Owing to their small mass, hydrogen atoms exhibit strong quantum behavior even at room temperature. Including these effects in first-principles calculations is challenging because of the huge computational effort required by conventional techniques. Here we present the first ab initio application of a recently developed stochastic scheme, which allows to approximate nuclear quantum effects inexpensively. The proton momentum distribution of lithium imide, a material of interest for hydrogen storage, was experimentally measured by inelastic neutron-scattering experiments and compared with the outcome of quantum thermostatted ab initio dynamics. We obtain favorable agreement between theory and experiments for this purely quantum-mechanical property, thereby demonstrating that it is possible to improve the modeling of complex hydrogen-containing materials without additional computational effort.

Background: the gamma-emitting radionuclide Technetium-99m (^99mTc) is still the workhorse of Single Photon Emission Computed Tomography (SPECT) as it is used worldwide for the diagnosis of a variety of phatological conditions. ^99mTc is obtained from ⁹⁹Mo/^99mTc generators as pertechnetate ion, which is the ubiquitous starting material for the preparation of ^99mTc radiopharmaceuticals. ⁹⁹Mo in such generators is currently produced in nuclear fission reactors as a by-product of ²³⁵U fission. Here we investigated an alternative route for the production of ⁹⁹Mo by irradiating a natural metallic molybdenum powder using a 14-MeV accelerator-driven neutron source. Methods: after irradiation, an efficient isolation and purification of the final ^99mTc-pertechnetate was carried out by means of solvent extraction. Monte Carlo simulations allowed reliable predictions of ⁹⁹Mo production rates for a newly designed 14-MeV neutron source (New Sorgentina Fusion Source). Results: in traceable metrological conditions, a level of radionuclidic purity consistent with accepted pharmaceutical quality standards, was achieved. Conclusions: we showed that this source, featuring a nominal neutron emission rate of about 10¹⁵ s⁻¹, may potentially supply an appreciable fraction of the current ⁹⁹Mo global demand. This study highlights that a robust and viable solution, alternative to nuclear fission reactors, can be accomplished to secure the long-term supply of ⁹⁹Mo.

A strong temperature dependence of proton mean kinetic energy was observed for liquid water around the density maximum and for moderately supercooled water. Line shape analysis of proton momentum distribution, determined from deep inelastic neutron scattering measurements, shows that there are two proton kinetic energy maxima, one at the same temperature of the macroscopic density maximum at 277 K, and another one in the supercooled phase located around 270 K. The maximum at 277 K is a microscopic quantum counterpart of the macroscopic density maximum, where energetic balance giving rise to the local water structure is manifest in the temperature dependence of kinetic energy. The maximum in the supercooled phase, with higher kinetic energy with respect to stable phases, is associated to changes in the proton potential as the structure evolves with a large number of H-bond units providing both stronger effective proton localization, as well as proton quantum delocalization.