This is the third of three posts about helium, and the potential for a world shortage of this unique and wonderful element.
In Part 1, I talked a little bit about why helium is a nonrenewable resource. In Part 2, I tried to achieve a layman’s understanding of the world’s helium markets, and the various reasons why they’ve suddenly become unstable in the past 15 years (after decades of remarkable stability).
This is the last post of the three; it’s more of a list than an essay like the previous posts. Today I’m going to try to outline some of the many wonderful uses that make helium special, and make the case that a total depletion of the Earth’s helium reserves (both helium-4 [4He] and helium-3 [3He] ) would be a tragedy.
We stand to lose much more than party balloons and squeaky voices if we run out of helium.
Since I’ve been giving 3He short shrift this week, I’ll start with the lighter of helium’s isotopes.
Daddy, What Did You Do In The Days of 3He?
According to the October 2009 issue of Physics Today, worldwide usage of 3He in the previous five years roughly breaks down like so:
85% Neutron detectors for security
9.9% Neutron-scattering, laser, and other physics research
2.5% Oil and gas detectors
1.7% Medical research
1.2% Low-temperature research
I’ve already mentioned, in the previous post, that the largest use of 3He right now is in neutron detection technology for defense and security applications. 3He is the very best material around when it comes to neutron detection. As of 2009, the US Department of Homeland Security used roughly 25,000 liters annually for this and related applications. (That usage number is probably higher now.) I’d be the first person to suggest that detecting rogue shipments of fissile material is a really good idea. So I’m not against the notion of using neutron detectors, and even helium-based neutron detectors, to protect against nuclear terrorism. I do think, however, that the DHS would do better in the long run if it actually tried to cooperate with the international scientific community.
Almost 10% of the world’s 3He goes to things like neutron scattering research. But what the hell is that? Neutron scattering is a method for probing the structure of materials on very small scales, by carefully studying how neutrons are deflected (i.e., scattered) when they traverse the material.
Neutrons are particularly good for this fine-scale investigation of matter. Being electrically neutral (as the name suggests) means they can look straight at the heart of an atom: they aren’t pushed aside by the electrical charge of the atom’s fuzzy electron cloud, nor are they deflected by the wide Coulomb barrier of the atomic nucleus. Neutrons are scattered by nuclear forces, which only act deep inside the atom. So neutrons can give us a peek at very tiny scales. (It’s not true that neutrons don’t feel electrons at all. Neutrons do carry a magnetic moment, which means they can interact with electons in more subtle ways.)
It’s not surprising, then, that certain neutron scattering research avenues rely critically upon 3He, because as noted above, it makes for terrific neutron detectors.
What use is probling the structure of materials on very small scales? Well, for one thing, it’s useful for understanding how viruses work. It’s also good for studying the magnetic properties of nanomaterials (which has immediate technological application in the realm of high-density information storage); dissecting the microscopic structure of metallic alloys (thus potentially leading to stronger and better alloys); unraveling the internal workings of superconductors; and determining the molecular structure of misformed proteins that can lead to ailments like Huntington’s Disease, just to name a few applications. And that’s all just from the website for Oak Ridge’s Spallation Neutron Source. But there are neutron scattering research centers all around the world, all doing cutting-edge research into the nanoscale structure of materials. Neutron scattering research can improve our understanding of everything from car batteries to viruses.
But much of this research requires high-precision neutron detection, of a sort only available at present with 3He-based technology.
Oil and Gas Detectors
This one came as a surprise to me. But it turns out that helium, and in particular its more exotic isotope, is useful for assessing oil and gas reservoirs. As for how and why this is the case, I can only speculate. (At least until I’m less tired and my google skills improve.)
4He finds a lot of use in leak detection (see below); one can imagine a similar need in the petroleum industry. But the fact that there’s a specific need for 3He suggests a different application is at use here. It may very well come back to neutron scattering again.
“Hyperpolarized MRI” is a form of magnetic resonance imaging that takes advantage of the polarizability of particular isotopes to produce extremely high signal to noise ratios. It is particularly useful for imaging lung tissue in extremely fine detail, because conventional MRI techniques cannot probe such hollows (or even the surrounding tissue).
There are only two isotopes that make this approach viable: xenon-129, and helium-3.
But guess what? Turns out there’s a danger that 129Xe isn’t viable for infants, because there’s a danger of toxicity from (I think) xenon dissolving into the bloodstream. So if this potentially life-saving medical imaging technique is to be used on children, it requires 3He.
That 1.2% slice at the bottom of the pie looks to be an insignificant sliver, and so we might be tempted to disregard it. Anything that tiny couldn’t possibly be worth the fuss, could it? Well, yeah. Yeah it can. Research into the cryogenic properties of 3He is the stuff of Nobel Prizes*. (I’ve already mentioned laureate Robert Richardson’s stance on peak helium.)
The term “low-temperature research” on this list is really a proxy for “fundamental physics research”. The 1972 discovery of superfluidity in 3He was a major triumph for the BCS theory of superconductivity, and continues to offer great insights into quantum mechanics and condensed matter physics.
3He is also crucial when it comes to serious cryogenics. A helium-3 refrigerator can reach temperatures of a few tenths of a kelvin—that’s a few tenths of one degree Celsius above absolute zero. And helium dilution refrigerators take advantage of particular properties of both helium isotopes to produce temperaturs well below 1 kelvin. Why on Earth would anybody want to make something that frosty? Extreme cryogenic temperatures have crucial applications to bleeding-edge areas of research including Bose-Einstein condensates and quantum computing.
So that 1.2% might not look like much, but it’s pretty damn important.
*Two of the three 1996 winners were (and still are, perhaps) members of the faculty at Cornell University. I was there at the time, just beginning my second year of grad school, when the award was announced. The school hung an enormous banner over the front of the physics building to trumpet this achievement. (And who can blame them? Even I can’t, and I loathe the place.) The banner cut out most of my already meager exposure to natural sunlight that autumn. That summer, my department had forgotten to pay me for 3 goddamn months, so I was living on cold cereal and expired Rice-a-Roni. That’s because Cornell University is a miserable hole, and no amount of wicked superfluidity research could ever make me feel otherwise.
We’ll Regale Our Grandchildren With Tales Of Wine, and 4He, and Airships…
…because if the 4He shortage comes to pass, filling a single airship will become mind-bogglingly expensive. The tales will be all we have.
According to this piece in Scientific American (which again quotes Richardson), 28% of the helium used in 2007 went to cryogenics for MRI and NMR machines. The vast bulk of that was clinical usage; only a small fraction (3% of that 28%) went to scientific research.
Magnetic resonance imaging machines use superconducting electromagnetic coils. In order to achieve superconductivity, the coils must be cryogenically cooled to very low temperatures. Liquid 4He is used for this purpose. If liquid helium became unavailable, MRI machines would have to rely upon obsolete and subobtimal magnet designs.
So, the depletion of the world’s helium supply would have severe, negative implications for clinical medicine.
MRI machines aren’t the only gizmos that use liquid helium cooled electromagnets. The Large Hadron Collider contains over 9000 such magnets. (And they’ve been known to cause problems.) The research conducted at the LHC would be impossible with a higher-temperature technology.
NASA uses something on the order of a million cubic feet of helium before each launch of the space shuttle. Helium is the ideal gas for pressurizing and purging lines and fuel tanks. (According to that piece I linked above, 26% of the 4He usage in 2007 went to this very purpose.)
20% of the helium usage in 2007 went to welding applications. I like welding; I like that my car doesn’t fall apart when I’m driving home from the Park and Ride. Helium is also used to provide inert working environments for the fabrication of fiberoptics and LCDs.
Down in the comments, Steve Halter points out that helium is also used to keep out impurities during the growth of silicon and germanium crystals. I didn’t know about that! But I do know that modern semiconductor manufacturing requires crystals of very high purity.
The helium mass spectrometry leak detection method has been used around the world for decades. (It was invented, I note with some pride, by the great Dr. Alfred Nier of the University of Minnesota, my alma mater. Dr. Nier was both an inspiration and a patron to me; I benefited from a scholarship in his name. I had the opportunity to meet him not long before he passed away, but I deeply regret not having a chance to talk to him about his career.)
I’ve tried to make the case that helium is without equal in terms of its utility for cryogenics. Helium has the lowest boiling temperature of anything on the periodic table—lower even than hydrogen. And, because helium is inert, its liquid form has the pleasant side benefit of not being rocket fuel. Helium is the ideal cryogenic fluid when one needs to obtain temperatures below 10 kelvins. Until the 1980s, the only known superconductors worked in this temperature regime, which meant helium was crucial to superconductivity research. And, although the discovery of superconductors that work at much higher temperatures has enabled researchers to work with liquid nitrogen, helium is still critical to this area of research.
Like its lighter cousin, 4He attains a superfluid state when cooled sufficiently. The mechanism for the superfluid transition is very different in 4He and 3He. I’ve already mentioned the 1972 Nobel Prize for the discovery of superfluidity in 3He, but that wasn’t the only Nobel to come out of superfluid helium. The great physicist Lev Landau received the Nobel Prize in 1962 for his theoretical work on the superfluidity of 4He (the same year Crick and Watson and Wilkins won the Nobel for their work on the structure of DNA).
The superfluid state of helium is deeply related to the quantum mechanical phenomenon of Bose-Einstein condensation. The first experimental observation of the superfluidity of 4He, in 1938, was also the first experimental evidence of BECs, which had been purely theoretical up to that point. Superfluid helium also has technological applications. It can be used as a quantum solvent (and in fact is the only viable quantum solvent), which has applications to spectroscopy and nanoscale engineering. Superfluid 4He has also been used in the high-precision gyroscopes aboard the orbiting Gravity Probe B experiment.
More recently, researchers have uncovered evidence that when superfluid helium is subjected to high pressure (but kept at extremely low temperature), a supersolid phase may form. Neato.