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8.3. Quality Assurance Example
This section discusses how to set up QA for a new detector in GammaVision, then perform background and check-source measurements for the detector.
1) From the detector droplist on the toolbar, select the MCB that has the new detector. This
MCB will now be displayed in the active spectrum window.
2) We will assume our check source was calibrated at 1.0
μCi of
60
Co activity and 2.0
μCi of
137
Cs activity on June 27, 2000. The total expected activity measured today and decaycorrected back to the calibration date is 3.0
μCi. We will count the source in the same position for 10 minutes each day to verify the detector efficiency and calibration have not changed. It is unlikely the actual detector efficiency has changed, but the calibration file might have changed or electronic noise might be interfering with the spectrum collection.
We will count background for 120 seconds to verify the detector is not contaminated (if the detector were contaminated with the same isotopes as in the QA source, the QA activity would be incorrect) .
3) Use the GammaVision Library Editor on the Library menu to prepare a QA library containing only
60
Co and
137
Cs, and save it the library as
QA.lib
.
4) Select Acquire/QA/Settings... to display the Quality Assurance Settings dialog for this detector (Fig. 296), then go to the SAMPLE Type Analysis Settings File section and click the Edit button. This will open the Analysis Options dialog (Fig. 297), which will allow us to create a sample defaults (
.SDF
) file for analyzing the QA acquisitions for this detector.
5) We will now enter the following analysis options for this
.SDF
file:
! On the Sample tab, click the Presets button to open the Presets dialog for this MCB type, then enter a Live Time preset of 600 seconds.
! In the Nuclide Library section, unmark the Internal box, then browse to retrieve the newly created
QA.lib
file.
! Click the Decay tab. Mark the Collection checkbox and enter 06/27/2000 as the Date and
12:00:00 as the Time. The format for the date and time will be determined by the
Windows settings for the host PC.
! Return to the Sample tab, click Save As..., and save this file as
QA.SDF
.
371
GammaVision
®
v7 (A66-BW)
Fig. 296. Example of Quality Assurance Settings.
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372
Fig. 297. Typical Settings for Quality Assurance Analysis.
783620H / 1013 8. QUALITY ASSURANCE
! Click OK to close the Analysis Options dialog. This will return you to the Quality
Assurance Settings dialog.
6) In the BACKGROUND Acquisition section, enter a Live Time preset of 120 seconds.
Enter arbitrary count-rate values for the Low and High background settings until you know what the realistic numbers should be. Do not use zero for the Low limit; if you do, you will not receive a warning if the detector is not counting (for instance, if it is disconnected).
Remember that these values are count rates, so are independent of the counting time.
7) Select the
QA.SDF
file in the SAMPLE Type Analysis Settings File section.
8) The expected value of the activity of the sample is 1.1E+5 Bq (3.0
μCi). Scale this up and down by 10% for Low/High and 20% for Minimum/Maximum into activity fields. These values are shown in the SAMPLE Analysis Parameter Limits section in Fig. 296.
You are now ready to collect data for the QA background followed by the QA check source measurements.
9) Select Acquire/QA/Measure Background... to start the background process. You will be prompted to remove all the sources from the detector and click OK-Start. The background spectrum will be collected and summed, and stored in the QA database,
GvQa32.Mdb
. If any limits were exceeded, a warning message will be displayed.
10) Select Acquire/QA/Measure Sample... to start the sample process. You will be prompted to place the QA source in the proper place on the detector and click OK-Start. The sample spectrum will be collected and analyzed, and the results stored in the QA database. If any limits were exceeded, a warning message will be displayed.
11) Note the Lock Acquire on Violation checkbox in the QA settings dialog. If this box is marked and a limit is exceeded, GammaVision will display a QA warning each time you try to use the detector until the QA problem is corrected.
12) The background and sample spectra will automatically be stored according to the QA File
Prefix and QA File Sequence number entered in Fig. 296.
You have now completed a QA setup and system verification, and have stored the results in the QA database.
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