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 G a in the ''stabilized'' delta phase (fcc) of the Pu-3.6 at. % Ga alloy by measuring the Doppler broadening of neutron resonances as a functi on 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 a nd the value of the (-1)st moment determined from. Debye-Waller factor s from neutron powder diffraction are consistent with a Debye model wi th 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)-we ighted value of 15.3 meV expected from the value for Pu (however, the measured value cannot be distinguished from the latter value within ex perimental error). These results show that Pu-3.6 at. % Ga behaves ver y much like a Debye solid at ambient pressures and low temperature and that the Ga impurity experiences approximately the same (or a slightl y stiffer) force field compared with the Pu it replaces. [S0163-1829(9 8)04538-X].