BNC 970 Portable Multi-Channel Analyzer (MCA) - Manual (Page 23)

Model 970 Instruction Manual 20
Spectrum Clear (red background). Indicates that the Spectrum Display contains no data, and
the 970 is not acquiring data.
Acquiring (light green background). Indicates that a spectrum is currently accumulating.
Acquisition Stopped (yellow background). Indicates that the 970 is not currently acquiring data,
but the Spectrum Display contains data.
Spectrum Loaded (yellow background). Indicates that the 970 is not currently acquiring data, but
the Spectrum Display contains data that has been loaded to Live from a file.
The second (and lower) of these displays gives information about the Background Spectrum, and
will only be visible if a Background Spectrum has been loaded. The text of this display may be:
Bkgd Subtracted (green background). Indicates that a Background Spectrum has been loaded
and is currently being subtracted from the visual Spectrum Display. It will also be subtracted
from any spectral analysis performed, including peak searches.
Bkgd Loaded (green background). Indicates that a Background Spectrum has been loaded but is
not being subtracted from the visual Spectrum Display. The Background Spectrum will still be
subtracted from any spectral analysis performed.
Moving downward, the next object is the white Time (sec) input box, with a checkbox immediately
to its left. If the checkbox is checked, the 970 will stop acquiring a spectrum when the total
counting time equals this value. Time units are in seconds. An Acquisition cannot be started or
continued if the checkbox is checked and the Acquisition time equals or exceeds the amount of
time in the input box. Typing in the Time (sec) box will immediately un-check it; pressing Enter on
the keyboard after changing the Time (sec) value will re-check it.
Directly underneath the Time (sec) input box is the white Total Counts input box, with a checkbox
immediately to its left. If the checkbox is checked, the 970 will stop acquiring a spectrum when
the total number of accumulated counts equals this value. An Acquisition cannot be started or
continued if the checkbox is checked and the total accumulated overall counts equals or exceeds
the number of counts in the input box. Typing in the Total Counts box wills immediately un-check
it; pressing Enter on the keyboard after changing the Total Counts value will re-check it.
The final item in this area is the gray Time (sec) box. This displays the total counting time, in
seconds, for the spectrum currently displayed. If a spectrum has been loaded to Live from a file,
this display will reflect the amount of time for which that spectrum was counted.
3.9 Spectrum Smoothing
The photomultiplier tubes used in NaI (Tl) gamma detectors (as well as many others) do not
supply a smooth continuum of energies. This fact is not apparent when the spectrum is displayed
in 256 or 512 channels. SNAP-MCA’s 4096 channels of data can be filtered to give a smoother
representation of the energy continuum.
Try using different values of smoothing to get the “best looking” Spectrum Display. Smoothing is
applied only to the visual display and has no affect whatsoever in performing peak searches and
analysis.