Standard Test Method for Determination of Uranium Isotopic Composition by Gamma-Ray Spectrometry

Importancia y uso:

4.1 The determination of uranium isotopic composition by gamma-ray spectrometry is a nondestructive technique and when used with other nondestructive techniques that quantify a single isotope, such as Test Methods C1133 (Segmented Gamma Scanning), C1221 (Solution Assay), C1455 (Holdup),and C1718 (Tomographic Gamma Scanning), can provide a wholly nondestructive assay of uranium mass necessary for material accountancy and safeguards needs. This method can be used with calorimetry (Test Method C1458) for kilogram quantities of high-enriched uranium and is also used to convert an Active-Well Coincidence Counter (4) measurement of ²³⁵U mass to total uranium mass.

4.2 Because gamma-ray spectrometry systems are typically automated, the routine use of the test method is fast, reliable, and is not labor intensive. The test method is nondestructive, requires no sample preparation, and does not create waste disposal problems.

4.3 The test method does not require that the system be calibrated to a specific geometry.

4.4 The test method assumes that all uranium in the measured item has the same isotopic distribution. This is often termed isotopic homogeneity.

4.5 The application of the test method does not depend upon the physical or chemical form of the material being analyzed.

4.6 The ²³⁶U abundance is not measured by this test method and must be estimated from isotopic correlation techniques, stream averages, historical information, or other measurement techniques.

4.7 The isotopic composition of a given item of uranium is an attribute of that item and, once determined, can be used in subsequent inventory measurements to verify the identity of an item within the measurement uncertainties.

4.8 The method can also measure the ratio of other gamma-emitting isotopes in the measured item to uranium assuming they have the same spatial distribution as the uranium in the item. Some of these “other” gamma-emitting isotopes include daughter isotopes of uranium, cesium, and other fission products.

4.9 The method can be applied to gamma and x rays in two overlapping energy regions, depending upon the nature of the measured item, its containment, and the characteristics of the detector used for data acquisition.

4.9.1 60 keV to 250 keV—This energy range requires good energy resolution provided by planar or semi-planar HPGe detectors. The analysis methods must be capable of deconvoluting the x-ray peak line shapes from the gamma-ray peak shapes.

4.9.2 120 keV to 1010 keV—This energy range generally requires higher efficiency detectors typified by larger coaxial detectors (> 25 % relative efficiency) or large semi-planar detectors (> 30 mm thick).

4.10 Fig. 1 shows the decays that produce most of the prominent gamma and x rays that are measured in this analysis.

(A) Energies and Branching Intensities from Ref (1).(B) Uncertainties in parentheses are absolute 1σ values.(C) Relative values from unweighted mean of plutonium decay data from Ref (1).

Subcomité:

C26.10

Volúmen:

12.01

Número ICS:

27.120.30 (Fissile materials and nuclear fuel technology)

Palabras clave:

enrichment; gamma-ray spectrometry; isotopics; nondestructive assay; peak ratio; special nuclear material; uranium;