8. QUALITY ASSURANCE
CAUTION
Running the MCB Configuration program can affect the continuity of your QA measurements in GammaVision. Be sure to read Section 2.4!
8.1. Introduction
The accuracy and reproducibility of results of a data acquisition system should be verified on a periodic basis. Quality Assurance (QA) in GammaVision supplies a means for doing this in accordance with ANSI N13.30 and N42.14. The detector-shield background, detector efficiency, peak shape, and peak drift can be tracked with warning and acceptance limits. The latter use a check source. These results are stored in a database and can be displayed and charted. The database can be accessed with commercially available database products, including Microsoft
Access. The information stored in the database for each detector includes:
! Total Background — The count rate (counts/sec), over the entire spectrum, of the environmental background (that is, with no source present).
! Total Activity — The sum of the decay-corrected activities of the nuclides measured in the source, as defined in the analysis library.
where:
N
= the number of nuclides in the analysis library
DC = the decay correction factor for nuclide x in the analysis library
A
= the calculated activity, in becquerels, for nuclide x in the analysis library
! Average FWHM Ratio — The sum of the ratio of each peak’s measured FWHM vs. its calibrated FWHM, divided by the total number of peaks, for all peaks defined in the analysis library.
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where:
P
FWHM
Meas
FWHM
Cal
= the number of identified peaks in the spectrum
= the measured FWHM of analysis library peak x, in keV
= the calibrated FWHM of analysis library peak x, in keV
! Average FWTM ratio — The sum of the ratio of each peak’s measured FWTM vs. its effective calibrated FWTM, divided by the total number of peaks, for all peaks defined in the analysis library.
where:
P
FWHM
Meas
FWHM
EffCal
= the number of identified peaks in the spectrum
= the measured FWTM of analysis library peak x, in keV
= the effective calibrated FWTM of analysis library peak x, in keV
! Average Library Peak Energy Shift — The average of the deviation of the measured peak enegy from the expected peak energy, for all energies defined in the analysis library.
where:
E
= the number of identified peak energies in the spectrum
E
Meas
E
Lib
= the measured peak energy corresponding to analysis library energy x, in keV
= the expected peak energy x from the analysis library, in keV
The background should be monitored to verify that the detector and shield have not been contaminated by radioactive materials. The value stored is the total count rate which is independent of the count time and any specific isotopic contamination. A background analysis report can be printed after the analysis completes.
The total activity of a calibration or check source will check the efficiency calibration currently in use and the general operating parameters of the system, including source positioning, contamination, library values, and energy calibration. This activity calculation uses the general analysis program to ensure that the total system is checked.
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