Quantum oscillations of nitrogen atoms in uranium nitride

TL;DR

This paper reports the discovery of well-defined, high-energy vibrational modes of nitrogen atoms in uranium nitride, resembling quantum harmonic oscillators, with implications for nuclear reactor design.

Contribution

It provides the first experimental observation of nitrogen atom oscillations in uranium nitride, modeled as independent quantum harmonic oscillators, revealing fundamental quantum mechanical behavior.

Findings

Observation of equally-spaced vibrational modes in UN

Spectrum matches that of a quantum harmonic oscillator

Implications for nuclear reactor fuel design

Abstract

The vibrational excitations of crystalline solids corresponding to acoustic or optic one phonon modes appear as sharp features in measurements such as neutron spectroscopy. In contrast, many-phonon excitations generally produce a complicated, weak, and featureless response. Here we present time-of-flight neutron scattering measurements for the binary solid uranium nitride (UN), showing well-defined, equally-spaced, high energy vibrational modes in addition to the usual phonons. The spectrum is that of a single atom, isotropic quantum harmonic oscillator and characterizes independent motions of light nitrogen atoms, each found in an octahedral cage of heavy uranium atoms. This is an unexpected and beautiful experimental realization of one of the fundamental, exactly-solvable problems in quantum mechanics. There are also practical implications, as the oscillator modes must be accounted for in the design of generation IV nuclear reactors that plan to use UN as a fuel.