We sliced open radioactive particles from soil in South Australia and found they may be leaking plutonium


National Archives of Australia

Barbara Etschmann, Monash University; Joel Brugger, Monash University, and Vanessa Wong, Monash UniversityAlmost 60 years after British nuclear tests ended, radioactive particles containing plutonium and uranium still contaminate the landscape around Maralinga in outback South Australia.

These “hot particles” are not as stable as we once assumed. Our research shows they are likely releasing tiny chunks of plutonium and uranium which can be easily transported in dust and water, inhaled by humans and wildlife and taken up by plants.

A British nuclear playground

After the US atomic bombings of Hiroshima and Nagasaki in 1945, other nations raced to build their own nuclear weapons. Britain was looking for locations to conduct its tests. When it approached the Australian government in the early 1950s, Australia was only too eager to agree.

Between 1952 and 1963, Britain detonated 12 nuclear bombs in Australia. There were three in the Montebello Islands off Western Australia, but most were in outback South Australia: two at Emu Field and seven at Maralinga.

British nuclear tests left behind a radioactive legacy.
National Archives of Australia

Besides the full-scale nuclear detonations, there were hundreds of “subcritical” trials designed to test the performance and safety of nuclear weapons and their components. These trials usually involved blowing up nuclear devices with conventional explosives, or setting them on fire.

The subcritical tests released radioactive materials. The Vixen B trials alone (at the Taranaki test site at Maralinga) spread 22.2 kilograms of plutonium and more than 40 kilograms of uranium across the arid landscape. For comparison, the nuclear bomb dropped on Nagasaki contained 6.4 kilograms of plutonium, while the one dropped on Hiroshima held 64 kilograms of uranium.

These tests resulted in long-lasting radioactive contamination of the environment. The full extent of the contamination was only realised in 1984, before the land was returned to its traditional owners, the Maralinga Tjarutja people.

Hot potatoes

Despite numerous cleanup efforts, residual plutonium and uranium remains at Maralinga. Most is present in the form of “hot particles”. These are tiny radioactive grains (much smaller than a millimetre) dispersed in the soil.

Plutonium is a radioactive element mostly made by humans, and the weapons-grade plutonium used in the British nuclear tests has a half life of 24,100 years. This means even 24,100 years after the Vixen B trials that ended in 1963, there will still be almost two Nagasaki bombs worth of plutonium spread around the Taranaki test site.

Plutonium emits alpha radiation that can damage DNA if it enters a body through eating, drinking or breathing.




Read more:
Dig for secrets: the lesson of Maralinga’s Vixen B


In their original state, the plutonium and uranium particles are rather inactive. However, over time, when exposed to atmosphere, water, or microbes, they may weather and release plutonium and uranium in dust or rainstorms.

Until recently, we knew little about the internal makeup of these hot particles. This makes it very hard to accurately assess the environmental and health risks they pose.

Monash PhD student Megan Cook (the lead author on our new paper) took on this challenge. Her research aimed to identify how plutonium was deposited as it was carried by atmospheric currents following the nuclear tests (some of it travelled as far as Queensland!), the characteristics of the plutonium hot particles when they landed, and potential movement within the soil.

Nanotechnology to the rescue

Previous studies used the super intense X-rays generated by synchrotron light sources to map the distribution and oxidation state of plutonium inside the hot particles at the micrometre scale.

To get more detail, we used X-rays from the Diamond synchrotron near Oxford in the UK, a huge machine more than half a kilometre in circumference that produces light ten billion times brighter than the Sun in a particle accelerator.

Studying how the particles absorbed X-rays revealed they contained plutonium and uranium in several different states of oxidation – which affects how reactive and toxic they are. However, when we looked at the shadows the particles cast in X-ray light (or “X-ray diffraction”), we couldn’t interpret the results without knowing more about the different chemicals inside the particles.

To find out more, we used a machine at Monash University that can slice open tiny samples with a nanometre-wide beam of high-energy ions, then analyse the elements inside and make images of the interior. This is a bit like using a lightsaber to cut a rock, only at the tiniest of scales. This revealed in exquisite detail the complex array of materials and textures inside the particles.

Plutonium and uranium show up as bright lumps embedded in darker iron-aluminium alloy in this electron microscope image.
Cook et al (2021), Scientific Reports, Author provided

Much of the plutonium and uranium is distributed in tiny particles sized between a few micrometres and a few nanometres, or dissolved in iron-aluminium alloys. We also discovered a plutonium-uranium-carbon compound that would be destroyed quickly in the presence of air, but which was held stable by the metallic alloy.

This complex physical and chemical structure of the particles suggests the particles formed by the cooling of droplets of molten metal from the explosion cloud.

In the end, it took a multidisciplinary team across three continents — including soil scientists, mineralogists, physicists, mineral engineers, synchrotron scientists, microscopists, and radiochemists — to reveal the nature of the Maralinga hot particles.

From fire to dust

Our results suggest natural chemical and physical processes in the outback environment may cause the slow release of plutonium from the hot particles over the long term. This release of plutonium is likely to be contributing to ongoing uptake of plutonium by wildlife at Maralinga.

Even under the semi-arid conditions of Maralinga, the hot particles slowly break down, liberating their deadly cargo. The lessons from the Maralinga particles are not limited to outback Australia. They are also useful in understanding particles generated from dirty bombs or released during subcritical nuclear incidents.




Read more:
Friday essay: the silence of Ediacara, the shadow of uranium


There have been a few documented instances of such incidents. These include the B-52 accidents that resulted in the conventional detonation of thermonuclear weapons near Palomares in Spain in 1966, and Thule in Greenland in 1968, and the explosion of an armed nuclear missile and subsequent fire at the McGuire Air Force Base in the USA in 1960.

Thousands of active nuclear weapons are still held by nations around the world today. The Maralinga legacy shows the world can ill afford incidents involving nuclear particles.The Conversation

Barbara Etschmann, Research officer, Monash University; Joel Brugger, Professor of Synchrotron Geosciences, Monash University, and Vanessa Wong, Associate Professor, Monash University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Climate explained: how particles ejected from the Sun affect Earth’s climate


Earth’s magnetic field protects us from the solar wind, guiding the solar particles to the polar regions.
SOHO (ESA & NASA)

Annika Seppälä


CC BY-ND

Climate Explained is a collaboration between The Conversation, Stuff and the New Zealand Science Media Centre to answer your questions about climate change.

If you have a question you’d like an expert to answer, please send it to climate.change@stuff.co.nz


When the Sun ejects solar particles into space, how does this affect the Earth and climate? Are clouds affected by these particles?

When we consider the Sun’s influence on Earth and our climate, we tend to think about solar radiation. We are acutely aware of the skin-burning dangers of ultraviolet, or UV, radiation.

But the Sun is an active star. It also continuously releases what is known as “solar wind”, made up of charged particles, largely protons and electrons, that travel at speeds of hundreds of kilometres per hour.

Some of these particles that reach Earth are guided into the polar atmosphere by our magnetic field. As a result, we can see the southern lights, aurora australis, in the southern hemisphere, and the northern equivalent, aurora borealis.

Aurora Australis
Aurora australis observed above southern New Zealand.
Shutterstock/Fotos593

This visible manifestation of solar particles entering Earth’s atmosphere is a constant reminder there is more to the Sun than sunlight. But the particles have other effects as well.




Read more:
Why is the sun’s atmosphere so hot? Spacecraft starts to unravel our star’s mysteries


Solar particles and ozone

When solar particles enter the atmosphere, their high energies ionise neutral atmospheric nitrogen and oxygen molecules, which make up 99% of the atmosphere. This “energetic particle precipitation”, named because it’s like a rain of particles from space, is a major source of ionisation in the polar atmosphere above 30km altitude — and it sets off a chain of reactions that produces chemicals that facilitate the destruction of ozone.

The impact of solar particles on atmospheric ozone was first observed in 1969. Since the early 2000s, thanks to new kinds of satellite observations, we have seen growing evidence that solar particles play an important part in influencing polar ozone. During particularly active times, when the Sun releases large amounts of particles into space, up to 60% of ozone at altitudes above 50km can be depleted. The effect can last for weeks.

Lower down in the atmosphere, below 50km, solar particles are important contributors to the year-to-year variability in polar ozone levels, often through indirect pathways. Here, solar particles again contribute to ozone loss, but a recent discovery showed they also help curb some of the depletion in the Antarctic ozone hole.

How ozone affects the climate

Most of the ozone in the atmosphere resides in a thin layer at altitudes of 20-25km — the “ozone layer”.

But ozone is everywhere in the atmosphere, from the Earth’s surface to altitudes above 100km. It is a greenhouse gas and plays a key role in heating and cooling the atmosphere, which makes it critical for climate.

In the southern hemisphere, changes in polar ozone are known to influence regional climate conditions.

Satellite image of Earth's atmosphere
Solar particles ionise nitrogen and oxygen molecules in the atmosphere, which leads to other chemical reactions that contribute to ozone destruction.
Shutterstock/PunyaFamily

Its depletion above Antarctica had a cooling effect, which in turn pulled the westerly wind jet that circles the continent closer. As the Antarctic hole recovers, this wind belt can meander further north and affect rainfall patterns, sea-surface temperatures and ocean currents. The Southern Annular Mode describes this north-south movement of the wind belt that circles the southern polar region.

Ozone is important for future climate predictions, not only in the thin ozone layer, but throughout the atmosphere. It is crucial we understand the factors that influence ozone variability, be it man-made or natural like the Sun.

The Sun’s direct influence

The link between solar particles and ozone is reasonably well established, but what about any direct effects solar particles may have on the climate?

We have observational evidence that solar activity influences regional climate variability at both poles. Climate models also suggest such polar effects link to larger climate patterns (such as the Northern and Southern Annular Modes) and influence conditions in mid-latitudes.

The details are not yet well understood, but for the first time the influence of solar particles on the climate system will be included in climate simulations used for the upcoming Intergovernmental Panel on Climate Change (IPCC) assessment.




Read more:
Solar weather has real, material effects on Earth


Through solar radiation and particles, the Sun provides a key energy input to our climate system. While these do vary with the Sun’s 11-year cycle of magnetic activity, they can not explain the recent rapid increase in global temperatures due to climate change.

We know rising levels of greenhouse gases in the atmosphere are pushing up Earth’s surface temperature (the physics have been known since the 1800s). We also know human activities have greatly increased greenhouse gases in the atmosphere. Together these two factors explain the observed rise in global temperatures.

What about clouds?

Clouds are much lower in the atmosphere than where most solar particles penetrate. Particles know as galactic cosmic rays (coming from the centre of our galaxy rather than the Sun) may be linked to cloud formation.

It has been suggested cosmic rays could influence the formation of condensation nuclei, which act as “seeds” for clouds. But recent research at the CERN nuclear research facility suggests the effects are insignificant.

This doesn’t rule out some other mechanisms for cosmic rays to affect cloud formation, but thus far there is little supporting evidence.The Conversation

Annika Seppälä, Senior Lecturer in Geophysics

This article is republished from The Conversation under a Creative Commons license. Read the original article.