How Is Proper Calibration Achieved for SCAs Using Cesium-137?

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Discussion Overview

The discussion focuses on the calibration process for Single Channel Analyzers (SCAs) using Cesium-137, exploring the definitions and methodologies involved in achieving proper calibration for these instruments.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions what constitutes a proper calibration process for SCAs.
  • Another participant suggests that the calibration of a Photomultiplier Tube (PMT) could be achieved by measuring quantum efficiency as a function of wavelength using a weak light source.
  • A different participant proposes the use of a PMT connected to an NaI detector along with a NIM, amplifier, SCA, and counter for calibration purposes.
  • It is noted that calibrations are typically performed on SCAs and MCAs rather than the probes themselves, emphasizing the need to establish a relationship between voltage settings and photon energy detected, particularly using a region of interest (ROI) around the 612 keV to 712 keV range with Cesium-137.

Areas of Agreement / Disagreement

Participants express differing views on the calibration process, with no consensus reached on the best approach or definition of proper calibration.

Contextual Notes

The discussion does not clarify certain assumptions regarding the calibration process, such as the specific configurations of instruments or the implications of varying parameters during calibration.

Nomy-the wanderer
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What can be defined as a proper calibration process for such an instrument?
 
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The PMT itself ? Or integrated in an instrument ?

In pulse mode, what would give you the "calibration" of a PMT is the quantum efficiency as a function of wavelength. That can be done by having a weak light source of variable wavelength, and calibrating the count rate against the count rate of a PMT with known quantum efficiency for instance.
 
How about a PMT connected to an NaI detector, and a nim with an amplifier and a SCA + counter...
 
Calibrations are performed on SCAs and MCAs, not the probes (ie. the NaI probe)themselves. Since this is an SCA, you want to create a relationship between the knob that increases voltage and the energy of the photons being detected. This is done by creating a region of interest (ROI) and finding which setting of the knob creates the highest count rate in that ROI. Typically its performed with cesium-137 and an ROI of 612keV to 712 keV.
 

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