How do we exactly use neutrinos to probe the core of the Sun (if they can only interact weakly)?

Question

Neutrinos are interacting with ordinary matter weakly. They pass through matter mostly unimpeded.

Thus, neutrinos typically pass through normal matter unimpeded and undetected. Neutrinos' low mass and neutral charge mean they interact exceedingly weakly with other particles and fields. This feature of weak interaction interests scientists because it means neutrinos can be used to probe environments that other radiation (such as light or radio waves) cannot penetrate. Using neutrinos as a probe was first proposed in the mid-20th century as a way to detect conditions at the core of the Sun. The solar core cannot be imaged directly because electromagnetic radiation (such as light) is diffused by the great amount and density of matter surrounding the core. On the other hand, neutrinos pass through the Sun with few interactions.

https://en.wikipedia.org/wiki/Neutrino

Based on this, neutrinos interact with matter they pass through, just very weakly, and with few interactions.

This could mean they lose some energy as they pass through matter and interact with it weakly with few interactions.

I am curius as how we exactly can probe the core of the Sun when neutrinos only interact weakly. Do they lose any energy through this process or how do we use them?

https://dx.doi.org/10.1103/PhysRevD.88.045006 (RG)

Question:

1. How do we exactly use neutrinos to probe the core of the Sun (if they can only interact weakly)?

Answer 1

The neutrinos are produced by nuclear reactions in the core of the Sun. About 2% of the mass lost in the conversion of hydrogen to helium ends up in neutrinos (almost entirely in the form of kinetic energy, since neutrinos have a negligible mass here).

The neutrinos interact very weakly with matter and therefore they basically all escape from the Sun. The neutrino flux from the Sun can be measured and compared with the predictions of theoretical models, hence probing the conditions (temperature and density) in the core.

Note that your neutrino detector detects a very, very small fraction of the neutrinos incident upon it; but so long as you know what that fraction is, then there is no problem estimating the neutrino flux from the Sun.

Answer 2

To enlarge slightly on Rob's answer, for a neutrino to interact with (for example) a proton requires it to strike the proton essentially "head on" which greatly reduces the chance that any neutrino will interact with a given chunk of matter, even if traveling vast distances through solid rock. But if you collect enough matter together that reacts with neutrinos in a particular way and wait long enough, you can make a neutrino detector out of it even though the vast majority of neutrinos that pass through it do not register on it.

This means two things: you can easily filter out false signals by putting your neutrino detector a couple of miles underground, and you can increase your chances of catching a few by making the detector really big. So the most sensitive neutrino detectors we have are big and placed deep underground.