[ RadSafe ] Pb-210 Accumulation on Supply Fan Filters

[Conway, Ken C]

I have seen this on outside metals. The Pb 210 rusts right into  the metal.  The daughter Po-210 a strong alpha emitter should accompany it. Lead 210 as you describe it is expected.


From the Multi-Agency Radiation Survey and Assessment of Material and Equipment (MARSAME) manual (USEPA, 2009) 
"
Radon progeny tend to become fixed to solid particles in the air. These particles can become attached to surfaces as a result of electrostatic charge or gravitational settling. Air flow through ventilation ducts can produce an electrostatic charge that will attract these particles. A decrease in atmospheric pressure often precedes a rainstorm, which increases the radon emanation rate. Immediately prior to an electrical storm, an electrostatic charge can build up on equipment resulting in elevated radiation levels from radon progeny. Rainfall acts to scavenge these particles from the air, potentially resulting in elevated dose rates and surface activities during and immediately following rainfall.

Pb-210 is a decay product of 222Rn and 238U. The 22-year half-life provides opportunities for buildup 210Pb and progeny in sediments and low-lying areas. As mentioned previously, rain acts to scavenge radon progeny from the air. Areas where rain collects and concentrates can result in elevated levels of 210Pb and progeny over time. In addition, lead is easily oxidized and can become fixed to surfaces through corrosion processes. Rust or oxide films on equipment can be indicators of locations with a potential for elevated background radioactivity."

NCRP 45 states that Pb-210 is present in ground level atmosphere at 1 E-14 uCi/ml. I would expect that air handling devices constantly exposed to such air would accumulate  Pb-210 as discussed in MARSAME. Similarly rain contains ~ 3 pCi/l Pb-210 and is also a potential source( NCRP 77).

This radon daughter washout process is a known and established natural process.


-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu [mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Randy.Redmond at cns.doe.gov
Sent: Monday, February 15, 2016 4:42 PM
To: 'radsafe at health.phys.iit.edu'
Subject: EXTERNAL: [ RadSafe ] Pb-210 Accumulation on Supply Fan Filters

Anyone else run across supply fan filters that have detectable beta-gamma that will not decay away like typical short-lived radon progeny?  Gamma spec shows a large Pb-210 peak.  Our thought process is there is an accumulation of Pb-210 on the filters because of the amount of air being moved and filtered;  the filters remain in use for several years; and the Pb-210 has a 20.4 year half-life.


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Randy Redmond
Y-12 Radiological Control
Radiological Engineering
Randy.Redmond at cns.doe.gov<mailto:Randy.Redmond at cns.doe.gov>
(865) 574-5640 Office
(865) 574-0117 Fax




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