How it Works: X-ray Fluorescence Spectroscopy

What is it?

: All types of light are made up of a spectrum of different colours. That’s why when the sunlight hits raindrops the light is dispersed and you end up with a rainbow.

In its purest sense, spectroscopy is understood to be the interaction between energy and matter as a function of wavelength – but don’t let that put you off. Spectroscopy is an amazing technique for studying the properties of matter; it helps astronomers explore space, reveals the molecular structure of our natural world, and it produces some pretty cool pictures too.

There are three key types of spectroscopy; X-ray fluorescence (XRF) is just one of them. To understand exactly how XRF works, you first need to know a few of the fundamentals: the universe is made up of atoms and inside those atoms are electrons. Each element – hydrogen, oxygen, carbon – has its own atomic fingerprint, because the arrangement of electrons is different for each.

So that’s atoms, now for light: all types of light are made up of a spectrum of different colours. That’s why when the sunlight hits raindrops the light is dispersed and you end up with a rainbow. There are different types of light, including visible, infrared, and X-ray light. All light moves in peaks and troughs like waves, and the different types of light have different wavelengths. For XRF, we need X-rays because their small wavelength is able to pick up individual atoms in material.

When X-ray light passes through an atom, some of the colours of light will be absorbed by the electrons and some will pass straight through. Which colours are absorbed is determined by the arrangement of the electrons inside the atom; this means that different elements absorb different colours. So if you shine X-rays onto a sample, different colours will come out of the other side depending on what elements are in the sample.

Scientists use XRF to determine the elements present in various materials. The technique can be used on something smaller than a grain of sand or as large as a planet. From stars to rainbows, spectroscopy often reveals nature at its best and most beautiful.

The History

: Colours indicate the trace metal content in wheat grains, important information for nutrition and global food resourcing.; Courtesy of Andy Neal

Spectroscopy began with Isaac Newton, who was fascinated by the rainbow of colours produced when white light is shone through a prism. Newton theorised that visible light is made up of many different colours which, when passed through the prism, are revealed and form a spectrum.

Subsequent scientists began setting alcohol on fire and examining the change in the flames’ colour when salt was added. The theory began to emerge that, when exposed to energy, different elements produce different colours.

Later, in the 1860s, German scientists Gustav Kirchhoff and Robert Bunsen (of Bunsen burner fame) developed a more systematic approach to using fluorescence to study matter. They determined that different elements produce different spectrums of light when exposed to energy like a flame. The team began cataloguing the different elements based on the colour spectrum they produced. They used this technique to determine the elemental make up of many different samples, laying the foundations for science’s Magna Carta: the periodic table.

In 1913, English physicist Henry Moseley created a formula which showed that the spectrum of light each element revealed when exposed to energy was linked to its atomic characteristics. Moseley studied at Trinity College Oxford, just a few miles from Diamond. Unfortunately he died in the First World War at the age of just 27, missing out on what some believe would have been a Nobel Prize in Physics. But his legacy lives on; Moseley’s work meant that the elemental mix of any sample could be determined by the light spectrum it emitted, and from this grew XRF as we know it today.

The Technique

These days, XRF is often carried out at synchrotrons like Diamond. Scientists expose their sample – like a meteorite, a drop of oil, or a grain of wheat – to energy in the form of intense light. The light passes through the sample and leaves it in the form of colours, creating a spectrum. This spectrum is captured on a detector and displayed as an image or graph on a computer screen, and it’s from this data that scientists determine the elements inside.

It’s a bit like biting into a slice of cake and trying to work out all of the different ingredients that went into it, except your cake is a scientific sample and you’re not biting it but firing at it with an X-ray beam.

XRF at Diamond

: The metal composition of a sixth century Anglo Saxon brooch found at Oakington, Cambridgeshire. This information shows us that manufacturing methods included a fusion of Roman and Anglo-Saxon methods, indicating the complexity of ancient societies.; Courtesy of Duncan Sayer

X-ray fluorescence spectroscopy can be used to study the chemical composition of virtually anything, and Diamond has supported some extraordinary research in this field. XRF at the synchrotron has helped scientists to study historical artefacts, develop highly nutritious food, and investigate Alzheimer’s disease.

So there you have it, XRF in a nutshell. Who knew science could be so pretty?

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How it Works: X-ray Fluorescence Spectroscopy

What is it?

The History

The Technique

XRF at Diamond