The possibility that neutrinos interact coherently with the nucleus of an atom was first theoretically described in 1974 - and now physicists report the first observation of such an event. Coherent elastic neutrino-nucleus scattering (CEνNS) has been proposed as a valuable means to probe the properties of neutrinos, particles with particularly small mass relative to others. As well, CEνNS could yield useful technological applications, such as non-intrusive nuclear reactor monitoring. The ability to directly observe neutrinos scattering upon impact of an atom's nucleus has eluded scientists for several reasons, including the technological difficulty in detecting the extremely low-energy recoil of the nucleus, the single outcome of the interaction. To detect CEνNS, Dmitri Akimov and colleagues turned to a specialized basement alley within the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory, which was bolstered with more than 12 meters of additional materials, such as concrete and gravel, to block out interference with other particles. The scientists then exposed the neutrinos to a sample of sodium-doped cesium iodide, which contains ideal-sized nuclei and which generates a sufficient flash of light for the detection of the nuclear recoil upon impact. Their data were taken over the course of 15 months, and adjusted for interactions with other particles. Akimov et al. report that CEνNS behaves as physicists have long suspected.
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Science