The Helium-Jet Ion Source

I've talked a little about what I've learned and about a few tasks I've finished/I'm currently working on, but I haven't said much about the project I'm working on. So I think I'll do that now!

JJ and I are trying to develop a helium-jet ion source so that we can examine ions of refractory metals. That's a lot of jargon, eh? First off, what is an ion source? Well, it's a source of ions! Ions are atoms that have a charge due to gaining or losing electrons. How do we get these ions, though? There are lots of ways, but our method involves using a Tandem accelerator to send protons to collide with a uranium target that causes proton induced fission. Protons collide with uranium nuclei and break it into two separate, usually radioactive, nuclei.

When something is radioactive, that means that the nucleus is unstable and it must emit something until the nucleus becomes stable. Depending on what is emitted determines what kind of radiation it is: alpha, beta-plus, beta-minus, gamma, etc. Alpha radiation is when a nucleus spontaneously emits 2 protons and 2 neutrons bound together (which actually is the nucleus of a Helium atom) and the original nucleus loses those protons and neutrons. Since an element is defined by how many protons it has, the original nucleus is now a different element! The other types of decay involve protons converting to neutrons, or vice-versa, photons being emitted, and a plethora of other things. The point I'm trying to make is that radiation involves things flying off of radioactive elements.

Back to my project. So these nuclei that are shot off from the uranium target are themselves decaying into other nuclei, which then decay further, etc. etc. What we now have is a ton of different elements flying around. We use an isotope separator to select the specific element we want and then those atoms are shot towards the ion source, which is what I'm working on.

We now have a beam of electrically neutral atoms that we want to turn into ions by stripping them of one or more electrons. Normally, the helium jet isn't needed but it's currently the only way we think we can ionize certain elements called refractory metals. Normally, the beam is directed straight to the ion source, but with refractory metals they end up sticking to the walls of the transport tubes (due to some chemistry that none of us understand).

To fix this problem, we employ the use of a sodium chloride (NaCl) aerosol. Any pressurized spray can (like spray paint) consists of an aerosol inside and this NaCl aerosol relies on the same concept. We then direct the beam through a chamber of the NaCl aerosol, moving the atoms using a stream of helium, and the atoms stick to this aerosol. Since the aerosol + atom clusters are so much heavier than the helium, they all flow in the center of the tube (called laminar flow) and don't bounce around, which means they don't stick to the walls. I'll save what happens next for tomorrow!

I also figured out today our setup for the Argon gas delivery system! We ended up going with the Matheson setup. I'm particularly excited about this part of the project because it's mainly been designed by me. I'd report to JJ every so often and he'd poke and prod me in the right direction, but most of the research has been done by myself. I've learned a lot about how one should go about designing experimental setups and it's really awesome to know that this system will be one of many parts that make this project work. Woo!