ST365 Radiation Counter Technical Manual
May 2020 – Revision 2.0
Spectrum Techniques, LLC
www.spectrumtechniques.com
Page 12 of 14
BASIC SCINTILLATION SYSTEM SETUP AND OPERATION
Step 1
CONNECT THE SCINTILLATION DETECTOR TO THE ST365
Connect one end of the BNC cable to the BNC connector on the detector. Then connect the other end of
the BNC cable to the BNC connector on the back of the ST365. Connect the HV cable in the same
manner.
Step 2
CONNECT THE POWER SUPPLY TO THE ST365
Connect the power supply to the connector on the back of the ST365 and plug the ST365 into a wall
outlet.
Step 3
POWER ON THE ST365
Press the ‘POWER’ button. Use the ‘UP’ and ‘DOWN’ arrow buttons, move to the SCINT mode. Then
use the ‘LEFT’ and ‘RIGHT’ arrow buttons to make sure the ST365 is set to ‘SCINT’ setting the
appropriate thresholds for use with a scintillation detector.
Step 4
SET HIGH VOLTAGE
Use the ‘UP’ and ‘DOWN’ arrow buttons, move to the HV mode. Then use the ‘LEFT’ and ‘RIGHT’ arrow
buttons to set the high voltage to the recommended value for the Scintillation detector.
Step 5
SET PRESET TIME (IF WANTED)
Use the ‘UP’ and ‘DOWN’ arrow buttons, move to the TIME mode. Then use the ‘LEFT’ and ‘RIGHT’
arrow buttons to set the desired preset time – for an indefinite count, set the preset time to zero.
Step 6
COUNT A RADIOACTIVE SAMPLE
Place a radioactive source close to the scintillation detector. Press the ‘OK’ button to start acquiring data.
To stop counting, press the ‘STOP/RESET’ button once, then to begin counting again, press the ‘OK’
button. To reset the elapsed time, press the ‘STOP/RESET’ button twice.
Sodium Iodide (NaI) Detector High Voltage Sweep
Unlike the Geiger Plateau of GM tubes, there is not an obvious ‘correct’ operating voltage for a scintillation detector.
The ST365 sets the gain of the sodium iodide (NaI) detector by the high voltage it applies to the photo multiplier tube
(PMT) – a higher voltage operates the PMT at a higher gain. By performing a ‘sweep’ of the high voltage using the
known energies of different radioactive sources, the user can experimentally determine the voltage threshold for the
ST365. The procedure below describes this process in detail.
Step 1
DETERMINE WHICH RADIOACTIVE SOURCE HAS THE HIGHEST NUMBER OF COUNTS AND SET
AN APPROPRIATE PRESET TIME
Set the ST365 high voltage to the maximum 1200 Volts. Count each source for the same time. Find the
sample with the highest count rate. Increase or decrease the count time to give a reading that does not
overflow the counter display.
