The Field Guide to Particle Physics
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A few References and Resources for you.

Isotopes of Helium:
https://en.wikipedia.org/wiki/Isotopes_of_helium

Helium Fact Sheet from NIST:
https://webbook.nist.gov/cgi/inchi/InChI%3D1S/He

Superconducting Magnets from the National Magnetic Field Laboratory
https://nationalmaglab.org/about/maglab-dictionary/superconducting-magnet

The US Federal Helium Program
https://www.blm.gov/programs/energy-and-minerals/helium/federal-helium-program

The American Chemical Society Podcast on the Helium Shortage
https://cen.acs.org/business/specialty-chemicals/Podcast-helium-shortages-changed-science/98/web/2020/10

The Helium Privatization Act of 1996
https://www.govinfo.gov/app/details/PLAW-104publ273

Planet Money Episode on the Helium Shortages
https://www.npr.org/2019/08/16/751845378/episode-933-find-the-helium

The Alpha Particle
Part 2 - The Helium Shortage

It may have been a while, but have you ever been to a birthday party in a big auditorium?  You know, lots of tables. Party favors. Screaming kids. Maybe a clown or a magician? And balloons. Helium filled balloons. Where do all the balloons that kids “accidentally” let go wind up? 

Yeah. Exactly. The ceiling. 

Last time, we pondered the question, where on Earth do you go to find Helium gas? Raw. In the wild. Hopefully, thanks to this party analogy, the answer is now clear.

We can collect helium when it’s trapped by a ceiling. Trapped Underground.

Helium is mined with natural gas. While drilling into gas wells, through the capstone rock at the top of the Earth’s crust, helium is released. 

Some wells have more helium than others. Some of the biggest sources of helium - apparently - come from natural gas wells near the biggest deposits of heavy elements like Uranium and Thorium. 

Like natural gas, there’s a huge, international commodities market for helium. Because Helium does not interact with other chemicals, it is strongly preferred for numerous industrial applications.

For example.

Helium is used whenever you want to avoid exposure to reactive elements, particularly those in air. Welders use helium as a shield to keep the weld itself from exposure to reactive chemicals like oxygen and water vapor. 

Ship builders use helium to detect leaks in the hull of ships. It’s not corrosive and unusual to find in the surrounding environment. If you fill part of a ship’s hull with pressurized helium, and find some helium gas outside the ship - especially near a weld or some other joint - you probably have a leak.

Rocket scientists and engineers use helium to clean and pressurize rocket fuel tanks. 

And of course, we use it for balloons: both of the weather and party varieties. Actually, that’s something that might be surprising. Hundreds of weather balloons are launched every day - all over the globe - to collect data about atmospheric conditions for weather forecasting. I should say that these balloons are enormous, bigger than a typical human at launch. Many - although certainly not all - of those weather balloons are filled with helium gas. Some are filled with hydrogen gas, which though much cheaper is arguably much more dangerous to work with.

So far, most of those applications are pretty intuitive. Helium doesn’t form chemical bonds, so it’s a good gas to use for physical, industrial purposes. But there is another application of helium that is far less intuitive: cooling.

Modern air conditioning and refrigeration systems typically use a working fluid to absorb heat and carry it away, so it can be vented. If you’ve ever put coolant in the engine of your car, you’re familiar with this idea. Liquid helium plays the role of coolant in devices that need to be really, really cold. Like minus -452 degrees F cold. That’s like negative -269 C. By comparison, the average temperature on the surface of the dwarf planet Pluto is -387°F (-232°C). 

What on Earth would need to be kept colder than that?

In a word, Magnets. 

MRI machines - magnetic resonance imaging - is a three dimensional, medical technology that lets us explore what’s going on in inside of our bodies, noninvasively. MRI works by generating a huge magnetic field. The nuclei of all the atoms inside the machine - say the atoms in our bodies - all have tiny little magnetic fields themselves. The huge magnetic field of the machine causes those little atomic fields to line up and dance, returning a magnetic field signal that we can measure, and use to build images. Sort of like a three-dimensional X-ray, although without the potentially harmful dosage of high energy radiation.

Since the chemistry of living tissue really only depends on the atomic electron clouds that surround the nucleus - no harm is done to the body by the MRI machines.

MRI machines use helium to keep their superconducting magnets cold. Really cold. Colder than Pluto cold. Why?

At such cryogenic temperatures, the electrical resistance in the wires completely vanishes. It’s a phenomena from quantum mechanics known as superconductivity. And that TECHNOLOGY ALONE is fascinating and deserves a podcast in its own right. But for now, let’s see how superconducting magnets work at really cold temperatures.

Electromagnets are made by coiling lots and lots of wire in to lots and lots of loops. The more loops the better. The more loops you make - and the more current you can push through that looped wire, the bigger the magnetic field. Just ask any high school physics student. 

Now, big magnetic fields are useful for all kinds of things, for instance MRI machines.

Electrical resistance limits the amount of current that an electromagnet can hold. The longer the wire, the more resistance that builds up. The more loops we wrap, the more wire we need. So unfortunately for those who want to build big magnets, electrical resistance gives us a trade off between lots of wire loops and lots of current.

But as it turns out, when you cool some wires down far enough - like beyond sub plutonian temperatures - that resistance disappears completely. Not approximately. Completely. The current you put into such a cold wire can flow practically forever.

This phenomena makes it practical build an electromagnet that can hold a lot of current - and therefore generate a huge magnetic field - for a long time. But we need to keep them cold. Liquid helium cold.

Liquid Helium is the main, practical working fluid for these kinds of cryogenic conditions.

Over the past twenty years, there’s been at least three major supply shortages e...