I ended up drawing a circle of about 2 inches in diameter, and you could sort of see the whole of the [radio]activity within that one little area. And Mal [Malcolm Cooper] got a shovel and dug it up and put it in a plastic bag. We monitored the hole again and there was nothing there, so we started squeezing around in this plastic bag and there was a lump of metal in the bottom.
Williams uses two garden trowels bought at his local hardware store in Melbourne to investigate. He halves the soil sample repeatedly, with smaller and smaller portions containing all the activity, until he isolates the small metallic grey lump. Williams holds it in the palm of his hand – a discrete piece of blown-apart bomb debris loaded with plutonium. ‘Until that time, we had no idea we were looking for bits and pieces like that’, Burns will say.
The British team testing the site in 1966 took soil samples back to the UK, but not the metallic lumps. The soil samples showed nothing untoward back then. Routine soil sampling would be highly unlikely to capture a discrete lump of extremely active material. But the ARL team now finds large quantities of plutonium on the ground.
Plutonium. The material is not found in nature. It is created in a nuclear reactor by bombarding uranium with fundamental atomic particles called neutrons. In the words of nuclear chemist Glenn Seaborg, one of the team who created this dense, silvery substance in February 1941, plutonium ‘is unique among all of the chemical elements. And it is fiendishly toxic, even in small amounts’.
Various kinds of plutonium were used in bomb experiments at Maralinga, but one of grave concern is particularly abundant – an isotope of plutonium known as plutonium-239 or 239Pu. Isotopes of an element have the same number of protons but differing numbers of neutrons. Protons define the elements, while neutrons can vary their properties. This means that while it is the same element chemically, each isotope has slightly different nuclear properties, and this leads to different physical behaviour. Plutonium in fact has up to 20 isotopes, each with the same number of protons but different numbers of neutrons. The highly toxic plutonium-239 has 145 neutrons and 94 protons in its nucleus, giving it a total atomic weight of 239.
All the plutonium isotopes are radioactive and undergo a process of ‘decay’, releasing radioactivity in several different forms and eventually turning into other elements over time. The radioactive half-life (the time required for half of the nuclei of a radioactive isotope to undergo radioactive decay) of plutonium-239 is more than 24 000 years, much longer than the other plutonium isotopes. This long half-life means that plutonium-239 will be present in the environment so far into the future that it might as well be called forever. The persistence of its radioactivity is not the only reason plutonium-239 is especially dangerous. Even in small doses, it can cause terrible damage if absorbed into the body. By the time of the 1984 expedition the scientists know that it is subject to the strictest of controls; when the British were at Maralinga it was released onto the open range. To make it worse, much of the Maralinga plutonium was turned by the Vixen B tests into a fine form that could be inhaled. This made it potentially hazardous for anyone who encountered the dust of the area. The risks are well known: if you inhale 20 milligrams you will probably die of pulmonary fibrosis within a month. Inhaling a milligram will lead to lung cancer. The strange thing about plutonium is that it is relatively safe outside the body, and in fact you can touch a lump of it (as Williams does that Sunday). The alpha rays that it emits would not get past your skin. But once it’s inside the body, it turns deadly. It can be inhaled into the lungs, ingested through the mouth or absorbed through a wound, and if it enters the body through these pathways, there is a strong statistical probability that it will cause various kinds of cancers.
The Pearce Report does not mention any fragments contaminated by plutonium. As a consequence, the AWTSC, whose job was to oversee safety standards at the Maralinga range during the tests and afterwards, disregarded the possibility that later visitors to the site might unknowingly pick up these fragments and take them away.
The fragments are ejecta, metallic debris from firing simulated nuclear warheads during the Vixen B experiments. These so-called minor tests left terrible contamination, far greater than the more dramatic mushroom clouds. The simulated warheads containing plutonium were exploded using TNT. As a direct result the metallic scaffolds that held the assemblies aloft, the oddly named feather beds, were imbued with plutonium-239, as the ARL scientists, to their growing concern, are now discovering. The nature of the fragments varies. In some places, they will say in the report to be written directly after this landmark survey, are fractured pieces of steel, light alloy or other material coated with plutonium. The most radioactive piece found is a concave trapezoidal sheet of 12-millimetre steel plate, about 250 millimetres long and 120 millimetres wide, roughly the dimensions of a piece of A4 paper folded lengthways and pulled slightly out of shape. This metal has a massive 7 gigabecquerels (7 billion becquerels) of plutonium-239 on its inner surface. Most of the fragments are smaller, though, ranging from about half a millimetre to a few centimetres in length.
The scientists also find evidence of plumes. These elongated hand-shapes on the ground trace the curves of the great clouds of fine plutonium oxide particles that lifted 1000 metres with each Vixen B detonation, were dispersed in the direction of the prevailing winds, then drifted down to the surface. The plumes splay out to the west, northwest, north and northeast of the firing pads. They can be detected because the plutonium carried back down still sits close to the surface.
The Pearce Report says that 20 kilograms of the 22.2 kilograms of plutonium-239 is safely buried in pits at Taranaki, bulldozed and sealed in years ago. Why are the ARL scientists finding lumps of the stuff, and plumes picked out in surface-dwelling plutonium? An evenly dispersed sprinkling of sparse tiny particles would barely trouble the Geiger counters. But they are finding a web of hotspots that together contain kilograms of the most deadly form of plutonium known. It turns out the Pearce team back in the 1960s was made up of low-rank military personnel told to take various measurements without ever understanding the physics of what they were doing. Their measurements were effectively worthless. Because of the spotty nature of the plutonium hotspots, their monitoring methods totally missed the plutonium scattered all over the Maralinga range. The Australian Government accepted the return of the site from the British in 1968 on the basis of a fundamentally flawed report.
As Peter Burns will drily observe years later, ‘If they had been as far out in their design of the bomb, they would never have been allowed to build atom bombs in the first place’.
The analytical techniques of 1984 are more sophisticated than those of the 1960s, but there was still enough knowledge to survey the area properly back then. The wonder is why the British chose not to do the job they should have done but instead ordered untrained junior troops to walk around a relatively small part of the range taking surface alpha radiation measurements and picking up a few soil samples for analysis in the UK. Alpha radiation measurements are notoriously difficult to detect in the field because alpha particles emitted by radioactive elements travel only a short distance through the air. ‘Take the lackeys out there, start at ground zero, take a compass bearing, walk every 100 metres and measure, which is what they did. And frankly if you go out and try to measure like that now you would get the wrong answer’, Burns will later say.
This inadequate technique produced a politically acceptable and expedient outcome but did not get anywhere near the truth. The ARL scientists are using a range of methods, including specially designed portable field probes for detecting the gamma ray emissions from the radioactive element americium, an excellent marker for plutonium in the environment. The peculiar physics of plutonium means that as it emits radioactivity over time, part of the plutonium is transformed into americium in a predictable way. Measuring the ratio of plutonium to americium gives a sensitive gauge of the true plutonium concentrations in the field. By 1966–67, americium would have been present in the surface soil at the site. Although the British did not have the same techniques for measuring americium then, they could have performed other kinds of experiments that would have given them a workable ratio. As Williams will tell Ian Anderson in 1993, ‘It is hard to see why they didn’t appreciate the physical deficiencies in the method that they used’.