Time and Space-Resolved Thermometry Using Neutron Resonance Spectroscopy (NRS): Requirements and Prospects for Laser-Driven Neutron Sources

Neutron spallation sources have enabled localized volumetric (bulk) thermometry of materials based on NRS. Temperature, an independent thermodynamic variable in the equations of state, is needed to validate theoretical models of condensed and warm-dense matter. Yet bulk thermometry of materials under transient extreme conditions is an unmet scientific need due to the difficulty of dynamic measurements and of co-locating dynamic drivers at a spallation facility. Thus NRS thermometry of dynamic materials has been reported only once [1]. Alternatives to NRS have drawbacks or are inapplicable. More compact neutron sources would enable dynamic bulk NRS thermometry. Ultrafast high-intensity optical lasers may deliver such a source. To evaluate such possibilities, we determine the sensitivities of the temperature estimate on neutron-beam and diagnostic parameters. Based on those, requirements are set on a pulsed neutron-source and diagnostics to make a meaningful dynamic measurement. Forward MCNP6 calculations of fast-neutron generation with lasers are discussed. With a high-intensity high-contrast ultrafast laser pulse of sufficient energy (~ a few hundred Joules), a suitable compact neutron source is within reach.

[1] V. W. Yuan, et al., PRL 94, 125504 (2005)