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Nuclear Detection Methods and Instrumentation

Radiochemical Methods

  1. A. Tsechanski1,2

Published Online: 15 SEP 2006

DOI: 10.1002/9780470027318.a6307

Encyclopedia of Analytical Chemistry

Encyclopedia of Analytical Chemistry

How to Cite

Tsechanski, A. 2006. Nuclear Detection Methods and Instrumentation. Encyclopedia of Analytical Chemistry. .

Author Information

  1. 1

    Ben-Gurion University of the Negev, Israel

  2. 2

    Soroka University Medical Center, Israel

Publication History

  1. Published Online: 15 SEP 2006

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Abstract

Nuclear detectors and associated electronics are among the most important components of analytical chemistry involving nuclear methods. Historically, the first and simplest particle detectors were gas-filled counters using an electric field to collect the free charge carriers, electrons and ions, produced in the counter by ionizing radiation. These detectors include ion chambers, proportional counters and Geiger counters. The charge created at the proportional counter is directly proportional to the energy deposited in the detector by a nuclear particle and, therefore, this kind of detector can be used for energy measurements of nuclear radiation (nuclear spectrometry). The main disadvantage of gas-filled detectors is their low efficiency for γ-rays. This is because the gas detection medium is low in density. From this point of view, solid detectors are considerably more advantageous. Of these detectors, the scintillation counter is one of the earliest and most widely used detectors of nuclear radiation. It consists of a detection medium (inorganic or organic scintillator) and a photomultiplier tube (PMT). The incident particle enters the scintillator and interacts with its atoms, raising them to excited states. De-excitation follows very rapidly by emission of light photons. The emitted photons are multiplied in the PMT, resulting in an output pulse of up to several volts. The high efficiency scintillation detectors are widely used in instrumental analytical chemistry including neutron activation analysis (NAA), both prompt neutron activation analysis (PNAA) and delayed neutron activation analysis (DNAA), and in X-ray flourescence analysis (XRFA). Contemporary high-resolution γ-spectrometry is based on solid-state ionization chambers. Only after the successful development of the technology for production of highly purified single crystals of germanium (Ge) and silicon (Si) did it become possible to develop Ge- and Si-based solid-state detectors by forming reverse-biased junctions and cooling the semiconductor to liquid nitrogen temperature (77 K). The most prominent feature of the semiconductor detectors is their excellent energy resolution and availability of large crystals with relative efficiencies up to 120% compared with a standard NaI(Tl) detector. High-resolution γ-ray spectrometry is widely used in evaluation of γ-emitting radioactive nuclides in various samples, in NAA, in a high-sensitivity particle-induced X-ray emission (PIXE) method and others. Nuclear detectors provide a variety of information on detected radiation (energy, type of the radiation, timing data, etc.) in the form of electronic signals. To obtain this information, the signal must be processed by the appropriate nuclear electronic system, which includes power supply, preamplifier, main amplifier and multichannel analyzer (MCA) for digital processing of the analog signals.