Personal dose equivalent for

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

Use of Personal Dose Equivalent for a Strongly-Penetrating Radiation Value Determined with One Personal Monitor as a Sxurogate for Effective Dose Equivalent or Effective Dose... 

It is not practical in the work environment to measure the absorbed doses in the various organs and tissues necessary to compute He or E directly. Therefore, a number of quantitative relationships between He or E and various field or operational quantities have been developed and are available in the literature. The operational quantity named personal dose equivalent, HJ d), has been developed for the purpose of personal monitoring (ICRU, 1992), where d is the depth below a specified point on the body. For strongly-penetrating radiation, a depth of 10 mm is employed and the quantity is then specified as H iVS). The relationship between He or E and /fp(lO) is the most practical for use in determining He or E to workers for external exposure to low-LET radiation. 

For the purpose of demonstrating compliance with dose limits, the sum of the personal dose equivalent from external exposure to penetrating radiation in the specified period and the committed equivalent dose or committed effective dose, as appropriate, from intakes of radioactive substances in the same period shall be taken into account. 

This quantity is defined by the ICRU, not by the ICRP, and is used mainly for operational aims in measurement of the radiation impact together with the quantities of directional dose equivalent and personal dose equivalent (see description of equivalent dose). The quantity ff (d) at a point in the radiation field is defined as the dose equivalent that would be produced by the corresponding aligned and expanded field in the ICRU-sphere at a depth d on the radius opposing the direction of the aligned field. The depth d = 10 mm is recommended for strongly penetrating radiation such as y- or neutron radiation. 

A particular set of values for tissue doses does not lead to the same numerical value for He and E. For example, assume a case in which the body is partially irradiated, the exposure is primarily to the chest, and the tissue doses are breast, 2 mSv lungs, 1 mSv active bone marrow, 0.2 mSv skin, 0.2 mSv other specific tissues and remainder tissues, negligible. The resulting values are He = 0.44 mSv and E = 0.25 mSv. For this reason, one cannot directly compare previous numerical values of He to current numerical values of E. Note also that a personal monitor located on the front at the chest would have indicated a dose equivalent in excess of 2 mSv, which is an overestimate of either or E. 

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. 

For many situations where protective aprons are worn, the exposure is primarily to the front of the individual. Under these circumstances, a personal monitor located under the apron on the trunk of the individual indicates the dose equivalent to the shielded trunk of the body, and unshielded parts of the body may receive higher exposure. A monitor located outside and above the apron indicates the dose equivalent to the unshielded parts of the body. 

Figure 3.1 reproduces the conversion coefficients provided in ICRU (1988) for FrE/[ 3fp(10)]. For these conversion coefficients, i p(10) was approximated by the dose equivalent at a depth 10 mm along an appropriate radius (i.e., the central axis) in the ICRU sphere (ICRU, 1988). Conversion coefficients are given for personal monitors located on the body at the center of the chest (i.e., the front) or the center of the back (i.e., the back) for the following irradiation geometries ... 

Fig. 3.1. Ratio of He to as a function of photon energy. ffp(lO) is approximated by the dose equivalent at depth 10 mm along the central axis in the ICRU sphere (ICRU, 1988). Five geometries and two locations for the personal monitor are considered in the calculations (see Section 3.1) (adapted from ICRU, 1988 and reproduced with permission).

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. 

USE OF PERSONAL MONITORS TO ESTIMATE EFFECTIVE DOSE EQUIVALENT AND EFFECTIVE DOSE TO WORKERS FOR EXTERNAL EXPOSURE TO LOW-LET RADIATION... 

Use of personal monitors to estimate effective dose equivalent and effective dose to workers for external exposure to low-LET radiation, p. cm.—(NCRP report no. 122)... 

This Report is one of the series developed under the auspices of Scientific Committee 46, a scientific program area committee of the National Council on Radiation Protection and Measurements (NCRP) concerned with operational radiation safety. The Report provides practical recommendations on the use of personal monitors to estimate effective dose equivalent (Hg) and effective dose (E) for occupationally-exposed individuals. The Report is limited to external exposures to low-LET radiation. Recent additions to the radiation protection literature have made the recommendations possible. In order to avoid delay in utilizing the recommendations in the United States, the quantity as well as E, has been included until such time as the federal radiation protection guidance and associated implementing regulations are revised to express dose limits in E as recommended by the NCRP. 

Use of Personal Monitors to Estimate Effective Dose Equivalent and Effective Dose to Workers for External Exposure to Low-LET Radiation (1995)... 

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. 

As regards the dietary intake of radionuchdes, the average exposure of an adult amounting to approximately 1.7 mCy/year was found in Germany in the 1970s. The amount of 0.2 mGy was accounted for by natural radionuchdes (mainly and C). The total intake of radionuchdes °Sr and Cs was in units of Bq per person per day. As a result of the Chernobyl disaster in 1986, the fohowing year-long dietary intake of radionuchdes were 4600 Bq 1760 Bq Cs, 3400 Bq Cs and the total dose equivalent increased by 0.04-0.26 mSv. 

Dosimetry services should be provided for assessing the effective doses (external and internal) received by persons. Effective doses and dose equivalents should be recorded to demonstrate compliance with regulatory requirements. Records of such data make further analyses possible for determining trends and future needs (for further details, see Ref. [22]). 

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