WHAT MAKES A SUBSTANCE RADIOACTIVE?
Radioactivity is the random spontaneous disintegration of an atom of an
element. The stability of the nucleus depends on the relative numbers
of protons and neutrons present. The most stable nuclides tend to have
an even number of protons and an even number of neutrons as each group
of two protons and two neutrons, in the nucleus, makes an especially
stable combination. A number of elements have atoms or nuclei which are
unstable and consequently split up to form smaller atoms. This is due
to all elements wanting to achieve equilibrium or stability in the
nucleus.
A substance is said to be radioactive if it contains unstable nuclei
and is able to naturally release energy in the process of shedding high
speed charged particles, in an attempt to reach a stable state. With
this, a non-radioactive substance will remain intact indefinitely
unless acted upon by an external force.
In the process of transmutation, known as decay, the radioactive nuclei
emits charged particles or electromgnetic rays depending on the nature
it's instability. This results in a daughter nuclide being produced
which may be radioactive or stable, but if it is radioactive it will in
turn decay into a daughter nuclide, continuing to do so until it
reaches the point of stability, an isotope of lead.