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γ-Spectrometry, High-Resolution, for Radionuclide Determination

Radiochemical Methods

  1. Harri I.K. Toivonen,
  2. Mika T. Nikkinen

Published Online: 15 SEP 2006

DOI: 10.1002/9780470027318.a6304

Encyclopedia of Analytical Chemistry

Encyclopedia of Analytical Chemistry

How to Cite

Toivonen, H. I. and Nikkinen, M. T. 2006. γ-Spectrometry, High-Resolution, for Radionuclide Determination. Encyclopedia of Analytical Chemistry. .

Author Information

  1. Radiation and Nuclear Safety Authority, Helsinki, Finland

  1. Preparatory Commission for the Comprehensive Nuclear Test-Ban-Treaty Organization, Vienna International Centre, Vienna, Austria

Publication History

  1. Published Online: 15 SEP 2006

Abstract

High-resolution γ-spectrometry is a nondestructive assay method that gives low detection limits for many radioactive nuclides. γ-Spectrometers use an electric field to collect the free charge carriers, electrons and holes, in a semiconductor detector. Modern detectors are based on high-purity germanium (HPGe). The material properties of germanium containing extremely low concentrations of impurity atoms are excellent at low temperature (77 K) for creating and collecting charges in the sensitive region of the detector. The major components of the spectrometer are the detector, cooling system, shielding system, signal processing unit, and analysis software. The charge created at the detector is directly proportional to the energy deposited in the detector by the radiation. The weak charge pulse is transformed, shaped and amplified to a voltage pulse, which is then converted to digital form. A multichannel analyzer (MCA) collects and stores the spectrum, which comprises counts partitioned among different channels according to energy dissipated in the detector. The spectrum contains peaks that can be unequivocally associated with certain radionuclides. Peak areas are proportional to the activity of the nuclide. Meticulous calibrations are required to operate the instrument properly. Software plays a major role in the analysis of the spectra, and interactive human work and artificial intelligence, i.e. an expert system, are needed to handle complex cases. Stable elements can be analyzed through neutron activation and subsequent γ-spectrometric determination. γ-Spectrometry is not a sensitive method for radionuclides that have a long half-life (≫30 years).