Ionisation of atomic hydrogen by 9-75 keV protons

A crossed beam method incorporating time-of-flight analysis and coincidence counting of the collision products was used previously in this laboratory to study H + -H ionisation in the range 38-1500 keV. The same approach has now been used to extend measurements down to 9.4 keV. The authors measured cross sections involve only small uncertainties and, for the first time, permit a detailed assessment of a number of theoretical descriptions of ionisation in slow collisions. Comparison is made with the modulated cross beam measurements of Fite et al.(1960), the only previous measurements which extend down to keV energies. While the agreement is good at 40 keV, the author's measured cross section at 9.4 keV is only about 27% of the value based on the data of Fite et al. This large discrepancy is consistent with an error arising from neglect of secondary electron emission in their experiment.