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What is Penetrating Ability?
The ability of radioactivity to pass
through materials is called its
penetrating ability. Penetrating ability depends on the size of
the radioactive particle. The table of the summary of properties
shows that alpha particles are the biggest,
beta particles are very much smaller and gamma rays have no mass.
The bigger the particle, the more likely it is to have a collision
with the atoms of the material.
The collision will stop the particle going through the material.
Alpha particles are the
biggest and are least able to penetrate
a material. Paper or smoke particles will stop them.
Even in air, alpha particles can only travel for a few centimetres
before they are stopped by collisions with the air molecules.
Beta particles are
stopped by a few millimetres of
but some beta particles will penetrate thin aluminium foil or paper.
Gamma rays are the
most able to penetrate
and will even find their way through metres of concrete.
below shows the relative penetrating ability of
the three types of radioactivity.
When the particle or ray
collides with the material
it can knock an electron off the atom and form an ion.
Ionising ability is related to penetrating ability.
As penetrating ability increases, ionising ability decreases.
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