Standard Practice for NaI(Tl) Gamma-Ray Spectrometry of Water

Importancia y uso:

5.1 Gamma-ray spectrometry is used to identify radionuclides and to make quantitative measurements. Use of a computer and a library of standard spectra will be required for quantitative analysis of complex mixtures of nuclides.

5.2 Variation of the physical geometry of the sample and its relationship with the detector will produce both qualitative and quantitative variations in the gamma-ray spectrum. To adequately account for these geometry effects, calibrations are designed to duplicate all conditions including source-to-detector distance, sample shape and size, and sample matrix encountered when samples are measured. This means that a complete set of library standards may be required for each geometry and sample to detector distance combination that will be used.

5.3 Since some spectrometry systems are calibrated at many discrete distances from the detector, a wide range of activity levels can be measured on the same detector. For high-level samples, extremely low efficiency geometries may be used. Quantitative measurements can be made accurately and precisely when high activity level samples are placed at distances of 1 m or more from the detector.

5.4 Electronic problems, such as erroneous deadtime correction, loss of resolution, and random summing, may be avoided by keeping the gross count rate below 2000 counts per second and also keeping the deadtime of the analyzer below 5 %. Total counting time is governed by the activity of the sample, the detector source distance, and the acceptable Poisson counting uncertainty.

Subcomité:

D19.04

Referida por:

C1475-17

Volúmen:

11.02

Número ICS:

13.060.30 (Sewage water)

Palabras clave:

gamma pulse height analysis; gamma ray spectrometry; multichannel analyzer; sodium iodide detector;