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Beta radiation is the one in the middle and because it's the one in the middle between
alpha and gamma it's a bit odd. It's not as big as alpha and not as ionising
as alpha. But it's not as penetrating as gamma.
Now if you think its odd you're not the only one- because for 50 years it puzzled the best
brains in physics.
It is so strange that physicists had to invent a new force to explain it. And even now particles
that you can virtually not detect had to be invented to explain it.
So you may have some questions about it even after this session.
But here are the basics.
Well let's start with the nucleus. Sometimes a nucleus is formed with too many
neutrons.
This can happen in many ways for example it can happen in outer space or in a supernova
or even in alpha decay.
To make it more stable it wants to change this neutron into a proton.
So that's where the beta particle comes in. *** there it goes and the neutrons become
a proton.
Now how do you think it does this? The answer is the answer to explaining beta
decay.
A neutron has no charge so if it changes into a proton, which is positive, it doesn't lose
much mass. But it does give away a negative charge.
So to make a beta particle we want to make a particle which has a very small mass and
a negative charge. There is a candidate for this role- have a
quick think to see if you can work out what it is. Did you work out that the particle
is actually an electron?
Now what are the properties of beta radiation? Well firstly we know now that it is an electron
and electrons have not got very much mass but they have got a negative charge so the
charge is minus 1. The beta particle isn't just a normal electron
though it's got lots of energy. When it comes out of the nucleus it goes whizzing out.
It whizzes out at very, very close to the speed of light, and that's 300,00 km per
second. That's about as fast as you can get.
The charge means it can change its direction through a magnetic field.
So if you put beta particles into a magnetic field then they start to move to one direction
but it is so fast that it doesn't have much time to stay in there.
Now when it goes past other particles like atoms and molecules and DNA it doesn't have
much time to spend when it goes past it. So it whizzes past the first one- it might
wiz past 30 or 40 but eventually because it does have a charge it is going to take electrons
off of some of the atoms.
That means that it is ionizing- but not as ionizing as alpha decay. So when you look
at beta radiation it travels a long way in air and it just zooms through paper but it
is stopped by a piece of metal or aluminium a few millimetres thick and it certainly doesn't
get through lead.