ORTEC radEAGLE, User Manual

Page: 129 / 147

radEAGLE User Manual Technological Background, Limitations
After entering the calibration screen, it takes some time until the peak fit is established.
The shown percentage value represents the progress of acquiring the minimum counts
to establish the measured peak position. This depends on the strength of the calibration
source you are using. Once the peak fit quality is sufficient and enough counts are contained
in the spectrum, the
Calibration button becomes active. You can press it to perform
the manual recalibration and to definitively update the internal gain.
After recalibration, the calibration check acquisition is reset and you will get an up-
dated view of the peak fit. You can now again inspect the results of the recalibration.
C.3 Effective Range of Measurement
Detection and identification depend on the dose rate on the detector surface. This value
can be defined by either varying the distance of the source and detector or by simply using
stronger or weaker sources.
C.4 Determination of the Full Width at Half Maximum
radEAGLE detectors have a specified FWHM, sometimes also denoted as resolution given
in percentages relative to their peak position. Our usual reference is the
137
Cs peak at
661.6 keV. It is the common peak to specify a resolution. The procedure used to determine
this value is given as follows:
1. Acquire a background spectrum.
2. Acquire a
137
Cs spectrum with at least 1 µSv/h at the detector surface.
3. Use a qualified background subtraction method to subtract the background from the
cesium spectrum.
4. Perform a Gaussian fit on the peak data (using e.g. Matlab).
5. Locate both positions where the Gaussian curve reaches the half of its maximum.
6. Calculate the difference in terms of energy. The latter is the FWHM.
For sodium iodide based instruments, we specifiy a resolution better than 7.2 % at
661.65 keV which corresponds to a FWHM of 47.6 keV.
C.5 Over-Range Characteristics for the Scintillator and the Nuclide
Identification
Nuclide identification results depend on the quality of the spectrum. For extremely high
count rates, the scintillation spectrum degrades and for dose rates greater than 200 µSv/h
at the detector surface, the
radEAGLE switches off the scintillation subsystem and uses the
fall-back GM tube for dose rate measurements.
© innoRIID GmbH • 2019-04-11 Software 3.2.12 • Document 3.3.0o 129/147