Matt Daubneys Blog

(Hopefully people on the Ubuntu planet will excuse this slightly off topic wander…)

This is my final term in University (hooray!) so that means final year project time. Being worth a lot of marks, I’m quite excited to say that the work I’m doing will be feeding into the KATRIN experiment. Why is this exciting? Well, it’s fundamental physics which will help shape our view of how the universe formed, and ultimatley may lead to technological advances in future years.

So what is KATRIN? The Karlsruhe Tritium Neutrino experiment will hopefully find the mass of the neutrinos. Neutrinos are tiny, uncharged subatomic particles, which until recently where believed to have no mass at all. We know that there are three types of neutrinos, those associated with electrons, those associated with muons and those associated with tauons. These three types of neutrinos are commonly called flavours and each one may have a slightly different mass. Since they have no charge, neutrinos don’t interact very much with other particles, this makes detecting neutrinos very difficult. There have been some experiments designed to detect neutrinos, such as Super-Kamiokandi in Japan, which are essentially enormous lakes of water, deep underground surrounded by light detecting sensors (photomultiplier tubes and CCD’s I’d imagine). When a neutrino interacts with one of the water molecules, a tiny flash of light is emitted and is recorded by the equipment surrounding it.

Back to KATRIN, the reason we’d like to know the mass of the neutrino is manyfold. The first reason, as normal in science, is because it’s a question that currently has no answer. The second reason is that there are countless numbers of neutrinos in the universe, the only known particle more numerous that neutrinos are probably photons (tiny packets of light), because of this, neutrinos make up a small, but possibly significant amount of the mass of the universe. If we know the mass of the various neutrino flavours then we can improve our models of how our universe came into being.  The question of how the universe came into being is enormously complex to answer, and the more information we know about the particles that currently make up our universe, the better idea we get of what the universe was like a few seconds after it began.

To understand my small role in the KATRIN experiment we now need to understand how it works. What will happen in the KATRIN equipment is a gas of Tritium will be passed into the machine. Tritium decays into an isotope of Helium (Helium-3), an electron and an electron neutrino. The energies of the Helium-3 and the electron can be measured, then by using simple conservation laws we can calculate the neutrino mass. My part in this is quite small, the gas passing into the machine needs to be of a known purity. They will need to know how much other stuff is in the gas with the Tritium. This can be done using a technique known as Raman Spectroscopy.

In Raman Spectroscopy, you fire a laser at a sample (be it a gas, liquid or solid) and the individual photons that make up the light collide with the atoms in the sample. Most of these atoms bounce off with the same energy they started with from the laser, but a small fraction bounce off with a smaller energy. Using some filters and a spectrometer we can measure these energies and each different substance will have a different spectrum or “fingerprint” if you like.

Before we can find the spectrums fingerprint, the spectrometer has to be calibrated to remove all the patterns and noise from the various components inside it. That is my job. A small part of an incredibly large, complex and amazing experiment.

More will come when I figure out how to do this.