Construction Of Calibration Curve Research Articles

External standardization in liquid scintillation counting of homogeneous samples labeled with one, two, or three isotopes

By properly selecting gain and discriminator settings for counting the external standard γ-source it is possible to obtain an exponential relationship between external standard count rate and quencher concentration. This allows the construction of linear calibration curves for counting efficiency of β-emitters versus external standard count rate for singlelabeled, as well as double- or triple-labeled, samples by using double logarithmic and semilogarithmic graphs. The degree of quenching of the sample is determined by a short preliminary count of the external standard source, using constant gain and discriminator settings regardless of the isotope under study. This allows the selection of optimal gain and discriminator settings for counting a sample containing up to three isotopes of different energy (e.g., 3H, 14C, and 32P) and an unknown quencher. Derivation of these instrument settings and of the resulting absolute efficiencies for the three isotopes in three different channels from the observed external standard count rate is described in detail.

The Preliminary Curve Method of Plate Calibration When Densities of Spectral Lines are Measured in Seidel Values or Changed to Seidel Values

A procedure is described for the precise and convenient construction of preliminary emulsion calibration curves using Seidel values. The method employs the calculation of coordinate points representing averages of readings within specific Seidel unit intervals A standard deviation of 1.15% was obtained for gamma values on repetitive calibration exposures using the described preliminary curve construction techniques. The reading of galvanometer deflection directly in Seidel units is recommended for maximum efficiency.

Simplified Method for Construction of Emulsion Calibration Curves

A modification of the two step method described by Cyrus Feldman (1) for construction of film calibration curves has simplified and speeded up this task in our spectrographic laboratory. Formerly we used a nomograph or a conversion table (1, 2) to find the value of the Seidel Function for a given transmittance to use in plotting the preliminary curve on linear graph paper. By making use of a specially prepared graph paper whose coordinates are labeled in terms of percent transmission but are proportional to values of the corresponding Seidel Functions, the data for the preliminary curve may be plotted directly (Figure 1), each point representing the percent transmission of the light step versus the percent transmission of the dark step for a given spectral line. These data are then averaged by drawing the best straight line through these points.