Electron-potassium spin-exchange cross section

A spin-exchange optical-pumping experiment to measure the electron-potassium spin-exchange cross section in a He buffer gas is reported. Electrons are polarized by spin-exchange collisions with optically pumped K atoms. The value of the spin exchange cross section at thermal energy is measured to be (6.8+or-1)*10-14 cm2. The electron-spin resonance linewidths are measured over the temperature range 85-120 degrees C. They fit the theoretical temperature dependence Delta nu (T) varies as P(K)T-32/, indicating that the width of the free electron resonance is caused mainly by spin-exchange collisions.