THE KINETIC-ENERGY OF LI-7 ABOVE AND BELOW THE MARTENSITIC-TRANSFORMATION

The atomic momentum distribution of lithium-7 in natural Li has been d etermined as a function of temperature from 20 to 300 K. The experimen ts were undertaken within the impulse approximation using the electron volt spectrometer at ISIS. Final state effects were present above the statistical accuracy of our data and were accounted for by symmetrizin g the neutron Compton profiles. The mean atomic kinetic energy of the Li nucleus was obtained directly from our measurements and was found t o be approximately 10% higher than that predicted by a harmonic model incorporating a density of states derived from previous phonon measure ments. A fit of the data to the Debye model gave a Debye temperature o f 419 +/- 3 K.