Neutrinos from a nuclear reactor are caught by a technique known as coherent scattering

Miniature neutrino detector promises to test laws of physics

Neutrinos from a nuclear reactor are caught by a technique known as coherent scattering

A nuclear power plant in Liebstadt, Switzerland, hosted the CONUS+ neutrino detector.Credit: KietzmannBjorn/Action Press/Shutterstock

Physicists have caught neutrinos from a nuclear reactor using a device weighing just a few kilograms, orders of magnitude less massive than standard neutrino detectors. The technique opens new ways to stress-test the known laws of physics and to detect the copious neutrinos produced in 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 Nature¹.

Challenging quarry

Neutrinos are elementary particles that have no electrical charge and generally don’t interact with other matter, making them extraordinarily difficult to detect. Most neutrino experiments catch these elusive particles by observing flashes of light that are generated when a neutrino collides with an electron, proton or neutron. These collisions occur extremely infrequently, so such detectors typically have masses of tonnes or thousands of tonnes to provide enough target material to gather neutrinos in relevant numbers.

Scholberg and her collaborators first demonstrated the mini-detector technique in 2017², using it to catch neutrinos produced by an accelerator at Oak Ridge National Laboratory in Tennessee. The Oak Ridge particles have slightly higher energies than those made in reactors. As a result, detecting reactor neutrinos was even more challenging, she says. But lower-energy neutrinos also allow for a more precise test of the standard model of physics.

Scholberg’s COHERENT detector was the first to exploit a phenomenon called coherent scattering, in which a neutrino ‘scatters’ off an entire atomic nucleus rather than the atom’s constituent particles.

Coherent scattering uses the fact that particles of matter can act as waves — and the lower the particles’ energy, the longer their wavelength, says Christian Buck, a leader of the CONUS collaboration. If the wavelength of a neutrino is similar to the nucleus’s diameter, “then the neutrino sees the nucleus as one thing. It doesn’t see the internal structure”, says Buck, who is a physicist at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. The neutrino doesn’t interact with any subatomic particles, but does cause the nucleus to recoil — depositing a tiny amount of energy into the detector.