4 ms·

Building on your "lots of places" comment: I've got memories of an experiment we did in undergraduate physics labs, which involved a directional array of Geige

by femto 9y ago

Building on your "lots of places" comment: I've got memories of an experiment we did in undergraduate physics labs, which involved a directional array of Geiger tubes. Pointing them at the view through the window gave a low count, but pointing them at the concrete structure of the building gave an elevated count. My understanding at the time was that it was due to naturally occurring uranium and thorium in the raw materials of the concrete. Given that fly ash is a common component of concrete [1], I wonder how much of the elevated radiation from concrete can be put down to the concentrating effects of coal combustion that you mentioned in one of your comments? [1] http://www.cementaustralia.com.au/wps/wcm/connect/website/bulk/Bulk-Home/our-products/fly-ash/ http://www.cementaustralia.com.au/wps/wcm/connect/website/bu...

femto 9y ago
I just did a guesstimate: Combustion concentrates radioactivity by a factor of 5x to 10x [1]. Fly ash can replace 25-50% of cement [2]. A typical concrete is 16% cement (1 part cement, 2 parts sand and 3 parts gravel) [3]. Hence a concrete might be 4%-8% fly ash. If the ratio of fly ash is 'A', the concentrating caused by combustion is 'C' and the background radiation of other concrete ingredients is uniformly taken to be 'B', then the radiation count of concrete without fly ash will be: B and the radiation count of concrete with fly ash will be A.C.B + (1-A).B Plugging in values for A (0.04 to 0.08) and C (5 to 10), we find that fly ash increases the radiation from concrete by a factor of 20% to 70%. That strikes me as a significant proportion of the radiation from concrete. [1] https://phys.org/news/2015-09-radioactive-contaminants-coal-ash.html https://phys.org/news/2015-09-radioactive-contaminants-coal-... [2] http://www.theconcreteproducer.com/how-to/concrete-production/whats-the-allowable-fly-ash-limit_o http://www.theconcreteproducer.com/how-to/concrete-productio... [3] http://www.cementaustralia.com.au/wps/wcm/connect/website/packaged-products/home/hints-and-tips/FAQ-Working-with-Concrete/ http://www.cementaustralia.com.au/wps/wcm/connect/website/pa...
- pmiller2 9y ago
  But how radioactive is concrete compared to a similar volume of bananas? I would like to know this, but I'm on my phone at the moment. :)
  - femto 9y ago
    An interesting question! Typical banana dose: 0.1 μSv per banana [1]. Typical concrete building dose: 100μSv per year [2] ie. 1 year in a concrete building = eating 3 bananas a day. I'm not claiming that fly ash laden concrete is going to kill anyone, but I think it's interesting that (given my assumptions) the concentrating effects of coal combustion are causing a decent proportion of concrete's radioactivity (even if the total is still negligible). [1] https://en.wikipedia.org/wiki/Banana_equivalent_dose https://en.wikipedia.org/wiki/Banana_equivalent_dose [2] https://www.euronuclear.org/info/encyclopedia/r/radiation-exposure-building-mat.htm https://www.euronuclear.org/info/encyclopedia/r/radiation-ex...
    - jballanc 9y ago
      My understanding is that more than direct exposure to radioactive materials in fly ash, the real risk is Radon. As Thorium and Uranium decay they will produce Radon, which can accumulate especially in low-lying areas with poor ventilation (e.g. basements, which tend to rely on concrete as a key building material). Since Radon can be inhaled, it has the potential to cause far more harm than anything "baked into" the concrete itself.
    - simonh 9y ago
      > I'm not claiming that fly ash laden concrete is going to kill anyone... That's the thing though, these low 'safe' levels of radiation do actually kill people. Every now and then somewhere, someone will be hit by a radioactive emission from Fly Ash that happens to hit one of their chromosomes and trigger cancer. If Fly Ash increases cancer cases in a year by x% then we can be pretty sure that x% of cancer patients were victims of Fly Ash, it's just that x is actually fairly small and we just don't know which ones they are. But they still have cancer.
      - ageofwant 9y ago
        If you can absolutely correlate the cancer to the presence of fly ash then yes. But that is going to be rather hard. How do you normalize for other equally chromosome-destroying environmental factors? Maybe drinking two cans of Coke a year less gives you exactly the same level of risk than someone living in a fly-ash free building?
autokad 9y ago
marble counters emit radiation (radon) due to the break down of iridium that occurs naturally. your actually supposed to test your marble counters for excessive radon release. It comes to no surprise that concrete would have an elevated count - anything with any kind of stone probably would.
- njarboe 9y ago
  Iridium in nature has two stable isotopes and is not radioactive. The longest half-life of the radioactive isotopes of Iridium is 241 years and quickly disappears over geologic timescales. Potassium is what will make stone counters radioactive as Potassium 40 has a half-life of 1.25 billion years and will release beta particles but not radon. Radon is a radioactive gas created in the decay chains of Uranium and Thorium. Stone used for counter tops will have some Uranium and Thorium, but usually at very low levels.
- wycx 9y ago
  The iridium content of marble is going to be in ppt or more likely ppq abundances. I see no decay chain leading to Radon. https://en.wikipedia.org/wiki/Isotopes_of_iridium https://en.wikipedia.org/wiki/Isotopes_of_iridium
gnufx 9y ago
If you use a decent (high resolution γ-ray) detector, you'll find that the background (from UK concrete, at least) is dominated by the ⁴⁰K decay line, whose energy might be ingrained in ex-γ-ray spectroscopists years later. Geiger counters may indicate radiation, but not what radiation.

by femto 9y ago

femto 9y ago

I just did a guesstimate: Combustion concentrates radioactivity by a factor of 5x to 10x [1]. Fly ash can replace 25-50% of cement [2]. A typical concrete is 16% cement (1 part cement, 2 parts sand and 3 parts gravel) [3]. Hence a concrete might be 4%-8% fly ash. If the ratio of fly ash is 'A', the concentrating caused by combustion is 'C' and the background radiation of other concrete ingredients is uniformly taken to be 'B', then the radiation count of concrete without fly ash will be: B and the radiation count of concrete with fly ash will be A.C.B + (1-A).B Plugging in values for A (0.04 to 0.08) and C (5 to 10), we find that fly ash increases the radiation from concrete by a factor of 20% to 70%. That strikes me as a significant proportion of the radiation from concrete. [1] https://phys.org/news/2015-09-radioactive-contaminants-coal-ash.html https://phys.org/news/2015-09-radioactive-contaminants-coal-... [2] http://www.theconcreteproducer.com/how-to/concrete-production/whats-the-allowable-fly-ash-limit_o http://www.theconcreteproducer.com/how-to/concrete-productio... [3] http://www.cementaustralia.com.au/wps/wcm/connect/website/packaged-products/home/hints-and-tips/FAQ-Working-with-Concrete/ http://www.cementaustralia.com.au/wps/wcm/connect/website/pa...

pmiller2 9y ago
But how radioactive is concrete compared to a similar volume of bananas? I would like to know this, but I'm on my phone at the moment. :)
- femto 9y ago
  An interesting question! Typical banana dose: 0.1 μSv per banana [1]. Typical concrete building dose: 100μSv per year [2] ie. 1 year in a concrete building = eating 3 bananas a day. I'm not claiming that fly ash laden concrete is going to kill anyone, but I think it's interesting that (given my assumptions) the concentrating effects of coal combustion are causing a decent proportion of concrete's radioactivity (even if the total is still negligible). [1] https://en.wikipedia.org/wiki/Banana_equivalent_dose https://en.wikipedia.org/wiki/Banana_equivalent_dose [2] https://www.euronuclear.org/info/encyclopedia/r/radiation-exposure-building-mat.htm https://www.euronuclear.org/info/encyclopedia/r/radiation-ex...
  - jballanc 9y ago
    My understanding is that more than direct exposure to radioactive materials in fly ash, the real risk is Radon. As Thorium and Uranium decay they will produce Radon, which can accumulate especially in low-lying areas with poor ventilation (e.g. basements, which tend to rely on concrete as a key building material). Since Radon can be inhaled, it has the potential to cause far more harm than anything "baked into" the concrete itself.
  - simonh 9y ago
    > I'm not claiming that fly ash laden concrete is going to kill anyone... That's the thing though, these low 'safe' levels of radiation do actually kill people. Every now and then somewhere, someone will be hit by a radioactive emission from Fly Ash that happens to hit one of their chromosomes and trigger cancer. If Fly Ash increases cancer cases in a year by x% then we can be pretty sure that x% of cancer patients were victims of Fly Ash, it's just that x is actually fairly small and we just don't know which ones they are. But they still have cancer.
    - ageofwant 9y ago
      If you can absolutely correlate the cancer to the presence of fly ash then yes. But that is going to be rather hard. How do you normalize for other equally chromosome-destroying environmental factors? Maybe drinking two cans of Coke a year less gives you exactly the same level of risk than someone living in a fly-ash free building?

autokad 9y ago

marble counters emit radiation (radon) due to the break down of iridium that occurs naturally. your actually supposed to test your marble counters for excessive radon release. It comes to no surprise that concrete would have an elevated count - anything with any kind of stone probably would.

njarboe 9y ago
Iridium in nature has two stable isotopes and is not radioactive. The longest half-life of the radioactive isotopes of Iridium is 241 years and quickly disappears over geologic timescales. Potassium is what will make stone counters radioactive as Potassium 40 has a half-life of 1.25 billion years and will release beta particles but not radon. Radon is a radioactive gas created in the decay chains of Uranium and Thorium. Stone used for counter tops will have some Uranium and Thorium, but usually at very low levels.
wycx 9y ago
The iridium content of marble is going to be in ppt or more likely ppq abundances. I see no decay chain leading to Radon. https://en.wikipedia.org/wiki/Isotopes_of_iridium https://en.wikipedia.org/wiki/Isotopes_of_iridium

gnufx 9y ago

If you use a decent (high resolution γ-ray) detector, you'll find that the background (from UK concrete, at least) is dominated by the ⁴⁰K decay line, whose energy might be ingrained in ex-γ-ray spectroscopists years later. Geiger counters may indicate radiation, but not what radiation.