Ionizing radiation

What is Ionizing Radiation?

Isotopes and Activity


Atoms in their normal state are electrically neutral because the total negative charge of electrons outside the nucleus equals the total positive charge of the nucleus .

Atoms with the same number of protons and different number of neutrons are called ISOTOPES. An isotope may be defined as one or two or more forms of the same element having the same atomic number (Z), differing mass numbers (A), and the same chemical properties.

Isotopes status image

These different forms of an element may be stable or unstable (radioactive). However, since they are forms of the same element, they possess identical chemical and biological properties.

The simplest atom is the hydrogen atom. It has one electron orbiting a nucleus on one proton. Any atom which has one proton in the nucleus is a hydrogen atom, like both of the ones shown here. Hydrogen-2 is called deuterium, hydrogen-3 is called tritium. However, while their chemical properties are identical their nuclear properties are quite different as only tritium is radioactive.


  • The activity of a radioisotope is simply a measure of how many atoms undergo radioactive decay per a unit of time.
  • The SI unit for measuring the rate of nuclear transformations is the becquerel (Bq). The becquerel is defined as 1 radioactive disintegration per second.
  • The old unit for this is the curie (Ci), in honour of Pierre and Marie Curie who discovered radium and polonium. The curie is based on the activity of 1 gram of radium-226, i.e. 3.7 x 1010 radioactive disintegrations per second.