Humboldt HS-5001EZ, Руководство по эксплуатации продукта

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5.5 Statistical Stability Test
This test is a simple method of testing the short-term stability of the
detectors and electronic counting circuits. The basis for it is explained in
section 7.3 covering radiation statistics.
Radioactive decay is a binary process (an atom decays or it does not).
The average rate of decay determines the half life (the time for half of the
material to disintegrate) of the material. For Cs 137 this is 30.17 years and
for Am 241: Be, it is 433 years. The decrease in the average rate of decay for
Cs 137 is 2.3% per year and for Am 241: Be is 0.16% per year. Calibrating
the Gauge in forms of a ratio eliminates the effect of this change on the
measurement.
The short-term fluctuation of binary decay is predictable. The predicted
standard deviation is the square root of the average count rate (m):
s
=
√
m
The Gauge electronics divide the actual events counted in a one-minute
period by a factor of 16 before using the number, so the above expression is
actually:
√
m
s
=
4
This equation can be used to predict the standard deviation of the count
rate for a series of measurements. By taking a series of 16 measurements
and computing the actual standard deviation, the value obtained can be
compared as a ratio to the predicted value thus:
∑
(n – m)²
R = 4
√
[ ]
m (N-1)
Where:
s
= Standard deviation of count rate
n = Individual measurement
N = Number of measurement
m = Mean of the measurement
R = Statistical ratio
" STAT" automatically runs this series of measurements and displays the R
values for the density and moisture channels. See section 3.2.