Mobility determination of lead isotopes in glass for retrospective radon measurements

• In retrospective radon measurements, the 22-y half life of Pb-210 is used as an advantage. Pb-210 is often considered to be relatively immobile in glass after alpha recoil implanted by Rn-222 progenies. The diffusion of Pb-210 could, however, lead to uncertain wrong retrospective radon exposure estimations if Pb-210 is mobile and can escape from glass, or lost as a result of cleaning-induced surface modification. This diffusion was studied by a radiotracer technique, where Pb-209 was used as a tracer in a glass matrix for which the elemental composition is known. Using the ion guide isotope separator on-line technique, the Pb-209 atoms were implanted into the glass with an energy of 39 keV. The diffusion profiles and the diffusion coefficients were determined after annealing at 470-620 degrees C and serial sectioning by ion sputtering. In addition, the effect of surface cleaning on diffusion was tested. From the Arrhenius fit, the activation enthalpy (H) was determined, which is equal to 3.2 +/- 0.2 eV, and also the pre-exponential factor D-0, in the order of 20 m(2)s(-1). This result confirms the assumption that over a time period of 50 y Pb-209 (and Pb-210) is effectively immobile in the glass. The boundary condition obtained from the measurements had the characteristic of a sink, implying loss of Pb-209 in the topmost surface at high temperatures.

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Radiologi och bildbehandling (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Radiology, Nuclear Medicine and Medical Imaging (hsv//eng)

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