| 1. |
- Colonna, N., et al.
(författare)
-
The fission experimental programme at the CERN n_TOF facility : status and perspectives
- 2020
-
Ingår i: European Physical Journal A. - : Springer Science and Business Media LLC. - 1434-6001 .- 1434-601X. ; 56:2
-
Forskningsöversikt (refereegranskat)abstract
- Neutron-induced fission reactions play a crucial role in a variety of fields of fundamental and applied nuclear science. In basic nuclear physics they provide important information on properties of nuclear matter, while in nuclear technology they are at the basis of present and future reactor designs. Finally, there is a renewed interest in fission reactions in nuclear astrophysics due to the multi-messenger observation of neutron star mergers and the important role played by fission recycling in r-process nucleosynthesis. Although studied for several decades, many fundamental questions still remain on fission reactions, while modern applications and the development of more reliable nuclear models require high-accuracy and consistent experimental data on fission cross sections and other fission observables. To address these needs, an extensive fission research programme has been carried out at the n_TOF neutron time-of-flight facility at CERN during the last 18 years, taking advantage of the high energy resolution, high luminosity and wide energy range of the neutron beam, as well as of the detection and data acquisition systems designed for this purpose. While long-lived isotopes are studied on the 185 m long flight-path, the recent construction of a second experimental area at a distance of about 19 m has opened the way to challenging measurements of short-lived actinides. This article provides an overview of the n_TOF experimental programme on neutron-induced fission reactions along with the main characteristics of the facility, the various detection systems and data analysis techniques used. The most important results on several major and minor actinides obtained so far and the future perspectives of fission measurements at n_TOF are presented and discussed.
|
|
| 2. |
- Gatera, A., et al.
(författare)
-
Prompt-fission γ -ray spectral characteristics from Pu 239 (nth,f)
- 2017
-
Ingår i: Physical Review C. - : American Physical Society. - 2469-9985 .- 2469-9993. ; 95:6
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we present new results for prompt fission γ-ray spectral characteristics from the thermal neutron induced fission of Pu∗240. The measured spectra were unfolded by using the detectors' response functions, simulated with geant4. We obtained in average per fission a γ-ray multiplicity Mγ=(7.35±0.12), a mean photon energy ϵγ=(0.85±0.02) MeV, and an average total energy released in fission Ēγ,tot=(6.27±0.11) MeV. Our results are in good agreement with historical data measured in the 1970s by Verbinski et al. and results from recent calculations in the framework of Monte Carlo Hauser-Feshbach models. Our measured average total energy is slightly smaller than the one deduced previously and present in evaluated data. From this we conclude that the Pu239(nth,f) reaction may be ruled out as possible source of γ heating underestimation, when compared with benchmark calculations based on existing nuclear data.
|
|
| 3. |
- Oberstedt, S., et al.
(författare)
-
High-precision prompt-gamma-ray spectral data from the reaction Pu-241(n(th), f)
- 2014
-
Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 90:2, s. Art. no. 024618-
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we present results from the first high-precision prompt-gamma-ray spectral measurements from the reaction Pu-241(n(th), f). Apart from one recent experiment, no data are reported in the literature for this fissioning system, which motivated a new dedicated experiment. We have measured prompt-fission gamma rays with three cerium-doped LaBr3 (two 5.08 cm x 5.08 cm and one 7.62 cm x 7.62 cm) and one CeBr3 (5.08 cm x 5.08 cm) scintillation detectors, which all exhibit excellent timing and good energy resolution. The average gamma-ray multiplicity was determined to be (nu) over bar (gamma) = (8.21 +/- 0.09) per fission, the average energy to be epsilon(gamma) = (0.78 +/- 0.01) MeV, and the total energy to be E-gamma,E-tot = (6.41 +/- 0.06) MeV as the weighted average from all detectors. Since the results from all detectors are in excellent agreement, and the total released gamma energy is modestly higher than the one in the present evaluated nuclear data files, we suspect that the underestimation of the prompt-gamma heating in nuclear reactors is due to fast-neutron-induced fission on U-238 or rather from fission induced by gamma rays from neutron capture in the construction material.
|
|
| 4. |
- Oberstedt, S., et al.
(författare)
-
Prompt fission γ -ray spectrum characteristics from Pu 240 (sf) and Pu 242 (sf)
- 2016
-
Ingår i: Physical Review C. - : American Physical Society (APS). - 2469-9985 .- 2469-9993. ; 93:5
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we present first results for prompt fission γ-ray spectra (PFGS) characteristics from the spontaneous fission (sf) of Pu240 and Pu242. For Pu242(sf) we obtained, after proper unfolding of the detector response, an average energy per photon ϵγ=(0.843±0.012) MeV, an average multiplicity Mγ=(6.72±0.07), and an average total γ-ray energy release per fission Ēγ,tot = (5.66 ± 0.06) MeV. The Pu240(sf) emission spectrum was obtained by applying a so-called detector-response transformation function determined from the Pu242 spectrum measured in exactly the same geometry. The results are an average energy per photon ϵγ=(0.80±0.07) MeV, the average multiplicity Mγ = (8.2 ± 0.4), and an average total γ-ray energy release per fission Ēγ,tot = (6.6 ± 0.5) MeV. The PFGS characteristics for Pu242(sf) are in very good agreement with those from thermal-neutron-induced fission on Pu241 and scales well with the corresponding prompt neutron multiplicity. Our results in the case of Pu240(sf), although drawn from a limited number of events, show a significantly enhanced average multiplicity and average total energy, but may be understood from a different fragment yield distribution in Pu240(sf) compared to that of Pu242(sf).
|
|
| 5. |
- Salvador-Castiñeira, P., et al.
(författare)
-
Neutron-induced fission cross section of Pu 240 from 0.5 MeV to 3 MeV
- 2015
-
Ingår i: Physical Review C. Nuclear Physics. - : American Physical Society (APS). - 0556-2813 .- 1089-490X. ; 92:1
-
Tidskriftsartikel (refereegranskat)abstract
- Pu240 has recently been pointed out by a sensitivity study of the Organization for Economic Cooperation and Development (OECD) Nuclear Energy Agency (NEA) to be one of the isotopes whose fission cross section lacks accuracy to meet the upcoming needs for the future generation of nuclear power plants (GEN-IV). In the High Priority Request List (HPRL) of the OECD, it is suggested that the knowledge of the Pu240(n,f) cross section should be improved to an accuracy within 1-3 %, compared to the present 5%. A measurement of the Pu240 cross section has been performed at the Van de Graaff accelerator of the Joint Research Center (JRC) Institute for Reference Materials and Measurements (IRMM) using quasi-monoenergetic neutrons in the energy range from 0.5 MeV to 3 MeV. A twin Frisch-grid ionization chamber (TFGIC) has been used in a back-to-back configuration as fission fragment detector. The Pu240(n,f) cross section has been normalized to three different isotopes: Np237(n,f), 235U(n,f), and 238U(n,f). Additionally, the secondary standard reactions were benchmarked through measurements against the primary standard reaction 235U(n,f) in the same geometry. A comprehensive study of the corrections applied to the data and the associated uncertainties is given. The results obtained are in agreement with previous experimental data at the threshold region. For neutron energies higher than 1 MeV, the results of this experiment are slightly lower than the ENDF/B-VII.1 evaluation, but in agreement with the experiments of Laptev et al. (2004) as well as Staples and Morley (1998).
|
|
| 6. |
- Salvador-Castiñeira, P., et al.
(författare)
-
Neutron-induced fission cross sections of Pu 242 from 0.3 MeV to 3 MeV
- 2015
-
Ingår i: Physical Review C. Nuclear Physics. - : American Physical Society. - 0556-2813 .- 1089-490X. ; 92:4
-
Tidskriftsartikel (refereegranskat)abstract
- The majority of the next generation of nuclear power plants (GEN-IV) will work in the fast-neutron-energy region, as opposed to present day thermal reactors. This leads to new and more accurate nuclear-data needs for some minor actinides and structural materials. Following those upcoming demands, the Organisation for Economic Cooperation and Development Nuclear Energy Agency performed a sensitivity study. Based on the latter, an improvement in accuracy from the present 20% to 5% is required for the Pu242(n,f) cross section. Within the same project both the Pu240(n,f) cross section and the Pu242(n,f) cross section were measured at the Van de Graaff accelerator of the Joint Research Centre at the Institute for Reference Materials and Measurements, where quasimonoenergetic neutrons were produced in an energy range from 0.3 MeV up to 3 MeV. A twin Frisch-grid ionization chamber has been used in a back-to-back configuration as fission-fragment detector. The Pu242(n,f) cross section has been normalized to three different isotopes: Np237(n,f), U235(n,f), and U238(n,f). A comprehensive study of the corrections applied to the data and the uncertainties associated is given. The results obtained are in agreement with previous experimental data at the threshold region up to 0.8 MeV. The resonance-like structure at 0.8 to 1.1 MeV, visible in the evaluations and in most previous experimental values, was not reproduced with the same intensity in this experiment. For neutron energies higher than 1.1 MeV, the results of this experiment are slightly lower than the Evaluated Nuclear Data File/B-VII.1 evaluation but in agreement with the experiment of Tovesson et al. (2009) as well as Staples and Morley (1998). Finally, for energies above 1.5 MeV, the results show consistency with the present evaluations.
|
|
