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Radionuclides in Drinking Water

Module 4: Detection Techniques


There are four principal methods of radiation detection used in the radiochemical laboratory. These are:

  • alpha spectrometry,
  • gas proportional counting,
  • gamma spectrometry, and
  • liquid scintillation counting.

The methods of interaction of radiation with matter are discussed in great detail in the individual sub-parts to this module. In each case either ionization or excitation of the detection medium caused by the decay particle is used for detection.

The practical details of calibration and maintenance of the instruments are also covered in these modules. Each section of this module should take 45-60 minutes to complete.

Instructional Resources

This module is divided into 6 tutorials. Each tutorial is presented as a self-paced Adobe Flash video with audio narration. The learning aids that are provided for you to use in this module, which you may access via the links in the "Instructional Resources" panel on the right, include the "Multi-Agency Radiological Laboratory Analytical Protocols Manual" (MARLAP) chapter on the quantification of radionuclides. Information about alpha particle energy standards and the NuDat database is provided under "Links to Additional Information". You may wish to print out the PDF transcript of the audio narration, also available from a link in the "Instructional Resources" panel. The "Links to Additional Information" provide more in-depth discussions of these topic areas.


Tutorial 4.1 - Basics of Radiation Interaction with Matter

At the end of this tutorial you will be able to:

  • Explain the different ways that alpha and beta particles interact with matter.
  • Identify which type(s) of detector are appropriate for which type of alpha or beta interaction.
  • Describe the three ways that gamma rays interact with matter.
  • State which gamma ray interactions lead to full energy peaks, Compton continuums, and annihilation peaks on gamma spectra.
  • Define the terms "decay scheme" and "fractional abundance factor" and describe their importance in gamma ray spectrometry.

Tutorial 4.2 - Liquid Scintillation Counting: Theory and Analysis

At the end of this tutorial you will be able to:

  • List the components of a liquid scintillation cocktail and describe their function.
  • Define the terms "background," "coincidence circuit," "quench," "QIP," and "efficiency" as they relate to liquid scintillation counting.
  • Describe how the "H Number" is determined and how it relates to counting efficiency.
  • Examine a liquid scintillation spectrum to identify possible radionuclide contamination.

Tutorial 4.3 - The Basics of Gas Proportional Counting

At the end of this tutorial you will be able to:

  • Define "voltage plateau" and "operating voltage" and describe how they are established for a GPC.
  • Explain how a GPC distinguishes between alpha and beta pulses.
  • Describe how the alpha and beta discriminators are set.
  • Define the terms "crosstalk" and "dead-band" and identify one means of minimizing cross-talk in radionuclide specific analysis.
  • Explain why GPC can be used for quantitative evaluations only after the sample has been radiochemically separated.

Tutorial 4.4 - Alpha Spectrometry 1: Principles

At the end of this tutorial you will be able to:

  • Understand the characteristics of alpha particles as they relate to solid-state alpha spectrometry detection.
  • Discuss the terms "energy levels" "region of interest (ROI)" "full width half maximum (FWHM)," and "resolution" as they apply to alpha particle detectors.
  • Describe the methods used to obtain accurate alpha particle counts.
  • List the steps that can be taken to improve poor alpha particle peak resolution.

Tutorial 4.5 - Alpha Spectrometry 2: Calibration and Calculations

At the end of this tutorial you will be able to:

  • Describe the principles for calibrating an alpha spectrometer.
  • Calculate the efficiency of an alpha detector.
  • Calculate the alpha activity of a sample in the presence of a tracer.
  • Discuss how the terms "efficiency" "decay factor" and "abundance factor" are applied to the analytical calculation.

Tutorial 4.6 - Gamma Spectrum Analysis

At the end of this tutorial, you will be able to:

  • Describe how gamma spectrometers record signals resulting from the photoelectric effect, the Compton effect, and the pair production effect.
  • Discuss how software parameters such as key line, peak centroid, energy tolerance, and FWHM are used to determine if a peak is "valid."
  • Identify the most common features and artifacts present in gamma spectra.
  • List at least four factors that should be considered when attempting to identify an unidentified peak.

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