Measurements of the total charge-changing cross sections for collisions of target gases with a 1-MeV K+ -ion beam

The sum of ionization and charge-exchange cross sections of several gas targets (H2, N2, He, Ne, Kr, Xe, Ar, and water vapor) impacted by a 1-MeV K+ beam are measured. In a high-current ion beam, the self-electric field of the beam is high enough that ions produced from the gas ionization or charge exchange by the ion beam are quickly swept to the sides of the accelerator. The flux of the expelled ions is measured by a retarding field analyzer. This allows accurate measuring of the total charge-changing cross sections (ionization plus charge exchange) of the beam interaction with gas. Cross sections for H2, He, and Ne are simulated using classical trajectory Monte Carlo method and compared with the experimental results, showing good agreement.