(a) Some substances give out atomic or
radiation all the time, whatever is done to them, and these are said to be
.
(b) There are
types of radiation emitted by radioactive
:
(c)
radiation is easily absorbed by a few centimetres of
or a thin sheet of
.
(d)
radiation easily passes through air or paper but is mostly absorbed by a few millimetres of
.
(e)
radiation is very
and requires many centimetres of
or several metres of
to absorb most of it.
(f) There are radioactive substances all around us, including e.g. granite
in the ground, in the air, in building materials and in food.
(g) Radiation also reaches us from outer
. The radiation from all these sources is called
radiation.
(h)
is the
warning symbol for
.