25 MN1007-C
4.4.2 cps Minus Background Mode
Press the Mode
key to change the measuring units from cps to cps minus background mode.
The display shows an analogue scale and digital numeral readout. The measurement units and mode are indicated
by the “cps” and “– Background” text.
In this mode the digital display will show the cps count rate with the last stored background count subtracted.
Figure 10 - Background subtracted CPS screen
The value subtracted for background cps will be that held in memory by the instrument. The operator may update
the background value at any time. [See section 4.7]
Stored background counts are held for each probe type. When the SA50 scintillator probe and SA49 GM probe
are interchanged, then the corresponding background readings are automatically loaded.
4.4.3 Becquerels per cm squared mode (Bq/cm
2)
This mode of operation uses a background-subtracted measurement along with a factory set calibration factor in
order to calculate the Bq/cm
2
response. The user should ensure that a valid background reading has been logged
prior to the target measurement.
This operating mode is intended for use where a specific nuclide is known to exist in the source of scale
contamination to be measured. To carry out the measurement the user should select the Bq/cm
2
operating mode
then select the required nuclide from the following list:
Radium-226 wet (Ra226w)
Radium-226 dry (Ra226 d)
Lead-120 wet (Pb210w)
Lead-120 dry (Pb210 d)
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