Scintillation, rare gases

Small amounts of organic compounds of low ionization potential (see Section 4.2) can be dissolved in liquefied rare gases. The solubility increases from argon to xenon. The scintillation light leads to single photon ionization from which electron/ion pairs originate. The electrons are detected in the usual manner with a charge-sensitive amplifier (see Section 2.10). This way the sensitivity and resolution of rare gas liquid detectors can be improved. Another method uses the scintillation photons to eject electrons from a photocathode (Aprile et al., 1994). 

Alpha rays are counted with the use of an ioniration chamber, a windowless gas-flow proportional counter, a liquid scintillation counter, or a Si barrier detector. Autoradiography is also effective for a particles. However, a-emitting nuclides are rarely used in ordinary tracer works. 

Gas-filled detectors, such as ionization chambers, proportional counters, and Geiger-Miiller counters are mainly sensitive to P-radia-tion. They rarely allow any selection on the basis of energy. Gamma counting with a selection for energy is called gamma spectrometry and is performed by means of scintillation or semiconductor detectors. Currently the gamma spectrometric measurements in neutron activation analysis are only performed with semiconductor detectors. Scintillation counters will therefore be discussed only briefly. 

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