APPENDIX C. FORMULAS page 46

C.4. RELIABLE DETECTABLE ACTIVITY (RDA) FORMULA

This formula calculates the minimum activity, in disintegrations per minute, that can be reliably detected under a given set of operational conditions.

BKG = total background counts per count time

CON = confidence sigma

CT = count time in seconds

E = system efficiency in percent

F = false alarm level in cps

FA = false alarm sigma

G = intermediate variance

RDA = reliable detectable activity in DPM

C.5. SIGNAL TO BACKGROUND RATIO

The following formula is helpful is determining the optimum discriminator settings. Always perform a variance test at the final setting of the lower-level discriminator to ensure that system noise is not being introduced into the amplifier stage.

Where:

Q = Quality factor

S = Net signal (count with source - background)

B = Background count

B = Background count

Higher values of Q result in better sensitivity

Model BM-286A

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Image 49
Sigma BM-286A service manual Reliable Detectable Activity RDA Formula