late a dose in tissue in rad (Goetz et al., 1985). The whole-body equivalent dose in rem is then calculated by applying an estimated spectrum-weighted quality factor (QF) of 13 (Goetz et al., 1985); QF accounts for the biological effectiveness of neutrons relative to that of gamma rays in inducing stochastic radiation effects, such as cancer. However, a QF of 8.5 was used for participants at the PLUMBBOB test series (Goetz et al., 1979). The dose to any organ or tissue from external exposure to neutrons is assumed to be the same as the equivalent dose to the whole body.
Energetic electrons are emitted by most fission and activation products and were an intrinsic component of the radiation to which atomic veterans were exposed. Most of the electrons are beta particles, which are electrons emitted as a direct result of a radioactive decay process in which a neutron transmutes to a proton and an electron is discharged. As beta particles from sources outside the body enter tissue, the dose falls off rapidly with depth, and tissues and organs lying deeper than 10 mm in the body are unaffected. Thus, beta particles are appropriately ignored in considering external dose to most tissues and organs, which lie deeper than 10 mm, and for them the appropriate quantities are gamma dose and neutron dose. The two exceptions are the skin, with its sensitive component (basal cells) at a depth of 0.07 mm, and the eye, with its sensitive component (lens) at a depth of 3 mm. The potential contribution from beta particles should be considered whenever the dose to skin or the lens of the eye is assessed.
The current method used in the NTPR program to assess beta-particle doses from sources outside the body is described by Barss (2000). Before 1998, skin doses were not estimated in the NTPR program except on a case-by-case basis (Schaeffer, 2002c). Before the 2000 publication of the Barss report, beta doses were computed by using information from references cited in the publication (Schaeffer, 2002c), principally the user’s manual for the CEPXS radiation transport code (Lorence et al., 1989) and a report that specified the beta and gamma energy spectra as functions of time after a detonation (Finn et al., 1979). Those two references were often cited in the individual beta-dose reconstructions before 2000. Although the data used in calculations have changed, the general method has remained substantially the same since routine assessment of skin dose began in 1998. Accordingly, the Barss report can be considered to generally document the method used in 1998 and 1999 and to present the method used since January 2000.
In the Barss (2000) report, external beta dose from standing on a contaminated surface, from being in contaminated air and water, and from contaminated skin is considered in some detail. The report describes models for calculation and, for the case of external beta dose from standing on contaminated ground, makes numerous comparisons with other methods of calculation and with measurement data. Pertinent information from the report is summarized below.