Not shown was a continual build-up of radioactivity for about two hours, as Radon daughters collected on the filter element, finally reaching equilibrium. The plot shows what happened after the fan was turned off. A classic decay curve was generated, as the collected Radon daughters (Pb-214 & Bi-214) decayed into a longer half-life material (Pb-210). Superimposed are four pseudo plots generated by Aware's MAKDECAY program. The MAKDECAY pseudo plots aid in verifying Radon daughter decays, and percentage due to Thorium.
Thoron gas (Radon isotope from Thorium) has a half-life of just 55 seconds, and decays into Pb-212 (Pb-212 half-life 10.7 hrs.). Since Thoron gas half-life is so much shorter than Radon, if Thoron is present, one can assume Thorium is nearby, and therefore one should focus more attention on close by materials when attempting to reduce Radon and Thoron from living space air. For example, one may decide to paint a cinder block wall with a latex paint to stop Thoron gas from escaping from the block, etc.
Other, man made isotopes (Nuclear Fleas) can be spotted as well. Use MAKDECAY to zero out Radon-Thoron daughters. Also, if a decay plot with two or more decaying materials is loaded into a spreadsheet and a log plot is generated, decay curves with different half-life material can be spotted using a "Feather" analysis. (A single species log plot will generate a straight line. A log plot of two species with different decay curves will generate a plot with two flat segments, corresponding to the two decay curves).
We've added a new program to the MAKDECAY package. It is called 3DECAY.EXE. With it you can generate pseudo decay plots of any isotope or mixtures of isotopes, by supplying 3DECAY.EXE with the halflife of each isotope of interest.
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