Anomalous penetration of Cs, Ba and Tl through thin Si films

Abstract Proton backscattering studies of 0.1 mol/L aqueous solutions of CsNO 3 , Ba(N0 3 ) 2 and TlNO 3 , at atmospheric pressure, have been made through thin (⪅ 0.8 μ m) Si windows. In all three cases, the heavy element (Cs, Ba or Tl) was observed to penetrate the Si window and the maximum concentration was centred about the beam position. This can be understood by assuming that mupores of ≈ 100 A radius occupy 0.01% of the window area. For thicker windows (⪅ 0.9 μ m) the effect does not occur.