Thermo Scientific SAM12, Manual

Page: 138 / 176

Setting Up Procedure Issue: 1.0
9-4 SAM12 User Manual Thermo Fisher Scientific
The SAM12 is designed to detect activities down to release
levels and otherwise ‘as low reasonably achievable’. However,
the SAM12 is also very linear in response, so a wide range of
source activities may be used for set-up and calibration.
Depending upon energy / detector efficiency, source activity
should ideally be in the 100 nCi (3.7 kBq) to 11
μ Ci (400 kBq)
range, and in any case not more than 20 μ Ci (740 kBq). Long
count times will be required for small sources to maintain
statistical accuracy against adverse background influences.
The calibration of the SAM12 to
60
Co when CCM is installed,
requires a longer counting time than would be required if CCM
was not installed. The reason being that CCM mode has a
lower efficiency than the standard “gross counting” mode,
typically 1% for a 6 detector instrument. Therefore it is
recommended that a
60
Co source of activity in excess of 40 kBq
be used to undertake the CCM calibration. Note that the CCM
calibration is undertaken at the same time as the standard
60
Co
calibration.
NOTE:
For all the measurements performed below, the
door(s) should be fully closed in order to minimise the effect of
background fluctuations. All counts read from the detectors are
corrected to compensate for the amplifier “dead time”.
With the SAM12 and surrounding area free of sources, enter
the
Administrator Mode (page 5-1) as ‘Health Physicist’. From
the function tabs on the left side of the screen select the
‘Calibration’ option. Then from the tabs along the top of the
screen select ‘HV Scan’. There will be a choice between
performing a ‘New Scan’ and viewing the ‘Last Scan’. Press
the ‘New Scan’ button.
The new screen allows for the setting of the scan parameters
Start, Stop and Step voltages as well as the counting time. The
recommended values for these parameters are;
Start = 500 volts
Stop = 1200 volts
Step = 5 volts
Time = 10 seconds
NOTE:
Short voltage steps are required in order to make
the location of the optimum operating voltage easier. Using the
recommended values, this process will take approximately one
hour to complete.
Once there parameters have been set and the ‘Start’ button has
been pressed. A series of onscreen instructions are displayed to
step the user through the scan process.
Derivation of the Optimum
Operating Voltage
Calibration Source Activity
Performing the HV Scan