Significance and Use
The enrichment meter principle provides a nondestructive measurement of the 235U fraction of uranium-bearing items. Sampling is not required and no waste is generated, minimizing exposure to hazardous materials and resulting in reduced sampling error.
Use of a low resolution detector (e.g., NaI detector) to measure uranium with 235U fraction approximately 10 % which is contained in a thin-walled container can provide a rapid (typically 100 s), easily portable measurement system with precision of 0.6 % and bias of less than 1 %.
Use of a high resolution detector (e.g., high-purity germanium) can provide measurement with a precision better than 0.2 % and a bias less than 1 % within a 300-sec measurement time when measuring uranium with 235U fraction in the range of 0.711 % to 4.46 % which is contained in thin-walled containers.
In order to obtain optimum results using this method, the chemical composition of the item must be well known, the container wall must permit transmission of the 185.7 keV gamma ray, and the uranium-bearing material within the item must be infinitely thick with respect to the 185.7 keV gamma ray.
Items must be homogeneous with respect to both 235U fraction and chemical composition.
The uranium-bearing materials in the measured items and calibration reference materials used for calibration must fill the detector field of view.
When measuring items, using low-resolution detectors, in thin-walled containers that have not reached secular equilibrium, either the method should not be used, additional corrections should be made to account for the age of the uranium, or high-resolution measurements should be performed.
The method is typically used as a verification technique, not to establish enrichment.
1.1 This test method covers the quantitative determination of the fraction of 235U in uranium using measurement of the 185.7 keV gamma ray produced during the decay of 235U.
1.2 This test method is applicable to items containing homogeneous uranium-bearing materials of known chemical composition in which the compound is considered infinitely thick with respect to 185.7 keV gamma rays.
1.3 This test method can be used for the entire range of 235U fraction, from depleted (0.2 % 235U) to very highly enriched (97.5 % 235U).
1.4 Measurement of items that have not reached secular equilibrium between 238U and 234Th, may not produce the stated bias when low-resolution detectors are used with the computational method listed in Appendix B.
1.5 This standard may involve hazardous materials, operations, and equipment. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.