Cerium Magnesium Nitrate Temperature Scale from Nuclear Orientation

Abstract

Systematic deviations were found below 0.003°K in the temperature dependence of nuclear orientation of ${\mathrm{Ce}}^{137m}$ in cerous magnesium nitrate, using the temperature scale proposed by Daniels and Robinson. The temperature scale below 0.006°K was redetermined using a new method: nuclear orientation. This has the advantage over the $\gamma$-ray heating method of high sensitivity at the lowest temperature. The most striking result is that a value of $\frac{1}{T}$ of 520, rather than the previously accepted 324, is obtained by demagnetization from initial conditions of 18.8 kG ${\mathrm{deg}}^{-1\mathrm{}}$. The useful absolute temperature range is thus extended by at least 60% in $\frac{1}{T}$. Auxiliary experiments on oriented ${\mathrm{Pm}}^{144}$ gave similar results and provided independent confirmation both of the inadequacy of the old temperature scale and of the validity of the new one.