Radiological Assessment for the Removal of Legacy BPA Power Lines that Cross the Hanford Site Page: 7 of 20
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are being continuously resupplied from the U-238 in the soil.
Many of these charged atoms apparently attach to dust particles, which are then electrically
attached to the wire. The bright copper wire is, after years of service, a shiny black, which is
likely the buildup of dust particles and chemical compounds on the surface of the wire. See
the photo in Figure 5, below. When wire is immediately de-energized, there is a lot of surface
activity that decays very quickly (early radon daughters) leaving activity that decays slowly.
The early, short-lived radon daughters decay quickly to lead-210, which has a 22.2 year half-
life. Lead-210 beta decays to bismuth-210 (5 day half-life), which in turn beta decays to
polonium-210. Polonium-210 has a 138 day half-life and alpha decays to stable lead-206.
Since lead-210 has a half-life of 22.2 years, the activity on the wire decays very slowly and will
remain for many decades.
Similarly, uncharged, weathered metal, particularly rusted metal, also, apparently by chemical
attraction, accumulates natural alpha activity, although not to the level found on electrical
wire. The alpha activity has been found to be Po-210, and there is also an energetic beta
component present. This is also believed to be due to the sequence Pb-210, Bi-210 and Po-
210 to stable Pb-206.
This explanation is consistent with field observations, since bare conducting wire collected
years ago from a background area is still radioactive, and activity on weathered metal is also
long-lived. Also, the alpha radioactivity measured on the wire has been shown to be due to
polonium-210. The alpha detector is also sensitive to high energy beta particles from bismuth-
210 that are present in the spectra measured. See Figure 8, below, and the associated
Thus, in summary, the partial radon decay chain believed to be causing the natural activity is
22.2y 5d 138d
Pb-210 0 Bi-210 0 Po-210 o Pb-206 (stable)
low- 1.16 MeV 5.3 MeV
energy beta alpha
beta 100% 100%
The overall decay rate is determined by Pb-210 at 22.2 years; the observed high-energy beta
particle is supplied by Bi-210; and the alpha particle is supplied by Po-210.
Hanford Inter-Facility Area Contamination Guidelines
Hanford is a large site and much of it is at some distance from contaminated facilities. Within
these areas that are not near a facility, referred to as the inter-facility area, it is possible to
conservatively estimate the relative proportions of natural and Hanford-made activity generally
present. The proportion of gross alpha activity generally measured that is of Hanford origin is
unlikely to exceed 10% in the inter-facility area. Also, since beta activity is not normally limiting,
the proportion of natural beta activity to Hanford-made beta activity is not normally estimated,
and all beta activity is assumed to be from Hanford. Furthermore, 10% of the beta activity is
assumed to be hard-to-detect, that is, not readily detectable with commonly-used field survey
Based on this conservative assessments of the amount of natural, alpha radioactivity present
in the inter-facility area and the amount of hard-to-detect, beta-gamma radioactivity present,
10 Nov 13 Draft
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Millsap, William J. & Brush, Daniel J. Radiological Assessment for the Removal of Legacy BPA Power Lines that Cross the Hanford Site, article, November 13, 2013; Richland, Washington. (https://digital.library.unt.edu/ark:/67531/metadc871756/m1/7/: accessed April 20, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.