Concentration of Rn-222 in upholstery foam

[Bob-O-Rama]

So after abandoning lead shielding entirely to eliminate competing lead signals, using just a Sn-Cu shield, I finally got the first confirmation that an upholstery foam ( chair seat cushion in this case ) can sequester hundreds of times the concentration of radon in the surrounding air. Here is a baseline for the shielded probe with similar sized foam sample that showed intermittent surface contamination on a mica window G-M counter.



This is from a 27cc ( non-compressed, at rest volume ) sample of foam exposed to ambient radon in the workplace for probably 3 years.



For both samples, the entrapped gasses in the cells of foam sample were purged with CO2. The samples were isolated in hermetically sealed containers under CO2 to exclude "new" radon from sneaking in. Then the samples rested for > 24 hours to let the existing Pb-214 and Bi-214 decay out. The NORM peaks from Bi-214 / Pb-214, a tiny peak at around 46 keV - so Pb-210, and a strong Pb XRF peak entirely absent in the control foam. This suggests significant radon is adsorbed into the foam. So how much radon? IDK, but based on the excess counts for the Bi-214 and Pb-214 peaks, at least 400x the action level for radon in air, on a volumetric basis.

[Sesselmann]

Bob,

Interesting result, I assume both recordings were the same length in time, if so how long.

Did you try background subtraction?

Where are these foam cushions/ chairs stored, are they in a basement?

Steven

[Bob-O-Rama]

The BG above was only the first 3 hours, but it ran for 25 hours total.



The sample run was 12 hours, with subtraction of the above I get:



"This is my first rodeo" but on some level the BG subtraction results don't make sense to me yet. PRA seems to hide the "negative" counts - which to me would be equally as interesting.

[Sesselmann]

Yes PRA hides negative numbers, but if you do the same with Impulse you will see negative as well.