How do I convert CPM to mR/hr?

Converting CPM to mR/hr

Sensitivity is expressed in cpm per mR/h. Mathematically the cpm units cancel leaving mR/h.

For example, if you have collected 200CPM with the Radiation Alert Ranger, which has a typical gamma sensitivity of 3500 cpm per mR/hr, you would divide the 200 cpm by the 3500cpm per mR/hr sensitivity. The cpm cancels out and you are left with 200/3500 mR/hr = 0.057 mR/hr

2 thoughts on “How do I convert CPM to mR/hr?

  1. Radiation Alert Clifford D. Weiss, CPO says:

    Dear Sir,

    What would be the X-Ray sensitivity factor in cpm/mR/hr? Is it similar to the gamma sensitivity of 3,500 cpm per mR/hr? Thanks.


    • Hi Cliff,

      X-rays and Gamma are treated the same by the detector. The difference comes in with the pulse width of the X-ray itself. If the pulse width is smaller than the dead time of the tube (15 microseconds for the SentryEC), then you might miss some of the counts. Otherwise, you can use the Gamma Energy Response graph on the SentryEC page to find your answer for specific energies.

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