where DLow-LET and DHigh-LET denote the absorbed doses due to electrons and photons of low linear energy transfer (LET) and alpha particles of high-LET, respectively, and 20 is the radiation weighting factor for alpha radiation (ICRP 1991). Equivalent dose is a dosimetric quantity of radiation protection and is of limited utility in health risk assessments because the radiation weighting factor embodies consideration of the relative biologic insults of the different kinds of radiation.

For reference purposes, table 4.5a gives the equivalent dose received by various tissues of adults, assuming an intake of a unit activity of 222Rn dissolved in water. Results are presented for the base case and the bounding cases describing the extent to which radon is assumed to diffuse into the blood vessels and tissue of the stomach wall. The dose to the stomach calculated for these cases can be compared with the values in table 4.4, which were extracted from the literature.

The equivalent doses received by individuals of various ages, assuming an intake of a unit activity of 222Rn in water, is given in table 4.5b for the base-case assumption regarding radon uptake in the stomach wall. These dose values reflect

Table 4.5a

Committed Equivalent Dose per Unit Activity of 222Rn Ingested (S.v Bq-1) in the Adult as a Function of Diffusion Into the Stomach Wall

 

Uptake in Stomach Wall

Organ

No Diffusion

Base Case

Saturated Diffusion

Adrenals

7.8E-10

2.0E-10

3.0E-10

Bladder

3.4E-10

9.9E-11

1.4E-10

Endosteal Tissue

7.0E-09

1.8E-09

2.8E-09

Brain

7.7E-10

2.0E-10

3.0E-10

Breast Tissue

2.8E-10

8.5E-11

1.2E-10

Stomach Wall

8.9E-10

2.4E-08

3.1E-02

Small Intestine

1.2E-09

1.6E-10

3.1E-09

Upper Large Intestine

1.5E-09

1.3E-10

5.5E-10

Lower Large Intestine

2.6E-09

1.7E-10

6.5E-10

Kidneys

4.2E-09

1.2E-09

2.0E-09

Liver

1.1E-09

1.7E-09

2.1E-09

Muscle

5.0E-10

1.4E-10

2.0E-10

Ovaries

3.1E-10

8.7E-11

1.3E-10

Pancreas

8.8E-10

9.3E-11

3.4E-10

Red Marrow

7.2E-09

1.8E-09

2.7E-09

Spleen

6.8E-10

1.4E-10

3.0E-10

Testes

5.8E-10

1.5E-10

2.2E-10

Esophagus

2.8E-10

8.4E-11

1.2E-10

Thyroid

7.6E-10

2.0E-10

2.9E-10

Uterus

3.0E-10

8.6E-11

1.3E-10

Lung

4.7E-10

1.36E-10

1.9E-10

Effectivea

2.1E-09

3.5E-09

3.8E-08

a Sum of weighted equivalent doses (see ICRP 1991).



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