Studies on colour quenching liquid scintillation counting

Investigations of the relationship between absorbance, wavelength of absorption, and counting efficiency led to the development of an empirical method for the calculation of counting efficiency depending only on the spectral characteristics of the sample solution. Correlation of the separation between the wavelength of maximum absorbance of the sample and emission of the fluor was achieved, with this approach making the method quite general for any counter or fluor used. A separation of 20-30 nm indicates severe quenching whereas separations of 100 nm, and 150 nm or more indicate moderate and negligible quenching respectively. Comparison of the external standard ratio quench correction curves for colour and chemical quenching indicated a very slight difference between the two suggesting that the external standard ratio could be used for correction of both. A more detailed study than has been presented in the literature confirmed this view and established that the error incurred by use of one curve was at most six percent, which is quite acceptable for most uses. Pulse height distributions indicated that the counter response was the same for colour and chemical quenching in agreement with a previous proposition concerning logarithmically amplified counters. Further investigations, however, suggested that the original interpretation of the distributions could be in error, although it is not exactly clear at this stage what the cause is.