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Measurement of nuclear decay data of U-235

Progress Report 2004-05-31

The project is close to be finished. All measurements have been finished at IRMM and CIEMAT and 5 reference spectra have been sent to all participants. Significant improvements have been attained in the quality of spectra as compared to previous measurements.Spectral processing has been carried out at participant laboratories using proprietary codes (CIEMAT, IRMM, UEX) or codes from other national laboratories (NPL from LNHB). The final coordination meeting was held at University of Extremadura, Badajoz, Spain, 26-28 April 2004. Results from all participants were discussed and a preliminary set of values for alpha-particle emission probabilities and energies of U-235 have been obtained. A few additional calculations are still needed before a final set of values is proposed. They concern the energies of the alpha lines whose accurate determination is hampered by the non-linear response of the measurement system.The final results will be sent for publication as soon as they become available during this year. U-235 is one of the most important nuclides in the nuclear fuel cycle, with special significance in safeguards problems. This project will focus on the determination of some selected nuclear decay data, which are necessary for the standardization of this nuclide. In particular, alpha-particle emission probabilities will be remeasured. Previous measurements were made 30 years ago and it can be expected that, with the advances in detectors and spectral fitting techniques, a new set of values with significantly lower uncertainties will be obtained. Gamma-ray emission probabilities for some selected transitions will also be determined.

The output will contribute towards obtaining a consistent set of decay data of U-235, which is the basis for a complete study of the decay scheme. Measurements of U-235 in environmental and nuclear materials will directly benefit from this project.

Final Report 2005-05-18

The project was successfully completed.

Alpha-particle emission probabilities and energies of 13 alpha transitions of 235U have been determined with improved accuracy. High purity sources were measured with silicon detectors and the resulting spectra processed in all participant laboratories.

The main results were quoted in the paper:

"Alpha-Particle Emission Probabilities in the Decay of 235U", Eduardo García-Toraño, M. Teresa Crespo, Miguel Roteta, Goedele Sibbens, Stefaan Pommé, Alejandro Martín Sánchez, M. Pilar Rubio Montero, Simon Woods, Andy Pearce. (Accepted for publication in Nuclear Instruments and Methods, section A.)

Ionising Radiation (IR)
Eduardo Garcia Torano, CIEMAT (Spain)
Phone: +34 91 34 66 225
Fax: +34 91 34 66 442
Coordinating Institute
CIEMAT (Spain)
Participating Partners
NPL (United Kingdom)
Further Partners
Univ. of Extremadura
JRC-Geel (BE)


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