All atoms of each element have a set number of
protons (each nucleus has a given positive charge).
The number of protons in an atom is its atomic
number.
The mass number of an atom ( the
mass of the nucleus) is number of
protons + the number of neutrons in
its nucleus.
Isotopes of an element are atoms
with the same number of protons (
the same atomic number, and so
the same charge on the nucleus)
but a different number of neutrons
( a different mass number).
All elements have different
isotopes, but there are usually
only one or two stable ones.
The other unstable isotopes tend to decay into
other elements and give out radiation as they
try to become more stable (they try to balance
the number of protons and neutrons in their
nucleus or get rid of any excess energy). This
process is called radioactive decay.
Radioactive give out one or more types of ionising
radiation for their nucleus- these are alpha, beta and
gamma radiation.
They can also release neutrons when they decay to
rebalance the number of protons and neutrons.
Ionising radiation is radiation that knocks electrons off
atoms, creating positive ions.
Alpha Particle
Alpha radiation is where an alpha
particle is emitted from the nucleus.
An alpha particle is two neutrons and two protons (
like a helium nucleus).
They don't penetrate very far into materials and are
stopped quickly- they can only travel a few cm in air and
are absorbed by a sheet of paper. Also because of their
size they are strongly ioninsig.
Beta Particle
A beta particle is simply a fast-moving
electron released by the nucleus . Beta
particles have virtually no mass and a
charge of -1.
They are moderately ionising. They penetrate
moderatley far into materials before colliding and
have a range in air of a few metres. They are
abosorbed by a sheet of aluminium (around 5mm).
For every beta particle emitted, a neutron in the nucleus has turned into a proton.
Gamma Particle
Gamma rays are waves of
electromagnetic radiation
released by the nucleus.
They penetrate far into materials
without being stopped and will travel a
long distance through air.
This means they are weakly ionising because they tend to pass
thriugh rather than collide with atoms. Eventually hit something and
do damage.
They can be absorbed by thick sheets of lead or metres
of concrete.