| 1. |
- Al-Adili, Ali, et al.
(författare)
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Neutron-multiplicity experiments for enhanced fission modelling
- 2017
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 9782759890200
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Konferensbidrag (refereegranskat)abstract
- The nuclear de-excitation process of fission fragments (FF) provides fundamental information for the understanding of nuclear fission and nuclear structure in neutron-rich isotopes. The variation of the prompt-neutron multiplicity, ν(A), as a function of the incident neutron energy (En) is one of many open questions. It leads to significantly different treatments in various fission models and implies that experimental data are analyzed based on contradicting assumptions. One critical question is whether the additional excitation energy (Eexc) is manifested through an increase of ν(A) for all fragments or for the heavy ones only. A systematic investigation of ν(A) as a function of En has been initiated. Correlations between prompt-fission neutrons and fission fragments are obtained by using liquid scintillators in conjunction with a Frisch-grid ionization chamber. The proof-of-principle has been achieved on the reaction 235U(nth,f) at the Van De Graff (VdG) accelerator of the JRC-Geel using a fully digital data acquisition system. Neutrons from 252Cf(sf) were measured separately to quantify the neutron-scattering component due to surrounding shielding material and to determine the intrinsic detector efficiency. Prelimenary results on ν(A) and spectrum in correlation with FF properties are presented.
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| 2. |
- Al-Adili, Ali, et al.
(författare)
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Studying fission neutrons with 2E-2v and 2E
- 2018
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Ingår i: SCIENTIFIC WORKSHOP ON NUCLEAR FISSION DYNAMICS AND THE EMISSION OF PROMPT NEUTRONS AND GAMMA RAYS (THEORY-4). - : EDP Sciences. - 9782759890316
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Konferensbidrag (refereegranskat)abstract
- This work aims at measuring prompt-fission neutrons at different excitation energies of the nucleus. Two independent techniques, the 2E-2v and the 2E techniques, are used to map the characteristics of the mass-dependent prompt fission neutron multiplicity, 7(A), when the excitation energy is increased. The VERDI 2E-2v spectrometer is being developed at JRC-GEEL. The Fission Fragment (FF) energies are measured using two arrays of 16 silicon (Si) detectors each. The FFs velocities are obtained by time-of-flight, measured between micro-channel plates (MCP) and Si detectors. With MCPs placed on both sides of the fission source, VERDI allows for independent timing measurements for both fragments. Cf-252(sf) was measured and the present results revealed particular features of the 2E-2v technique. Dedicated simulations were also performed using the GEF code to study important aspects of the 2E-2v technique. Our simulations show that prompt neutron emission has a non-negligible impact on the deduced fragment data and affects also the shape of 17(A). Geometrical constraints lead to a total-kinetic energy-dependent detection efficiency. The 2E technique utilizes an ionization chamber together with two liquid scintillator detectors. Two measurements have been performed, one of Cf-252(sf) and another one of thermal-neutron induced fission in U-235(n,f). Results from Cf-252(sf) are reported here.
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| 3. |
- Hambsch, Franz-Josef, et al.
(författare)
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Prompt fission neutron emission from 235U(n,f): thermal and resonance region
- 2015
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Ingår i: Conference: 14th International Conference on Nuclear Reaction Mechanisms - CERN-Proceedings-2015-001, At Villa Monastero, Varenna, Italy. - 9789290834182
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Konferensbidrag (refereegranskat)abstract
- For nuclear modelling and improved evaluation of nuclear data, knowledge of fluctuations of the prompt neutron multiplicity as a function of incident neutron energy is requested for the major actinides 235U and 239Pu. Experimental investigations of the prompt fission neutron emission in resonance-neutron induced fission on 235U are taking place at the GELINA facility of the IRMM. The experiment employs an array of scintillation detectors (SCINTIA) in conjunction with a newly designed 3D position-sensitive twin Frisch-grid ionization chamber. In addition, the mass-dependent prompt neutron multiplicity, (A), has attracted particular attention. Recent, sophisticated nuclear fission models predict that the additional excitation energy, brought into the fission system at higher incident neutron energies, leads to an increased neutron multiplicity only for heavy fragments, as observed in the 237Np(n,f) reaction. A first feasibility study has been performed at the JRC-IRMM VdG accelerator to measure nu(A) for 235U(n,f).
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| 4. |
- Jansson, Kaj, et al.
(författare)
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Measurement of the 6Li(n, α) neutron standard cross-section at the GELINA facility
- 2016
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Ingår i: EPJ Web of Conferences. - : EDP Sciences. - 2100-014X. ; 122
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Tidskriftsartikel (refereegranskat)abstract
- The 6Li(n,α) reaction cross-section is commonly used as a reference cross section. However, it is only considered a neutron standard up to 1MeV. For higher energies, there are discrepancies of several per cents between recent measurements and evaluated data files. In order to extend and establish 6Li(n,α) as a neutron standard above 1MeV these discrepancies must be resolved. Our measurement at the GELINA facility at JRC-IRMM in Geel, Belgium is ongoing. We are using a double twin Frisch-grid setup to detect both α-particles from two 6Li targets and fission products from two 235U reference targets. Our targets have thick backings but are employed in pairs, one forward facing and one backward facing. In this way we still cover, in principle, a solid angle of 4π. We present some preliminary results showing that the existing cross-section data is well reproduced around the resonance at 240 keV. The final data taking will start in the beginning of 2016, when the GELINA facility goes online again after a few months of shut down.
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| 5. |
- Jansson, Kaj, 1987-, et al.
(författare)
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Measurement of the 6Li(n,α)t neutron standard cross-section at the GELINA facility
- 2017
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Ingår i: ND 2016. - Les Ulis : EDP Sciences. - 9782759890200
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Konferensbidrag (refereegranskat)abstract
- The Li-6(n,alpha)t reaction cross-section is an established standard due to its relatively high crosssection as well as its high Q-value. However, it is only considered a neutron standard up to 1 MeV, because in the neutron energy region 1-3 MeV there exist discrepancies of several per cents between recent measurements [1,2] and evaluated data files [3]. It has been speculated [4] that neglecting of the particle leaking effect might be part of the explanation why there is a disagreement in this region. Based on R-matrix calculations, in the region around 2 MeV, one also expects three excitation levels of Li-7 to significantly influence the cross section [5]. In order to resolve these discrepancies, we perform measurements at the GELINA facility at JRC-Geel with two Frisch-gridded ionisation chambers. The Li-6(n,alpha)t cross section is measured relative to the U-235(n,f) standard. In order to solve previous encountered problems [6], the setup has been modified and moved to a new flight path station. In this proceeding we show that several problems have been eliminated and discuss possible solutions to newly arisen problems, due to the changed experimental conditions. Preliminary results from new data taken during 2016 with the updated setup are presented.
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