CHAPTER 8
160 PerkinElmer Life and Analytical Sciences
A misclassification (spillover) curve is created automatically by varying the PDD
values when counting a pure beta and a pure alpha standard. An instrument
determined optimum PDD value is established at the crossover point of the two
curves where there is minimal alpha and beta misclassification. The
misclassification curve information and its associated optimum PDD value is
stored in a library of such curves called the Alpha Beta Standards Library.
Figure 8-12 Alpha Beta Standards Curve
A specific misclassification curve can be associated for use with an alpha beta
radionuclide in the Alpha Beta Nuclide Library. By selecting the appropriate alpha
beta radionuclide in an assay, the PDD from the Alpha Beta Nuclide Library is used
by the assay as the criterion for alpha/beta separation.
Note: Alpha and beta standards are not mandatory in order to use
the alpha beta discrimination feature. You can enter a PDD value
manually for an alpha beta radionuclide. In this case, no alpha beta
misclassification curve is associated with the alpha beta
radionuclide. The PDD value is empirically determined. This
capability is useful when no alpha and beta standards are available
or it is not possible to obtain a pure beta and alpha standard as is
the case when counting
222
Rn which decays by both alpha and
beta emission.
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