MEASUREMENT OF SYMMETRIC CHARGE-EXCHANGE CROSS-SECTION IN HELIUM AND ARGON IN IMPACT ENERGY-RANGE 1-10 KEV

The total (He+,He) and (Ar+,Ar) charge-exchange cross sections have been measured in the energy range 1 keV<Elab<10 keV, using the condenser-plate method. Special emphasis was placed on accurately controlling and measuring the target gas pressure, and this resulted in an uncertainty of less than 0.5% in the relative values of the cross section and 2.5% in their absolute values. The measured cross sections fit the expression ( sigma )12/=k1-k2 ln nu to within the experimental errors, and no oscillatory behaviour was observed. The cross section for (He+,He) has been calculated in the JWKB approximation using published 2 Sigma g+ and 2 Sigma u+ potential curves. The calculated and experimental values agree within 10%. The experimental data have been analysed in order to obtain the cross section for electron loss in neutral (Ar,Ar) collisions, and this cross section was found to increase monotonically from (0.39+or-10%) *10-16 cm2 at 1.5 keV to (2.47+or-10%)*10 16 cm2 at 10 keV.