Table 6 -2. Tissue Weighing Factors

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiation Protection in Uranium Facilities

exposed to radiation in the workplace. Limits were also established for nonstochastic effects that prevented

these effects from occurring even if the exposure occurred at the annual limit over the lifetime of the

worker.

For stochastic effects, the ICRP specified in Publication 26 that radiation exposure be limited by

the effective dose equivalent, HE, which can be expressed by the relation:

(6.1)

Table 6-2 lists the weighing factors, taken from 10 CFR 835. Effective dose equivalent has the

benefit that it is additive, and internal and external radiations can be added numerically to derive 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-26 has been incorporated into 10 CFR 835. Table 6-3 lists the annual

radiation dose limits for DOE activities. However, DOE contractors usually establish lower annual

administrative control levels, typically 500 mrem/year or less.

In practice, it is 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

6-2