Measurement of the Pauli susceptibility of sodium and lithium

The Pauli susceptibility ${\chi }_P$ of sodium and lithium was measured by the magnetic resonance method of Slichter and Schumacher. Analysis of the experiment in terms of linear response theory has established the validity of the method on very general grounds, requiring only that the spectrum of internal fluctuations be independent of the external field, a condition confirmed by detailed analysis of our data. Improved apparatus and data analysis resulted in significantly greater precision than in previous applications of the method. The results are ${\chi }_P=(1.092\mathrm{}\pm 0.012)\times {10}^{-6\mathrm{}}$ cgs volume units for sodium at 77 K and ${\chi }_P=(2.165\mathrm{}\pm 0.039)\times {10}^{-6\mathrm{}}$ cgs volume units for lithium at 295 K. These are in reasonable agreement with recent theoretical calculations and with values of ${\chi }_P$ inferred from other measurements.