Table 4.2

Cumulative Energy of Radiations Emitted in the Decay of 222Rn and Members of Its Decay Series

 

Energy (MeV per 222Rn atom)

 

 

 

Nuclide

T1/2

Alpha

Electron

Photon

Total

Rn-222

3.8235 d

5.49

0.000399

5.49

Po-218

3.05 m

11.5

0.000408

11.5

Pb-214

26.8 m

11.5

0.293

0.250

12.0

Bi-214

19.7 m

11.5

0.952

1.76

14.2

Po-214

164.3 µs

19.2

0.952

1.76

21.9

Pb-210

22.3 y

19.2

0.990

1.76

22.0

Bi-210

5.01 d

19.2

1.38

1.76

22.3

Po-210

138.38 d

24.5

1.38

1.76

27.6

Radon is readily absorbed from the GI tract and distributed among the tissues, in part because of its relative solubility in blood and in tissue. The ratio of solubility in tissue to that in blood is referred to as the partition coefficient. Measurements of the solubilities and partition coefficients of argon, krypton, xenon, and radon have been reported. Considerable data are available on xenon because of its use in assessing blood flow. Data on radon are less plentiful; the work of Nussbaum (1957) is their major source. Data on the partition coefficients of krypton, xenon, and radon are summarized in table 4.3. Of particular note are the higher partition of radon in blood (7 times that of krypton) and its higher partition in adipose tissue. Adipose tissue is the major tissue of deposition of radon that has entered the systemic circulation.

Estimates of Dose from Ingested Radon

The inhalation hazard of radon and its short-lived decay products has long been of concern in occupational radiation protection and public health. Ingestion

Table 4.3

Partition Coefficients of Noble Gases

Organ

Krypton

Xenon

Radon

Blood/air

0.06

0.18

0.43

Adipose tissue/blood

5.50

8.00

11.2

Muscle/blood

1.09

0.70

0.36

Brain/blood

1.13

0.75

0.72

Kidney/blood

0.65

0.66

Testes/blood

0.43

Liver/blood

0.70

0.71

Bone/blood

0.41

0.36

Lung/blood

0.70

0.70a

GI-tract/blood

0.81

0.70a

Other/blood

0.70

a Default values used in analysis.



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