A building block of nuclear medicines


What am I looking at?

This is a scale model of the smallest building blocks of the metal molybdenum, often just known as Moly. Each of the blue shapes represents a molybdenum atom. Within the box you will find one whole molybdenum atom sitting in the middle, and then eight quarters of a molybdenum atom sitting in each of the corners. If you were to take many of these cubic boxes and stack them up with each other you would build the crystal structure of this important metal.

What’s the scale of this model?

The atoms are contained in a box that is 1 metre by 1 metre by 1 metre. However, in real life, each side of this box would only be about 0.3 nanometres in length. That’s 0.00000003 metres. The boxes of atoms are so small that millions of them could fit across one of the hairs on your arm.

Why is this crystal structure important?

This is one of the most basic crystal structures. In other words, there is only one type of atom contained in the box. The box itself is often referred to as a unit cell. As well as being the structure of molybdenum, this is also the structure of many other materials, including potassium, lithium and iron; the box itself will adjust to fit the bigger or smaller elements.

Now there’s currently not many microscopes that can see down to the atomic level, so how do we know for sure where all the atoms in this structure are? The main method scientists use is called diffraction, when we shine x-rays or neutrons past the sample (in this case Molybdenum) we get a pattern of scattering emerge.

For Molybdenum this pattern, when fully processed looks like this:

moly diffraction

It is from patterns like this that scientists, known as crystallographers, can work out where the atoms are in materials. 

What’s going on in Australia with this material?

So have you ever heard of molybdenum before? You might be thinking that it’s a strange choice of material to feature in an exhibition like this, but hopefully you’ll soon find out how important it is to all Australians. Molybdenum is an element - like carbon, for instance - and it’s one of the simplest materials that makes up our universe. You can find this element on the 42nd spot on the periodic table.


 Like its near neighbours, iron and nickel, molybdenum is a metal, and is characteristically shiny and metallic. Though it looks like many other metals, the molybdenum atoms themselves are pretty special.

On close inspection, each of the molybdenum atoms are made up of 42 protons, 42 electrons and about 42 neutrons, on average. However, unlike many other elements, molybdenum can remain stable even when additional neutrons enter its nucleus. The atoms with more neutrons are known as isotopes. They are the same material (i.e. still molybdenum) just with a different number of neutrons.

One isotope that is particularly important is molybdenum 99, which is made up of 42 protons, 42 electrons and 57 neutrons. Molybdenum 99 is produced when molybdenum 98 (which is the most stable form of this element) is fed with neutrons inside a small nuclear reactor.

molybedum metal

Molybdenum is incredibly important as it is the only way to produce Technetium 99, which is the most commonly used medical radioisotope across the world.

Why is it important, you say? It’s important because it is used to identify and diagnose many things that can go wrong with our bodies. For example, when it is paired with a certain drug it can be used to understand how blood is flowing through our brains. It is estimated that over 20 million procedures use Technetium 99 every year, and every one of these started with molybdenum 99.

Chemotherapy vials

 There are only a handful of places that can make molybdenum 99 in the world, and one of them is down the road at the Australian Nuclear Science and Technology Organisation.  

 OPAL at night



Cronulla Central building