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The coming helium shortage

Where will you be when the world runs out of helium?

It’s surprising how many scientists and nonscientists alike are oblivious of the pending helium shortage. But it is a fact—we will run out of helium. According to the Committee on the Impact of Selling the Federal Helium Reserve, formed from members of the Board on Physics and Astronomy and the National Materials Advisory Board of the National Research Council, the question is when, not if, this will happen. Conservative estimates of the helium remaining indicate that the U.S. private reserves may run out by 2015, assuming the rate of helium consumption stays constant at the 1998 rate (1). Obviously, a continued increase in helium demand could significantly advance the date when the world’s supply becomes critical.

Many people might say that their lives are not greatly influenced by the available helium supply, but the loss of this unique resource is not likely to go unnoticed. Helium, which primarily exists as the ⁴He isotope, is a gas under standard temperature and pressure conditions. The low density of this gas has uses ranging from circumnavigating the world in a Rozier balloon to upper atmosphere probes to festive party balloons.

Liquid helium displays very unusual properties. Helium becomes liquid when it is cooled below 4.2 K (–269 °C). When cooled to even lower temperatures, <2.17 K, the liquid undergoes a phase transition to a superfluid state, in which the viscosity becomes vanishingly small.

The superfluidity of ⁴He continues to fascinate experimental and theoretical investigators. Researchers are now embedding molecules and atoms in ultracold helium nanodroplets because ultracold helium is an excellent nonreactive spectroscopic matrix for low-temperature studies (2). For someone not doing low-temperature research, the only close encounter with liquid helium may be as a patient undergoing a magnetic resonance imaging (MRI) scan.

The nonrenewable resource
Helium is a product of hydrogen fusion reactions, making our Sun the largest “local” supplier of this element. On Earth, it is primarily produced by the radioactive decay of heavier elements, mainly uranium and thorium (3). As a result of these reactions, helium is formed below the surface of the earth and slowly percolates through rock into large cavities that also contain reserves of natural gas. Helium diffusion from these pockets results in a relatively low atmospheric concentration of 5 ppmv (1). Once released from soil or water, a given helium atom remains in the atmosphere for a million years on average, after which it is irreversibly lost in space (3). Despite this long residence time, helium is considered a nonrenewable resource.

The purified, compressed helium gas sold today is extracted during natural gas refining. Because of the low atmospheric concentration of helium, it is unlikely that air will become a cost-effective source to augment our helium supply in the near future (1). The United States is the world’s largest producer of helium; but Algeria, Russia, and China also have important helium extraction facilities. Samples of U.S. natural gas contain very high concentrations of helium, at times as much as 8 vol % (1). This is significantly higher than the helium concentrations found elsewhere, which are generally <0.50 vol % (4). Extracting U.S. helium at concentrations <0.3% is not considered economically viable at present (1).

Unfortunately, some companies are only concerned about extracting hydrocarbons and allow the helium to escape into the atmosphere. Isolation of this noble gas may slowly accelerate in the future as higher prices stimulate an increase in the number of extraction sites, as well as the use of more efficient extraction techniques. How much helium is available remains unknown; it depends in part on how many helium pockets are undiscovered.

Helium for cryogenics

Figure 1. Some important uses for helium. The equation at the bottom is an example of a radioactive decay reaction that produces helium nuclei (α-particles).

The aerospace industry uses helium to purge and pressurize tanks of cryogenic fuel, whereas the microelectronics industry uses it to create nonreactive atmospheres. Helium is also found in lightbulbs using gas discharge tubes (commonly called “neon” lights) and in helium–neon lasers (1, 4). Some uses of helium likely to be encountered by scientists and engineers are shown in Figure 1.

Today’s largest consumption of helium is for cryogenic use. Because it has the lowest boiling point of all elements, helium is an excellent very low-temperature refrigerant. By 1996, cryogenics represented 24% of all helium use (5); and in 2000, cryogenics was reported to consume 60% of all isolated helium (6). Although helium gas is commonly used in closed-cycle refrigerators because of its excellent thermal conductivity, greater quantities of helium are used in the liquid form to cool the superconducting wires needed to generate high magnetic fields. These magnets are key components in particle accelerators and magnetic resonance instruments.

Helium is essential for the proper functioning of high-field magnets. If the superconducting wires are not effectively cooled and they are allowed to warm above their critical temperatures, the wires become resistive, causing irreversible magnet quenching. Commercially available superconducting magnets, generally made from wires composed of a ductile titanium–niobium alloy, require that the wires be kept at 4 K to generate fields of 9 T (7). Such high fields are often required for research using NMR and magnetometer instruments. Developing new superconducting materials capable of operating at higher temperatures will likely lead to the replacement of the current wires in magnets with compounds requiring a less valuable refrigerant.

An exciting advance is the newly discovered conventional superconductor magnesium diboride (MgB₂) that displays the relatively high critical temperature (T_c) of 40 K (8). Already superconductors such as YBa₂Cu₃O₇ with very high T_c values are capable of carrying high currents at liquid-nitrogen temperature (77 K); this class of materials is generally referred to as the cuprates. Although cuprate crystals can sustain high operating temperatures, the presence of grain boundaries between crystals stops the current flow; however, recent research to overcome this serious obstacle to device fabrication is encouraging. Materials processing and controlled crystal growth have produced polycrystalline material that displays high current densities (9). Continued studies in this field will likely lead to tapes or wires of these superconductors to be used in high-field magnets.

MRI instruments, now integral to medical diagnostics, have grown in popularity because of magnet power and the affordability of helium. Newer MRI machines have been modified with cryocoolers that recondense the helium gas released as the liquid boils inside the instrument’s Dewar flask. Such modifications have already shown that helium consumption can be significantly decreased; refilling with liquid helium can be reduced to once every several years (1). MRI instruments that use permanent magnets, such as NdFeB, can be good low-field systems (0.2–0.3 T) that do not require expensive refrigeration (10). Although innovative machines operating with high-T_c wires are not yet commercially available, such systems or those with permanent magnets may soon be necessary alternatives.

It is likely that when recognition of the coming helium shortage becomes sufficiently widespread, increased efforts will be made to harvest and conserve this resource. In the meantime, perhaps some forward thinking might ease the difficult transition to helium-free technologies.

References

1. National Research Council. The Impact of Selling the Federal Helium Reserve; National Academy Press: Washington, DC, 2000; http://books.nap.edu/books/0309070384/html/R1.html (accessed June 2001).
2. Jacoby, M. Chem. Eng. News 2000, 78 (40), 47–52.
3. Ozima, M.; Podosek, F. A. Noble Gas Geochemistry; Cambridge University Press: Cambridge, U.K., 1983; p 367.
4. Hwang, S.-C.; Weltmer, W. R., Jr. Helium Group (Gases). In Kirk– Othmer Encyclopedia of Chemical Technology; Kroschwitz, J .I., Howe-Grant, M., Eds.; Wiley & Sons: New York, 1995; Vol. 13, pp 1–38. Accessed online.
5. U.S. Department of the Interior, U.S. Geological Survey. Mineral Industry Surveys: Helium. USGS: Reston, VA, 1996.
6. MacDermott, K. Chem. Eng. News 2000, 78 (18), 68–69.
7. Intermetallic Compounds; Westbrook, J. H., Fleischer, R. L., Eds.; Wiley & Sons: New York, 1994; Vol. 2, pp 351–388.
8. Nagamatsu, J.; Nakagawa, N.; Muranaka, T.; Zenitani, Y.; Akimitsu, J. Nature 2001, 410, 63–64.
9. Larbalestier, D. Science 1996, 274, 736–737.
10. Benz, M. G. NdFeB for MRI Medical Imaging Systems; General Electric Co.: Schenectady, NY, 1997; www.crd.ge.com/.

Laura Deakin (ldeakin@attcanada.ca) is a freelance writer and editor based in Edmonton, Alberta. She is a regular contributor to Heart Cut and Patent Watch.