G. P. Westphal, F. Grass, H. Lemmel, J.H. Sterba, P. Schröder, Ch. Bloch:
"Automatic activation analysis";
Journal of Radioanalytical and Nuclear Chemistry,
Automatic activation analysis (AAA) is rendered possible by a unique neutron activation analysis facility for short-lived isomeric transitions based
on a fast rabbit system with sample changer and sample separation, and an adaptive digital gamma-spectrometer for very high counting rates of up
to 106 cps. The system is controlled by a computer program performing irradiation control, neutron flux monitoring, and gamma-spectrometry with
real-time correction of counting losses, spectra evaluation, nuclide identification and calculation of concentrations in a fully automatic procedure.
As spectrometry is done by means of hundreds of sequentially measured pairs of concurrently recorded loss-corrected and non-corrected spectra,
concentrations are derived from an optimally weighted average of all individual occurrences in this sequence of spectra which also enable the
separation of isomeric transitions with coinciding energies but different half-lives such as 116m2In (162.4 keV, T1/2 = 2.2 s) and 77mSe (162.2 keV,
T1/2 = 17.4 s). To clear up repeatedly voiced misconceptions concerning the errors of loss-free counting our findings of 1978 and 1981 are
reiterated, namely that the counting error of a peak in a corrected spectrum may be derived consistently from the error of the same peak in the
respective non-corrected spectrum and from the error of weighting factors in the corresponding region of interest, according to the principle of
propagation of errors. Experimental proof is provided for conditions of stationary as well as rapidly varying counting rates and spectral shapes.
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