**1. Introduction to radioisotopes and radiopharmaceuticals**

Scientist has discovered that earth contains many elements with varying configuration. These elements with varying configuration are called isotopes. Isotopes are atoms with same atomic number with varying atomic weight. Isotopes can be divided into two parts depending on the ability to emit radiation. One that does not emit radiations is called stable isotopes and other are called unstable isotopes. Unstable isotopes emit radiations to achieve a more stable configuration. These are called as radioisotopes. Instability of radioisotopes is due to presence of unstable combination of neutron and proton in their atoms and nucleus contains excess of energy. This characteristic of radioisotopes can be natural or instability can be created artificially by changing the atoms. Naturally radioisotope is uranium-238 and it accounts to 0.7% of total naturally occurring isotopes. Artificial radioisotopes are fluorine and molybdenum which are produced artificially by using cyclotrons and nuclear reactors respectively. Presently there are

around 3800 radioisotopes out of which 200 radioisotopes are being used. Among the isotopes that are used most of them are of artificial origin. Artificial radioisotopes are primarily made by two methods as mentioned above i.e. through nuclear reactor and by cyclotron. By nuclear reactor neutrons are introduced into the nucleus of atom whereas in case of cyclotron proton are introduced. To become stable radioisotopes emits alpha or beta particle along with electromagnetic radiation of gamma rays. This phenomenon is called as radioactive decay. These radioisotopes have variety of uses, when they are used in the field of pharmaceuticals they are termed as radiopharmaceuticals.
