Explanation of anomalous shock temperatures in shock-loaded Mo samples measured using neutron resonance spectroscopy

Abstract

Neutron resonance spectrometry ͑NRS͒ 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, a discrepancy which we now explain. The effects of plastic flow and nonideal 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 53 K 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, and related experiments, indicated that the projectile was significantly curved on impact, and still accelerating. The resulting spatial variations in load, including radial components of velocity, should increase the apparent temperature that would be deduced from the width of the neutron resonance by 160 K. These corrections are sufficient to reconcile the apparent temperatures deduced using NRS with the accepted properties of Mo, in particular, its equation of state.

Dynamic compression of copper to over 450 GPa: A high-pressure standard

“…The plastic work heating along the Hugoniot can be calculated based upon the waste heat generated along the Rayleigh line by the longitudinal deviatoric stress, s x [42],…”

A Review of Neutron Scattering Applications to Nuclear Materials

“…Besides concentration measurements, the neutron absorption resonances also allow remote sensorless temperature measurements [130][131][132][133][134][135][136][137][138], including the possibility to obtain three-dimensional temperature distributions from tomographic reconstruction [139,140]. As high temperatures, potentially in combination with noninert (oxidizing or reducing) atmospheres, are desirable experimental conditions to investigate nuclear fuels under synthesis/processing or accident conditions, the sensorless temperature measurement via Doppler broadening of nuclear resonances provides an elegant mechanism to measure the sample temperature.…”

Spatially resolved remote measurement of temperature by neutron resonance absorption

“…The higher degree of penetration of epithermal neutrons compared to cold neutrons and their corresponding sensitivity to specific elements and their isotopes is attractive for many applications where other nondestructive methods are not capable of penetrating the samples or cannot differentiate between variousmaterials -such as imaging of high-Z materials mixed within other high-Z materials [27]- [31].In addition to elemental analysis, it has been demonstrated that the temperature of samples can be measured remotely via the Doppler broadening of observed resonance profiles [25], [32]- [39]. This method has been used, for example, to measure phonon spectral parameters [40]as well as to determine the temperature in a shocked metal [36], [38], and has even been suggested for remote tomographic reconstruction of temperature distributions [39]. The challenge of the resonance imaging technique is to detect both position (~100 µm) and time of arrival (~10-100 ns) of individual neutrons at the detection plane.…”

“…On existing beamlines typical flight times for epithermal neutrons are in the range of 10-1000 µs.Multiple events need to be detected for each neutron pulse and accumulated over many neutron pulses in order to acquire adequate counting statistics. To date, some experiments have been conducted with high spectral resolution, but limited spatial informationusing single-pixel detectors, [32]- [38], [40], [41]. In some cases coarsespatial resolutions with comparatively small numbers of pixels were achieved, however the spectral resolution and counting statistics were low due to count rate limitations of those neutron detectors [39], [42]- [44].…”