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--- textbook:nrctextbook:chapter12 [2025-04-24 15:37]
Merja Herzig
+++ textbook:nrctextbook:chapter12 [2025-04-28 11:17] (current)
Merja Herzig
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-The count rate of the unknown sample is then divided by the counting efficiency to get its activity, $A = \frac{{cpm_1 \times 100}}{{E(\%)}}$.
+The count rate of the unknown sample is then divided by the [[textbook:nrctextbook:chapter8#counting_efficiency|counting efficiency]] to get its activity, $A = \frac{{cpm_1 \times 100}}{{E(\%)}}$.
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 {{anchor:external_standard_ratio_lsc}}
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 The determination of [[textbook:nrctextbook:chapter11#alpha_emitters|alpha_emitters]] by liquid scintillation counter is a very convenient method. The sample preparation is considerably simpler than when measuring with [[textbook:nrctextbook:chapter11#semiconductor_detectors_alpha|semiconductor detectors]]. For measurement with semiconductor detectors the sample must be very thin, i.e. "massless", so that the alpha radiation is not absorbed into the sample. In liquid scintillation counting, this is not generally a problem, because alpha-emitting radionuclides mixed with liquid [[textbook:nrctextbook:chapter12#scintillation_cocktail|scintillation cocktail]]
-are in immediate contact with the scintillator. Since the energies of [[textbook:nrctextbook:chapter5#alpha_particle|alpha particles]] are high, generally 4-6 MeV, in practice their [[textbook:nrctextbook:chapter8#counting_efficiency|detection efficiency]] is nearly 100% and [[textbook:nrctextbook:chapter12# quenching |quenching]] is usually not a problem. In addition, because the liquid scintillation counters have sample changer, its measurement capacity is superior to that of the semiconductor. The disadvantage that liquid scintillation counting has compared to the semiconductor detectors is its significantly worse [[textbook:nrctextbook:chapter8#energy_resolution|energy resolution]]. The best semiconductor detectors will yield a peak width values at half maximum of 10-20 keV, while liquid scintillation counters get, at best, only 200 keV. Therefore, alpha energies that are close to each other are not able to be measured separately with a liquid scintillation counter. Another problem in measuring alpha radiation with a liquid scintillation counter h when measuring environmental samples is the fact that the beta radiation forms a high background that interferes with the measurement. Today, however, there are liquid scintillation counters capable of differentiating between the pulses caused by alpha particles from those caused by beta particles.
+are in immediate contact with the scintillator. Since the energies of [[textbook:nrctextbook:chapter5#alpha_particle|alpha particles]] are high, generally 4-6 MeV, in practice their [[textbook:nrctextbook:chapter8#counting_efficiency|detection efficiency]] is nearly 100% and [[textbook:nrctextbook:chapter12#quenching|quenching]] is usually not a problem. In addition, because the liquid scintillation counters have sample changer, its measurement capacity is superior to that of the semiconductor. The disadvantage that liquid scintillation counting has compared to the semiconductor detectors is its significantly worse [[textbook:nrctextbook:chapter8#energy_resolution|energy resolution]]. The best semiconductor detectors will yield a peak width values at half maximum of 10-20 keV, while liquid scintillation counters get, at best, only 200 keV. Therefore, alpha energies that are close to each other are not able to be measured separately with a liquid scintillation counter. Another problem in measuring alpha radiation with a liquid scintillation counter h when measuring environmental samples is the fact that the beta radiation forms a high background that interferes with the measurement. Today, however, there are liquid scintillation counters capable of differentiating between the pulses caused by alpha particles from those caused by beta particles.
 The electric pulse induced by beta particles is considerably shorter, around a few nanoseconds, than the alpha particle induced pulse that lasts several tens of nanoseconds. Below is a spectrum, in which there are alpha peaks of <sup>226</sup>Ra and its daughters, and the beta spectrum of <sup>226</sup>Ra daughter nuclides separated by the pulse shape analysis.
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