Measurement of the 21Ne Zeeman frequency shift due to Rb-21Ne collisions
  We compared the frequency shift of the 21Ne Zeeman resonance induced by polarized Rb vapor to the shift induced in the 3He Zeeman resonance. The 3He/Rb shift has recently been measured with high precision, permitting the conversion of our differential measurement to an absolute value for the 21Ne/Rb shift. We report a value of K = 31.8 +/- 2.8 for the Rb/21Ne enhancement factor at a temperature of 124.8 +/- 1.9 C. We propose high-precision differential contact shift measurements, the absolute accuracy of which would be limited by the error in the 3He contact shift. 
R.E. Stoner and R.L. Walsworth