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Measurements of isomeric yield ratios of fission products from proton- induced fission on natU and 232Th via direct ion counting
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.
University of Jyväskylä, Department of Physics, Jyväskylä, Finland.
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2017 (English)In: ND 2016: INTERNATIONAL CONFERENCE ON NUCLEAR DATA FOR SCIENCE AND TECHNOLOGY / [ed] Plompen, A.; Hambsch, FJ.; Schillebeeckx, P.; Mondelaers, W.; Heyse, J.; Kopecky, S.; Siegler, P.; Oberstedt, S., Les Ulis: EDP Sciences, 2017, Vol. 146, article id 04054Conference paper, Published paper (Refereed)
Abstract [en]

Independent isomeric yield ratios (IYR) of 81Ge, 96Y, 97Y, 97Nb, 128Sn and 130Sn have been determined in the 25 MeV proton-induced fission of natU and 232Th. The measurements were performed at the Ion Guide Isotope Separator On-Line (IGISOL) facility at the University of Jyväskylä. A direct ion counting measurement of the isomeric fission yield ratios was accomplished for the first time, registering the fission products in less than a second after their production. In addition, the IYRs of natU were measured by means of γ-spectroscopy in order to verify the consistency of the recently upgraded experimental setup. From the obtained results, indications of a dependence of the production rate on the fissioning system can be noticed. These data were compared with data available in the literature, whenever possible. Using the TALYS code and the experimentally obtained IYRs, we also deduced the average angular momentum of the fission fragments after scission.

Place, publisher, year, edition, pages
Les Ulis: EDP Sciences, 2017. Vol. 146, article id 04054
Series
EPJ Web of Conferences, ISSN 2100-014X
National Category
Subatomic Physics
Identifiers
URN: urn:nbn:se:uu:diva-319348DOI: 10.1051/epjconf/201714604054ISI: 000426429500153ISBN: 978-2-7598-9020-0 OAI: oai:DiVA.org:uu-319348DiVA, id: diva2:1086629
Conference
ND 2016: International Conference on Nuclear Data for Science and Technology, 11-16 september 2016, Bruges, Belgium
Funder
Swedish Radiation Safety AuthoritySwedish Nuclear Fuel and Waste Management Company, SKBAvailable from: 2017-04-03 Created: 2017-04-03 Last updated: 2018-11-06Bibliographically approved
In thesis
1. 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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Rakopoulos, VasileiosLantz, MattiasAl-Adili, AliMattera, AndreaProkofiev, Alexander V.Solders, AndreasPomp, Stephan

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