Helium-3—a variation of the helium used in balloons—can reduce temperatures to nearly absolute zero, provide non-radioactive medical lung imaging, and detect neutrons emanating from smuggled nuclear devices. It may even be an element of a clean energy source. For decades, this non-toxic and non-corrosive gas has been in adequate supply, but now that supply is dwindling just as demand is rising dramatically.
At a AAAS-organized workshop, participants from academia, industry, government and national labs met to discuss how to meet the growing need for helium-3. The numbers tell a stark story:
This year, there’s about 12,000 liters of helium-3 available. For the next five years, about 8000 liters of helium-3 each year will accumulate from the decay of tritium, said Steve Fetter, assistant director at large in the White House Office of Science and Technology Policy (OSTP). But demand is at least 40,000 liters per year, Fetter said, and forecasts show a growing demand for helium-3 for neutron detectors, scientific research, medical imaging and other uses.
“It’s not a sustainable situation,” he said.
Helium-3 users have tried some obvious approaches to managing the supply, he said. The users have been notified of the diminished supply and asked to limit their use of the isotope. They’re considering a more random approach to positioning neutron detectors and trying to make the existing detectors more efficient. And some are working to recycle the gas.
“But the main response is to accelerate the development and deployment of alternative technologies, especially for portal detectors which are the largest users to helium-3,” Fetter said.
The 6 April workshop attracted 132 registrants from the United States, the United Kingdom, Canada, France, and other countries. It was organized by the AAAS Center for Science, Technology and Security Policy at the request of OSTP and the U.S. National Security Council.
“They realized that this was a problem that the government could not solve on its own,” said Benn Tannenbaum, a particle physicist and associate director of the AAAS center. “They need help getting the word out about the crisis and the new allocation methodology and identifying new technologies that will help to reduce demand and get these in the hands of the people who need them.”
About 80% of the helium-3 used in the United States is for homeland security, as it can detect neutrons emitted from plutonium that might be smuggled across international borders. Beyond monitoring for smuggled nuclear materials, helium-3 is used for basic research, oil and gas exploration, and medical lung imaging. Its unique properties may someday make it useful in nuclear fusion, said Fetter, who’s on leave from the School of Public Policy at the University of Maryland.
But helium-3, composed of two protons and one neutron, is exceedingly rare on Earth. It is found in the air at seven parts per trillion; such low concentrations make it too expensive to extract. It is believed to exist in larger quantities on the moon.
That leaves one main reliable source: Decaying tritium.
While manufacturing tritium just to obtain helium-3 also is prohibitively expensive, it is a reliable byproduct of the U.S. nuclear weapons program. Tritium—which has a 12.4 year half-life and decays to helium-3—is used to boost the yield of nuclear weapons. Tritium doesn’t contribute much to the explosion, Fetter said, but rather serves as a source of neutrons. The helium-3 produced from the decay of tritium can be recovered and repurposed.
After the Cold War, the United States had tens of thousands of nuclear weapons. U.S. tritium production ended in 1988 and the number of warheads was subsequently reduced. Throughout the 1990s, the supply of helium-3 exceeded demand. By 2000, the United States had accumulated over 200,000 liters of helium-3.
But after the 9/11 terrorist attacks in 2001, the demand for helium-3 increased for neutron detectors at border points, Fetter said. Then demand began to exceed helium-3 production through decay of tritium, and the stockpile was drawn down. The United States began to make tritium again in 2007, but in limited supply. In 2008, about 79,000 liters of helium-3 were used, more than half of the existing stock. “Then we realized, we can’t go this way much longer,” Fetter said. “We have to bring demand in balance with supply.”
The need for helium-3 in border protection is shared by other countries. At the AAAS workshop, Stephen White, nuclear and technology adviser at the British Defence staff at the British Embassy in Washington, D.C., said that the United Kingdom has “12,000 miles of shore to protect” and portal monitoring is the primary use of helium-3. White said that the U.K. also uses helium-3 for science and medical applications, and that they’re not looking to expand their uses of the gas.
Richard Kouzes, a laboratory fellow in the Pacific Northwest National Laboratory in Richland, Washington, said that alternatives for helium-3 for national security had to fit certain parameters. For instance, neutron detection systems have to physically fit into existing detection systems, which use long tubes containing helium-3.
Some possible alternatives to helium-3 are detectors filled with boron trifluoride (BF3) or lined with boron, which are two “existing alternatives that can be deployed today,” Kouzes said. Plastic fibers coated with lithium-6 are another possible alternative. Kouzes has tested these alternatives and said that they potentially will work for deployment, but that they will require hardware and software modifications and integration testing.
The alternatives have some disadvantages, though. BF3, which is toxic, has stringent transportation limitations. Litium-6 coated plastic fibers are not currently efficient enough. “Boron-lined tubes seem to be the best bet,” Kouzes said, but they require a multiple tube array in order to efficiently detect neutrons.
Outside the realm of national security, workshop participants said, helium-3 is seemingly indispensable in a variety of industries such as oil well drilling, road construction, basic science research that requires absolute zero temperatures, and medical imaging.
For some applications—like ultracold physics, missile research, and medical imaging of lungs—there are no known alternatives, said Ronald Cooper, detector team leader at the Oak Ridge National Laboratory in Tennessee. In this role, he has installed more than 3000 security systems for detecting neutrons; 75% of those systems have used helium-3. But Cooper said that helium-3 needs in some fields, including national security, oil well logging and road construction, could be met by developing alternatives.
The U.S. oil and gas industry, for instance, uses about 2% of U.S. supplies of helium-3. The gas is used in neutron detectors lowered into oil and gas wells to help determine the hydrocarbon content, which indicates the presence of oil and gas. Brad Roscoe, scientific advisor and nuclear program manager at Schlumberger-Doll Research Center in Cambridge, Massachusetts, said that a replacement for helium-3 must be reliable in the high-temperature, high-vibration, and small-size environment of oil well logging.
The industry is looking for alternatives, Roscoe said. But he’s “pretty sure there’s nothing off the shelf that we can use.” Alternative technologies could be several years away and the commercial roll-out and acceptance of these new technologies would take over 10 years, he added.
In one of several small-group discussions, participants explored how they could meet the helium-3 demands of the oil and gas industry. Without alternatives readily available, they said that they need to educate the consumers of their drilling equipment about the limited helium-3 supply and the need for alternatives. And they intend to encourage recycling programs that could procure 10-20% of the U.S. annual demand for helium-3 in the oil and gas industry.
Participants also discussed helium-3 alternatives in medicine, where use is approaching about 2000 liters of helium-3 per year in the United States. The non-toxic, non-corrosive isotope can be used as a diagnostic along with magnetic resonance imaging (MRI). A patient breathes in polarized helium-3 and the MRI reveals ventilation defects in the lungs, which can reveal chronic obstructive pulmonary diseases such as chronic bronchitis and emphysema. The technique is also used to evaluate the efficacy of drug treatments for these diseases.
Are there alternatives to helium-3 use in medicine? John Pantaleo, Isotope Program Director in the Office of Nuclear Physics at the U.S. Department of Energy, described some of the alternatives. The isotope xenon-129 could be used instead of helium-3, but xenon-129 does not produce as clear images as does helium-3. And, John Pantaleo said, xenon-129 has a sedative effect on patients and may not usable in children. He also said that inhaled helium-3 might be recaptured as the patients exhale it and then recycled for other uses.
Across all helilum-3 uses, AAAS workshop participants said that they could be more efficient at recovering existing and unused systems containing helium-3. Some industries, such as neutron detection systems for national security, have already made strides in developing alternatives that could be put into use soon while other industries have some ideas for alternatives.
“While the demand for helium-3 from the post-9/11 homeland security sector is pretty large, we’ve seen dramatic growth in the uses of helium-3 in several different industries,” said Tannenbaum, the workshop organizer. “It’s unfortunate that all of these demands came online at about the same time, and all well after we stopped making the tritium that decays to helium-3.
“In the short-term, things may look bleak for the sectors that rely on helium-3. However, several exciting new non-helium-3 technologies are coming on line in the next 12-18 months that will significantly decrease demand, and we should soon see some new helium-3 supplies come on to the market.”
[A report from the workshop will be available in late May on the AAAS Center for Science, Technology and Security Policy Web site.]
See speaker presentations and watch a video of the AAAS workshop on helium-3.
A report from the workshop will be posted in late May to the Web site of the AAAS Center for Science, Technology and Security Policy.