Counting Statistics - Panasonic PT-DZ12000U Operating Instructions Manual

Minimum Detectable Activity
(MDA) MDA =
Minimum Detectable Count Rate
LLD = L = MDCR
D
L =
C
k = 1.645 (for 95% Confidence Level)
t = sample count time
S+B
t = background count time
B
R = background count rate
B
Eff = efficiency of the detector (expressed as a decimal)
R = sample count rate
S+B
LLD is Lower Limit of Detection
L is the Decision Level
D
L is the Critical Level and generally expressed as counts (or
C
signal level) above background
K 0.674
% C.L. 50
If R is in DPM it must be converted to CPM before using the
B
above equations.
A 'k' of 1.645 is used as the 95% confidence level for a two-
tailed distribution.
Gaussian statistics should be used for > 30 counts and Poisson
statistics for < 30 counts. The typical formulas such as those
above are an attempt to blend the two statistical models.

COUNTING STATISTICS

k x R x t
B S+B
1
68.3
2
k + 2k R x t
2
k + 2k R x t
B
+ R x t
B B
1.645 1.96
90 95
x (1+t
B S+B
t x Eff
S+B
x (1+t
S+B S+B
t
S+B
2.58
99
/t )
S+B B
/t )
B
3.00
99.7