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|Title: ||A novel approach for neutron-capture studies of 235U and 238U|
|Authors: ||Wallner, A|
|Keywords: ||URANIUM 235|
|Issue Date: ||25-Mar-2011|
|Publisher: ||12th International Conference on Accelerator Mass Spectrometry, 20-25 March 2011, Wellington, New Zealand|
|Citation: ||Wallner, A., Belgya, T., Bichler, M., Buczak, K., Dillmann, I., Käppeler, F., 4, Mengoni, A., Quinto, F., (2011). A novel approach for neutron-capture studies of 235U and 238U. 12th International Conference on Accelerator Mass Spectrometry (AMS 12), 20th - 25th March 2011. Museum of New Zealand: Te Papa Tongarewa, Wellington, New Zealand.|
|Abstract: ||Improved and highly accurate nuclear data are urgently required for the design of advanced
reactor concepts. This demand holds for minor actinides but also for the main fuel materials.
Existing data were measured by detection of the prompt capture γ-rays. A major difficulty in these
experiments is the safe discrimination against the strong γ-background from the competing fission
channel. Recent studies exhibit critical discrepancies at keV energies for both, 235U(n,γ) and
238U(n,γ) with great impact on the keff-value of fission reactors. Neutron activation with subsequent
accelerator mass spectrometry (AMS) measurement of the reaction product represents an
independent technique, where interference from fission is completely excluded.
Within the European EFNUDAT project, new measurements were performed with the goal to
determine the neutron capture cross sections of 235U and 238U via neutron irradiations at thermal
(cold) and keV energies: Activations were performed with cold neutrons (Budapest Research
Reactor), thermal (Atominstitut, Vienna) and with neutrons of 25 and 450 keV (Karlsruhe Institute
of Technology). The produced long-lived 236U and the decay product of 239U, 239Pu were
subsequently counted by AMS at the Vienna Environmental Research Accelerator (VERA).
This method for measuring the neutron capture cross section has the advantages that the involved
systematic uncertainties are in no way correlated with those inherent to previous techniques.
Therefore, this experiment provides important and independent information for these key reactions
of reactor physics with uncertainties expected below 5%. The high sensitivity of AMS requires only
very small samples.
New results for 235U(n,γ)236U and 238U(n,γ)239U in the energy range from thermal to 500 keV will be
presented. The challenges of measuring 236U/238U isotope ratios at the 10-12 level and to quantify
239Pu with high precision will be highlighted. Finally, the potential for extending that method to
other isotopes in that mass range will be discussed. Copyright (c) 2011 AMS12|
|Appears in Collections:||Conference Publications|
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