and thorium. All are present, at least transiently, in any sample containing uranium-235, whether metal, compound, ore, or mineral. This series terminates with the stable isotope lead-207.

iii) Thorium series,

In the Thorium series, the mass no. of each member can be expressed as 4n. Here n = 58

The 4n chain of Th-232 is commonly called the "thorium series" or "thorium cascade". Beginning with naturally occurring thorium-232, this series includes the following elements: actinium, bismuth, lead, polonium, radium, radon and thallium. All are present, at least transiently, in any natural thorium-containing sample, whether metal, compound, or mineral. The series terminates with lead-208.

All the above three series are known as natural radio active series.

Neptunium series

The Neptunium series is known as artificial series. Neptunium series differ from the other series (natural) by the following points:

1) The stable end product of this series is not lead, but its is 20281.

2) In the series & Bi is the only member which is found in the nature. While all the other are artificial.

3) The other series contain gases emanations, thoron, radon and actinon, but neptunium series does not contain any gases emanation.

4) Francium Fr(221) and Astatine At (217) are direct and successive members of the neptunium series,

The 4n + 1 chain of Np-237 is commonly called the "neptunium series" or "neptunium cascade". In this series, only two of the isotopes involved are found naturally, namely the final two: bismuth-209 and thallium-205. A smoke detector containing an americium-241 ionization chamber accumulates a significant amount of neptunium-237 as its americium decays; the following elements are also present in it, at least transiently, as decay products of the neptunium: actinium, astatine, bismuth, francium, lead, polonium, protactinium, radium, thallium, thorium, and uranium. Since this series was only studied more recently, its nuclides do not have historic names. One unique trait of this decay chain is that it does not include the noble-gas radon, and thus does not migrate through rock nearly as much as the other three decay chains.