| While extensive research is being undertaken to study the role of thorium for sustainable and safe energy production, you might ask: what are its alternative uses? Let's take a look at the many different areas – from the archaeology of stars and dating the earth's crust to applications in medicine - where thorium comes into use. |  |
As one can see from these examples, there are many uses and applications of thorium beyond energy production. | While extensive research is being undertaken to study the role of thorium for sustainable and safe energy production, you might ask: what are its alternative uses? Thorium is a naturally occurring element, as common as lead and there is more thorium than tin on earth. However, biologically, it is not used and it is also harmful if ingested due to its alpha radiation. Thorium has certain useful properties: it’s slightly radioactive, it has the lowest nuclear excitation state, it has high melting and boiling points, it’s insoluble in water and releases energy when decaying and undergoing fission. Let's take a look at the many different areas – from the archaeology of stars and dating the earth's crust to applications in medicine - where thorium comes into use. |
| Building the most accurate clock, a nuclear clock Today we use atomic clocks for finding our way with our mobile phones through GPS satellites. But is there a way to make positioning more accurate? To do that one needs to improve the accuracy of the clocks used. A thorium based clock could become 100 times more accurate and would potentially not be very sensitive to its environment which is one of the problems of today’s methods.  The first Thorium-doped Calziumfluoride crystal illuminated. Research is still ongoing, but it has been observed that the radio isotope 229-thorium shows a remarkable and unique property: it possesses an extremely low-energy excited (isomer) state of the nucleus. It may hence be possible to create an excited state of an atomic nucleus using light from a laser. Researchers have proposed building a nuclear clock that would lose only one-tenth of a second over 14 billion years, the current age of the universe. The design would be 100 times more accurate than current atomic clocks and might be used in applications such as higher-precision GPS satellites and experiments that probe fundamental physics. Atomic clocks measure time using the oscillations of a single atom and are accurate to 17 decimal places. They are in widespread use for GPS measurements and synchronization in particle accelerator experiments, and you can even set your laptop to one. While all the technical components are possible, it may be a while before physicists can actually create the clock — they don’t yet know the exact frequency of ultraviolet laser emissions that can excite the thorium nucleus in just the right way. The research is due to appear in an upcoming issue of Physical Review Letters. The basics are that today’s atomic clocks are very accurate but based on the electrons of the atoms. The energies of a nucleus are vastly bigger and the timescales much shorter than those for electrons. An isotope of thorium is believed to be the easiest (still very hard) way to get access to a nuclear transition line that can be used to create the world’s first nuclear clock and increase precision timing far beyond what todays atomic clocks can achieve. |
| Moon's chemical composition The Gamma-ray Spectrometer Experiment was established to measure the composition of the lunar surface. In order to better understand the Moon's overall chemical composition, the Gamma-ray Spectrometer and the X-ray Fluorescence Spectrometer studied the composition of the Moon's surface from lunar orbit. Some elements, such as uranium and thorium, are naturally radioactive and emit gamma-rays as part of their radioactivity. The bombardment of the lunar surface by galactic cosmic rays causes some other elements to emit gamma-rays. The Gamma-ray Spectrometer measured this radiation from lunar orbit to produce maps of the abundances of thorium, iron, and titanium on the lunar surface. This experiment found high iron abundances over all mare regions and lower abundances elsewhere. Thorium and titanium abundances were also highest over mare regions, but these two elements varied considerably in abundance in different parts of the maria. More details about these measurements and their relationship to lunar rock compositions can be found here.  Concentration of thorium on the moon, red shows high concentration. |
Dating the earth’s crust
Scientists from the University of Wisconsin have confirmed that earth’s crust was first formed about 4.4 billion years ago, 160 million years after the formation of our solar system. A new study showed that a zircon crystal discovered 15 years back from the Jack Hills region of Australia dates some 4.374 billion years ago. “The study reinforces our conclusion that Earth had a hydrosphere before 4.3 billion years ago,” said Professor John Valley of University of Wisconsin-Madison geosciences.
Scientists from the University of Wisconsin have confirmed that earth’s crust was first formed about 4.4 billion years ago, 160 million years after the formation of our solar system. A new study showed that a zircon crystal discovered 15 years back from the Jack Hills region of Australia dates some 4.374 billion years ago. “The study reinforces our conclusion that Earth had a hydrosphere before 4.3 billion years ago,” said Professor John Valley of University of Wisconsin-Madison geosciences.
Zircons are considered the oldest terrestrial materials found in sedimentary, igneous and metamorphic rocks. They contain fine traces of uranium and thorium and, having survived erosion and metamorphism, they are bundled with rich and varied records of geological processes. “The zircon formed 4.4 billion years ago, and at 3.4 billion years, all the lead that existed at that time was concentrated in these hotspots,” Valley said.
In another article, science also estimated that the Earth is around 4.5 billion years (Ga) old. It goes on to explain how this can be deduced through radiometric dating of minerals which function, effectively, as mineralogical ‘clocks’. Radioactive decay converts isotopes (types of element) of one element – the so-called parent isotope – to another, which is known as the daughter. But going back so far in time, into a period known as the Hadean, inevitably involves a degree of uncertainty, as rocks can be destroyed as well as created. The most suitable dating material comes from tiny grains of a durable mineral known as zircon, which can be dated by the decay relationship between uranium, thorium and lead (U-Th-Pb). This material, the researchers note, provides: “The only physical evidence from the earliest phases of Earth’s evolution.”
In another article, science also estimated that the Earth is around 4.5 billion years (Ga) old. It goes on to explain how this can be deduced through radiometric dating of minerals which function, effectively, as mineralogical ‘clocks’. Radioactive decay converts isotopes (types of element) of one element – the so-called parent isotope – to another, which is known as the daughter. But going back so far in time, into a period known as the Hadean, inevitably involves a degree of uncertainty, as rocks can be destroyed as well as created. The most suitable dating material comes from tiny grains of a durable mineral known as zircon, which can be dated by the decay relationship between uranium, thorium and lead (U-Th-Pb). This material, the researchers note, provides: “The only physical evidence from the earliest phases of Earth’s evolution.”
| Application in medicine and radiotherapy Thorium-227 is an alpha-particle emitting element that can be linked to monoclonal antibodies to create localized tumor- killing cancer treatments. Algeta is already working with Sanofi, Ablynx NV, Affibody AB and Immunomedics Inc. in studying their monoclonal antibodies linked with thorium-227, a technology that shows potential across a broad range of cancer targets, CEO of Algeta, Andrew Kay said in an interview in March 2013 in London.  Antibody to deliver thorium-227 to kill cancer cells. Algeta says that the monoclonal antibody rituximab has been linked to thorium-227 and tested in pre-clinical lymphoma models. The cooperation has proved very successful and work with this potential cancer therapy continues. The antibody would in effect give the radiation treatment a piggyback ride into the center of a cancer cell, in order to attack cancer with fewer side effects. |
| Heating the earth Thorium is believed to stand for as much as 25% of the earth heat production through its decay. This heat drives the plate tectonics which is the major driver of the carbon cycle, without which we would not have much of a useful atmosphere. In fact we are all traveling through space on a nuclear reactor called earth.  Eart’s core is heated by the decay and possibly the fissioning of thorium. "One thing we can say with near certainty is that radioactive decay alone is not enough to account for Earth's heat energy," says KamLAND collaborator Stuart Freedman of the Lawrence Berkeley Laboratory in California. "Whether the rest is primordial heat or comes from another source is an unanswered question." One possibility that has been floated in the past is that a natural nuclear reactor exists deep within the Earth and produces heat via a fission chain reaction. According to this article, searing from the formation of the solar system, the core of Earth is a nuclear reactor generating heat from the breakdown of radioactive elements like uranium, thorium, and potassium. Scientists have been harnessing that heat for decades by drilling deep wells to power turbines. But now researchers have been able to tap into even greater energy by drilling into volcanoes and exploiting the heat of molten rock. |
| Archeology of the stars Thorium, given its known rate of decay, offers uniquely valuable tools to date a star’s contents since it decays over time at specific known rate and so can essentially serve as a clock. From comparisons with how much thorium was produced by the previous supernova, you can get an age range. Astronomer, Anna Frebel is a part of a team that reported the discovery of a star that is almost as old as the universe, using a technique reminiscent of traditional archaeology.  A star's age can be determined by its thorium concentration. In an interview with New Scientist, Frebel says that “ages in astronomy are some of the hardest things to judge, and for individual stars there is no way of determining age unless there is a clock inside the star.” However, Frebel says that they found a few old stars containing radioactive elements like thorium and uranium, which decay over time at specific known rates and so can essentially serve as clocks. From comparisons with how much thorium and uranium was produced by the previous supernova, you can get an age-range. “We have found that these kinds of chemically primitive stars that we are fishing out, they are something like 13 billion years old. Our new star is likely on this order,” she is quoted saying in the interview. A New York times article, also on the same star, mentions how thorium plays a part: “The star, SMSS 0313-6708, is presumably very old, perhaps the oldest yet identified. The astronomers who found it estimate that it formed over 13 billion years ago. But they cannot say exactly how old it is. One of the few ways to get a precise age for a star is to find one with radioactive elements like uranium and thorium, whose half-lives are known and can be used — like carbon 14 on earth — to date an object with certainty.” As one can see from these examples, there are many uses and applications of thorium beyond energy production. Do you know of other ways thorium can be used? Let us know by sending it to info (at) itheo.org |