5 background mode, Background mode – BNC SAM 935 Portable Gamma Spectroscopy System User Manual

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SAM 935™ Instruction Manual


The peak labeling function allows you to display the gamma lines associated with particular nuclides
superimposed on the current spectrum. This feature is available both during and at the end of data acquisi-
tion. The I


- (F2) and I


+ (F3) keys cycle through the list of all enabled nuclides in the nuclide data-

base. For each, the enabled lines are shown with a height proportional to the log of their intensity.


Background Mode

The SAM 935 requires that an ambient background spectrum be taken before it will allow fine energy cali-
bration and will not perform monitoring operations without one. The procedure for taking background spec-
tra is described in Section 3.2.2.

The background mode screen looks like this:

The initial set of function keys have the following functions:


This key changes the spectrum display so that the spectrum occupies the full width of
the display.


This changes the display to a log display. The function key label changes to L



Pressing the key again returns to linear mode.

AcceptAt various times the F4 key may display A


or R


. When A


is displayed, it means

that data has been collected and the opportunity is given to accept it, erase and start over, or cancel the
operation. Pressing A


causes the operation (usually an analysis of some kind) to proceed, and the

spectrum will be placed into the spectrum storage as well.

The ambient background spectrum is stored and then subtracted from other spectra on a channel-
by-channel basis before they are analyzed. This provides a correction for any ambient radioactivity in the
vicinity of the detector and for background from cosmic rays, etc.

Because the counting statistics in the background spectrum directly affect the uncertainty in the analyzed
spectra, it is very important that the background be counted for a long time relative to the sampling interval.

Note: he hardware controls, preset controls, and ROI controls are only functional in
manual MCA mode.