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# Helium-3 Shortage Could Put Freeze On Low-Temperature Research

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Science  06 Nov 2009:
Vol. 326, Issue 5954, pp. 778-779
DOI: 10.1126/science.326_778

The weird effects of quantum mechanics often emerge at extremely low temperatures. So 3 years ago, Moty Heiblum, a physicist at the Weizmann Institute of Science in Rehovot, Israel, ordered a large “dilution refrigerator,” which uses frigid liquid helium as a coolant and can chill tiny electronic devices to within a thousandth of a degree of absolute zero, or 1 millikelvin. But now the manufacturer, Leiden Cryogenics B.V. in the Netherlands, cannot deliver the completed fridge: It cannot get enough helium-3—100 liters of room-temperature gas, as it's sold on the market—to fill the rig.

Heiblum has fallen victim to a severe shortage of helium-3, the lighter isotope of the most inert element. Two weeks ago, he also lost about 15 liters of helium-3 from an existing fridge when an electronic valve failed. When Heiblum tried to buy more, a supplier in the United States turned him away and a European company wanted an unaffordable €1300 per liter, up from €100 just 2 years ago. “If this continues, then low-temperature physics will just disappear,” Heiblum says.

No end to the shortage is in sight, however. In recent years the supply of helium-3 has dwindled, while the demand has skyrocketed—especially since 2002, when the U.S. Department of Homeland Security (DHS) and Department of Energy (DOE) began deploying thousands of helium-3–filled neutron detectors to help prevent the smuggling of plutonium and other radioactive materials into the country. In the short term, demand will likely top 65,000 liters per year, while supply will hover between 10,000 and 20,000 liters per year, according to a DOE study. The shortfall threatens several research fields, and DOE, the major supplier, is releasing the gas only to researchers with U.S. funding.

Helium-3 also fills neutron detectors at large neutron-scattering facilities used to probe materials, such as the one at the new Japan Proton Accelerator Research Complex (J-PARC) in Tokai. The projected need for that application alone exceeds 100,000 liters over the next 6 years. J-PARC researchers need 16,000 liters of helium-3 to complete detectors for 15 of 23 beamlines, says J-PARC's Masatoshi Arai: “If we cannot get helium-3 and detectors, … [then] we cannot perform sufficiently good experiments from the neutron facility at J-PARC, for which we spent $1.5 billion for construction.” Low-temperature physicists say they need between 2500 and 4500 liters of helium-3 per year, primarily to fill new dilution refrigerators. Helium is the only substance that remains liquid at absolute zero, and only by pumping the vapor off a liquefied mixture of helium-3 and heavier helium-4 can physicists achieve steady temperatures below 0.8 kelvin, says William Halperin, a physicist at Northwestern University in Evanston, Illinois. “If we lose our helium-3 [supply], we're totally screwed,” says Halperin, who notes that work on quantum computing and nanoscience often requires extremely low temperatures. Helium-3 also serves a role in medical imaging. When inhaled by a patient, it allows researchers to image the lungs with an MRI. The helium-3 supply likely won't return to its former levels. Rare in nature, the gas comes mainly from the radioactive decay of tritium generated in nuclear reactors. Pure tritium is an ingredient in hydrogen bombs, so for decades the United States and the Soviet Union kept large reserves of it and sold the helium-3 skimmed from it. But after the Cold War ended, the United States and Russia reduced their tritium reserves. Prior to 2009, DOE released 60,000 liters of helium-3 annually. In fiscal year 2009, it released 35,000 liters. Russia releases a few thousand liters annually, and Canada has accumulated tritium from civilian reactors that, if purified, could provide a one-time boost of 80,000 liters of helium-3 and several thousand liters per year thereafter, DOE estimates. To ease demand, researchers are looking for alternatives to helium-3, especially for neutron detectors for security. Within a sealed tube of gas, a helium-3 nucleus can absorb a passing neutron and then split into charged fragments that create a detectable electrical signal. Several alternative technologies exist, such as tubes filled with boron trifluoride gas or glass fibers that emit light when struck by a neutron. None of them is a “one-to-one replacement” for the helium-filled tubes in terms of sensitivity, specificity, and ease of use, says Daniel Stephens, a nuclear engineer at Pacific Northwest National Laboratory in Richland, Washington. But as the projected demand for helium-3 for security alone outstrips the U.S. supply, DHS and DOE will likely begin to deploy other technologies soon, he says. Meanwhile, an interagency working group convened by the White House has set three principles to guide the distribution of helium-3, says Steve Fetter, assistant director at-large at the White House's Office of Science and Technology Policy. DOE, which controls the U.S. supply, would give priority to uses for which helium-3 is irreplaceable, restrict its use to security applications in which it offers a decisive advantage, and give priority to projects in which the United States already has a substantial investment, Fetter says. That approach should ensure a supply for science. But it shuts out overseas researchers. Fetter says that “non-U.S. requests are not excluded from consideration.” However, DOE brings helium-3 to market through Spectra Gases Inc. in Branchburg, New Jersey. In a 6 October e-mail message to a would-be buyer, Spectra Vice President Jack Faught said that DOE must approve sales of recently released helium-3 and that it “is reserved for research projects that are funded by certain specific agencies of the United States Government.” Spectra did not reply to requests for comment. That means scientists overseas cannot start new projects and equipment manufacturers may go out of business. “We only make dilution refrigerators,” says Giorgio Frossati, co-founder of Leiden, one of three leading manufacturers of the devices. “If the helium-3 supply stops, it means that we have to close down.” Under current conditions, Frossati says, the company, which employs 10 people and has annual receipts of €5 million, can hang on for a year. Even if the current crunch can be ameliorated, the price of helium-3 will likely never return to the traditional$100 to \$200 per liter. So certain types of research may become much more expensive. Meanwhile, reserves of helium-4 may be exhausted within decades, an even bigger problem that the National Academy of Sciences will weigh in on soon.

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