Effective equivalent dose

The effective dose equivalent (M ) is the formulation for the weighted dose equivalents in irradiated tissues or organs stipulated in 1977 by the International Commission on Radiological Protection [ICRP (1977a)]. He is based on an ICRP analysis of the risk information in the 1977 report of the United Nations Scientific Committee on the Effects of Atomic Radiation [UNSCEAR (1977)]. The formulation is given in Table 1.1, where Wi is the weighting factor for the relative radiosensitivity of the tissue and H-y is the dose equivalent in the irradiated tissue or organ. 

The Wt values used in the formulation for He take into account only the mortality risks from cancer and the risk of severe hereditary effects (in the first two generations) associated with irradiation of the different tissues and organs. He is, therefore, a limited measure 

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NRC. 1992. Residual radioactive contamination form decommissioning Technical basis for translating contamination levels to annual total effective dose equivalent. Washington, DC Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission. NUREG/CR-5512. 

D.5.3 Effective Dose Equivalent and Effective Dose Equivalent Rate... 

Table D-4. Weighting Factors for Calculating Effective Dose Equivalent for Selected Tissues...

Vanmarcke, H., A. Janssens, F. Raes, A. Poffijn, P. Berkvens, and R. Van Dingenen, On the Behavior of Radon Daughters in the Domestic Environment and Its Effect on fht Effective Dose Equivalent, this volume (1987). 

A survey of the radon concentrations in a representative sample of more than 2000 dwellings in the UK has been completed and provisional results are now available. On average, concentrations are 29% lower in bedrooms than in living areas. The mean radon concentration weighted for room occupancy is 22 Bq m 3. Assuming an equilibrium factor of 0.35 and a mean occupancy of 75%, the mean annual exposure in UK homes is assessed as 0.08 Working Level Months (WLM) and the mean annual effective dose equivalent as 0.43 mSv. 

The average annual effective dose equivalent received by a member of the UK population is currently estimated to be 2150 ySv. Of this total, 87% arises from exposure to radiation of natural origin, the largest single contributor being inhalation of the short-lived decay products of radon. This exposure occurs predominantly in the home. 

In order to compare exposures to radon decay-products with those to other forms of ionising radiation, it is useful to assess the effective dose equivalent expressed in sieverts (Sv). A conversion coefficient of 15 Sv per J h m"3, equivalent to 5.5 mSv per WLM, has been recommended (UNSCEAR, 1982). With this conversion factor, the... 

This value of 0.43 mSv for the average annual effective dose equivalent for the UK as a whole is somewhat lower than the currently used value of 0.70 mSv (Roberts and Hughes, 1984). The difference arises partly from taking into account the lower exposure in bedrooms revealed in the national survey. Another reason is that no allowance is made in this survey (Table 2) for exposure received during the 15% of the time spent indoors at other locations nor while in the open. 

The average concentration of radon in outdoor air in the UK is 2.6 Bq m"3. Comprehensive data on the equilibrium factor in outdoor air in the UK is not available. Assuming equilibrium, the average exposure to radon decay products received by a member of the UK population during the 10% of time spent in the open is 0.0036 WLM, an annual effective dose equivalent of 0.02 mSv. 

On the basis of a conversion coefficient of 5.5 mSv WLM"1, occupants of the vast majority of dwellings in the UK receive annual effective dose equivalents less than 2 mSv. Even in the areas surveyed because of their potential for high radon exposures, the annual effective dose equivalents are unlikely to exceed a few tens of mSv. However, in certain areas of Cornwall and Devon, annual effective dose equivalents higher than 25 mSv may be received in a small percentage of dwellings. In some dwellings more than 50 mSv per year may be received. 

It is noted that the ICRP has assumed a higher conversion coefficient between annual effective dose equivalent and radon concentration (ICRP, 1984) in recommending an action level for remedial measures in homes, i.e. 1 mSv y"1 per 10 Bq m"3 of equilibrium equivalent radon gas concentration (9 mSv per WLM). If this conversion coefficient were applied to our regional survey data, we would estimate, from the distribution parameters given in table 3, that about 15% of the residents of certain areas of Devon and... 

Cornwall receive more than 25 mSv effective dose equivalent per year. 

Indoor air radon concentrations measured in a randomly selected sample of 220 Irish houses have been found to range from about 20 Bq/nr to as high as 1740 Bq/nr with a median value of 61 Bq/nr. Using current dose estimation methods the estimated effective dose equivalents due to radon daughter inhalation in these houses are 1.6 mSv/year (median value) and 46 mSv/year (maximum value). 

In the radon surveys the primary quantity determined is the indoor air mean radon activity concentration. From a radiological health perspective it is the dose arising from the inhalation of radon daughters that is of interest. The conversion from radon exposure to annualised effective dose equivalent for the survey was carried out using the factors given in Table I which are similar to those being used in other European surveys. The occupancy and equilibrium factors given in this table are assumed mean values for Irish... 

The results for the first phase of the national survey are also presented in histogram form in Figures 1 and 2 together with the annualised effective dose equivalents estimated using the factors given in Table I. It is evident from the data that in the majority of households surveyed the radon concentrations and associated doses are low. In a small percentage of cases however individual households have been found with very high radon... 

Vanmarcke, H., Janssens, A., Raes, F., Poffijn, A., Berkvens, P. and Van Dingenen, R., On the Behaviour of Radon Daughters in the Domestic Environment and its Effects on the Effective Dose Equivalent. Presented at ACS Symposium on Radon and its Decay Products, New York (April 1986). 

Then the unattached fraction was calculated in each measurement and was found to be between. 05 and. 15 without aerosol sources in the room and below. 05 in the presence of aerosol sources. The effective dose equivalent was computed with the Jacobi-Eisfeld model and with the James-Birchall model and was more related to the radon concentration than to the equilibrium equivalent radon concentration. On the basis of our analysis a constant conversion factor per unit radon concentration of 5.6 (nSv/h)/(Bq/m ) or 50 (ySv/y)/(Bq/m3) was estimated. 

The fraction of unattached daughters (fp), the equilibrium factor (F) and the activity median diameter (AMD) are plotted in Figure 6 for all the measurements. The AMD is derived from the aerosol measurements. These three parameters are important in the dosimetric models. At the top of Figure 6 the effective dose equivalent is plotted, computed with two models called the J-E (Jacobi-Eisfeld) and J-B (James-Birchall) models in the NEA-report (1983, table 2.9, linear interpolation between AMD=0.1 and 0.2 ym). The figure also shows the effective dose equivalent calculated from the equilibrium equivalent radon concentrations with the NEA dose conversion factor (NEA,1983, table 2.11). 

Figure 6a. Evolution of the activity median diameter (A.M.D.), the equilibrium factor (F), the unattached fraction and the effective dose equivalent (AJ-B, V J-E, + NEA) during the case studies.

Figure 7. Effective dose equivalent per hour and per unit radon concentration (AJ-B, 7 J-E) as a function of the equilibrium factor. The full lines are calculated with the mean values of the 72 measurements (Xa -. 37/h, XVent . 41/h, P -. 53, A.M.D. —. 15 lJm) and changing attachment rates.

Figure 9. Effective dose equivalent per hour and per unit radon concentration (A J-B, V J-E), equilibrium factor ( ) and unattached fraction (o, right ordinate) versus the attachment rate. The curves are calculated as in Figure 7.

The risk of lung cancer from exposure to radon daughters in homes is derived by assessing lung dose, either absolutely by evaluating an effective dose equivalent (UNSCEAR, 1982 NEA, 1983) or by scaling the... 

It is to be noted that the conversion factor of 20 mSv effective dose equivalent per 200 Bq m 3 equilibrium equivalent radon concentration, considered by the ICRP (ICRP, 1984) in recommending an Action Level for remedying high indoor radon concentrations, corresponds to a dose rate of about 40 pGy per y per Bq m 3 radon gas concentration. 

Effective dose equivalent. If it is assumed that the weighting factor for bronchial dose equivalent is 0.06, the unattached fraction of potential alpha-energy in room air is typically about 570, and that the aerosol AMD is typically 0.12 pm (Reineking et al., 1985), the... 

Jacobi, W. and K. Eisfeld, Dose to Tissues and Effective Dose Equivalent by Inhalation of Radon-222, Radon-220 and their Short-lived Daughters, GSF Report S-626, Gesellschaft fur Strahlen-und Umweltforschung, Munich-Neuherberg (1980). 

The calculation of effective dose equivalent is sometimes used even when reporting values for natural radioactivity. The concept of effective dose equivalent was developed for occupational exposures so that different types of exposure to various organs could be unified in terms of cancer risk. It is highly unlikely that the general population would require summation of risks from several sources of radiation exposure. 

The normal or average risk from whole body gamma-ray exposure in the environment is only about 10% of that from average radon daughter exposure and much less in elevated indoor environments. Considering that the radon daughter lung cancer risk can be derived directly from exposure in most cases, effective dose equivalent is an unnecessary step. 

Before standards for indoor exposure to radon can be formally established, work is necessary to determine whether remedies are feasible and what is likely to be involved. Meanwhile, the Royal Commission on Environmental Pollution (RCEP) in the UK has considered standards for indoor exposure to radon decay products (RCEP, 1984). For existing dwellings, the RCEP has recommended an action level of 25 mSv in a year and that priority should be given to devising effective remedial measures. An effective dose equivalent of 25 mSv per year is taken to correspond to an average radon concentration of about 900 Bq m 3 or an average radon decay-product concentration of about 120 mWL, with the assumption of an equilibrium factor of 0.5 and an occupancy factor of 0.83. 

Annual effective dose equivalent to humans from natural sources of ionizing radiation... 

Annual effective dose equivalent from nuclear weapons testing to humans in the north temperate zone... 

Table 32.4 Annual Effective Dose Equivalent to Humans from Natural Sources of Ionizing Radiation...

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