Question

introduction of radio active substances

Answer 1

Radioactive substances are atoms that decay naturally. They can give off alpha particles, beta particles and gamma radiation. Unlike X-ray sources they cannot be turned off, so their control is more difficult. Sources for industrial radiography such as iridium 192 are emitters of gamma radiation and they can be used to radiograph thick sections of steel and other metals. These, too, are used inside shielded enclosures, but since the sources cannot be turned off electrically, they are housed in shielded containers. 

Answer 2

the substances which is used for nuclear weapons , fusion, fusion in power plants is called radioactive substances

ex uranium.