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| DOE-STD-1121-98
A.2 MEASUREMENTS OF THORON PROGENY EQUILIBRIUM FACTORS
Because of thoron's short half-life, measurements of thoron progeny are generally made, rather than
of thoron gas. Thus, equilibrium factors for thoron are less well known, and more research needs to be
done (UNSCEAR 1993). Recommended values for indoors and outdoors are given in Table XIX
(UNSCEAR 1988; UNSCEAR 1993). The outdoor numbers, 0.02 (1988) and 0.01 (1993) are lower than
the 0.04 default number given above, while the indoor numbers, 1/6 and 0.1, are higher than the 0.04
number. Because of this, it is good practice to measure thoron progeny directly when possible.
Table XIX. Thoron (220Rn) Equilibrium Factors
[Country]
avg
sd
min max Reference
Environment
Rec.
Outdoors
recommendation
UNSCEAR (1988)
0.02
recommendation
UNSCEAR (1993) Annex A Para 120
0.01
Indoors - Home
recommendation
UNSCEAR (1988)
1/6
recommendation
UNSCEAR (1993) Annex A Para 120
0.1
130
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