SIGMA AM-255 - Manual (Page 25)

APPENDIX C. FORMULAS page22
Model AM-255
C. FORMULAS
The following formulas are used in various systems manufactured by TSA Systems, Ltd. They
are provided to assist in verifying system operation and to give our customers a better
understanding of how the systems operate
C.1. ACTIVITY FROM COUNTS
Activity = Activity in nCi
Eff = Decimal efficiency (i.e. 10% = 0.1.)
Where:
N = Net counts per second (cps – background cps)
C.2. EFFICIENCY
N = cps with source – background cps
Where:
activity = test source activity in nCi
C.3. N*SIGMA ALARM LEVEL
This formula calculates the minimum activity, in disintegrations per minute, that can be reliably
detected under a given set of operational conditions.
bkg = Background counts
Sigma = 1bkg Where:
N = N*Sigma value