Unfortunately the early workers with
radioactivity did not know of its dangers; Marie Curie, for instance, died of leukaemia, a
disease of the blood produced by prolonged exposure to radiation. With all types of
radioactivity shielding is important, the thickness and type of shielding depending on the type
of radiation.
Alpha particles are not penetrating and aluminium sheet will stop them.
Their only biological effects are to the surface of the skin, with the production of radiation
'burns'. The term burns is perhaps misleading - although the temperature rise produced is
only a few thousandths of a degree, the bums do not heal since the molecular structure of
the cells has been destroyed
The penetration of beta particles is rather greater than
alpha particles and thicker aluminium is needed to stop these. Gamma radiation is intensely
penetrating, and many centimetres of lead are required to reduce the intensity from a large
source to safe levels. Since gamma-radiation obeys the inverse square law in air, the best
thing is to get as far away from a gamma-source as possible. Gamma-radiation also affects
the internal organs of the body due to its high penetrating power.
Neutron radiation
presents special problems. Because neutrons are uncharged they produce few ions and so
have a relatively long range in body tissue, but because of their large mass they cause
considerable damage when they collide with living cells. A neutron has about the same
mass as a hydrogen nucleus, and since the body contains large numbers of hydrogen nuclei
in its cells the neutrons lose a lot of energy and thus the cells are severely damaged. For the
same reason neutrons are best stopped by materials containing a large amount of hydrogen
atoms such as paraffin wax
Radiation can cause immediate damage such as
radiation burns out but possibly its long-term effects are even more serious. Besides
leukaemia, it causes cancer and genetic damage since it affects the rapidly dividing cells in
the body, such as those in the liver and the reproductive organs. Radiation can also damage
the eye, causing cataracts which destroy its clarity. For these reasons radioactive sources
must always be handled carefully and sensibly.