Scientists at the G.I. Budker Institute of Nuclear Physics SB RAS (Novosibirsk Institute of Nuclear Physics) and Novosibirsk State University (NSU) are developing unique detectors for the TAIGA gamma-observatory. These will help register gamma-quanta in a previously inaccessible energy range, fr om 100 TeV and higher. The source of these particles is the Crab Nebula. In the future, the INP SB RAS and NSU equipment will make it possible to find new sources and to test the hypotheses of the origin of particles with high energy.
"The universe is a great cosmic accelerator that produces particles with much more energy than the most famous LHC collider in the world.", commented Yevgeny Kravchenko, Senior Researcher at the Institute of Nuclear Physics SB RAS, Head of the NSU Laboratory and Candidate of Physical and Mathematical Sciences. He continued, “If the energy of gamma quanta (photons with high energy) is comparatively small, composed of several tens of GeV, they are registered on special satellites. The flows of these particles are large, but the higher the energy, the smaller the gamma-quanta.
In comparison, the maximum energy of colliding protons at the Large Hadron Collider is 7 TeV, and the energy of gamma quanta that have come to Earth fr om space can be more than 100 TeV. It is assumed they can be born during supernova explosions. Charged particles, mainly protons, are deflected by intergalactic magnetic fields and the field of the solar system itself, in contrast to which neutral gamma quanta retain the direction of motion. Therefore, when we register them on Earth, we can find out wh ere they came from. Entering the atmosphere, the particles give birth to a whole shower of charged particles, that are recorded. Charged particles and gamma quanta interact differently with matter, they can be distinguished from each other using the Cherenkov telescope, which "photographs" the very beginning of the shower. However, at energies of 100 TeV and higher this difference becomes weak.
Sieve for particles. If a high energy atmospheric shower is formed from a proton or a nucleus, it contains a large number of muons, and in the showers from gamma quanta they are for the most part absent. The ability of muons to penetrate through a layer of earth turned out to be a very useful property for astrophysicists. It makes it possible to arrange a kind of sieve from the detector system: the Cherenkov light is recorded by ground-based telescopes and optical stations, and muons are detected by underground detectors. As a result, gamma quanta are reliably released from the common stream. For the system to be effective, approximately 1 to 2 thousand muon detectors each with an area of 1 m2, must be placed on an area of 1 km2. Thus, the most critical requirement is a detector price that is affordable.
New technology. Employees at the Institute of Nuclear Physics SB RAS and Novosibirsk State University developed a technology in which a detector can be made using Russian elements. The cost of this detector is approx. one thousand dollars per square meter. A thousand detectors manufactured using this technology will cost about $1 million, not a large sum for experiments at this level considering the cost for foreign produced detectors can be $20,000 per square meter.
The first in a new area of energy. Participants in the TAIGA project will be the first in the world to register gamma quanta in this area. There is an international project, the CTA (Cherenkov Telescope Array), that is performing similar tasks, noted Yevgeny Kravchenko. "Of course, this is a kind of scientific rivalry." The scientist continued, “We have a significant advantage, CTA is at the project stage, and the first stage of the TAIGA observatory is already operating and we are implementing a scientific program. The planned effectiveness for the observatories is approximately the same, but our approach is much cheaper. Within two years we hope to see signals from the Crab Nebula and this will allow us to observe for the first time events in a new energy field.
Stove, stars and two dogs. The observatory is located in the Tunkinsky Valley, 50 kilometers from Lake Baikal in the Baikal region mountains and forests. The Console is a small house with a wood stove wh ere the detector control system is located. Scientists come for 10 day rotation watch tours. "I will go to Tunku again in June," reported Yevgeny Kravchenko. The watch tasks include following the set of experimental data, monitoring the detectors operation and feeding two dogs.
Irkutsk State University is the primary institution organizing the TAIGA project. The project involves more than ten organizations from Italy, Germany, Romania, Russia, including the Joint Institute for Nuclear Research (Dubna). In 2016 a group from the Institute of Nuclear Physics SB RAS and Novosibirsk State University joined the project including students who participated in the development of detectors. The total contribution from foreign participants exceeded 300 million rubles.