783620H / 1013 8. QUALITY ASSURANCE
NOTE
Use nuclides with long half-lives for your QA measurements. Short-lived nuclides will develop poor peak shapes as they decay.
ORTEC Application Note 55 contains more information and help on starting and running QA for gamma spectroscopy.
The FWHM and FWTM values will check the electronic noise and pole-zero adjustment of the amplifier. The peak shift checks to verify that the system gain and zero offset have not changed.
8.1.1. Using QA Results to Diagnose System Problems
A gradual deterioration of the FWHM
Meas
/FWHM
Cal
ratio usually means the detector leakage current has increased.
A sudden deterioration of the FWHM
Meas
/FWHM
Cal
ratio suggest that additional noise has been introduced into the system. Commonly, this can arise from:
! A noisy motor introduced into the ac line
! RF interference
! Electronic failure of a component in the detector, preamplifier, or MCB
Generally, these problems will also cause the FW.1M ratio check to fail.
If the FW.1M ratios fail but the FWHM ratios are acceptable, this could indicate:
! Incorrect pole zero
! Neutron or other radiation damage to the detector
8.2. QA Submenu
Figure 280 shows the QA submenu under the Acquire menu. These commands allow you to accomplish the three major QA functions in
GammaVision:
The three parts of QA in GammaVision are:
1) Establishing and entering the settings, or “ground rules,” for QA.
Fig. 280. QA Submenu.
2) Measuring background and sample. You perform this periodically, and it is automatically logged into a database by the program.
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