Abstract
In a crossed-beam experiment polarised potassium atoms have been ionised with a beam of polarised electrons. A measurement of the ionisation for the two relative spin orientations yields the asymmetry factor A which is related to the total interference cross section for ionisation. The measurements extend over an energy range from 6 to 80 eV. The measurements of A cannot be compared directly with theoretical results since no calculations of the interference cross section have been made for potassium. However, theoretical values of A for lithium and sodium exist and, when plotted against reduced energy units, it is apparent that for energies less than about five times the ionisation energy, the measurements disagree with theory. At higher energies the agreement is satisfactory.