= Liquid scintillation counting
\b[Liquid scintillation counting] measures radiation through <light> produced in a liquid <scintillator> containing the radioactive sample. Energy deposited in the medium leads to optical emission, which <photomultipliers> detect as pulses. The apparatus is a <scintillation counter>, but the measured pulse rate still needs a model connecting it to <radioactive activity>.<A Review of NIST Primary Activity Standards for 18F: 1982 to 2013 by Denis E. Bergeron and others>[Section 2.1: scintillation medium, light conversion and photomultiplier detection.]{ref}
In an idealized one-count-per-decay model with background subtracted and other corrections negligible,
$$
r_{\mathrm{net}}=\varepsilon A,
$$
where $A$ is <radioactive activity> and $\varepsilon$ is <detection efficiency>. A hypothetical net rate of $100\,\mathrm{s^{-1}}$ with $\varepsilon=0.40$ corresponds to $A=250\,\mathrm{Bq}$. At the same activity, an efficiency of $0.20$ would produce only $50\,\mathrm{s^{-1}}$. A smaller count rate need not mean that fewer decays occur.
A motivating measurement example is <L. L. Lucas>'s comparison of <tritium>-containing water standards. <Liquid scintillation counting> supplied <massic activity> ratios that could be compared with independently recorded mass-based dilutions. Agreement within stated <measurement uncertainties> supports consistency of the standards; it does not turn the counting apparatus into an uncertainty-free activity meter.<Massic Activity Ratios of the NBS NIST Tritiated-Water Standards Issued Between 1954 and 1999 by L. L. Lucas>[Abstract, Journal of Research of NIST 105 (2000), pp. 535–539; DOI 10.6028/jres.105.042.]{ref}
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