TABLE B-13 Properties of the 220Rn decay chain

 

Type of Radiation

Half-Life

Radiation Energies (Move)

Radon-220 (Th)

α

55.6s

6.2883

Polonium-216 (ThA)

α

0.15s

6.7785

Lead-212 (ThB)

β

10.64h

0.331, 0.569

 

γ

 

0.23863, 0.30009

Bismuth-212 (ThC)

β (64%)

60.6m

0.67, 0.93, 1.55, 2.27

 

γ

 

0.7272

 

α (36%)

6.051, 6.090

 

Polonium (ThD)

a

0.298 ms

8.7844

Thallium-208 (ThC')

b

3.053 min

1.796, 1.28, 1.52

 

g

 

2.6146, 0.5831, 0.5107

Lead-208

Stable

 

across the volume of a room because of the short half-life. Consequently, it is difficult to define representative values of 220Rn. Thus, most of the available measurements have been made of the 220Rn progeny rather than 220Rn. The available data for the ratio of PAEC arising from 220Rn decay products to that from 222Rn are summarized in Table B-14. Rannou (1987) has examined the variation of the PAEC(220Rn) as the PAEC(222Rn) changes and found that

PAEC(220Rn) = PAEC (222Rn)0.4 (4)

so that the exposure from the 222Rn progeny increases more rapidly than the 220Rn decay products. Thus, for dwellings with high 222Rn concentrations, it appears

TABLE B-14 Approximate ratio of PAEC for 220Rn progeny to 222Rn progeny at various locations (Schery 1990)

Location

PAEC (222Rn)

PAEC (220Rn)

Italy (Latium), 50 dwellings

1.3

Canada (Elliot Lake), 90 dwellings

0.3

Hungary, 22 dwellings

0.5

Norway, 22 dwellings

0.5

Germany (western), 150 dwellings

0.8

Germany (southwestern), 95 dwellings

0.5

France (Finistere), 219 dwellings

0.3

United States (20 states), 68 measurements

0.6

United States (Colorado), 12 indoor locations

(Martz and others 1990)

0.3

Hong Kong, 10 indoor sites

0.8



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