Neutrinos are very antisocial particles. They are the most reluctant to interact with other particles. Trillions of neutrinos pass right through your body every second, but the weekly average number that grazes one of the atoms in your body is 1.
The rarity of this phenomenon has made life difficult for physicists, who had to build huge underground detector tanks in order to get a chance at catching the odd neutrino. However, in a study published in Science researchers still managed to detect something using a detector the size of a coffee pot!
Previous approaches show that a neutrino reveals itself by producing a flash of light or a single-atom chemical change whenever it bounces off an atomic nucleus. But neutrinos do communicate with other particles via the “weak” force – the fundamental force that causes radioactive materials to decay. Because the weak force is only applied at short (subatomic) distances, there is a small chance that a tiny neutrino can find an individual proton or neutron and bounce off of it. But as soon as it finds one, the next thing happens.
The neutrino bounces off and continues its inexplicable wandering, but the nucleus also suffers a tiny push from the impact. That collision kicks a few electrons out of their orbits and as they fall back into their places, they release the acquired amount of energy in form of photons (flashes of light).
Problems with detecting neutrinos (COHERENT)
The first problem was a smallness of a “tiny push” from the above paragraph. Imagine you throw a ping-pong ball at a bowling ball and then try to distinguish the difference in bowling ball’s energy from before and after the impact. The challenge for COHERENT was to find a material with atomic nuclei large enough for neutrinos to hit easily, but at the same time small enough so they would fill the kick and in consequence have a higher value of the change in energy. In addition, the material had to be transparent so the light could reach the detectors.
The second problem lies in the neutrinos themselves! The theory implies that recoil from a speeding neutrino would be larger, and therefore easier to detect. But if they move too fast, they would have too much energy to interact coherently. So the scientists had to adjust everything so good in order to achieve their goal.
Juan Collar and his colleagues came up with the solution that involved using sodium doped cesium iodide – CsI(Na), a transparent crystal that is an ideal target for the neutrinos which are produced as a by-product by the Spallation Neutron Source. SNS (shortened) is neutron-producing particle collider that also generates a high flux of neutrinos, which enter the COHERENT detector in the SNS basement. However, using the SNS as a source of neutrinos added the third complication. Neutrons have no charge, so they do not show up on electromagnetic detectors, but they do hit nuclei of the material with the same effect as neutrinos do. This occurrence is followed by such big detector noise that it seemed like the SNS would be useless right from the start.
Fortunately, there is always a guy who doesn’t just agree with the failure. The professor of particle physics Yuri Efremenko discovered that a basement hallway (beneath the SNS collider) can be used for placing the neutrino detector. Despite being close to the neutron source (20m), it happened to be shielded by a dense layer of dirt and therefore it represents a perfect spot for the detector.
As regards the neutrino detector, this new model will be of great benefit to researchers. Because supernovae release 99% of their energy as neutrinos, the discovery will open a door to new supernova research as well as searches for dark matter, and even nuclear non-proliferation monitoring.
The story about the new detector is just the tip of the iceberg. There is a lot more mysterious stuff to come when it comes to neutrinos from supernovae!
If you find this story interesting, you may enter HERE and read the full paper.