case for direct radiation1 from energetic gamma rays or internal irradiation from inhalation or ingestion of cesium-137, it is common to use the term whole-body absorbed dose.

The quantity referred to as dose equivalent (HT) is also used in some dose calculations, for example, for calculating doses to the maximally exposed individual, or MEI2 (USNRC, 1977a) around nuclear facilities (see Table 3.1). Dose equivalent is defined as the absorbed dose modified by a quality factor (QF) that represents the relative biological effectiveness of a radiation type:

HT = D × QF(1)

In the U.S. Nuclear Regulatory Commission’s (USNRC’s) fundamental regulatory radiation protection guidance (10 CFR Part 20, Standards for Protection Against Radiation), QF takes on values of unity (1) for X rays, gamma rays, and beta radiation; 20 for alpha particles, fission fragments, and heavy particles of unknown charge; and 10 for high-energy protons and neutrons of unknown energy.

More recent radiation protection guidance from the International Commission on Radiological Protection (ICRP) defines other dose quantities. These include equivalent dose and effective dose (ICRP, 1991; see Table 3.1).

As radiation protection guidance has evolved over the years, the application of various dose quantities has become more clearly prescribed. For example, as stated in ICRP Publication 103 (2007b):

The main and primary uses of effective dose in radiological protection for both occupational workers and the general public are:

  • prospective dose assessment for planning and optimization of protection; and
  • retrospective dose assessment for demonstrating compliance with dose limits, or for comparing with dose constraints or reference levels.

Thus, effective dose and equivalent dose have been used for regulatory

1 As noted in Chapter 2, direct radiation exposure refers to external whole-body radiation exposure from ionizing radiation emitted by radionuclides in the air, soil, sediments, or water bodies as well as radiation from sources within the site boundary. The latter includes radioactive wastes buried or stored onsite as well as N-16 produced in the turbines of boiling water reactors.

2 MEI is a regulatory construct for assessing compliance with radiation protection standards. It refers to a hypothetical individual who is postulated to receive the maximum possible radiation dose from a facility because of his or her location relative to the facility as well as lifestyle habits.

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