Re: Radon-222 and Radon-220 (thoron) Measurement and Action Level

[Kai Kaletsch <info@eic.nu>]

I don't think that most passive track etch detectors will pick up thoron.

These detectors often require radon to diffuse through a membrane to get

into the active volume. Thoron would decay before it has a chance to get

into the detector.



Another question is whether a measurement of Rn-220, even if you could get

one, would have any relevance. You want to limit the dose. There are some

arguments that Rn-222 measurements are actually a better indicator of Rn-222

progeny dose than Rn-222 progeny measurements (has to do with where the

unattached fraction of Rn-222 progeny gets trapped in the lung). These

arguments do not apply to the dose from Rn-220 progeny. To get an estimate

of the dose from Rn-220 progeny, you have to measure Rn-220 progeny.



I can't think of a situation where you would be interested in a Rn-220

measurement (except for engineering control), but you might be interested in

a Rn-220 progeny measurement. For example, if you are working 5 minutes

downwind of a pile of thorium ore: There will be very little Rn-222 (none in

the ore) and very little Rn-220 (most of it decayed in 5 half lives), but

you would still get a big dose from Rn-220 progeny (half life ~ 12 hours).



Hope this helps.



Kai Kaletsch

Environmental Instruments Canada Inc.

http://www.eic.nu





----- Original Message -----

From: "Redmond, Randy (RXQ) " <rxq@y12.doe.gov>

To: <radsafe@list.vanderbilt.edu>

Sent: Tuesday, June 25, 2002 4:55 AM

Subject: Radon-222 and Radon-220 (thoron) Measurement and Action Level





> I need a sanity check from the radon experts.  If I place track etch

> detectors in my facility to measure radon-222, the radon-220 (thoron) will

> also be detected and included in my total radon measurement.

> -  Does the EPA action level of  4 picocuries per liter also apply to the

> radon-220?

> -  Any situations where the radon-220 contribution should be separately

> considered?

>

> Randy Redmond

> BWXT Y-12 L.L.C.

> Y-12 National Security Complex

> Radiological Control Organization

> Email:  rxq@Y12.doe.gov

> Phone:  865-574-5640

> Fax:  865-574-0117

>

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