Monday, 7 December 2015

Radon is not nearly as scary as the authorities make it out to be.

Under normal circumstances, radon is not a threat to your health. No matter what the EPA tell you. There's no positive correlation between lung cancer rates and the distribution of background radiation. Radon-222 is a decay produce of radium-226, which is a decay product of uranium-238. Radon is a heavy gas which accumulates in homes and offices. According to the EPA it is a huge threat to life. In reality it is not such a big threat. It can easily be demonstrated that the effect of other background radiation on the lungs (e.g. from carbon-14 and potassium-40 decay) greatly exceeds the effect of radon-222 by about 100 to 1. So according to EPA logic there should be 100 times as much lung cancer due to potassium-40 and carbon-14 (compared to their projected radon cancers). There's not. There is no good evidence that, at the low doses found, radon-222 causes any measurable lung cancer. The EPA's worry about radon is based upon a projection of a bad mathematical model.

If anything, a map of the USA shows a negative correlation between radon concentration and lung cancer!

Perhaps better described as a positive correlation between radon concentration and no lung cancer!

For an average 70kg person:

  • Your lungs weigh approximately 1.3 kg; 1.86% of your body.[1]
  • We experience about 8300 Bq of radiation (mostly K-40 and C-14).[2]
  • It follows, our lungs experience about 158 Bq (mostly K-40 and C-14).
  • When doing mild activity, we breath about 14 litre/minute = 2.3 × 10-4
  • US average radon air concentration is 37 Bq m-3 (EPA).[4]
  • It follows that a US citizen's lungs are exposed to 37 × 2.3 × 10-4 = 0.00863 Bq radon

When accounting for the effect of that radon on the body we should assume it follows the main decay chain. That's because the other branches of the decay chain have very low probabilities. The main radon decay chain is shown below. It has 4 alphas in it [5]:

energy (MeV)½-life
Rn-222 → Po-218(alpha)5.593.8235 d
Po-218 → Pb-214(alpha)6.0023.1 min
Pb-214 → Bi-214(beta, gamma)1.02426.8 min
Bi-214 → Po-214(beta, gamma)3.27219.9 min
Po-214 → Pb-210(alpha)7.687164.3 µs
Pb-210 → Bi-210(beta)0.06422.2 y
Bi-210 → Po-210(beta)1.1635.012 d
Po-210 → Pb-206(alpha)5.305138.4 d

To convert to millisievert we need to weigh the decays. I won't convert to millisievert but we will weight radon far more heavily than other natural radiation experienced in our lungs. Comparing the effect of radon with other radionuclides we experience: mostly potassium-40 and carbon-14. When converting from grays to millisievert the weighting is normally:

alphabetagamma
2011

Because the EPA are so worried about radon, I'll assume they must know something I don't. So I will weight it twice and also assume every decay in the main decay chain counts. The main radon decay chain is worth 86 according to normal weighting. 4 alphas, 4 betas, and 2 gammas = 20 x 4 + 4 × 1 + 2 × 1. I'll double that to 172. Let's compare the lung radiation contribution of radon with K-40 and C-14:

radon= 172 × 0.00863= 1.5
K-40 and C-14= 158
The effect of K-40 and C-14 combined is about a hundred times that of radon. [even after I weighed radon twice as much as I should have!]

The following table shows the radioactivity found in a typical adult human body of 70,000 grams (about 154 pounds)[2]:

NuclideTotal MassTotal Activity (Bq)
Uranium90 µg1.1
Thorium30 µg0.11
Potassium-4017 mg4,400
Radium31 pg1.1
Tritium0.06 pg23
Polonium0.2 pg37
Carbon-1420 pg3,840
Total:8,302
Source: Radionuclides in the Ocean

References

  1. Lungs (Wikipedia)
  2. Radionuclides in the Ocean
  3. Radon decay chain
  4. Radon (Wikipedia)
  5. Radioactive series of radium-226
  6. EPA: The National Radon Action Plan
  7. Mohan Doss comment on radon at 'The Conversation'

Postscript

I said "perhaps better described as a positive correlation between radon concentration and no lung cancer!". Here it is:

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