8 analysis tools setup, Analysis tools setup – BNC SAM 935 Portable Gamma Spectroscopy System User Manual

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SAM 935™ Instruction Manual

Each detector has the following parameters associated with it:


The name for this detector.


Diameter of the actual NaI crystal in cm.


Thickness of the detector in cm.

Samp Dist:

Distance from the sample to the detector surface. For well-type detectors, enter zero.

Window 1:

First detector window. For most NaI detectors, this will be aluminum. The thickness is
in cm.

Window 2:

Second detector window thickness in cm.

Window 3:

Third detector window thickness in cm. Some detectors have a MgO packing that acts
as a window.

Note: The F2 key toggles between P


and W


. Because the SAM 935 does not support well detec-

tors, F2 should always be labelled W


, which indicates that P


is the current setting.

Note: Use of an external detector supplied by a third-party vendor will void the warranty! BNC recom-
mends the use of a semi-rugged detector system with the SAM 935. These systems are available in 1.5 x
2 inch, 2 x 2 inch, and 3 x 3 inch versions. They have internal high voltage power supplies and are sealed
from environmental contamination.


Analysis Tools Setup

The analysis tools setup sets up a number of parameters to control the peak search and peak matching
functions of the SAM 935. The minimum correlation and ROI width parameters affect the overall monitoring
operations; the others only influence the qualitative analysis done by the Manual mode of operation.

Once you enter the tools setup, you will be led through a series of five screens to review or change the fol-
lowing parameters: Energy Match Window A, Energy Match Window B, Minimum Correlation for Detection,
Peak Finder ROI Width, and Max Peak Uncertainty. You may cancel at any time to leave the current and
subsequent values unchanged; any changes you have made on earlier screens will be retained.

The two most important parameters, which affect the overall system operation, are the minimum correla-
tion value (default 0.65) and the ROI width (the default is 11 channels for planar detectors):

• Increasing the minimum correlation value (in the

range of 0.2 to 0.79) will increase the required accu-
racy of the measured relative intensities of multi-line
isotopes. Thus, increasing the value will lead to fewer
misidentifications of one isotope as another, at the
expense of possibly rejecting matches for one iso-
tope in the presence of another.

• The ROI width of 11 corresponds to a detector

FWHM of approximately 7.5% at 662keV. If your
detector resolution is significantly better or worse, it
may be useful to change this parameter so that peaks
are resolved from the background more accurately.

The other three parameters are used by the Manual mode of
operation to decide which isotopes will be identified: