Doc. # 5016
BM-185D/285D/286D
Rev. A
Operation and Service Manual
APPENDIX A
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. This is a general list, but most systems use some of
these formulas.
ACTIVITY FROM COUNTS
Where:
Activity = Activity in nCi
Eff = Decimal efficiency (i.e. 10% = 0.10)
N = Net counts per second (cps - background cps)
37 = bq per nCi
EFFICIENCY
where:
N = cps with source - background cps
activity = test source activity in nCi
N*Sigma Alarm Level
Used to calculate the alarm level on instruments using n*sigma alarm algorithm. Most systems
that use n*sigma alarm levels operate in counts/second.
where:
bkg = Background counts
Sigma = 1bkg
N = N*Sigma value
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