Table 6.1. Effective Depth of Tissue for Various Organs

DOE-STD-1128-98

Table 6.1. Effective Depth of Tissue for Various Organs

Depth of Tissue mg/cm2 .

Deep (penetrating)

1000

Lens of eye

300

Shallow (skin)

6.1.1

Limiting Quantities

Recently, DOE has made significant changes in the methodology used for

radiation protection. Previously, DOE used the concept of dose equivalent. For

whole body irradiations, dose equivalent was the product of absorbed dose

multiplied by the quality factor, which was evaluated by Monte Carlo

calculations in a cylindrical phantom of 30-cm diameter and 60-cm height. For

monoenergetic neutrons or photons normally incident on the phantom model, the

dose equivalent was the highest value calculated anywhere in the phantom. Dose

equivalent was non-additive because the maximum values occur at different

depths in the phantom for different energies. A detailed explanation of the

calculations can be found in an article by Auxier et al. (1968).

In 1977, the ICRP introduced a major revision in recommended radiation

protection with the introduction of ICRP Publication 26 (ICRP, 1977). The new

methodology establishes a "risk-based" system of dose limitation. The ICRP

introduced the terms stochastic and nonstochastic for radiation effects and set

limits for both types of effect. Stochastic effects are defined as those for which

the probability of the effect occurring (as opposed to the degree or severity of

effect) is a function of radiation dose. Nonstochastic effects were defined as

those for which the severity of the effect is a function of the dose; a threshold

may exist. Limits were established such that the risk of stochastic effects

occurring was equivalent to about the same risks faced by workers in "safe"

industries who were not occupationally 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.

The ICRP specified in Publication 26 that radiation exposure be limited by the

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

H E = ∑ w TD TQ T

(6.10)

6-2