Stabilization of the counting rate by irradiation of the liquid scintillation counting solutions with UV-light
While counting certain compounds, labeled with tritium or S 35, by liquid scintillation counting, we observed that the counting rates decreased rapidly during the first 2-3 hours. Even after this time, the counting rates continued to decline, but at a slower rate. The influence of temperature, agitation of the vials, and addition of alcohol upon this phenomenon was investigated. In each case the counting rates decreased, except with additions of 2 ml or more of ethanol. All ethanol additions to the stock solutions produced a quenching of the counting rates. However, an irradiation of the stock solutions with UV-light of 2537 Å (Hg-line) stabilized the counting rates even without appearance of quenching. A possible theoretical explanation of these observations is given.