I'm here at the joint institute for
nuclear research in Dubna in Russia the
place where so many of the super-heavy
elements have been created and I'm going
to show you an absolutely key component
from making those elements and it's also
probably the most expensive compound you've
ever seen. And the sample I'm going to show
you is here on the table. In many of our videos
about these heavy elements we've talked
about accelerating a light element onto
a target and creating the super-heavy
element, but we usually rather dismissed
what the light element is we said well
it's calcium... plus element calcium 20
plus 95 makes 115... it is actually a very special
isotope of calcium called calcium-48.
It occurs naturally but in a very very,
small abundance. So it has to be
separated from the other isotopes the
other atoms of calcium and because
calcium doesn't have any compounds that
are gaseous,
it literally has to be separated atom by
atom, in the large magnetic separator and
so it is very expensive. So here we have
calcium carbonate but which just
contains calcium-48. It's so valuable and
my hand shakes so much; I'm not allowed to
touch it, but here with this pen you can
see the approximate scale the two grams
of calcium carbonate here which is worth
at least if you wanted to buy it would
cost you about half a million dollars.
This is 250 dollars per milligram.
A milligram is about the smallest amount you
can see easily. You're paying for the calcium.
The carbon dioxide and oxygen
come free. All things come with a bonus
when you buy them in the supermarket.
If you buy Ca-48 you get the carbonate
free. The reason why it is so expensive
is because you have to produce ions of
calcium by heating it to very very high
temperature and then separating it in a
high vacuum under a magnetic field.
And so you need a very big piece of apparatus
with huge electromagnets using a vast
amount of electricity and apparently the
industrial scale production of this
material is 10 grams a year. So they produce about five times as much as you
can see in this bottle in a year.
This isotope is only used in nuclear
physics and most of it is used for
synthesizing super-heavy elements.
It is only made in one place in the world.
The so-called: the Electro combine
Elektrokhimpribor, which is in the town
called Lesnoy which is about 200
kilometers north of the big city of
Yekaterinburg in the Ural Mountains.
So there's a monopoly supplier but if you
want to make money, making calcium 48 is
probably not the market that you should
go in for because there's so few customers.
You can't use calcium carbonates in the
accelerators. You need to use calcium metal.
There is quite interesting and
simple two-stage chemistry.
First of all you heat the calcium carbonate to drive
off the carbon dioxide. The second stage
involves a variation of the so called
thermite reaction, which we have shown
you before, when you mix the calcium
oxide with aluminium powder and heat
them up and the aluminium powder reacts
with the oxygen because it has a
stronger affinity for the oxygen from
the calcium. The calcium metal, this tiny
sample, sample of calcium-48 is then put
into the ion source of the cyclotron.
This is where they make the calcium
ions. The ion source then generates calcium
ions which are accelerated up to about
the tenth of the speed of light and
smashed into the target. The apparatus
runs at the rate of about one milligram
of calcium 48 per hour. So, here we have
two grams of calcium carbonate which is
probably one and a half grams of calcium
metal, well perhaps a little less, so this is
enough to run for more than a thousand
hours of cyclotron time, but you can see
with this sort of price it's an
expensive experiment but the other costs
of running the cyclotron are also large
so even if you've spent half-a-million
dollars on buying this
you still have to spend some more money
to start synthesizing your su--
super-heavy elements. You might ask
yourself what is special about calcium
48 that people go to all this trouble
whereas they could get tons of the cheaper
calcium for the same price?
The answer is that calcium 48 has
the largest excess of neutrons.
Calcium is atomic number 20, so it has 20 protons and
because it's 48 it has 28 neutrons.
When you're making the super-heavy element
the more neutrons you can get into the
final nucleus of the heavy element the
more likely it is to be stable, by and
large the number of neutrons in the
target nucleus is fixed. So you want to choose
the light element, the projectile, to be
containing as many neutrons as possible.
Now, you don't have much choice because
the identity of the element is dictated
by the number of protons if you want to
add 20 to the atomic number of your
target you have to use calcium so you
want the calcium isotope that has the
most neutrons and the number of neutrons
and number of protons in calcium are both
so called magic numbers for particularly stable
nucleus. So 28 is a magic number of
neutrons, 20 for protons. So, calcium 48 is a
double magic nucleus. You can't get
better than that and when you bang that
projectile into the target if the two
nuclei fused together then the
nucleus still has a lot of energy and it
loses part of that energy as neutrons
coming out and because he's got lots of
neutrons you'll still have plenty left
in the final nucleus. And calcium 48 has
been the absolute key to the success of
the synthesis of these super-heavy
elements in Dubna, which is why they are
the principal customer for the
production of the calcium 48. The problem
is the future synthesis of elements is
that the highest atomic number
of any target that has been successfully
used so far is 98. Californium. So
you can see it just works for element 118.
Calcium: 20. Californium: 98. Put them
together you get a 118, but if you
want to make a 119 or
120 you've got to go to a
heavier projectile. The scientists
working here looking at titanium 50.
But titanium 50 is not as good as calcium
48 it doesn't have a magic number so
they're going to have to build a much
more sensative
apparatus if they have any chance of
success in detecting the new elements.
You go on throwing and throwing more and
more and eventually after days perhaps
they stick together and you make a big atom.