PerkinElmer QuantaSmart 1694267, Reference Manual

Page: 218 / 218

CHAPTER 12
208 PerkinElmer Life and Analytical Sciences
Optimum Pulse Decay Discriminator
The optimum pulse decay discriminator minimizes the misclassification of alpha
events being counted as beta events, and vice versa. If the discriminator is set too
low, beta events are erroneously counted as alpha events. If the discriminator
time is set too high, alpha events are erroneously counted as beta events. An
optimum Pulse Decay Discriminator is established when counting an Alpha Beta
Standard Set.
To optimize the pulse discriminator setting, you must perform an Alpha Beta
Standards assay to count two standard sources, a pure beta emitter and a pure
alpha emitter. The composition of the standards must be as close as possible to
the chemistry and volume of the subsequent samples to be counted. When
counting the pure beta emitter source, the percent of beta events counted as
alpha events is plotted (and stored) as %Spill versus Discriminator value
(misclassification curve). When counting the pure alpha emitter source, the
percent of alpha events counted as beta events is also plotted. The optimum
discriminator value is where the spillover for both radionuclides is at a minimum.
Note:After counting the two standards, the optimum computed
discriminator setting is determined (minimal spill for both alpha
and beta events). You can manually adjust this setting to favor
either the alpha or the beta nuclide by entering the desired
discriminator setting for In Use.
Refer to page 156 for more information.