Miniature Neutrino Detector Catches Elusive Particles at Nuclear Reactor

Miniature Neutrino Detector Promises to Test the Laws of Physics

By Davide Castelvecchi & Nature journal

Physicists have caught neutrinos from a nuclear reactor utilizing a tool weighing only a few kilograms, orders of magnitude much less huge than standard neutrino detectors. The method opens new methods to stress-test the recognized legal guidelines of physics and to detect the copious neutrinos produced within the hearts of collapsing stars.

“They finally did it,” says Kate Scholberg, a physicist at Duke University in Durham, North Carolina. “And they have very beautiful result.” The experiment, called CONUS+, is described on 30 July in Nature.

Challenging quarry

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Neutrinos are elementary particles that haven’t any electrical cost and usually don’t work together with different matter, making them terribly tough to detect. Most neutrino experiments catch these elusive particles by observing flashes of sunshine which can be generated when a neutrino collides with an electron, proton or neutron. These collisions happen extraordinarily sometimes, so such detectors sometimes have plenty of tonnes or hundreds of tonnes to offer sufficient goal materials to collect neutrinos in related numbers.

Scholberg and her collaborators first demonstrated the mini-detector technique in 2017, utilizing it to catch neutrinos produced by an accelerator at Oak Ridge National Laboratory in Tennessee. The Oak Ridge particles have barely increased energies than these made in reactors. As a outcome, detecting reactor neutrinos was much more difficult, she says. But lower-energy neutrinos additionally permit for a extra exact take a look at of the usual mannequin of physics.

Scholberg’s COHERENT detector was the primary to take advantage of a phenomenon known as coherent scattering, during which a neutrino ‘scatters’ off a complete atomic nucleus fairly than the atom’s constituent particles.

Coherent scattering makes use of the truth that particles of matter can act as waves — and the decrease the particles’ vitality, the longer their wavelength, says Christian Buck, a frontrunner of the CONUS collaboration. If the wavelength of a neutrino is just like the nucleus’s diameter, “then the neutrino sees the nucleus as one thing. It doesn’t see the internal structure”, says Buck, who’s a physicist on the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. The neutrino doesn’t work together with any subatomic particles, however does trigger the nucleus to recoil — depositing a tiny quantity of vitality into the detector.

Catching sight of a nucleus

Coherent scattering happens greater than 100 occasions as regularly because the interactions utilized in different detectors, the place the neutrino ‘sees’ a nucleus as a group of smaller particles with empty area in between. This increased effectivity signifies that detectors might be smaller and nonetheless spot an identical variety of particles in the identical time-frame. “Now you can afford to build detectors on the kilogram scale,” Buck says.

The draw back is that the neutrinos deposit a lot much less vitality on the nucleus. The recoil induced on a nucleus by a neutrino is similar to that produced on a ship by a ping-pong ball, Buck says — and has till current years has been extraordinarily difficult to measure.

The CONUS detector is made of 4 modules of pure germanium, every weighing 1 kilogram. It operated at a nuclear reactor in Germany from 2018 till that reactor was shut down in 2022. The group then moved the detector, upgraded to CONUS+, to the Leibstadt nuclear energy plant in Switzerland. From the brand new location, the group now stories having seen round 395 collision occasions in 119 days of operation — in line with the predictions of the usual mannequin of particle physics.

After COHERENT’s landmark 2017 outcome, which was obtained with detectors fabricated from caesium iodide, Scholberg’s group repeated the feat with detectors made of argon and of germanium. Separately, final yr, two experiments initially designed to hunt for darkish matter reported seeing hints of low-energy coherent scattering of neutrinos produced by the Sun. Scholberg says that the usual mannequin makes very clear predictions of the speed of coherent scattering and the way it adjustments with various kinds of atomic nucleus, making it essential to match outcomes from as many detecting supplies as potential. And if the method’s sensitivity improves additional, coherent scattering may assist to push ahead the state of the art of solar science.

Researchers say that coherent scattering will in all probability not fully exchange any present applied sciences for detecting neutrinos. But it could possibly spot all three recognized varieties of neutrino (and their corresponding antiparticles) right down to low energies, whereas another methods can seize just one kind. This capability means it may complement huge detectors that purpose to choose up neutrinos at increased energies, such because the Hyper-Kamiokande observatory now beneath development in Japan.

This article is reproduced with permission and was first published on July 30 2025.