Determination of lithium by instrumental neutron activation analysis

The fast transfer system in the DR 2 reactor for irradiation at a thermal neutron flux density of 10¹³ n·cm⁻²·sec⁻¹ was used for the determination of lithium by the⁷Li(n, γ)⁸Li reaction. β-counting with a large perspex Cerenkov detector begun at 0.3 s after the end of irradiation, and multi-scaler data was accumulated in 300 channels at 0.1 s per channel. With a suitable choice of discrimination level only¹⁶N and background interfere, and the 0.84 s half-life of⁸Li was resolved by the method of weighted least squares. Results are presented for 36 international geochemical reference materials, and for a few biological samples, including BOWEN's kale and the NBS Standard Reference Material 1571 Orchard Leaves.     

A gamma-spectrometry system for activation analysis

Based on a Preloaded Digital Filter operating on a 20% n-type HpGe detector with transistor reset preamplifier, and on a software implementation of a loss-free counting MCA, storing immediately into the multi-megabyte main memory of a low-cost 486-type PC, the new system enables the collection of up to 120 pairs of simultaneously recorded loss-corrected and non-corrected spectra of 16 k channels each, in a true sequence without time gaps in between, at a throughput rate of up to 140 kc/s. Intended for activation analysis of short-lived isomeric transitions, the system for the first time makes possible peak to background optimizations and even separations of lines with different half-lives without an a priori knowledge of sample composition by summing up appropriate numbers of spectra over appropriate intervals of time. The speed of this programmable system also made possible the direct comparison of two methods of real-time correction of counting loss, by simultaneous recording of LFC-corrected, ZDT^tm -corrected and non-corrected spectra together with their corresponding weighting factor distributions.