Significant detection of Lead-210 in roof sludge

[Peter (vital1)]

Here is a test of 214 grams of roof sludge collected from a stainless steel mesh rainwater tank inflow filter. It was collected after a rain event passed over the area on the 20th June 2016. The amount of rainfall for the day was 74.5 mm.

There are significant detections of Be-7 and Pb-210 in this sample. The Beryllium-7 was most likely created by spallation in the upper atmosphere, by cosmic rays and solar activity. As there was a 21 day delay between collection, drying, and testing, some of the Be-7 would have decayed.

The source of the PB-210 detection is possibly from a combination of Radon-222 decay daughter washout, and Radium-224 decay. The Pb-212 detection indicates the possible presence of volcanic ash. The Radium-224 is a decay daughter of Thorium-232. Thorium-232 can be released during volcanic activity in volcanic ash, see Th-232 decay chart below.

http://periodictable.com/Isotopes/090.2 ... .full.html

This is a significant detection of Pb-210. I don't have a check source for this region of energy. A very rough estimate is that the Pb-210 activity is ~ 28 Bq/Kg or greater, assuming this type of scintillator has approximately 50% efficiency around this keV region.


Test chart of roof sludge:




There was a small spike in local background levels a day before this rain event occurred.

[Sesselmann]

This is a significant detection of Pb-210. I don't have a check source for this region of energy. A very rough estimate is that the Pb-210 activity is ~ 28 Bq/Kg or greater, assuming this type of scintillator has approximately 50% efficiency around this keV region.

Peter, your 2" NaI(Tl) crystal should give you full absorption for energies under 200 KeV, but the aluminium casing will be attenuating some of the lower energies, especially if you are in the 40-50 keV region. pretty sure Karl Brehwens looked into a calculation for this once.

Interesting anyway to see such a significant peak on the 47k line. There are quite a few papers on Pb210 measurements in the atmosphere.

Steven

[Peter (vital1)]

Steven,

your 2" NaI(Tl) crystal should give you full absorption for energies under 200 KeV

The dynamics of the testing procedure suggest that if you have a sample on and around a scintillator crystal at these low keV energies, the best efficiency you could get would be ~ 50%, as half of the sample radiation would radiate away from the crystal.

Yes, it would be nearly full absorption for the material facing the crystal.

Correct?

It is a significant Pb-210 environmental detection. I posted it because it was a good clean well defined spectrum, and demonstrated what you can be achieved with your Gammaspectacular device. It would be nice to see more environmental tests in this forum.

Theory

The isotopes that decay to Pb-210 must stick to the fine particles on the roof and in the gutters. When you get a large downpour a lot more contaminated material is dislodged. This means that the Pb-210 accumulation in this roof sludge sample probably occurred over a long period. It was not just deposited by the rain event on the 20th.

There was loads more Beryllium-7 that Pb-210 detected. The scintillator crystal is only ~7% efficient around the Be-7 energy area. Some of the Be-7 had already decayed, because it was 21 days from collection to testing

The test shows it is a very good idea to have a good well maintained filter on your water tank inflow. :)

[Sesselmann]

Peter,

There are quite a few people working on testing atmospheric and environmental fallout, including some government departments using the Gammaspectacular, I do invite everyone to participate here. I agree there is more work to be done, and I am sure there will be more discussion around this subject.

Your measurements are always well documented..

Steven