Limiting Quantities

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

Measurements (NCRP). The limits are given in Table 6.1 for the appropriate depths in tissue for

the whole body, lens of the eye, "unlimited areas of skin," forearms, and hands and feet.

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 =G w T D T Q T

(6.10)

6-2