The AMS itself, an accelerator mass spectrometer,
has really three components: one is called the low-energy end.
Let's take the example of carbon and radiocarbon is present in the environment
at one million millionth of an atom, so it's a very, very
trace isotope, so what we do is we take any sample,
we convert it to graphite, they're like a little aluminium button
with the graphite in the center of it and we can mount up to 200
of these graphite targets into a cartridge type... we call an ion source,
because what we're going to do is take the atoms of carbon in that graphite
and convert them to ions. We're going to ionize them.
Once you get things ionized, you can move them because we use electrical fields
and voltage fields, voltage gradients magnetic fields,
to move these ions around. So we're going to create an ion beam.
It's a beam of carbon, racing out of our source,
we bend that beam around
with magnets an electrostatic devices and
aim it into a big tank. So we're looking at a tank right here, it's a T-shaped tank,
filled with an insolent--sulfur hexafluoride--
because we're going to create a huge voltage in that tank.
So it's like a big transformer that you see in
hydro systems, except ours is three million volts.
So we're gonna race those ions towards that positive pole
and then we're gonna switch them; we're gonna strip those electrons off the carbon
and turn into a positive ion just as it hits that positive pole
and it's gonna shoot them out the other end.
Now we're going up to a few percent of the speed of light
so our ion beam is really rocketing as we're walking over here now
to the west side of the machine, we're at the high energy end.
So our ion beam is racing out and the flight path goes into a magnet.
And we've got a few
control centers along it; these are electronic lenses so we can change the
shape with that beam.
So now we're looking at a magnet, it's actually our
big, what we call the analyzer magnet. It's 18 tons,
a whack of energy, because we have to bend that beam ninety degrees.
And so we've got just pure carbon coming down there but carbon has these isotopes
carbon-12 and carbon-13 with an extra neutron
and carbon-14 with an extra two neutrons and that's the guy we're looking for.
So as we bend that beam, the lighter isotope,
carbon-12 bends the most, carbon-13 likewise,
but carbon-14 continues on
straight on down that pipe. So we're gonna
now count, we're going to measure the strength of the carbon-12 and the carbon-13 beams.
But carbon-14 is a very weak beam and we can't measure its
strength with current. We have to actually count the
atoms of carbon in that beam. So at the very end, we have a
detector filled with the gas isobutane
and the carbon-14 atoms come down and collide
with the isobutane and they give off their energy.
So this is a high-speed collision. All that energy is dissipated and
each time there's a collision, we measure that energy.
So now we come up with a count and the number of carbon atoms is compared
to the carbon-12 that we measured, and that tells us the concentration.