Radioactivity Is So Famous, But Why?



The discovery of radioactivity provided another evidence of the electrical nature of matter.



The phenomenon of radioactivity was discovered by a French scientist Henri Becquerel in 1896. He was studying the properties of uranium salts. One day, he placed a uranium salt wrapped in a black paper and a photographic plate together in drawer.



To his great surprise, he noticed that the photograph plate below the crystals was darkened. There was no sunlight coming in the drawer and, therefore, he had no reasons to believe that the plate would be exposed to light. When he developed the plate, he observed that it had clear image of the salt.



This led him to interpret that the uranium salt emitted certain high energy radiations capable of penetrating the black paper and therefore, affected the photographic plate. Later on, it was observed that these rays can ionize air, penetrate solid matter and produce luminosity.



The phenomenon of spontaneous emission of active radiations by certain elements is called radioactivity. The substances which emit such radiations are called radioactive substances. The common radioactive substances are uranium, radium, polonium, thorium, etc.





The effect of magnetic and electric fields in these radiations was studied by placing a small sample of radioactive substance, uranium in a cavity of a block of lea. The radioactive radiations coming out from a narrow slit were allowed to pass through a strong electric and magnetic field. The deflections of these rays were recorded on a photograph plate. These radiations were found to split into three types of rays. These are;



1. One type of rays were deflected towards the negative electrode which indicated that they carry positively charged particles and are called alpha rays. These rays were found to consists of positively charged he2+ particles.



2. The second type of rays were deflected towards the positive electrode which showed that these are negatively charged. These are called beta rays. These particles have the same e/m value as the cathode rays. Therefore, Beta rays were considered to be the streams of electrons.



3. The third type of rays were not deflected at all and are therefore, neutral. These are called gamma rays. These rays were regarded as high energy electromagnetic radiations having no charge and negligible mass