One of our technicians was complaining about helium. In particular, liquid helium. It turns out that one of the instruments that needs it was low and he was having trouble getting more. My first response was - well, of course you can't get it because of the budget issues. No, we have the money for helium. Instead there is a shortage of helium. Really, this is not good news. Why?
Ok, let me ask some questions and then answer them myself. For some of these questions and answers, I am just giving an approximate answer. It should be clear that I am not an expert on helium. I do know this. If you breath in lungs full of helium and then run down the hall to surprise someone with your high pitched voice, you will pass out. Right Scott?
Why is there a helium shortage?
Honestly, I don't know all the details. Part of the answer depends on politics. The US has a National Helium Reserve in Amarillo Texas. However, the Helium Privatization Act of 1996 aimed to start selling this off. The result is that there is not as much helium in the reserve.
On top of this, some of the producers of helium have had their own supply problems. The two of these issues together mean that there isn't as much helium to go around.
Where do you get helium from anyway?
You can usually find helium in places where you find natural gas. The problem is that it can be difficult to extra the helium from the other gas. It is easiest when mining "dry" natural gas (I really don't know the difference between dry and non-dry gas - I am just going by what I was told). However, energy companies are the ones usually getting natural gas. For them, they want the "wet" natural gas. So, this is part of the problem with getting helium.
Does this mean no more birthday balloons?
In terms of total helium usage, the amount used in birthday balloons is fairly small. Much bigger uses are for weather balloons and cooling things with liquid helium. However, most people would probably agree that in times of shortage birthday balloons are pretty low priority. So, yes, you will have trouble finding helium for your balloons. I guess you could fill them with hydrogen gas.
What about liquid helium?
The primary reason to use liquid helium is that it is cold. Super cold. At normal atmospheric pressure, liquid helium boils at at temperature of just 4.2 Kelvins (-452.11 Fahrenheit). Yeah. That's cold. What needs something that cold? Super conducting magnets. For some materials, when you get them cold enough the resistance of the material goes to zero ohms. This means that you can run some current through it and the material will act like a magnet. Not just any magnet, but a super strong magnet.
Who needs a super magnet? The two most common uses are for Nuclear Magnetic Resonance Spectroscopy (NMR) and Magnetic Resonance Imaging (MRI). Let's just say (for now) that both NMR and MRI instruments use large magnetic fields to interact with the nuclear properties of the sample. By doing this, you can get spatial data (in the MRI) or composition data (NMR). I know that is probably a terrible answer, but it should be good enough for now.
What happens if you stop putting liquid helium into an NMR?
You put the liquid helium into the NMR and it keeps the magnet cold. Of course, it does this because some of the helium makes the phase transition from a liquid to a gas and that takes energy. This energy comes from the magnet making it decrease in temperature. If the thing was perfectly insulated, there wouldn't be a problem. But it isn't perfect. So, the helium keeps evaporating to maintain the magnet temperature. For the NMR at Southeastern Louisiana University, you need to add about 30 liters of liquid helium every two and half months.
But what happens if you don't. Will it just not work? Well, if you don't do it, bad things happen. Remember, there is a constant current in this superconducting magnet. It can keep a constant current without a power source because the resistance is zero. When it warms up, it no longer has a zero resistance. When there is a resistance, there is an increase in thermal energy which increases the resistance. For our magnet, 49 kJoules of energy is stored in the current and this energy has to go somewhere when the magnet warms up. This process is called "quenching". When the magnet gets hot, more and more of the liquid helium (and usually there is some liquid nitrogen to help keep the liquid helium cool) boils off rather quickly. Here is an example.
Oh - and yes, there is a way to warm up the magnet without bad things happening. However, it isn't easy to get it back to working condition.
How do you make liquid helium?
It's not easy. You can't just put a helium balloon in a freezer until it turns into a liquid. Well, I guess you could if you had a cold enough freezer. The problem is that the freezer would have to be kept cold with liquid helium or something. Let me explain the process in over simplified terms.
Let me start with an example. Take one of those large plastic syringes. Just put your finger over the end and compress the gas inside. You might notice that the tube gets warmer. If you hold it like that for some time, the tube (and the gas inside) will cool off to room temperature. Now pull the plunger back out to expand the gas. When the gas expands, it gets colder.
For helium, you take the gas and compress it. Then you cool off the compressed gas and let it expand. That's it. You just keep doing this over and over until you get the stuff cold enough. There are some tricks, but that is the basic idea.
Couldn't you recycle the helium from the NMR?
Yes, this is technically possible. However it is also technically very expensive. You would need to have some device to capture the helium as it turns into a gas. Then you would need to collect it and run it into a helium liquefier. These liquefiers are really expensive. So, most facilities just get more liquid helium every couple of months.
Image: crdotx/Flickr
