Vibrational Properties Of Pu And Ga In A Pu-Ga Alloy From Neutron-Resonance Doppler Spectroscopy

We have determined some of the phonon spectral parameters for Pu and Ga in the ''stabilized'' delta phase (fcc) 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 spectrum) of Pu to be [hv] = 8.22 +/- 0.12 meV and the second moment to be [(hv)(2)] = (7.2 +/- 0.3) x 10(-5) eV(2). These moments and the value of the (-1)st moment determined from. Debye-Waller factors from neutron powder diffraction are consistent with a Debye model with a Debye temperature of 127.21 +/- 1.7 K. For Ga in the Pu-Ga alloy, [h v] = 16.3 +/- 1.4 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 error). 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 stiffer) force field compared with the Pu it replaces. [S0163-1829(98)04538-X].