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What about ground or food contamination?

2011-09-04

Most simple Geiger counters, as used on this site and in many  places, are good for a warning to stay indoors in case of black rain from nuclear fallout. Sensitive as they may be, they are hardly sensitive enough to quickly and reliably detect the small additional activity within the normal background radiation to isolate the contribution from a ground or food sample. It usually takes heavy shielding and good spectrometry to tell that story truthfully.

Relative radiation risk… Recently, we get a lot of radiation values in our news streams and very few have comparison data to estimate: is this normal, elevated, severe or hazardous? Distrust and panic may result. Here, I aim to provide a bit of grounding.

Ground surface contamination

For example, compare

  • Nikko, Japan (2011)  from Fukushima, some 170 km away
  • Munich, Germany (1996), from Chernobyl, some 1700 km away

According to this blog post, Nikko city and Munich now have similar radiation levels, around 10,000 – 80,000 Bq/m² from radioactive cesium, Cs-137.  Is it significant? Severe?  Compare for yourself. Ground contamination from some 2000 nuclear bomb experiments is about 4000 Bq/m² – everywhere on the planet.

To get a feeling for the specific activity not on a surface, but in a mass of matter, here is a  reference. According to the UNSCEAR report [UNSCEAR, 1982], the normal range for radium isotopes in earth’s crust is 10 – 50 Bq/kg, whilst the range for the potassium K-40 is 100-700 Bq/kg. Source

Food contamination

The Banana Equivalent Dose  leads us to an activity of 77Bq/kg for human tissue from potassium alone, a mineral that  does not accumulate in the body. So, this is a normal low level of activity. It seems that food safety limits like the 300 Bq/l for drinking water (in Japan 200 Bq/l for adults, 100 for children) were established on the basis of not significantly raising the normal low level with daily consumption over a lifetime. By significant I do not mean a factor of 2 or 3, rather 10 or 100. A biochemist or a radiation specialist might use more refined methods to assess relative risks, especially for elements that bioaccumulate.

Radiation is around us.

A bit is OK, usually. I know of no place where it would be zero. At these low normal levels, it may help to visualize it as a dim light in the darkness, whereas in a nuclear bomb it is a blinding light, and in severely contaminated areas an illumination too bright to be comfortable, like the sun that causes skin burns when we stay exposed for too long without protection. The brightness analogy  gives us relative importance for the dose rate values in μSv/h,  microSieverts per hour.  The accumulated dose is simply the rate multiplied by the time of exposure. Compare

Chart of relative radiation hazard levels

Relative radiation levels

What would you add here?

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7 Comments
  1. Maybe you’re also interested in using this open-source project for radiation monitoring as well: https://apollo.open-resource.org/lab:pigi

    We’re currently working on the software and will release a crowdfunding campaign to kick off soon 🙂

    • Thank you for finding me. That is great news. Makes radiation measurement more available to many. I have the counter and power supply. Will look into the Pi solution, because it seems this January, the cheap laptop I kept running to upload radiation data finally died. Windows 7 was unstable anyway, needed a reboot every few months.

      • Yeah exactly. We found that commercial geiger counters were way to expensive considering the small amount of features they actually provide. So we started developing our own cheap approach and are gathering knowledge and people to develop and produce the least expensive but most feature rich and open DIY geiger counter we can. But somehow the news never spread to Japan, where they’re needed the most right now 🙂

  2. Stan permalink

    Does anyone know of a handbook or pocket reference for radiation/fallout dose limits that is available and is EASYILY understandable offering quick access for newbies? Something small and not electronic in nature as an emp will make computers worthless.
    To be honest, the rem,rad,sievert conversion is totally confusing in a time of non-panic, imagine the likelihood of conversion error in a disaster where every second counts!!!!!
    I’m thinking laminated wire bound cards?

    Thank you

    • Good points. Maybe they have something like this at safecast.org

      • Stan permalink

        Don’t see anything useful there

      • Sorry for that. I guess you have seen the International Nuclear Event Scale on this related post. https://radiationyokohama.wordpress.com/2011/09/04/what-about-ground-or-food-contamination/

        Being in Japan at the time and having to decide to send the children back to Germany, I had to sort out the units and stuff in a hurry. So I applaud your approach to learn while there is time. Basically, there are only two useful units, and a number of more or less historic units. It helps to begin with their definitions. Here only a quick and dirty summary.

        1. Radiation dose rate in µsV/h in space reaching the body.This could be modeled like brightness as an effect on a surface. Multiplied by time of exposure reflects the accumulative body absorbed dose taken as a proxy for risk.

        2. Contamination level in Bq/kg or Bq/m² meaning counts per second per (food) mass or square meter of ground surface. This could be modeled like brightness of a source.

        If you find these properly defined and play with them, you will get a feeling feeling for what is normal, what would mean caution and how many factors of 10 we are away from a significant hazard.

        >

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