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Designing an upgrade of the Medley setup for light-ion production and fission cross-section measurements
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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2015 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 794, 141-150 p.Article in journal (Refereed) Published
Abstract [en]

Abstract Measurements of neutron-induced fission cross-sections and light-ion production are planned in the energy range 1-40 MeV at the upcoming Neutrons For Science (NFS) facility. In order to prepare our detector setup for the neutron beam with continuous energy spectrum, a simulation software was written using the Geant4 toolkit for both measurement situations. The neutron energy range around 20 MeV is troublesome when it comes to the cross-sections used by Geant4 since data-driven cross-sections are only available below 20 MeV but not above, where they are based on semi-empirical models. Several customisations were made to the standard classes in Geant4 in order to produce consistent results over the whole simulated energy range. Expected uncertainties are reported for both types of measurements. The simulations have shown that a simultaneous precision measurement of the three standard cross-sections H(n,n), 235U(n,f) and 238U(n,f) relative to each other is feasible using a triple layered target. As high resolution timing detectors for fission fragments we plan to use Parallel Plate Avalanche Counters (PPACs). The simulation results have put some restrictions on the design of these detectors as well as on the target design. This study suggests a fissile target no thicker than 2 µm (1.7 mg/cm2) and a PPAC foil thickness preferably less than 1 µm . We also comment on the usability of Geant4 for simulation studies of neutron reactions in this energy range.

Place, publisher, year, edition, pages
2015. Vol. 794, 141-150 p.
Keyword [en]
Neutron-induced fission, Light-ion production, Geant4, Standard cross-section, PPAC
National Category
Accelerator Physics and Instrumentation
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
URN: urn:nbn:se:uu:diva-255210DOI: 10.1016/j.nima.2015.05.001ISI: 000356356100019OAI: oai:DiVA.org:uu-255210DiVA: diva2:821273
Funder
Swedish Research Council
Available from: 2015-06-15 Created: 2015-06-15 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Improving the Neutron Cross-section Standards 238U(n,f) and 6Li(n,a): Measurements and Simulations
Open this publication in new window or tab >>Improving the Neutron Cross-section Standards 238U(n,f) and 6Li(n,a): Measurements and Simulations
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Improving or extending the range of cross-section standards, which in general are believed to be well known, require good control of the experimental conditions and the uncertainties involved. Two experiments that aspire to improve two different neutron cross-section standards, 238U(n,f) and 6Li(n,a, are presented in this thesis. Both standards have previously been extensively measured, but outside certain energy ranges discrepancies exist. In this thesis, a future precision measurement of the 238U(n,f) standard, relative to the elastic neutron scattering on hydrogen, is analysed through simulations. The status of the currently ongoing measurement of the second standard, 6Li(n,a), is also reported and some preliminary results are presented.Measurements of the uranium standard, with a total uncertainty better than 2%, are planned at the upcoming NFS facility. The new experimental situation requires our existing setup to be upgraded with new detectors. The simulation study has supplied limits on the target and detector designs but also provided estimates of the uncertainties that show the feasibility of a precision measurement. The design of the whole setup and the development of new detectors are guided by the simulation study presented in this thesis. When the upgrade is complete, the setup will consist of two parallel plate avalanche counters (PPACs), in addition to the eight detector telescopes already present in the existing setup.The 6Li(n,a) measurement is ongoing at the GELINA facility at IRMM in Geel, Belgium. A twin Frisch-grid ionisation chamber is employed measuring both 6Li(n,a) and 235U(n,f) in separate compartments. Although a problematic background was found, the preliminary cross section in the resonance region around 240 keV reproduces evaluated neutron library data fairly well. A recent move of the setup to a position closer to the neutron production shows promising improvements in the background situation.

Place, publisher, year, edition, pages
Polacksbackens repro, 2015
National Category
Subatomic Physics
Research subject
Physics with specialization in Applied Nuclear Physics
Identifiers
urn:nbn:se:uu:diva-255235 (URN)
Presentation
2015-05-29, 11:58 (English)
Opponent
Supervisors
Funder
Swedish Research Council
Available from: 2015-06-29 Created: 2015-06-15 Last updated: 2015-06-29Bibliographically approved

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Publisher's full texthttp://www.sciencedirect.com/science/article/pii/S0168900215005914

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Jansson, KajGustavsson, CeciliaAl-Adili, AliHjalmarsson, AndersAndersson Sundén, ErikProkofiev, Alexander V.Tarrío, DiegoPomp, Stephan

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Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Accelerator Physics and Instrumentation

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