Spin-polarised hydrogen

State selection and focussing of atoms by magnetic fields has been extensively reviewed over several decades (e.g. Ramsay, 1956 Reuss, 1988 lanotta, 1988), and only a brief description of a source of spin-polarised hydrogen atoms will be given here. 

It has been measured for hydrogen (Fletcher et al, 1985 Crowe et al, 1990) and for lithium, sodium and potassium (Baum et ai, 1985) at incident energies from threshold to several hundred electron volts. The data were obtained by ionisation of polarised target atoms by polarised electrons. The relative total ionisation cross sections for parallel and antiparallel spins were determined by counting the ions, regardless of the kinematics of the final-state electrons. 

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