Thursday, December 1, 2011

Converting CPM to MicroSieverts

There is no direct equation because beta CPM (counts per minute) is an electron count and (micro and milli) sieverts is an account of bodily damage.

Still, in the post below I site an EPA guideline dictating an intervention level at 300 CPM or 10 microsieverts an hour

So, let us for a moment presume that the two are roughly equivalent in a hypothetical scenario that allows us to speculate on the health implications of our current levels of exposure.

If that were the case, exposure to 700 CPM would be roughly 23 microsieverts an hour. That would mean that we in Phoenix yesterday would have hypothetically received 552 microsieverts in a 24 hour period.

In 18 days at 700 CPM we would be at approximately 10 millisieverts of exposure (there are 1000 microsieverts in 1 millisievert) just from exposure to air alone.

We also are exposed to radiation from the machines in our environment, radon gas, food, etc.
These numbers are not looking good. 

The EPA recommends that our exposure to background radiation should not exceed 100 millirem a year, which is 1 millisievert, although we ordinarily are exposed to about 300 millirem in the US from background (3 millisieverts). Considerable background radiation derives from nuclear power plants, past nuclear weapons testing and radon gas.

There is no "immediate" health risk from 18 days of exposure of 700 CPM in the sense that people not will develop radiation sickness at this level. However, cancer rates and other diseases have been proven to increase at every 3 millisievert increment over 10 millisieverts. See my previous post.



  1. Query: you have " roughly 23 sieverts an hour" -- typo?

  2. Thank you for catching that. I shouldn't post late at night...

  3. I am doing a project in Radiation Survey and i am recording an average of 60 CPM.Can this mean it is equivalent to 2.3 micro-sieverts?

  4. Handy chart from stock

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  11. Good info.
    I purchased geiger counter called the gamma Scout from Germany. during the Fukushima disaster my readings began @ .10 microsieverts in the months and years following.
    it is now leveling off at .20 but I am getting readings up .40 and .50. I am in Bend Oregon on the West Coast.
    Kent Sawyer

  12. You state that after 18 days you get a dose of 10 msV (millisierverts) simlilar to air. But from what I know the air a sea level reach only 0.27 msV or 37 times lower.

  13. Code, vital1, and I are posting related dialog at Cafe Rad Lab - 1) Bystander Effect // 2) Pacific Genocide // 3) Manganese

  14. Various live radiation monitoring station networks operate Geiger Counters or other detection equipment, that can have different sensitivities.

    Meaning, two different Geiger counter models using different Geiger counter tubes placed at the same location would show different counts per minute (CPM). One could show 12 cpm, while an another 120 cpm. If they used a scintillator for detection purposes, which is even a more sensitive Gamma radiation detector, it could be in the thousands of counts per minute.

    Monitoring station counts per minute measurement all depends on the type of detection equipment the monitoring station is using.

    uSv/hr or uRem/hr measurements are a way of defining human exposure dose rates independent of Counts Per Minute (CPM) equipment sensitivities.

    You can only compare detections of a monitoring station against it's average background for that location. If it usually averaged around 12 cpm, 0.10 uSv/hr or 10uRem/hr at that particular location, this would be considered the average background level at that location. It may not be unusual to get a very brief detection three times this. If it stayed 3x or more background for any length of time, then something more serious is possibly happening.

    International List of Live Radiation Monitoring Stations

    Free Geiger counter user guide. This Basic Guide will provide you with
    information on how to protect your Geiger Counter from contamination, plus how get the best out of it.

  15. Code elaborated on rad measurement conversion.