Table 6.2. Tissue Weighing Factors - STD-1128-98master0167

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

where

= tissue weighing factor for the relevant organ or tissue T

= absorbed dose in the tissue or organ of interest

= the quality factor averaged over the tissue or organ of interest.

The weighing factors are given in Table 6.2, which is taken from 10 CFR 835 (DOE,

1998a). Effective dose equivalent has the benefit that it is additive, and internal and external

radiations can be added numerically to drive an overall estimate of risk.

Table 6.2. Tissue Weighing Factors

Tissue or Organ

Tissue Weighing Factor, wT

Gonads

0.25

Breast

0.15

Bone marrow (red)

0.12

Lungs

0.12

Thyroid

0.03

Bone surfaces

0.03

Remainder(a)

0.30

Whole body(b)

1.00

(a)

Remainder means the five other organs or tissues with the highest dose

(e.g., liver, kidney, spleen, thymus, adrenal, pancreas, stomach, small

intestine, and upper large intestine). The weighing factor for each

remaining organ is 0.06.

(b)

For the case of uniform external irradiation of the whole body, a

weighing factor equal to 1 may be used in determining the effective

dose equivalent.

The methodology of ICRP Publication 26 (ICRP, 1977) has been incorporated into 10 CFR

835 (DOE, 1998a), and into the standard, Radiological Control (DOE, 1999a). The annual

radiation dose limits for DOE and its contractors are presented in Table 6.3.

However, DOE contractors usually establish lower annual administrative control levels,

typically 500 mrem/year.

In practice, it is very difficult to measure the effective dose equivalents specified in

Table 6.3 because it is necessary to know not only the type of radiation but also its energy

and direction. If the flux, energy, and direction of incidence are known, it is possible to

calculate effective dose equivalent using fluence to effective dose equivalent conversion

coefficients presented in ICRP Publication 51 (ICRP, 1987), which presents the effective

dose equivalent as a function of energy for various irradiation geometries. Conversion

coefficients for monodirectional beams of neutrons can be found in an article by Stewart et

al. (1994). Conversion coefficients for photons in various irradiation geometries, including

planar sources, can be found in a report by the Zankl et al. (1994). This will provide more

6-3