Abstract
Neutron resonance spectroscopy (NRS) has been used extensively to make temperature measurements that are accurate, absolute, and nonperturbative within the interior of material samples under extreme conditions applied quasistatically. Yet NRS has seldom been used in dynamic experiments. There is a compelling incentive to do so because of the significant shortcomings of alternative techniques. An important barrier to adopting dynamic NRS thermometry is the difficulty in fielding it with conventional spallation neutron sources. To enable time-dependent and spatially resolved temperature measurements in dynamic environments, more compact neutron sources that can be used at user facilities in conjunction with other diagnostic probes (such as x-ray light sources) are required. Such sources may be available using ultrafast high-intensity optical lasers. We evaluate such possibilities by determining the sensitivities of the temperature estimate on neutron-beam and diagnostic parameters. Based on that evaluation, requirements are set on a pulsed neutron-source and diagnostics to make a meaningful dynamic temperature measurement. Dynamic thermometry measurements are examined in this context when driven by two alternative fast-neutron sources: the Los Alamos Neutron Scattering Center (LANSCE) proton accelerator driving isotropic spallation neutrons as a baseline and a laser-plasma ion accelerator driving a neutron beam from deuterium breakup. Strategies to close the gap between the required and demonstrated performance of laser-based fast-neutron sources are presented. A short-pulse high-intensity laser with state-of-the-art pulse contrast and an energy of a few hundred Joules would drive a compact neutron source suitable for NRS thermometry that could transform the dynamic study of materials.
Highlights
AND REQUIREMENTSBulk thermometry is a critical and unmet scientific need for the study of the dynamics of materials subjected to transient extreme conditions.[1,2,3] The temperature of a material is an independent thermodynamic variable in the equations of state
Dynamic thermometry measurements are examined in this context when driven by two alternative fastneutron sources: the Los Alamos Neutron Scattering Center (LANSCE) proton accelerator driving isotropic spallation neutrons as a baseline and a laser-plasma ion accelerator driving a neutron beam from deuterium breakup
The resulting fast-neutron spectrum in that custom setup was not reported, as it bears on the moderator design but not directly on thermometry. It likely resembled the one from the Weapons Neutron Research (WNR) facility observed at 90○ presented in Fig. 2 of Ref. 35
Summary
Bulk thermometry is a critical and unmet scientific need for the study of the dynamics of materials subjected to transient extreme conditions.[1,2,3] The temperature of a material is an independent thermodynamic variable in the equations of state. While faster and better resolution helps, the threshold requirement for the project would be internal temperature measurements with ∼100 μm spatial and ∼100 ns temporal resolution With such a measurement coupled with faster surface thermometry and modeling, time-dependent volumetric temperature can be established to the extent necessary to challenge theoretical models. Current dynamic temperature measurements have many drawbacks.[5] They may be able to measure only the surface temperature of a material opaque to optical wavelengths, as in the case of pyrometry.[1,6,7] They may be perturbative as with thermocouples.[8,9] With techniques based on x-ray scattering, such as Thomson scattering,[10] the beam may not penetrate sufficiently into samples that are thick or have high atomic number. The requirements for a source of neutrons generated by an optical laser are determined
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