April 15, 2008 | 9:38 am
Before you build an experiment to find a rare particle, you need to find the rare material to make the detectors! The hunt for these materials is getting more challenging every year as the needs of science experiments, high-tech industries, and other disciplines turn what used to be everyday stuff into prized commodities.
I have been coming across a lot of tales at the APS conference about the difficulty of procuring the right materials for science experiments and have asked around on some of the topics. The common aspect to most of the searches for materials is the desire to obtain stuff that isn’t contaminated by or with some form of radiation. Combine that with the increasing demand by industry for many elements that were previously used primarily by science, and the entire market is changing, and causing scientists to get more creative about finding new supplies.
Xenon in demand
Some of the promising dark matter searches and neutrino experiments use noble gases as the detection medium. Dark matter experiments have had great success with xenon, but it is quite expensive, and now xenon is in huge demand from other places so the price has risen rapidly. It turns out that some semiconductor manufacturers have discovered that creating their chips in an atmosphere of xenon can be quite beneficial. The semiconductor industry is so big that it can suck up the world’s production of xenon pretty quickly, thereby inflating the prices. When a particle physics experiment needs 10kg, 100kg, perhaps a tonne of xenon, it can quickly get beyond the budget of science experiments.
Radioactive argon
So why not turn to a cheaper noble gas like argon? Argon is incredibly cheap. But argon from the atmosphere (the most plentiful supply) has a lot of argon-39, which is radioactive, due to the effects of cosmic rays, a big problem for experiments that rely on cutting down background sources of radiation so that they know any signals they are seeing come from the things they are looking for, like dark matter particles or neutrinos. Purifying argon to remove the radioactive isotope is extremely difficult and so it is expensive. Why not look for argon somewhere the cosmic rays don’t reach, like natural gas from underground, where it is also plentiful? Well, you can get argon there but it has been contaminated by radioactive elements in the Earth. So either way, you lose out. Argon is cheap and plentiful but it becomes as expensive as xenon when you have to purify it.
Searching for sunken lead
Even if you have a material that has low radioactivity, you still want to shield it from other external sources of radiation like cosmic rays, radon underground, or even the natural radioactivity of humans nearby, which is some cases can be enough to cause a measurable effect. Lead is a great shield for some forms of radiation but the lead from mines is contaminated with uranium and thorium. The contamination takes the form of lead-210. It has a half-life of 22 years so the radioactive component will die away but it takes time. Centuries-old lead, however, is perfect. But where to find it?
Some of the preferred options for purely lack-of-radioactivity reasons: ancient Roman ruins, sunken ships, and the lead from old stained-glass windows in churches. The lead in all of these is perfect to use, but it obviously incurs a significant cultural cost. Fortunately, some of the sunken ships contain ingots of Roman lead, so using it doesn’t cause any harm to anybody and cultural authorities in the past have given permission to use those ingots. The supply of this lead is limited so we can expect to see a second-hand trade in lead among scientific experiments as the found supply dwindles.
Demand for helium rising
Back to noble gases, helium is also in short supply. Despite being the second-most abundant element in the universe, there is not enough to go around to let kids inflate as many balloons as they want. Prices for balloon gas have spiked and many stores no longer stock it. The world can probably live without helium balloons but will they be prepared to say no more MRIs? When it comes to healthcare, people definitely want to have testing equipment available. MRIs have superconducting magnets inside them and they need to be cooled with liquid helium. The number of MRI machines and demand for their use is increasing, partly due to some ill-advised promotions by companies for full-body scans. Some physicists are looking at ways of creating MRI machines that don’t use liquid helium as the coolant for the magnets, so there is a promising way out of that bind.
Helium is used in many other places also, especially in the electronics industry. It is used to make flat-panel TVs and computer monitors, and in the production of computer chips and optical fibers. In total, demand for helium is up 80% in the past 20 years. Prices for helium have gone up 15-30% each year in recent years.
The list of materials in demand goes on; it seems that the resource struggle the whole world is facing has an impact on basic science research. Fortunately, the ingenuity of scientists generally finds a way around the problem, but this is one more challenge in the conduct of an experiment.
See all posts from the American Physical Society April 2008 conference here.
David Harris
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Clad in colorful goggles, three high school teachers put on the same show at the Batavia laboratory that has appeared, in part, on television programs including Late Night with David Letterman.
