Expert: Steve Nelson - 3/9/2009

Question
Hi. I recently watched a supernova documentary and it was stated that during the collapse of stars to neutron stars, the neutrinos produced where like "ghost". That is they past through the earth like it wasn't there. How then do these detectors work if that is the case?

Answer
On average, yes, they do.  But the sheer number is staggering (trillions pass through your body each second from the Sun and other sources).  Most pass through, because the probability of interaction is tiny.  It's like winning the lottery, it's unlikely but it does happen to one out of so many millions of people.  So a few interact and deposit their energy in the detectors.  That's how they work and why the detectors usually require tons upon tons of detecting material (to raise the probability that one of the nuclei in that material will interact with one of the neutrinos).  This rare interaction is also why such detectors must be buried deep underground to avoid most of the natural background radiation that we see on the surface.  Aside from that they work like most standard particle detectors.