Vibrational properties of Pu and Ga in a Pu-Ga alloy from neutron-resonance Doppler spectroscopy

Abstract

We have determined some of the phonon spectral parameters for Pu and Ga in the ''stabilized'' ␦ phase ͑fcc͒ of the Pu-3.6 at. % Ga alloy by measuring the Doppler broadening of neutron resonances as a function of temperature. We find the mean phonon energy ͑first moment of the phonon spectrum͒ of Pu to be ͗h͘ ϭ8.22Ϯ0.12 meV and the second moment to be ͗(h) 2 ͘ϭ(7.2Ϯ0.3)ϫ10 Ϫ5 eV 2 . These moments and the value of the ͑Ϫ1͒st moment determined from Debye-Waller factors from neutron powder diffraction are consistent with a Debye model with a Debye temperature of 127.2Ϯ1.7 K. For Ga in the Pu-Ga alloy, ͗h͘ ϭ16.3Ϯ1.4 meV, which is slightly larger than the m 1/2 -weighted value of 15.3 meV expected from the value for Pu ͑however, the measured value cannot be distinguished from the latter value within experimental error͒. These results show that Pu-3.6 at. % Ga behaves very much like a Debye solid at ambient pressures and low temperature and that the Ga impurity experiences approximately the same ͑or a slightly stiffer͒ force field compared with the Pu it replaces.

Remote determination of sample temperature by neutron resonance spectroscopy

“…A number of instrument resolution functions have been proposed that are appropriate for time-of-flight neutron sources. Of these, the most popular are those based around the convolution of a Gaussian or pseudo-Voigt function with leading and trailing exponential components [22][23][24][25] or a w 2 function [4,5]. The exponential components of these functions account for the effect of moderation of the neutrons between the spallation source and the moderator; they display a strong energy dependence.…”

“…Doping of a sample with a selected isotope or element therefore offers the opportunity of investigating the atomic environment of the dopant, albeit restricted to those environmental variables to which the neutron resonances are sensitive. In practice, this is limited to the temperature to which the dopant atoms are subjected [1,2]; however, a number of successful studies have been performed investigating characteristics of the phonon spectrum of tightly bound structures [3][4][5].…”

Neutron Imaging at LANSCE—From Cold to Ultrafast

“…Neutron resonance based methods probing the properties of the phonons within a solid and thus connecting nuclear physics with solid state physics [47] were demonstrated at LANSCE in the past, e.g., temperature measurements [48], including during dynamic events [49], or the discrimination between alloying elements being contained in the host matrix or forming nano-clusters [50]. J-PARC [51] and ISIS [42] also have performed neutron resonance temperature measurements.…”

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

“…Eventually, the resonance signal could be precise enough to allow moments of the density of phonon states to be measured in a shocked material, as has been demonstrated statically. 12 Now that the previous NRS results are understood, the technique can be used with more confidence for the wide range of temperature measurements of interest in material dynamics.…”