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RE: air filters and radon daughters
To
all:
During the "Fallout" period the then Center for
Radiological Health (CRH), Public Health Service, later the
Environmental
Protection Agency, used to gather information on the amount of
"radioactivity" in the atmosphere (air). They would first remove the
'filter' and then hold it for about 5 hours and then measure
it. The 'filters' would be sent to CRH to do a second count
after three days and again after 7, days a third count. The 5 hours were
to eliminate the very short-lived radionuclides and the 3 days ~75%
of
them.
The original count was done using a beta chamber attached to a survey
meter. The second and third counts on a low-background beta counter.
When EPA took over this surveillance, the 'fallout' had diminished, they
required counting at 5 hours,
and
again, 29 hours, whereby most of the radon and thoron daughters had
decayed. The counting was done on the same instrumentation. This
information could at one time be found
in
Radiological Data and Reports and later by the EPA in Radiation Data
Reports.
Ed
Baratta
E-Mail: ebaratta@ora.fda.gov
.
In a message dated 11/29/01 11:00:19 AM
Pacific Standard Time, blc+@PITT.EDU writes:
If there is a problem with high exposures, people can stay
away from the filter for an hour after the air flow is cut off; that
will
allow most of the radon daughters to decay away.
Radsafe:
The short-lived radon
daughters collected on any air filter have an approximate half life of about
30 minutes. An hour would reduce activity by a factor of about 4 and
that would meet the comment by Dr. Cohen about "most" [ie: about 75%] of
radon daughter activity having decayed away. Most but not all.
I
recall in rounting REMP programs in counting environmental particulate air
sampling filters for long-lived beta activity, the EPA recommended that
filters be counted after 24 hours of daughter product decay, a time when
essentially all the particulate radon daughters from the original sampling
would have decayed away allowing only long-lived beta activity to be counted.
Stewart Farber
email: SAFarberMSPH@cs.com
=====