h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

What does the salt do to make the detector more sensitive?

And thanks for making me want to stop in Sudbury when I'm next in that end of the country. I only drove through it before since the mine tailings made it look more like the dark side of the moon than a place I'd want to stop!

why does deutrino react in three different ways to result either in charged , neutralor elastic when the particle absorbed is simillar and are these particles plasma?

why does a proton react in positive to make charged, or neutral, or an elastic?

Hi,

The addition of the salt improves the efficiency of the neutral current reaction (which is sensitive to all three types of neutrino) and the associated Cerekov radiation. This means that a reaction is more likely to occur, and that there is more chance of detecting the resulting radiation with the array of photomultiplier tubes situated around the tank.


Megan

Hi,

The three reactions are all very different and are governed by the laws of particle physics.

In particle physics, various quantities have to balance out on either side of a reaction. One of these quantities is charge so, in the first reaction (CC), the deuteron has a positive charge, as do the protons on the right hand side. The electron has a negative charge, and the neutrino has a charge of zero. So the charge balances out as:
0 + (+1) = (+1) + (+1) + (-1) = +1
(both sides equal 1).

Another quantity that has to balance out is lepton number. The electron, muon tau, and their associated neutrinos are all leptons. An electron has a lepton number of +1 and an electron neutrino also has a lepton number of +1 (the corresponding antiparticles have opposite lepton numbers: the positron and the electron antineutrino have a lepton number of -1). Lepton number balances out as:
(+1) + 0 = 0 + 0 + (+1) = +1

Because of this second conservation law, neither a muon or tau neutrino can take part in the CC reaction producing an electron, as this would violate the conservation of lepton number.

The second reactions does not involve a lepton other than the same neutrino which caused the reaction in the first place and so lepton number is conserved by definition.

The third reaction involves no change in the nature of the incident particles other than an exchange of energy.

These particles are not technically a plasma. A plasma is generally defined as a fluid which contains large numbers of charged particles (large enough to make electromagnetic forces important in the large scale behaviour of the fluid) but which is neutral on a macroscopic scale.




Megan

So Cerekov radiation is related to current and thus conductivity? Sorry for being a bit thick, I'm definitely a layman with an interest.

Hi again,

To be honest, I had to go and look this one up myself! (I'm an astronomer, not a particle physicist!)

Anyway, as I understand it, this is how the efficiency is improved:

The neutron which is liberated in the NC reaction is observed when it is captured by another nucleus in the tank. The chlorine in the salt (the chemical formula of which is NaCl) has a very high absorption cross-section for neutrons so by adding the salt the likelihood of detecting the neutron is much higher. ("Cross-section" is a term used by particle and nuclear physicists to describe the probablility of an interaction: in this case, the higher the cross-section, the higher the probability of an absorption.) It is this absorbtion which results in the so-called Cerenkov radiation so, the more absorptions, the more radiation is produced.

Hope that makes sense!


Megan

Lots to chew on, thank you!