Re: Radon: Whole Body Dose Rate

[Brian_Gaulke@hc-sc.gc.ca]

Mark M. Hart wrote:

Secondarily,

1) I would like to know the average activity in curies/liter, or kilogram
tissue, once the human body has reached equilibrium with the surrounding 5
nanocurie/liter environment.

2) I would like to know the amount of time that is required for the human
body to reach approximately 90% of true equilibrium when entering the 5
nanocurie/liter environment from a "non-radon" environment.

3) I would like to know whether this is a linear solution that could be
scaled down to 5 picocurie/liter.

Thank you very much for your assistance, in advance.  Some facets of this
analysis require information that I cannot readily access.  I am very
interested in understanding how the answers are derived and the reference
sources/assumptions used.

According to Herman Cember in "Introduction to Health Physics", 3rd Edition,
pages 313-314, the concentration of a gas dissolved in a liquid is proportional
to the partial pressure of the gas above the liquid (Henry's Law):

P(gas) = KN where P(gas) is the partial pressure of the gas above the liquid,
          K is the Henry's Law constant (= 6.5E+6 for radon),
          and N is the mole fraction of the dissolved gas.

N = n(g)/(n(g) + n(s))   where n(g) is molar concentration of the dissolved gas
                    and n(s) is the molar concentration of the solvent.

To answer question 1:

The molar concentration of water is 55.6 moles/litre.

Alternatively, K is the ratio of the partial pressure of the gas in the
atmosphere above the liquid in mmHg to the mole fraction of the gas in solution.

5 nCi/litre corresponds to about 2.66E-12 mmHg partial pressure for Rn-220.

This gives a molar concentration of Rn-220 at equilibrium in water of about
2.3E-17 moles/litre.

This corresponds to about 1200 Bq in a 70 kg man with 43 litres of body fluids,
or an average of about 18 Bq/kg.

Question 3 would appear to be answerable in the affirmative since Henry's Law is
linear.

I can't shed light on question 2.

Brian R. Gaulke, CHP
Head, Dosimetry Section
Radiation Protection Bureau
Health Canada
Brian_Gaulke@hc-sc.gc.ca


************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html