Tag Archives: neutrino

Momentum and SNO

These past two weeks, I’ve been teaching a grade 12 physics class. And I’ve been reminded of how much I love physics: So much.

I’ve been teaching the momentum unit, which is pretty straight forward as far as units go. 1D momentum, 2D momentum, some impulse and elasticity … and that’s about it. So I thought I might as well sneak some fun physics stuff in.

One of the nifty outcomes from conservation of momentum was the discovery of the neutrino. One of the nifty outcomes of the discovery of the neutrino is the existence of SNO (the Sudbury Neutrino Observatory), which detects neutrinos. So, I made a little presentation about it.

2D Momentum 2 slide 1

Wolfgang Pauli, back in 1930, compared the momentum before and after a neutron decayed into a proton and electron – but he came up a little short. He concluded that there must be some tiny, undetectable particle carrying away some of the final momentum from the system. That particle was called the neutrino.

Pauli, an enjoyably eccentric physicist, said, “I have done a terrible thing, I have postulated a particle that cannot be detected.” Well, it turns out, you can detect neutrinos. The only problem is, it’s really hard to do, since neutrinos are teeny tiny. (Think of a neutrino going through an atom like a fly going through the skydome.)

2D Momentum 2 slide 2

Enter: the Sudbury Neutrino Observatory. A project designed to experimentally verify some important properties of the neutrino. In order for their detector to detect only neutrinos (and none of the other background radiation) they had to find a smart way of filtering out all of the extra radiation. The solution? Build the detector 2km underground in an active mine in Sudbury. Obviously.

SNO mine

This is picture that I took when I went to visit SNO back in 2007. You have to get up really early, get dressed in miner gear (coveralls, work boots, helmet with head lamp) and take a scary elevator ride 2km underground. You then walk a couple of kilometers through the mine before you hit the lab.

SNO lab

Once inside the lab, you have to shower and completely change into a new jumpsuit, hairnet, special shoes and safety glasses. They have to be very careful about any excess radiation that comes into the lab. (Side note: it turns out that coffee is nearly too radioactive for this place. Although, if you try to take coffee away from physicists they are likely to put up a fight. Which is what apparently happened in this case.)

The SNO lab itself looks a little like a James Bond villain lair. All of the outer walls are rough, since they were carved out of rock, so the whole effect is a little trippy.

Anyway, long story short, SNO was a success. They experimentally determined some spin properties of neutrinos, which apparently means they get cited everywhere nowadays. For me, it was a really cool trip. For my physics students, I think they thought that SNO looked like a pretty cool place.

Hopefully, it helped to bring some excitement and perspective to their momentum unit, too.

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