Explanation for Anomalous Shock Temperatures Measured by Neutron Resonance Spectroscopy

TL;DR

This paper investigates why neutron resonance spectrometry measures unexpectedly high shock temperatures in molybdenum, attributing discrepancies to plastic flow and projectile behavior, and provides corrections to align measurements with known material properties.

Contribution

It introduces a comprehensive analysis combining plastic flow calculations and projectile simulations to explain and correct anomalous shock temperature measurements in NRS.

Findings

Plastic flow accounts for 53K temperature increase.

Projectile curvature and acceleration cause 160K apparent temperature rise.

Corrected measurements align with Mo's known properties.

Abstract

Neutron resonance spectrometry (NRS) has been used to measure the temperature inside Mo samples during shock loading. The temperatures obtained were significantly higher than predicted assuming ideal hydrodynamic loading. The effect of plastic flow and non-ideal projectile behavior were assessed. Plastic flow was calculated self-consistently with the shock jump conditions: this is necessary for a rigorous estimate of the locus of shock states accessible. Plastic flow was estimated to contribute a temperature rise of 53K compared with hydrodynamic flow. Simulations were performed of the operation of the explosively-driven projectile system used to induce the shock in the Mo sample. The simulations predicted that the projectile was significantly curved on impact, and still accelerating. The resulting spatial variations in load, including radial components of velocity, were predicted to increase the apparent temperature that would be deduced from the width of the neutron resonance by 160K. These corrections are sufficient to reconcile the apparent temperatures deduced using NRS with the accepted properties of Mo, in particular its equation of state.