Ludlum Measurements 334A, Руководство по эксплуатации

Страница: 44 / 60

Model 334A Operations Manual
Ludlum Measurements, Inc 35 January 2021
Measurement Calculations
Acute & Chronic Moving-Windows
In order to calculate a concentration, the counts for each counting channel are saved—along
with the flow rate and volume—in a history array, so that the increase in counts over time
can be used to determine the net count rate. For each counting channel, two different time
intervals are used to determine concentrations and are referred to as the ‘acute’ and ‘chronic’
window times. These are sometimes referred to as the “fast window” and “slow window”.
The peak counts—based on the history values over one and two window times—are used to
determine the net count rates. For instance, if the window time is 60 seconds, then the net
count rates for the last minute and also the minute previous are calculated. For long-lived
isotopes, the increase in net count rates over the two intervals is proportional to the
concentration.
The Acute window time offers a very quick response to measurement data, sacrificing some
accuracy in the process.
The Chronic window time provides a very accurate dose reading, but must take place over a
substantial period of time.
Alpha Measurement Calculations
For alpha configurations, the curve fit function produces coefficients for each isotope that
correspond to the counts under the peak. Alpha channels use a history array, so that the
increase in counts over time can be used to determine the net count rate. The peak
counts—based on the history values over one and two window times—are used to
determine the net count rates. For long-lived isotopes, the difference in net count rates over
the two intervals is proportional to the concentration. Once the change in net count rate is
SECTION
5