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Production of Sn and Sb isotopes in high-energy neutron induced fission of natU
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.ORCID iD: 0000-0002-1990-5083
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.ORCID iD: 0000-0003-4725-3083
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2018 (English)In: European Physical Journal A, ISSN 1434-6001, E-ISSN 1434-601X, Vol. 54, article id 33Article in journal (Refereed) Published
Abstract [en]

The first systematic measurement of neutron-induced fission yields has been performed at the upgraded IGISOL-4 facility at the University of Jyvaskyla, Finland. The fission products from high-energy neutron-induced fission of U-nat were stopped in a gas cell filled with helium buffer gas, and were online separated with a dipole magnet. The isobars, with masses in the range A = 128-133, were transported to a tape-implantation station and identified using gamma-spectroscopy. We report here the relative cumulative isotopic yields of tin (Z = 50) and the relative independent isotopic yields of antimony (Z = 51). Isomeric yield ratios were also obtained for five nuclides. The yields of tin show a staggered behaviour around A = 131, not observed in the ENDF/B-VII. 1 evaluation. The yields of antimony also contradict the trend from the evaluation, but are in agreement with a calculation performed using the GEF model that shows the yield increasing with mass in the range A = 128-133.

Place, publisher, year, edition, pages
2018. Vol. 54, article id 33
National Category
Subatomic Physics
Identifiers
URN: urn:nbn:se:uu:diva-328572DOI: 10.1140/epja/i2018-12462-1ISI: 000428637900002OAI: oai:DiVA.org:uu-328572DiVA, id: diva2:1136264
Funder
EU, FP7, Seventh Framework Programme, 605203Swedish Radiation Safety AuthoritySwedish Nuclear Fuel and Waste Management Company, SKBAvailable from: 2017-08-26 Created: 2017-08-26 Last updated: 2018-11-06Bibliographically 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
2. Isomeric yield ratio measurements with JYFLTRAP: In quest of the angular momentum of the primary fragments
Open this publication in new window or tab >>Isomeric yield ratio measurements with JYFLTRAP: In quest of the angular momentum of the primary fragments
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, isomeric yield ratios of twenty nuclides produced in the fission of natU and 232Th by protons at 25-MeV and natU by high-energy neutrons were studied. The experiments were performed at the IGISOL-JYFLTRAP facility at the University of Jyväskylä. It is the first time that direct ion counting is used for the determination of the intensities of the states of interest, thus avoiding dependency on knowledge of nuclear decay schemes and properties. This was possible due to the superior resolution of a Penning trap which was utilized for this work. Two different techniques were employed, namely the sideband cooling technique and the phase-imaging ion-cyclotron-resonance technique. With the former, a mass resolving power of m/δm = 105 can be routinely achieved, while the latter, which was recently implemented at JYFLTRAP, offers an increase in the mass resolving power by a factor of ten. In addition, isomeric yield ratios were also determined by means of γ-ray spectroscopy.

From a comparison of the same isomeric pair from two different reactions, a dependency on the fissioning system can be observed. This indicates an effect of the fission mode to the yield ratio. Moreover, the evolution of the odd-A isotopes of Cd and In in the mass range A = 119 - 127 exhibit two distinguishably different trends. The ratios for the isotopes of In decrease with increasing mass, while the ratios for the isotopes of Cd are almost constant until mass number A = 125, where an increase can be noticed.

The origins of the angular momentum in the fission fragments is one of the long-standing questions regarding the fission process. Surprisingly, fission fragments have been observed to carry a considerable amount of angular momentum, even from fissioning systems with very low (or even zero) angular momentum. So far, the angular momentum can only be inferred from other fission observables, such as the isomeric yield ratios. In this work, a methodology was developed in order to deduce the root-mean-square angular momentum (Jrms) of the primary fragments by employing the nuclear reaction code TALYS.

Lower values of Jrms for the more spherical nuclei, near the closed-shell neutron configuration at N = 82, and higher ones for fragments with odd proton number have been deduced, in agreement with other studies. Moreover, a correlation between the angular momentum of the primary fragments with the electric quadrupole moments of the products was observed for the isotopes of In. The data can be used to gain insight into scission configuration and as guide for models that propose mechanisms for the generation of the angular momentum. Furthermore, the observed correlation is an indication of the role that the repulsive Coulomb force, together with the shape of the nascent fragment, play in the generation of the fragments’ angular momentum.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 120
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1743
Keywords
Nuclear physics, nuclear fission, angular momentum, fission fragments, isomeric yield ratios, fission products, scission, Penning trap.
National Category
Subatomic Physics
Research subject
Physics with specialization in Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-364951 (URN)978-91-513-0502-8 (ISBN)
Public defence
2018-12-13, 80127, Ångström, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2018-11-23 Created: 2018-11-06 Last updated: 2018-11-30

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Mattera, AndreaPomp, StephanLantz, MattiasSolders, AndreasRakopoulos, VasileiosAl-Adili, Ali

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