[ RadSafe ] Field determination of radon progeny
Andycgeo at aol.com
Andycgeo at aol.com
Tue Apr 13 14:25:43 CDT 2010
Besides heavy sustained rainfall, frost and icy soil conditions prevent
radon from escaping to the open air and the radon moves to dryer and more
porous parts of the soil pushing more radon indoors.
Andy George
In a message dated 4/13/2010 2:34:38 P.M. Eastern Daylight Time,
hreynolds at energysolutions.com writes:
Also as the soil saturates with water, this will form a radon cap and
inhibit migration from the soil to the air above it. This can cause the
radon to find its way into structures by below ground paths and increase indoor
levels.
Harry Reynolds
ASRSO
ENERGYSOLUTIONS
801-649-2219 Desk
801-349-9036 Cell
-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu
[mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Harry Reynolds
Sent: Tuesday, April 13, 2010 12:30 PM
To: Stewart Farber; radsafe at agni.phys.iit.edu; Eric.Goldin at sce.com
Subject: Re: [ RadSafe ] Field determination of radon progeny
The onset of rain will be accompanied by a drop in atmospheric pressure
which will cause a pressure differential between the soil and the air which
will literally 'suck' the radon out of the soil. This is a relatively short
term effect as the pressure soon equalizes.
Harry Reynolds
ASRSO
ENERGYSOLUTIONS
801-649-2219 Desk
801-349-9036 Cell
-----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 12:08 PM
To: radsafe at agni.phys.iit.edu; Eric.Goldin at sce.com
Subject: Re: [ RadSafe ] Field determination of radon progeny
In terms of the effective half-life of radon daughters on clothing, I
believe the good working value is just about 30 minutes. If clothing measured
contamination drops by a factor of 2 in 30 min, and 4 in 1 hour, it is
almost certainly Rn daughter contamination.
Bi-214 has a half-life of about 20 min, and Pb-214 about 27 min, with a
rough overall effective half life for the Rn-daughter mix of 30 min.
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]. The State of VT had set an annual limit at the site
boundary of only 5 mR/year [0.05 milli-Sv/hr] from plant operations, with
turbine shine being the major factor at only 700'.
I had plotted hourly average radiation exposure rates. I also had gathered
[for another purpose] concurrent data of hourly rainfall rates in mm/hr.
Putting the exposure rate data together with the rainfall rate in mm/hr
some very interesting things became evident.
During the start of initial hours of high rainfall, the exposure rate
increased from 8 uR/hr [0.08 uGy/hr] to about 14 micro-R/hr [0.14 microGy/hr],
an increase in background exposure rate of about 75%, due to ground-plane
deposition of Rn-daughters around the HPIC system located at the site
boundary.
Subsequently, after a few hours the rainfall rate went to almost zero. The
exposure increment began to drop with about a half hour half life,
returning toward 8 uR/hr. Then a few hours of increase and drop of rainfall rate,
and the total exposure rate went up and down concurrent with the rainfal
rate affecting the deposition of Rn daughters. After about 10 hours the
rainfall ended, and the 6 uR/hr [0.06 uSv/hr] increase in background due to
Rn-daughters decayed away, and the total exposure rate returned [with about a
30 minute half-life] to the background of about 8 uR/hr [0.08 uGy/hr] for
that location. Of note, the plant was not operating at the time, so there
was no contribution from N-16 turbine shine, and no plant releases occurring.
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.
So, it is worth being aware that background exposure rates at or near a
nuclear facility [which might be monitored by HPIC or detectors able to
measure slight increases in background] can increase by 75% [or who knows how
much more depending on rainfall rate and average Rn-daughter concentration in
the air mass at the location being measured at that time]. Then the
increase exposure rate above background, not due to plant releases, will decay
away with about a half hour half-life.
Stewart Farber, MSPH
Farber Medical Solutions, LLC
Bridgeport, CT 06604
[203] 441-8433 [office]
website: http://www.farber-medical.com
farber at farber.info
=======================
--- On Tue, 4/13/10, Eric.Goldin at sce.com <Eric.Goldin at sce.com> wrote:
From: Eric.Goldin at sce.com <Eric.Goldin at sce.com>
Subject: [ RadSafe ] Field determination of radon progeny
To: radsafe at agni.phys.iit.edu
Date: Tuesday, April 13, 2010, 10:46 AM
I didn't ever see too much on the actual answer to Rick Hansen's question
on field determination of radon progeny:
I have a question for radsafe:
What are some methods to use in the field to determine if low levels of
radiation detected on a person or clothing is due to radon daughters rather
than radioactive contamination from other sources?
Nuclear plants have a duty to not release people who are contaminated with
licensed radioactive material
(plant-related). So to distinguish between naturally occurring rad
material (i.e. radon progeny) and plant-related noble gases (typically Xe-133),
the worker is typically asked to simply wait for decay. With most radon
progeny having short half-lives (less than 20 minutes), a short decay period
will usually drop the electrostatically bound radon daughters to a
sufficiently low level such that they will pass the whole body contamination
monitors. Anything longer-lived is likely plant-related and therefore requires
documentation, decontamination, investigation, . . . . Of course an
option is to take the clothes and place them on a HpGe detector for a
qualitative evaluation
- if the count room has the time.
Eric M. Goldin, CHP
<Eric.Goldin at sce.com>
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