Abstract: Apparatus and a method for determining a quench-indicating parameter of a test sample utilizing a liquid scintillation counter are disclosed. The number of counts in a spectrum resulting from subtraction of a spectrum generated without an external source of radiation from a spectrum generated with an external source of radiation is utilized. The total number of counts is cumulatively summed from a higher energy level to a lower energy level and a curve representing this sum is generated. A portion of this curve is fitted with a function such as a straight line and the intersection of that function with the zero count axis is the intersection energy level which is an indication of the measure of quench of the test sample.