So this is one of our glove-boxes. Yeah, if you just look to the right of
the glove-box you’ll see that we’ve got these air locks and basically what
you do is you put whatever it is you want to take into the box in there
and then you evacuate it and then you refill it with dry, oxygen-free
nitrogen so then you can take compounds which react with air and
moisture into the box safely and store them. So this is a bit like what you
see pictures of a nuclear industry when you’ve got people handling
things.
Ok so next up is uranium, which is my favourite actinide, it’s the one I
handle in the lab, it’s also the bogeyman of the periodic table, I think. As
soon as you say uranium to people, people start going “Ooh, not sure
about that.”
This is the bogeyman. This is uranium turnings. You see they have a sort
of dull appearance because when they are cleaned up they are really
very reactive, and they react with oxygen extremely quickly, but if you
acid-treat them with concentrated nitric acid you get really beautiful
gleaming surfaces but it doesn’t hang around very long.
Uranium is the basis of much of nuclear power and it exists in two
isotopes, that’s two atoms of different weight, there’s uranium-238 which
is the most abundant one and the other, uranium-235 which is the one
which, when irradiated with neutrons will split in half and release nuclear
energy and a lot of work has been done, or was done in during the
Second World War on the separation of these isotopes of uranium and,
including the construction of the biggest mass spectrometers that had
ever been made. And, fortunately the separation of uranium isotopes is
really very difficult which is why it is only very large and rich countries
have been able to afford to make nuclear weapons.
This is just oil sat on the top so just like we had to have oil to protect the
potassium we also need oil to protect the uranium turnings. If you really
finely divide uranium turnings they are pyrophoric which means they
burst into flames in the air, just spontaneously.
But it’s actually a really interesting element to deal with. It’s got a wide
variety of oxidation states, and if you use it in its depleted form it’s
actually relatively safe to handle in the laboratory. Now, depleted
material only contains a very small quantity of fissile uranium which is
used in bombs and nuclear reactors, about 0.2 of a percent. It actually
means that the problem with handling depleted uranium is not the
radioactivity, although you have to make provision for this, the real
problem is that it is highly poisonous and about half a gram would kill
you in a very short period of time because it attacks your liver, very
effectively.
This is uranium tetrachloride. It’s solvent free, it’s a nice free-flowing
emerald green powder and if you dissolve this up in solvents like THF,
you get beautiful green solutions from it. And here’s another form of
uranium. So this is uranyl dichloride which has got two organic molecules
co-ordinated to it as well. That’s this beautiful yellow colour.
So, once you’ve removed the uranium-235 you’re still left with a very
large amount, 99-point, more than 99% of the original mass of your
uranium is uranium-238, which you have removed most but not all of the
uranium-235 and this is so-called depleted uranium which is some of the
densest material you can get. And so it is used where you want
something very heavy that’s not too large. So for example, it’s used in
the counterweights that people put in aeroplanes and large aeroplanes to
balance the plane because you can use, it takes up only a small volume
of space.
We have to keep it safe and secure in a safe. And we have to fill out
huge amounts of paperwork, many-a-forest has been chopped down for
this paperwork I’m sure, but it’s all very important because you have to
be certain that when handling depleted uranium compounds that you are
not going to end up poisoning anybody and you are not going to end up
getting radioactive compounds all over the place. So we have log books
and we have to record how much we use and when and how we dispose
of it. We have detectors which we have to sweep the lab.
Well a lot of people usually start off with “I imagine you glow in the
dark,” which if I could do that I’d have passed away a long time before
that point. Yeah, it’s the bogeyman-thing again, a lot of people are quite
sort of surprised or you know sort of shocked to hear that you’re
handling this stuff but actually it’s just like most other chemicals on the
periodic table and once you get past the ‘bogeyman image’ of it, it’s
actually a very interesting element to work with.
Most metal or metalloid elements do look like this. It’s just that the
number of electrons they’ve got, the number of electrons they take or
they get rid of, is what defines their chemistry.
And is that not dangerous? You know uranium has this reputation of
being so dangerous. Are you not putting us in danger by holding that
there?
No, this is depleted uranium, so there is about 0.2% of this is what you
would consider fissile. The rest of it is not radioactive. So it’s all quite
toxic, but you’d have your work cut out to eat this stuff because it’s
extremely hard.