Capintec CAPRAC-t - Tests; Count Time; Auto Calibrate; Background

CAPINTEC, INC. CAPRAC
®
-t
April 2021 TESTS 9-1
CHAPTER 9
TESTS
GENERAL ....................................................................................................... 9-1
COUNT TIME .................................................................................................. 9-1
AUTO CALIBRATE ......................................................................................... 9-2
BACKGROUND .............................................................................................. 9-7
QUALITY ASSURANCE TESTS ..................................................................... 9-7
System Test ................................................................................................ 9-8
MDA (Minimum Detectable Activity) Test ................................................ 9-14
Chi Square Test ......................................................................................... 9-22
GENERAL
This section describes performing the Auto Calibration, measuring the Background and
performing the Quality Assurance Tests (System Test, MDA Test and Chi Square Test).
COUNT TIME
The CAPRAC
®
-t counts using Live Time. Live Time is defined as the time during which the
MCA can actually measure a pulse.
Real Time is defined as the actual clock interval. The Live Time and Real Time are displayed
above the MCA spectrum on some measurement screens.
The CAPRAC
®
-t counts until the MCA's Live Time reaches the specified counting period. The
actual counting time (Real Time) is always greater than or equal to the requested Live Time.
The count rate is calculated from measured Live Time.
The MCA in the CAPRAC
®
-t measures each pulse that comes out of the Sodium
Iodide/Photomultiplier tube detector. To measure each pulse requires a finite amount of time.
During the time the MCA is measuring the pulse, another pulse cannot be measured. Any
other pulse that occurs during this time is not measured, and therefore, lost. During this time,
the MCA is said to be dead.
The Dead Time increases as counting rate increases. To ensure accurate results, the Dead
Time should not exceed 80%. Moving the source further away from the detector can
decrease the Percent Dead Time.
To calculate the Dead Time,