Symposium on International Safeguards: Linking Strategy, Implementation and People - IAEA CN-220

Yields of Gamma- and X-Ray Radiation of Alpha-Decays of 235U

23 Oct 2014, 09:50

20m

Room M3 (M Building)

oral NDA Measurements I: Gamma Spectrometry

Speaker

Vladimir Danilenko (LSRM Ltd)

Description

Precise knowledge of gamma- and X-rays emission probabilities of uranium isotopes is vital for accurate gamma-spectrometric determination of the isotopic composition and quantity of uranium. The peak intensity ratio methods employing high resolution gamma-spectrometry and intrinsic efficiency calibration approach are known to provide most accurate and reliable isotopic information. When applied to unshielded and moderately shielded material, these methods largely benefit from de-convolution of the 90-100 keV narrow spectral interval, which contains intense gamma- and X-ray lines of major uranium isotopes 235U and 238U. These are the 92.37 keV and 92.79 keV gamma-rays of 238U/234Th, and the 93.35 keV ThK1 X-rays from alpha-decay of 235U. Although the emission probability ratios of these lines were accurately established, their absolute yields are still lacking accuracy. For instance, as resulted from recent study [1], the yields of 234Th lines become corrected by ~30%, compared with their previous values. This consequently raised a question regarding validity of the yield data for the 93.35 keV line of 235U and triggered the present experimental study. This study was later extended to the reexamination of emission probabilities of other 235U gamma-lines with energies above 205 keV. The experimental data used in the current work was collected using SRM 969 and CRM 146 reference uranium samples. [1] Abousahl, S.; van Belle, P.; Lynch, B.; Ottmar, H., New Measurement of the Emission Probability of the 63.290 keV 234Th Gamma Ray from 238U Alpha Decay. Nuclear Instruments & Methods in Physics Research A 517 (2004) 211-218.