Thorium? Rummage around in your brain to see if there’s anything you can dig up. Of course, it’s named after the Norse god of thunder. The chemical symbol is Th. It’s a lustrous silvery-white metal and is found in small amounts in most rocks and soils, where it is about three times more abundant than uranium.
It will come as no surprise that it was first found in Norway. The story goes that back in the early 1800s, one Morten Thrane Esmark found a black mineral on Løvøya island, Norway. He assigned this to a new oxide and the corresponding metal name was intended to honour Thor, the ancient Scandinavian god of thunder. However, in 1824, it turned out that this supposedly new earth was Yttrium phosphate.
He gave a sample to his father Jens Esmark, a noted mineralogist, but the elder Esmark was not able to identify it and sent a sample to Swedish chemist Jöns Jakob Berzelius for examination in 1828. Berzelius determined that it contained a new element. Berzelius reused the name of a previous element discovery from a mineral from the Falun which later proved to be a yttrium mineral. The metal seemed to have no practical uses until Carl Auer von Welsbach invented the gas mantle in 1885.
It took until 1898 for thorium to be identified as radioactive, independently, by Polish-French physicist Marie Curie and German chemist Gerhard Carl Schmidt. Between 1900 and 1903, Ernest Rutherford and Frederick Soddy showed how thorium decayed at a fixed rate over time into a series of other elements.
This observation led to the identification of half-life as one of the outcomes of the alpha particle experiments that led to their disintegration theory of radioactivity.
In 1909, there was an odd science experiment when a thorium radioactive incandescent gas mantle was placed above plant seeds to reveal its properties. (I only know of this gem courtesy of a ‘weird science’-type photograph on Wikimedia (pictured).
In 1925, the crystal bar process (or ‘iodide process’) was discovered by Anton Eduard van Arkel and Jan Hendrik de Boer in 1925 to produce high-purity metallic thorium. But thorium still languished on the sidelines.
The nitty gritty
Thorium occurs in several minerals, the most common being the rare earth-thorium-phosphate mineral, monazite, which contains up to about 12% thorium oxide, but average 6-7%. There are substantial deposits in several countries.
When pure, thorium is a silvery white metal that retains its lustre for several months. However, when it is contaminated with the oxide, thorium slowly tarnishes in air, becoming grey and eventually black. Thorium oxide (ThO2), also called thoria, has one of the highest melting points of all oxides (3300°C). When heated in air, thorium metal turnings ignite and burn brilliantly with a white light.
Because of these properties, thorium has found applications in light bulb elements, lantern mantles, arc-light lamps, welding electrodes and heat-resistant ceramics. Glass containing thorium oxide has a high refractive index and dispersion and is used in high quality lenses for cameras and scientific instruments. Thorium can also be used as a fuel for generating nuclear energy.
How come? To start with, it’s found on the bottom row of the periodic table of elements, along with other dense, radioactive substances, including uranium and plutonium, known as actinides.
Half life: the real thing
This is where thorium gets interesting. Actinides are dense because their nuclei contain large numbers of neutrons and protons. But what’s so startling about them is that at intervals, varying from every millisecond to every hundred thousand years, actinides spin off particles and decay into more stable elements.
If you pack together enough of certain actinide atoms, their nuclei will erupt in a powerful release of energy. Thorium-232 decays very slowly (its half-life is about three times the age of the earth) but other thorium isotopes occur in its and in uranium’s decay chains.
Most of these are short-lived and hence much more radioactive than Th-232, though on a mass basis they are negligible. So, thorium is only slightly radioactive, which means you could carry around a lump of it in your pocket without harm.
Thorium and the war
Things hotted up in the 1930s when scientists were struggling to crack the secrets of the atom. Enrico Fermi and his colleagues studied the results of bombarding uranium with neutrons in 1934. The first person who mentioned the idea of nuclear fission in 1934 was Ida Noddack.
After the Fermi publication, late in 1938, Lise Meitner, Otto Hahn and Fritz Strassman confirmed nuclear fission. Physicists everywhere realised that if chain reactions could be tamed, fission could lead to a promising new source of power. What was needed was a substance that could ‘moderate’ the energy of neutrons emitted in radioactive decay, so that they could be captured by other fissile nuclei.
Heavy water and graphite were the prime candidates for moderating the energy of neutrons. It is known that Nazi Germany investigated the possibility of building an atomic bomb, and that a range of options were identified. One assumes they sent scientists into Norway to examine the plant made famous by The Heroes of Telemark.
Although historical records provide limited detail on the German decision to pursue the heavy water approach, it became clear after the war that they had explored the option. Although ultimately unsuccessful, the approach chosen has been demonstrated to be technically viable. We couldn’t find any mention of thorium experiments, as such, but its potential (scientific and literary) was obvious.
And then, interestingly, in the 1950s, a chap called Weinberg and his team proved the efficacy of thorium reactors in hundreds of tests at Oak Ridge from the ’50s through the early ’70s. But they hit a dead end, becoming victim to the cold war with a nuclear-armed Soviet Union.
By the 1960s, the US government chose to build uranium-fuelled reactors, in part because they produced plutonium that could be refined into weapons-grade material. This set the course of nuclear industry for the next four decades, and, according to Richard Martin of wired.com, ‘thorium power became one of the great what-if technologies of the 20th century’.
But Weinberg wrote a book. Not just any book, but an epic 978-page tome on the subject.
It languished in science libraries for some years until, in 2000, a young Mormon called Sorensen, came across it. Even more amazingly, he read it, and thought to himself: ‘Forget uranium. Thorium could be big.’
In fact, he still believes it can be the saviour of the nuclear power industry. What got him excited was this. The key thing with thorium is that after it has been used as fuel for power plants, the element leaves behind tiny amounts of waste. This waste only needs to be stored for a few hundred years, not a few hundred thousand like other nuclear byproducts. Because it’s so plentiful in nature, it’s more or less inexhaustible. It’s also one of only a few substances that acts as a thermal breeder, in theory creating enough new fuel as it breaks down to sustain a high-temperature chain reaction indefinitely.
Finally, for the paranoid among us, it would be virtually impossible for terrorists or crazed Bond villains to use the byproducts of a thorium reactor to make nuclear weapons. Green power Today, Sorensen is pushing for a thorium revival, and is even running a blog called Energy From Thorium.
The site links to the Oak Ridge archives, which Sorensen arranged to have scanned. The project aims to resurrect long-lost energy technology using modern techniques. In his evangelical words, thorium energy can help us: check CO2 and global warming, cut deadly air pollution, provide inexhaustible energy increase human prosperity.
‘Our world is beset by global warming, pollution, resource conflicts, and energy poverty. Millions die from coal plant emissions. We war over mid-east oil. Food supplies from sea and land are threatened. Developing nations’ growth exacerbates the crises.
‘Few nations will adopt carbon taxes or energy policies against their economic self-interests to reduce global CO2 emissions. Energy cheaper than coal will dissuade all nations from burning coal. Innovative thorium energy uses economic persuasion to end the pollution, to provide energy and prosperity to impoverished peoples, and to create energy security for all people for all time.’
So, this blog site could be the springboard where thorium finally takes off. Industry chiefs are looking into thorium, and governments from Dubai to Beijing are funding research, while India is also heavily involved. Watch this space.
Of course, Half Life is pure fiction, yet we tried to base the story on authentic science, down to the atomic level. In doing so, we both became rather fixated on the topic, soon coming to the incredulous conclusion that the true story of this elusive element was even crazier than anything we could imagine for ourselves.
Uranium Is So Last Century: Enter Thorium, the New Green Nuke
Energy From Thorium