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The calibration of a low-energy photon germanium detector for use in the NAA kf0 standardization method

1990; Elsevier BV; Volume: 299; Issue: 1-3 Linguagem: Inglês

10.1016/0168-9002(90)90802-d

1872-9576

F. De Corte, M. C. Freitas, A. De Wispelaere,

Advanced X-ray and CT Imaging

To extend the NAA k0 method to LEPD counting, procedures were elaborated for determining the full-energy peak detection efficiency ϵp and the peak-to-total ratio P/T (yielding the total efficiency ϵt = ϵp/(P/T). ϵp is needed for concentration calculation. ϵp and ϵt are needed to correct for true coincidences (including KX and LX lines) in case of small source-detector separation. First the “reference” efficiency curve (logϵp,ref vs log E) was determined with calibrated point sources (from 4.65 keV (139Ce) to 383.9 keV (133Ba)) measured at ∼ 16 cm distance from the LEPD. The accuracy is ∼ 1–2% for E > 11 keV, and ∼ 5% for E < 11 keV. In view of actual analyses, ϵp,ref was converted to ϵp,geo (i.e. at a small distance from the LEPD) based on the calculation of the effective solid angles Ω with the program SOLANG. The accuracy of this, checked with practically coincidence-free lines of point sources measured close to the LEPD, was ∼ 5% on the average. After identifying the origin of all the pulses in the spectra, a P/Tcurve (logP/Tvs log E) was constructed from results obtained for the most prominent lines of some nine sources (from 5.9 keV (55Fe) to 320.1 keV (51Cr)). P/T was found to be practically independent of the source-detector separation. Its accuracy of ∼ 5% is satisfactory in view of the large error reduction. The results and conclusions reached here were obtained from experiments with two different LEPDs at the INW, Gent and the LNETI, Sacavém.