This MDA calculator is provided as reference tool for estimating the MDAs that can be reached for various counting times. There are several MDA equations in use, and many facilities have modified equations to meet their specific requirements. The equation used here is from HASL-300. The results you get from this calculator may differ from those you get with the MDA equation you currently use. The equation is:


To use the calculator, enter the sample efficiency as a factor. For example enter .4 if the sample efficiency is 40%. Enter the background count rate in counts per minute. Enter your own specific count time in minutes if needed. Click the Calculate MDA button. The results in disintegration's per minute (DPM) will appear. Your count time specific MDA will appear first followed by the results for fixed count times from 1 to 1000 minutes.

Ways to use the calculator:

  1. Estimate counting time required for a new count routine.

  2. Compare the MDA available on two different systems by entering (typical vs. typical or warranted vs. warranted) efficiency and background values for one system and then the other.

Efficiency as 0.xx Background as CPM Time in MIN    

Time(minutes) 1 2 5 10 20 50 100 200 500 1000

Note: Protean Instrument systems have the lowest background, therefore the lowest MDAs (best sensitivity) of any systems manufactured.