Could I see neutrino interactions in a deep mine?

17 June 2012

Part of the show Why Do I See Stars when I Stand?

Question

Hi,

I thought up this question whilst sitting in the dark between taking photos a few hundred feet underground in a slate mine. I'm aware that weakly interacting neutrinos can make through a few hundred feet of rock and these can be detected by equipment. I've also heard that cosmic rays have been detected by photographic sensors. My question is if I am at a depth shallow enough for particles to reach me, would anything such as the particle itself or the decay products produce anything visible if they were to hit my retina?

How long would I have to wait? Thanks

Answer

Neutrinos are very interesting particles. They almost don't interact with the rest of the universe at all. In fact, the neutrinos which come from the Sun, billions and billions of them are created in nuclear reactions in the Sun, they can travel the equivalent of 10 times the distance between the Earth and the Sun through water before they hit anything to make any kind of interaction at all. And not all of those interactions will actually produce a light which you'll be able to see. So, just working on the number of interactions, that sounds incredibly unlikely, but there's also about 65 billion neutrinos going through every square centimetre of everything in the world all the time every second.

You can work out the relative ratios, how often they interact in a cubic centimetre (for this purpose, let's assume your eyes are very roughly about a cubic centimetre). In that liquid in your eye, it's probably going to take about 200 seconds for a neutrino to interact with some of that liquid.

The number of those that produce enough light for your eye to see is probably going to be a relatively low proportion, so you're probably talking thousands of seconds; every few hours maybe a neutrino hits your eye and produces some light, but actually, would you be able to see that? I think that's almost entirely unlikely because it's going to produce a tiny amount of light, and the sensors in your back of your eye getting triggered by thermal radiation. Probably radiation from radioactive elements inside your eye and in the atmosphere around you is going to be far, far greater effect than neutrinos.

I think camera sensors will be even less likely [to record a neutrino interaction] because your eyes are filled with water which will interact with neutrinos whereas a camera sensor, in front of it is just air, therefore there're fewer particles from the neutrinos to interact with. You need to have that interaction with a very thin layer of a camera sensor, so probably slightly more likely with your eye.