THE EFFECT OF ENERGY AND INTEGRATED FLUX ON THE RETENTION AND RANGE OF INERT GAS IONS INJECTED AT KEV ENERGIES IN METALS

Abstract

Two experimental factors limiting the use of ion-bombardment techniques in atomic range studies have been investigated: namely, the fractional retention of the incident beam, and the target saturation phenomenon. The fractional retention, or sticking factor, has been measured for Xe133 in Be, Al, Ni, Zr, Ag, Ta, W, and Au, and for Ar41 and Kr85 in Al and W, as a function of bombardment energy from 1 to 150 kev. The results indicate that, below about 5 kev, range measurements are of doubtful significance; in some cases, this energy limit for a reliable range measurement is considerably higher than 5 kev. A qualitative interpretation of the observed sticking factors is given. The saturation phenomenon in aluminum has been studied by injecting radioactive Xe in trace amount, either before, after, or during a bombardment with one of the stable Xe isotopes, and measuring the final distribution of the embedded radiotracer. The results provide information on the mechanism of target saturation. Bombardment with 2–3 μg of xenon/cm2 is found to reduce markedly the observed penetration depth of a 30-kev beam, thereby indicating the necessity of trace bombardments for accurate range measurements in this energy region.