[ RadSafe ] Field determination of radon progeny

[Stewart Farber]

Hi Mike,
Regarding your question. There are many fine points about the behavior of radon, and background variations related to rainfall, snow cover, ground freeze, etc. Many of these are documented in the literature.

I should have written up the data on rainfall rate, radon daughter washout, and short term gamma exposure rate measurements in the case mentioned as a note to Health Physics at the time [the data was gathered in 1975 or so!!! ].  The data did document an interesting situation. Somewhere, buried in old files are graphs of the variation of background mentioned, plotted along with the rainfall rate. At the time I was acting as staff meteorologist for a central corporate nuclear services division, and also responsible for overseeing environmental rad monitoring at the nuclear plant in question. So continuously monitored rad exposure data measured with a HPIC at the site boundary,   and met data [including rainfall rate] for the same time
 period from a new met tower about 1000' [900 m] away were available, which allowed the relationship mentioned to be clearly seen.

Once used the info mentioned in my prior post  in an Emergency Planning training class to let folks know that you can get short term 75% increases [or perhaps more] in background at any distance from a facility that have nothing to do with a nuclear plant's operation. It is conceivable that such an observation would throw some into a tizzy if there was some report of a problem at the facility and suddenly someone, perhaps dozens of miles away, measured a 75% increase in exposure rate. As an aside, it is possible to infer if the increases in exposure rate at some location are due to airborne plant releases, since the standard deviation of 5 minute averages about the hourly mean generally exceeds a value that is not seen due to other causes.

Stewart Farber, MSPH

Farber Medical Solutions, LLC

Bridgeport, CT 06604



[203] 441-8433 [o]

website: http://www.farber-medical.com

======================

--- On Tue, 4/13/10, McCarty, Mike (DNRE) <MCCARTYM1 at michigan.gov> wrote:

From: McCarty, Mike (DNRE) <MCCARTYM1 at michigan.gov>
Subject: Re: [ RadSafe ] Field determination of radon progeny
To: radsafe at agni.phys.iit.edu
Date: Tuesday, April 13, 2010, 2:39 PM

Stewart

Thank you for your enlightening and detailed posting.  It has given me some things to think about with our systems.  Have you noticed a correlation between the spring thaw and radon emergence?

Our environmental monitoring network collects air samples from around the nuclear power plants in the state.  We wait for three days after sample collection to count the particulate filters for gross beta activity.  This allows the short-lived natural nuclides
 adequate decay time, and yet leaves the longer-lived fission products to be measured if they should be present.  It also doesn't hurt that the usual sample shipping time is a minimum of three days.

When I slid into this position 10 years ago I played with the fresh filter from our local background station just to observe the decay from prompt to delayed counting.  That was entertaining--at least from a techno-geek viewpoint.

Mike McCarty
Physicist

517-335-8196

Radiological Protection Laboratory
Michigan Department of Natural Resources and Environment
815 Terminal Road
Lansing, MI  48906
==============
-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu [mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Stewart Farber
Sent: Tuesday, April 13, 2010 2:08 PM
To: radsafe at agni.phys.iit.edu; Eric.Goldin at sce.com
Subject: Re: [ RadSafe ] Field determination of radon progeny

<snip>


Another interesting source of Rn-daughter contamination  that
 might show up at a nuclear plant is that due to rainfall.  I was involved with gathering and reviewing High Pressure Ionization Chamber measurements of exposure rate  near an operating nuke plant 30 years ago. Measurements were being made with a custom built instrument [like the Reuter Stokes 
 RSS-111, which had a 10" diameter sealed sphere, pressurized to 25 atm with Ar, so it was quite sensitive to ionization from x rays
 and gamma rays]. I had a custom unit built because I needed to record data to a tape unit for long-term exposure rate measurements at the site boundary a BWR nuclear plant [only 700' from the turbine]. <snip>

<snip>
This 75% increase in background measured at the time was due to rain washing ["scrubbing"] Rn-daughter particulates from the air column and depositing them to the ground where they caused an increase in exposure rate measured
 by the fixed HPIC. <snip>
Stewart Farber, MSPH

Farber Medical Solutions, LLC
Bridgeport, CT 06604
[203] 441-8433 [office]
website: http://www.farber-medical.com
farber at farber.info