In late 1895, a German physicist, W.C. Roentgen while working with a cathode ray tube passed a high electric voltage through it when it produced a fluorescent glow which could not be shielded with heavy black paper. He named this new ray X-ray, because in mathematics "X" is used to indicate the unknown quantity. He received the first Nobel Price in Physics in 1901
Wilhelm Rontgen ca. 1895. Inset photo: Radiograph of Frau Rontgen's hand
In his discovery Roentgen found that the X-ray would pass through the tissue of humans leaving the bones and metals visible. One of Roentgen’s first experiments late in 1895 was a film of his wife Bertha's hand with a ring on her finger.
In 1896,French Scientist, Henri Becquerel, conducted an experiment in which he put a uranium-containing phosphor on top of an unexposed film wrapped in black paper and placed them under sunlight. Unfortunately, or rather fortunately, it was very cloudy. He placed his assembled experiment in the drawer. After several outcast days, he decided to develop the film. To his amazement, the film was highly exposed! His only explanation was that some sort of rays were leaving the uranium compound continuously, passing through the paper and thus exposing the film ->“Becquerel had discovered radioactivity”
He received Nobel price in 1903
Henri Becquerel (1852-1908)

The term “radioactivity” was coined by Marie Curie.She was the first lady to receive Nobel price.
There are 92 naturally occurring elements which give about 300isotopes. Out of them 260 are stable and rest are unstable. These unstable isotopes, in order to become stable give out radiation in the form of alpha, beta, gamma rays.
Gamma Camera
In 1953 Hal Anger developed the first recognized gamma camera' in the AEC Donner Lab at Berkley, USA.
Penetrating powers of diff.rays