The neutron-induced fission cross section of Th-230 has been measured at the neutron time-of-flight facility n_TOF located at CERN. The experiment was performed at the experimental area EAR-1 with a neutron flight path of 185 m, using Micromegas detectors for the detection of the fission fragments. The Th-230(n, f ) cross section was determined relative to the U-235(n, f ) one, covering the energy range from the fission threshold up to 400 MeV. The results from the present work are compared with existing cross-section datasets and the observed discrepancies are discussed and analyzed. Finally, using the code EMPIRE 3.2.3 a theoretical study, based on the statistical model, was performed leading to a satisfactory reproduction of the experimental results with the proper tuning of the respective parameters, while for incident neutron energy beyond 200 MeV the fission of( 230)Th was described by Monte Carlo simulations.

Capture and total cross section measurements for 94,95,96Mo have been performed at the neutron time-of-flight facilities, n_TOF at CERN and GELINA at JRC-Geel. The measurements were performed using isotopically enriched samples with an enrichment above 95% for each of the 94,95,96Mo isotopes. The capture measurements were performed at n_TOF using C6D6 detectors and a new sTED detector. The transmission measurements were performed at a 10 m station of GELINA using a 6Li glass neutron detector. Preliminary results of these measurements are presented.

A measurement campaign to determine neutron induced fission cross sections of ^240 Pu and ^242 Pu at 2.51 and 14.83 MeV has been carried out at the 3.7 MV Van De Graaff linear accelerator at Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig. Two identical Frisch Grid fission chambers, housing back to back a ^238 U and a ^A Pu fertile sample (A = 240 or A = 242), were employed to detect the total fission yield. The neutron fluence was measured with the recoil proton telescope (T1) (Dangendorf et al. Nucl Instrum Methods Phys Res A 469:205–215, 2001), which is the German primary standard for neutron fluence measurements. The two measurements were related using a de Pangher long counter (Nolte and Thomas Metrologia 48:274–291, 2011) and the integrated beam current as monitors. The experimental results have an average uncertainty of 3–4 ^238 U σ _(n,f) in parallel. The results confirm the most recent standard libraries at 2.51 and 14.83 MeV.

Resonance parameters for neutron interactions with 92,94,95,96,97,98,100Mo in the energy region below 5 keV were evaluated. The parameters are the result of a compilation of experimental data available in the literature together with a least squares adjustment to transmission data obtained at the time-of-flight facility GELINA. The experiments were performed at a 50 m transmission station using a 6Li glass scintillator as neutron detector and metallic samples of natural Mo with a thickness of 2 mm and 5 mm. The REFIT code was used to adjust the resonance parameters, i.e. resonance energy and strength.

In the measurement of neutron capture cross-sections of fissile isotopes, the fission channel is a source of background which can be removed efficiently using the so-called fission-tagging or fission-veto technique. For this purpose a new compact and fast fission chamber has been developed. The design criteria and technical description of the chamber are given within the context of a measurement of the 233U(n, γ) cross-section at the n_TOF facility at CERN, where it was coupled to the n_TOF Total Absorption Calorimeter. For this measurement the fission detector was optimized for time resolution, minimization of material in the neutron beam and for alpha-fission discrimination. The performance of the fission chamber and its application as a fission tagging detector are discussed.

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.

A novel detector has been used, in order to perform measurements of spontaneous fission to α-decay ratios for 240Pu, 242Pu and 252Cf isotopes. The detectors are based on the well-known technique of liquid scintillating counting. The principle and advantages of the use of such detectors in nuclear physics is discussed. The application to the characterization of spontaneous fission is described and it is demonstrated that highly precise measurements are possible, and that the main limit is due to the isotopic content knowledge of the measured samples.

Measurement of neutron cross section data is a core activity of the JRC-Directorate G for Nuclear Safety and Security in Geel. After a period of reduced activity and in line with a renewed interest for nuclear data required for GenIV reactors and waste minimization, the demand for high quality actinide targets increased. Physical vapour deposition by thermal evaporation is a key technique to prepare homogeneous thin actinide layers, but due to ageing effects the earlier in-house developed equipment can no longer provide the required quality. Because of a current lack of experience and human resources cooperation with private companies is required for the development of new deposition equipment directly integrated in a glove box. In this paper we describe the design, implementation and validation of the first commercial actinide evaporator in a glove box as well as the optimization of the deposition process. Highly enriched (U3O8)-U-238 was converted to (UF4)-U-238 powder and several deposition runs were performed on different substrates. The deposition parameters were varied and defined in order to guarantee physical and chemical stable homogeneous UF4 layers, even on polished substrates which was not longer feasible with the older equipment. The stability problem is discussed in view of the thin layer growth by physical vapour deposition and the influence of the deposition parameters on the layer quality. The deposits were characterized for the total mass by means of substitution weighing and for the areal density of U-238 by means of alpha particle counting and thermal ionization mass spectrometry (TIMS). The quality of the layer was visually evaluated and by means of stereo microscopy and auto radiography.

We report here very precise measurements of the spontaneous fission branching ratio for the $^{240,242}\mathrm{Pu}$ and $^{252}\mathrm{Cf}$ isotopes, performed with a new kind of active scintillating target. It is shown that the method itself leads to unprecedentedly small uncertainties, and that these uncertainties are negligible compared to uncertainties on the isotopic content of the sample. Besides this capability we discuss the possibility to use this kind of detector for the systematic study of charged particle radioactivity, i.e., spontaneous fission, \ensuremath{\alpha} decay, and heavy-ion radioactivity.

We report here very precise measurements of the spontaneous fission branching ratio for the Pu-240,Pu-242 and Cf-252 isotopes, performed with a new kind of active scintillating target. It is shown that the method itself leads to unprecedentedly small uncertainties, and that these uncertainties are negligible compared to uncertainties on the isotopic content of the sample. Besides this capability we discuss the possibility to use this kind of detector for the systematic study of charged particle radioactivity, i.e., spontaneous fission, alpha decay, and heavy-ion radioactivity.

A. Gatera,1,2 T. Belgya,3 W. Geerts,1 A. Göök,1 F.-J. Hambsch,1 M. Lebois,4 B. Maróti,3 A. Moens,1 A. Oberstedt,5 S. Oberstedt,1,* F. Postelt,6 L. Qi,4 L. Szentmiklósi,3 G. Sibbens,1 D. Vanleeuw,1 M. Vidali,1 and F. Zeiser7 1European Commission, Joint Research Centre, Directorate G, Retieseweg 111, 2440 Geel, Belgium 2Ghent University, Department of Physics and Astronomy, Proeftuinstraat 86, 9000 Ghent, Belgium 3Centre for Energy Research, Hungarian Academy of Sciences, Nuclear Analysis and Radiography Department, 1525 Budapest, Hungary 4Institut de Physique Nucléaire Orsay (IPN-Orsay), 91406 Orsay, France 5Extreme Light Infrastructure-Nuclear Physics (ELI-NP)/Horia Hulubei National Institute for Physics and Nuclear Engineering (IFIN-HH), 077125 Bucharest-Magurele, Romania 6Hamburg University, Department of Physics, Hamburg, Germany 7University of Oslo, Department of Physics, Oslo, Norway (Received 9 March 2017; published 13 June 2017)

In this paper we present new results for prompt fission gamma-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 gamma-ray multiplicity (M) over bar (gamma) = (7.35 +/- 0.12), a mean photon energy (epsilon) over bar (gamma) = (0.85 +/- 0.02) MeV, and an average total energy released in fission (E) over bar (gamma,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 Pu-239(n(th), f) reaction may be ruled out as possible source of gamma heating underestimation, when compared with benchmark calculations based on existing nuclear data.

Accurate neutron induced fission cross section of 240Pu and 242Pu are required in view of making nuclear technology safer and more efficient to meet the upcoming needs for the future generation of nuclear power plants (GEN-IV). The probability for a neutron to induce such reactions figures in the NEA Nuclear Data High Priority Request List [1]. A measurement campaign to determine neutron induced fission cross sections of 240Pu and 242Pu at 2.51 MeV and 14.83 MeV has been carried out at the 3.7 MV Van De Graaff linear accelerator at Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig. Two identical Frisch Grid fission chambers, housing back to back a 238U and a APu target (A = 240 or A = 242), were employed to detect the total fission yield. The targets were molecular plated on 0.25 mm aluminium foils kept at ground potential and the employed gas was P10. The neutron fluence was measured with the proton recoil telescope (T1), which is the German primary standard for neutron fluence measurements. The two measurements were related using a De Pangher long counter and the charge as monitors. The experimental results have an average uncertainty of 3–4% at 2.51 MeV and for 6–8% at 14.81 MeV and have been compared to the data available in literature.

Accurate neutron induced fission cross section of Pu-240 and Pu-242 are required in view of making nuclear technology safer and more efficient to meet the upcoming needs for the future generation of nuclear power plants (GEN-IV). The probability for a neutron to induce such reactions figures in the NEA Nuclear Data High Priority Request List [1]. A measurement campaign to determine neutron induced fission cross sections of Pu-240 and Pu-242 at 2.51MeV and 14.83MeV has been carried out at the 3.7MV Van De Graaff linear accelerator at Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig. Two identical Frisch Grid fission chambers, housing back to back a U-238 and a Pu-A target (A = 240 or A = 242), were employed to detect the total fission yield. The targets were molecular plated on 0.25mm aluminium foils kept at ground potential and the employed gas was P10. The neutron fluence was measured with the proton recoil telescope (T1), which is the German primary standard for neutron fluence measurements. The two measurements were related using a De Pangher long counter and the charge as monitors. The experimental results have an average uncertainty of 3-4% at 2.51MeV and for 6-8% at 14.81MeV and have been compared to the data available in literature.

In this paper we present first results for prompt fission gamma-ray spectra (PFGS) characteristics from the spontaneous fission (sf) of Pu-240 and Pu-242. For Pu-242(sf) we obtained, after proper unfolding of the detector response, an average energy per photon (epsilon) over bar (gamma) = (0.843 +/- 0.012) MeV, an average multiplicity (M) over bar (gamma) = (6.72 +/- 0.07), and an average total gamma-ray energy release per fission (E) over bar (gamma,tot) = (5.66 +/- 0.06) MeV. The Pu-240(sf) emission spectrum was obtained by applying a so-called detector-response transformation function determined from the Pu-242 spectrum measured in exactly the same geometry. The results are an average energy per photon (epsilon) over bar = (0.80 +/- 0.07) MeV, the average multiplicity (M) over bar (gamma) = (8.2 +/- 0.4), and an average total gamma-ray energy release per fission (E) over bar (gamma,tot) = (6.6 +/- 0.5) MeV. The PFGS characteristics for Pu-242(sf) are in very good agreement with those from thermal-neutron-induced fission on Pu-241 and scales well with the corresponding prompt neutron multiplicity. Our results in the case of Pu-240(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 Pu-240(sf) compared to that of Pu-242(sf).

A set of neutron capture experiments based on the time-of-flight technique were performed in order to determine the 238U capture cross section in the unresolved resonance region. The GELINA facility of the Institute for Reference Materials and Measurements (IRMM) served as the neutron source. A pair of C6D6 liquid scintillators was used to register the prompt gamma rays emerging from the uranium sample. The analysis of the experimental data is based on the total energy principle applied in combination with the pulse height weighting technique. The experimental details along with the analysis process are described. The first results in the resolved resonance region are presented and their validity provide a solid base to extend the analysis and extract the average cross section in the keV region.

In this paper we present first results for prompt fission $\ensuremath{\gamma}$-ray spectra (PFGS) characteristics from the spontaneous fission (sf) of $^{240}\mathrm{Pu}$ and $^{242}\mathrm{Pu}$. For $^{242}\mathrm{Pu}(\mathrm{sf})$ we obtained, after proper unfolding of the detector response, an average energy per photon ${\overline{\ensuremath{\epsilon}}}_{\ensuremath{\gamma}}=(0.843\ifmmode\pm\else\textpm\fi{}0.012)$ MeV, an average multiplicity ${\overline{M}}_{\ensuremath{\gamma}}=(6.72\ifmmode\pm\else\textpm\fi{}0.07)$, and an average total $\ensuremath{\gamma}$-ray energy release per fission ${\overline{E}}_{\ensuremath{\gamma},\mathrm{tot}}$ = ($5.66 \ifmmode\pm\else\textpm\fi{}$ 0.06) MeV. The $^{240}\mathrm{Pu}(\mathrm{sf})$ emission spectrum was obtained by applying a so-called detector-response transformation function determined from the $^{242}\mathrm{Pu}$ spectrum measured in exactly the same geometry. The results are an average energy per photon ${\overline{\ensuremath{\epsilon}}}_{\ensuremath{\gamma}}=(0.80\ifmmode\pm\else\textpm\fi{}0.07)$ MeV, the average multiplicity ${\overline{M}}_{\ensuremath{\gamma}}$ = ($8.2 \ifmmode\pm\else\textpm\fi{}$ 0.4), and an average total $\ensuremath{\gamma}$-ray energy release per fission ${\overline{E}}_{\ensuremath{\gamma},\mathrm{tot}}$ = ($6.6 \ifmmode\pm\else\textpm\fi{}$ 0.5) MeV. The PFGS characteristics for $^{242}\mathrm{Pu}(\mathrm{sf})$ are in very good agreement with those from thermal-neutron-induced fission on $^{241}\mathrm{Pu}$ and scales well with the corresponding prompt neutron multiplicity. Our results in the case of $^{240}\mathrm{Pu}(\mathrm{sf})$, 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 $^{240}\mathrm{Pu}(\mathrm{sf})$ compared to that of $^{242}\mathrm{Pu}(\mathrm{sf})$.

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 Pu-242(n, f) cross section. Within the same project both the Pu-240(n, f) cross section and the Pu-242(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 Pu-242(n, f) cross section has been normalized to three different isotopes: Np-237(n, f), U-235(n, f), and U-238(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.

A wet chemical precipitation method to convert triuranium octoxide (U3O8), into uranium tetrafluoride (UF4) has been applied to determine the process yield. In this paper the wet chemical precipitation method is described in detail with a quantitative example and yield calculation. Also the vacuum deposition via sublimation of the uranium tetrafluoride is described and the prepared targets are shown.