Fig. 3.

Thermal equilibrium polarization P of spin active noble gas isotopes and a fictitious Kr isotope with spin I = 3/2 obtained from Eq. (A2). (A) Thermal equilibrium polarization curves as a function of temperature displayed at temperatures up to 0.05 K. (B) Semi-logarithmic plot of thermal equilibrium polarization curves as a function of temperature extended out to 3 K. To reach 1% polarization for hyperpolarized samples at 300 K and 9.4 T, the following enhancements are needed when compared to thermally polarized samples for each nuclei: 410 for ³He; 1121 for ¹²⁹Xe; 2373 for ²¹Ne; 2206 for ⁸³Kr; 2270 for ¹³¹Xe; and 4855 for the fictitious isotope with spin I = 3/2 and the same gyromagnetic ratio as ⁸³Kr. For the three quadrupolar isotopes (²¹Ne, ⁸³Kr, ¹³¹Xe) nearly identical polarization curves arise.