Deep-dose equivalent

Deep Dose Equivalent or Personal Dose Equivalent for Strongly-Penetrating Radiation... 

Current federal regulations limit the deep dose equivalent based on that part of the body likely to receive the highest exposure. If personal monitor results are not available or the personal monitor was not located at the position of highest exposure, the regulations allow the substitution of surveys and other radiation measurements (NRC, 1991). These requirements strongly influence the current practices in the United States for the number and location of personal monitors on individuals. 

This Section is limited to a general discussion on the number and location of personal monitors eind other devices used to monitor deep dose equivalent. Other devices are commonly used to monitor dose equivalents in the extremities, skin and lens of the eye, for demonstrating compliance with the separate dose limits for deterministic effects in those tissues. These latter devices are not germane to this Report. 

In addition, multiple personal monitors are often used for situations in which a worker is exposed to a nonuniform radiation field, in an attempt to assess the region of the body receiving the highest deep dose equivalent. Approaches to the use of multiple personal monitors vary widely, and the number used and their locations depend on the particular work activity. For example, during work inside a steam generator, where the radiation fields are potentially isotropic, a total of 12 to 14 personal monitors may be placed at specific locations on both the front and the back of the body, and on top of the head. In other work situations, when the radiation field may be relatively directional but variable (e.g., during control-rod drive maintenance in a boiling-water reactor) the individual may wear all of the personal monitors at locations on the front of the body. 

When only one individual monitoring device is used and it is located at the neck outside the protective apron, the reported deep dose equivalent shall be the [//g] for external radiation or 2. When only one individual monitoring device is used and it is located at the neck outside the protective apron, and the reported dose exceeds 25 percent of the limit specified. .., the reported deep dose equivalent value multiplied by 0.3 shall be the [ITe] for external radiation or 3. When individual monitoring devices are worn, both under the protective apron at the waist and outside the protective apron at the neck, the [He] for external radiation shall be assigned the value of the sum of the deep dose equivalent reported for the individual monitoring device located at the waist under the protective apron multiplied by 1.5 and the deep dose equivalent reported for the individual monitoring device located at the neck outside the protective apron multiplied by 0.04. ... 

Provision 1 is a continuation of current practice, but is used only when the reported deep dose equivalent does not exceed 25 percent of the specified limit. Provision 2 comes from application of a previous observation by NCRP (1978c) in conjunction with the proposal by Webster (1989) noted below. The observation was that exposure of the face and neck will exceed the exposure recorded under the apron by factors between 6 and 27. Using the smallest value in the range i.e., a factor of six) and the formula of Webster (1989), the result is the value of 0.3. Provision 3 comes from application of a proposal by Webster (1989) for the use of two monitoring devices, based on the experimental data of Faulkner and Harrison (1988). The proposal of Webster (1989) is discussed in Section 3.3.3. However, more recent information is available from which to derive conversions for both He and E from personal monitor values ofHp(lO). The current NCRP recommendations using this additional information are developed in Sections 3.3.2, 3.3.3 and 3.3.4. 

The dose equivalents in Faulkner and Harrison (1988) and Faulkner and Marshall (1993) were absorbed dose in tissue using a dosimeter placed at or near the surface of the body (NRPB, 1980). This dose quantity can be converted to deep dose equivalent [i.e., //p(lO)] by multiplying by a factor of 1.07 (NRPB, 1990). The original dose equivalents have been modified by this factor and converted to i7p(10) in this Report. 

Deep-dose equivalent (H ), which applies to the external whole-body exposure, is the dose equivalent at a tissue depth of 1 cm (l,000mg/cm2). 

Total effective dose equivalent (TEDE) is the sum of the deep-dose equivalent (for external exposure) and the committed effective dose equivalent (for internal exposure). 

The annual occupational dose limit to an adult radiation worker is the more limiting of (1) total effective dose of 5 rem (0.05 Sv) or (2) the sum of deep-dose equivalent and the committed dose equivalent to any individual organ or tissue, other than the lens of the eye, being equal to 50 rem (0.5 Sv). 

Deep dose equivalent It applies to external whole body exposure and is the dose equivalent at a depth of tissue of 1 cm (1000 mg/cm ). 

The assigned deep-dose equivalent and shallow-dose equivalent must be for the part of the body receiving the highest exposures. These data can be inferred from surveys or other measurements if direct data are not available. 

It is not necessary in every case to sum the external and internal doses if the licensee can show that the internal dose does not contribute significantly. If, for example, the only intake of radioactivity is by inhalation, the total effective dose equivalent is not exceeded if the deep-dose equivalent divided by the total effective dose equivalent, plus an estimate of the internal dose as determined by one of three procedures stipulated in the regulation does not exceed 1, the internal dose need not be added to the external dose. Similarly, unless the amount of radioactivity ingested is more than 10% of the applicable ALI, it need not be included in the total dose equivalent. Most laboratories using radioactive materials at reasonable levels under normal conditions will find that they need only consider external exposures, just as they once did. 

The deep-dose equivalent to the declared pregnant woman and... 

There are two sources of dose that must be considered when calculating a person s dose external dose and internal dose. External dose is commonly measured with a dosimeter worn on the torso. Section 25.3.1 provides more information regarding calculating external dose. External dose is received for discrete intervals of time, such as when a person enters and exits a radiation area. When the person exits the radiation area, they are no longer receiving any external dose. Three different types of external dose are typically measured deep dose equivalent (DDE), shallow dose equivalent (SDE), and the dose equivalent to the lens of the eye (LDE). The SDE and the LDE are measured or calculated specifically to track the dose to the skin and the lens of the eye. For all other body parts, the DDE is used. 

The radiation dose to an embryo/fetus during the entire pregnancy, due to the occupational exposure of a declared pregnant woman, shall not exceed 0.5 rem. Efforts should be made to insure a uniform monthly exposure rate when necessary. The dose to an embryo/fetus shall be taken as the sum of the deep-dose equivalent, and the dose to the embryo/fetus from radionuclides in the embryo/fetus and radionuclides in the declared pregnant woman. 

The Total Effective Dose Equivalent (TEDE) is defined as the sum of the deep-dose equivalent and the Committed Effective Dose Equivalent (CEDE). The deep-dose equivalent is related to ... 

NRC97) UWNR OTM, Health Physics I II, Section I, Definitions, letter e, Deep-Dose Equivalent ... 

The sum of the deep dose equivalent and the committed effective dose equivalent. 

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