Wednesday, June 15, 2011

More Biological Decay Chain

Besides the name sucking, the Radon Biological Decay Chain (RBDC), see I changed the name from Biological Half Life because that is confusing, has potential. The comparison of decay energy probability of known Radon, which we can't avoid, to other ionizing radioisotopes should be pretty easy to understand. Converting that to counts per minute is a little tricky.

Since we are comparing energy released over time for an isotope, a Radon atom will have one or two measurable counts in the decay chain, but the future counts have to be considered for biological impact. While Radon-222 has a lag of 22.3 years in the last half of the decay chain, the Pb-210 tends to stay in the body, so there is a high likelihood that the final energy in the decay chain will have a biological impact.

Since we are comparing decay energy, we compare to the probable decay energy of the other isotope, Uranium, Cesium, whatever, and few have the total biological decay chain of Radon. Radon has four alpha decays and five beta decays while most other isotopes will have one possibly two during a human life span. The RBDC ratio considers the decay energy, but the counts should be considered since that is the most common way of determining exposure. In the previous post I use the multiplier five. With one or two Radon counts out of nine probable being countable, 4.5 would be the worst case (9/2) with 9 being the best (9/1)case. Rounding to 5 should be reasonably conservative. The two multiplier just allows for normal biological tolerance and background fluctuations.

The 2 multiplier for comparing counts is most likely to be challenged. I include it because it allows for a multitude of uncertainty without pressing reasonable probability limits. One is the biological half life of the isotope. Another the the likelihood of absorption. To make the comparison more accurate, each could be considered resulting in a more complicated evaluation. The idea of the Radon Biological Decay Chain comparison is to simplify things. For the common isotopes that are likely to be fallout from a nuclear incident, it does the job.

Since Radon is naturally occurring and the leading cause of lung cancer in non-smokers, the RBDC ratio may not be all that comforting. The reality though is that life has risks and it is the magnitude of avoidable risk that is in question. Ten times the tested Radon count for most isotopes possibly causes the same risk of natural Radon exposure, remember, this is conservative. At this level other life choices cause more risk, over eating, alcohol, driving, sex you name it, all have equal or greater risk of shortening your life.

I will continue digging, but everything I have seen so far indicates that radiation risk is overly emphasized. Next I may tackle the risks in other forms of energy.

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