the factors to stop the radiation :
There are three factors that control the amount, or dose, of
radiation received from a source. Radiation exposure can be managed by a
combination of these factors:
Reducing the time of an exposure reduces the effective dose proportionally. An example of reducing radiation doses by reducing the
time of exposures might be improving operator training to reduce the
time they take to handle a source.
Increasing distance reduces dose due to the inverse square law. Distance can be as simple as handling a source with forsep rather than fingers The term 'biological shield' refers to a mass of
absorbing material placed around a reactor, or other radioactive source,
to reduce the radiation to a level safe for humans.
The effectiveness of a material as a biological shield is related to its cross section for scattering and absorption,
and to a first approximation is proportional to the total mass of
material per unit area interposed along the line of sight between the
radiation source and the region to be protected. Hence, shielding
strength or "thickness" is conventionally measured in units of g/cm2. The radiation that manages to get through falls exponentially with the thickness of the shield. In x-ray facilities, walls surrounding the room with the x-ray generator may contain lead sheets. Operators view the target through a leaded glass screen, or if they must remain in the same room as the target, wear lead aprons. Almost any material can act as a shield from gamma or x-rays if used in sufficient amounts.
Practical radiation protection tends to be a job of juggling the three factors to identify the most cost effective solution.