Specific Heat of Sodium at Low Temperatures

Specific heat measurements in the temperature range 0.4° to 1.5°K on two samples of sodium metal are reported. A thermal cycling procedure was used to partly inhibit the martensitic transformation and thus obtain information on the properties of the two phases of sodium. It is concluded that the electronic specific heat coefficient ($\gamma$) of the bcc phase is probably slightly larger than that of the hcp phase but with 95% confidence the difference does not exceed 20%. A statistically significant variation (of unknown cause) of the apparent $\gamma$ of one sample was observed. It is suggested that the wide variation in experimental $\gamma$ values reported may be due to this cause rather than to the martensitic transformation.