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A neutron source for IGISOL-JYFLTRAP: Design and characterisation
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
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2017 (English)In: European Physical Journal A, ISSN 1434-6001, E-ISSN 1434-601X, Vol. 53, no 173Article in journal (Refereed) Published
Abstract [en]

A white neutron source based on the Be(p,nx) reaction for fission studies at the IGISOLJYFLTRAP facility has been designed and tested. 30 MeV protons impinge on a 5mm thick water-cooled beryllium disc. The source was designed to produce at least 1012 fast neutrons/s on a secondary fission target, in order to reach competitive production rates of fission products far from the valley of stability.

The Monte Carlo codes MCNPX and FLUKA were used in the design phase to simulate the neutron energy spectra. Two experiments to characterise the neutron field were performed: the first was carried out at The Svedberg Laboratory in Uppsala (SE), using an Extended-Range Bonner Sphere Spectrometer and a liquid scintillator which used the time-of-flight (TOF) method to determine the energy of the neutrons; the second employed Thin-Film Breakdown Counters for the measurement of the TOF, and activation foils, at the IGISOL facility in Jyväskylä (FI). Design considerations and the results of the two characterisation measurements are presented, providing benchmarks for the simulations.

Place, publisher, year, edition, pages
2017. Vol. 53, no 173
National Category
Subatomic Physics
Identifiers
URN: urn:nbn:se:uu:diva-328569DOI: 10.1140/epja/i2017-12362-xISI: 000408661200001OAI: oai:DiVA.org:uu-328569DiVA, id: diva2:1136262
Funder
Swedish Radiation Safety AuthoritySwedish Nuclear Fuel and Waste Management Company, SKBAvailable from: 2017-08-26 Created: 2017-08-26 Last updated: 2017-12-01Bibliographically approved
In thesis
1. Studying neutron-induced fission at IGISOL-4: From neutron source to yield measurements and model comparisons
Open this publication in new window or tab >>Studying neutron-induced fission at IGISOL-4: From neutron source to yield measurements and model comparisons
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fission yields represent the probability of producing a certain nuclide in a fission event, and are important observables for fission research. For applications, accurate knowledge of the yields is fundamental at all stages of the fuel cycle of nuclear reactors, e.g., for reactivity calculations, or to estimate (spent) fuel inventory. Fission yields also help in the basic understanding of the fission process, for nucleosynthesis models, and for radioactive ion beam production.

This thesis was developed in the framework of the AlFONS project, the objective of which was to measure neutron-induced fission yields of relevance for partitioning and transmutation of spent fuel. The work is performed at the IGISOL-4 facility in JYFL (University of Jyväskylä).

The first part of this thesis work is dedicated to the development and characterisation of a suitable 9Be(p(30MeV),nx) neutron source for IGISOL-4. The neutron energy spectrum and the neutron yield from a 5mm thick converter were studied with Monte Carlo simulations. Two characterisation campaigns that validated the MCNPX code were also performed. At the maximum current available from the cyclotron at JYFL, a total neutron yield between 2 and 5×1012 neutrons/(sr s) can be obtained. This satisfies the design goal for studies of fission yields.

The neutron source was used in the measurement of fission yields from high-energy neutron-induced fission of natU at IGISOL-4, discussed in the second part of this thesis. The fission products were online-separated with a dipole magnet. The isobars, with masses in the range A = 128-133, were identified using γ-spectroscopy. Data for the relative yields of tin and antimony, as well as isomeric yield ratios for five nuclides will be reported. The yields show trends not observed in the ENDF/B-VII.1 evaluation, and only in part confirmed by the GEF model.

The final part of this thesis concerns a study of the performance of different nuclear model codes, that aim at describing the states of the fission fragments right after scission. Reproduction of experimental data serves to benchmark the models and it indicates, to some extent, how reliably the results can be extrapolated to regions where no data exist.

A methodology to compare and test these models has been developed, which was implemented in the DEℓFIN code. DEℓFIN takes the excited fission fragments, defined by the model under test, and de-excites them in a standardised way using the nuclear model code TALYS. Eliminating any variability in the way the final observables are extracted helps focusing on each model's assumptions. DEℓFIN was tested on five models, and interesting features in the prompt neutron multiplicity were found for some of them. This study will promote a better understanding of the ideas used in the development of fission models.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. p. 109
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1550
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-328484 (URN)978-91-513-0052-8 (ISBN)
Public defence
2017-10-13, 4001, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2017-09-20 Created: 2017-08-28 Last updated: 2017-10-17

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Mattera, AndreaPomp, StephanLantz, MattiasRakopoulos, VasileiosSolders, AndreasAl-Adili, AliPassoth, ElkeProkofiev, AlexanderAndersson, PeterHjalmarsson, Anders

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Mattera, AndreaPomp, StephanLantz, MattiasRakopoulos, VasileiosSolders, AndreasAl-Adili, AliPassoth, ElkeProkofiev, AlexanderAndersson, PeterHjalmarsson, Anders
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Applied Nuclear PhysicsThe Svedberg Laboratory
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