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Substances in Common Use

Preparation, Properties and Uses of Common Salt

Radioactive Elements

The elements that emit highly penetrating and high energy radiation beam are known as radioactive elements. The elements are subjected to spontaneous degeneration of nucleus along with the emission of radiations. Elements with the atomic number greater than 83 are considered as radioactive and some naturally occurring radioactive elements include uranium, radium and thorium.

Becquerel Rays

Bacquerel rays are radiations given out by radioactive elements.

Properties:

  • They are gas ionizers.

  • They affect photographic plate.

  • They can penetrate through matter.

  • They are affected by electric and magnetic fields.

Experiment to demonstrate the properties of Becquerel Rays

In this experiment, a lead cube was placed in a glass vessel and across its sides were placed two copper plates, connected to a very high d.c. potential. A photographic plate was placed over the cavity. The glass vessel was evacuated and then lead plug was removed.

It was found that the photographic plate developed the following pattern.

Alpha particles: By looking at the pattern, it was observed that the particles deflected towards the negative plate and having a dark spot are positive particles and are heavier than others.

Properties:

  • It is similar to doubly ionised helium atom and has the speed of the order of 107 ms-1.
  • Alpha particles have large kinetic energy and momentum.
  • It strongly ionises the gas through which it passes.
  • It rapidly dissipates its energy as it moves through a medium and therefore its penetrating power is quite small.
  • As alpha particles are positively charged, so they are deflected by electric and magnetic fields.
  • Alpha particles cause fluorescence on striking a fluorescent material.

Beta particles: The pa…

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