PerkinElmer QuantaSmart 1694267, Reference Manual

Page: 217 / 218

THEORY
PerkinElmer Life and Analytical Sciences 207
Alpha Beta Counting Theory
Alpha and beta emitting radionuclides may be counted simultaneously in the same
liquid scintillation sample. Some alpha and beta nuclide energies may overlap in
the LSC environment, and their spectra are not resolvable with simple energy
discrimination. To separate alpha and beta nuclide energies, you must take
advantage of their differing pulse decay times. The pulse decay analysis (PDA)
method of discrimination is used by the Tri-Carb instruments equipped with the
Alpha/Beta capability.
Pulse Decay Analysis (PDA)
A scintillation (light) pulse consists of a prompt (initial) component and delayed
(slow) component. Each component contributes to the total amount of light which
makes up the pulse, and determines the pulse decay time. Beta nuclides typically
produce a minimal slow component leading to a fast decay time. Alpha nuclides
produce a significant slow component which increases their overall decay time.
Pulse Decay Analysis uses the differences in pulse duration to discriminate
between alpha and beta nuclide pulses. The pulses are sorted into separate
multichannel analyzers for subsequent analysis and quantitation.
A time-based Pulse Decay Discriminator (PDD) is used to optimize the separation
of alpha and beta pulses. The PDD may be adjusted by the operator, or the
system, to determine the optimum setting for specific sample conditions.
The optimum PDD is influenced by sample chemistry, vial type, geometry and
degree of quenching. To obtain the best results, it is necessary to determine the
optimum PDD for each type of sample.
Refer to page 159 for more information regarding Alpha Beta counting.