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The MetroFission project, a Joint Research Project within the European Metrology Research Program, aims at addressing a number of metrological problems involved in the design of proposed Generation IV nuclear reactors. As part of this project a secondary neutron fluence standard is being developed and tested at the neutron time-of-flight facility GELINA of the JRCs Institute for Reference Materials and Measurements. Such a secondary standard will help to arrive at the neutron cross section measurement uncertainties required for the design and safety assessment of new generation power plants and fuel cycles. Such a neutron fluence device contains targets for which the neutron induced cross section is considered to be a standard. A careful preparation and characterization of these samples is an essential part of the development of the secondary standard. In this framework a set of U targets has been produced by vapour deposition of UF on aluminium backings by IRMMs target preparation laboratory. These targets have been characterized for both their total mass and mass distribution over the sample area. [ABSTRACT FROM AUTHOR]

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% both at 2.51 MeV and at 14.83 MeV and have been compared to the data available in literature. The employed set-up allowed measurements of 238 U σ (n , f) in parallel. The results confirm the most recent standard libraries at 2.51 and 14.83 MeV. [ABSTRACT FROM AUTHOR]

Charged particles emitted in ternary fission appear to have a Gaussian-shaped energy distribution, except for the α particles, for which mostly an important non-Gaussian low-energy tailing is reported. We realised good experimental conditions for studying the 235U(nth, f) ternary α energy distribution at the reactor of the ILL in Grenoble. Thanks to an intense and clean neutron beam, a small, thin sample of highly enriched U could be used, with an activity of only 1.6 Bq, so the measurements could be done without absorber in between the sample and the detector. With the resulting low detection limit of 6 MeV, a clearly asymmetric energy distribution was obtained, deviating by 6% from a Gaussian shape. This energy distribution has been deconvoluted into components corresponding to “true” ternary α''s and α''s originating from the decay of 5He particles. Ternary α emission yield data have been re-evaluated accordingly. [Copyright &y& Elsevier]

The cross section of the 89 Y(n, γ ) reaction has important implications in nuclear astrophysics and for advanced nuclear technology. Given its neutron magic number N = 50 and a consequent small neutron capture cross section, 89 Y represents one of the key nuclides for the stellar s-process. It acts as a bottleneck in the neutron capture chain between the Fe seed and the heavier elements. Moreover, it is located at the overlapping region, where both the weak and main s-process components take place. 89 Y, the only stable yttrium isotope, is also used in innovative nuclear reactors. Neutron capture and transmission measurements were performed at the time-of-flight facilities n_TOF at CERN and GELINA at JRC-Geel. Resonance parameters of individual resonances were extracted from a resonance analysis of the experimental transmission and capture yields, up to a neutron incident energy of 95 keV. Even though a comparison with results reported in the literature shows differences in resonance parameters, the present data are consistent with the Maxwellian averaged cross section suggested by the astrophysical database KADoNiS. [ABSTRACT FROM AUTHOR]

Neutron transmission and capture measurements have been performed at the time-of-flight (TOF) facility GELINA of the EC-JRC-Geel, using metallic discs of natural silver with different thicknesses. Resonances of neutron interactions with 107Ag and 109Ag were analysed in the energy region below 1 keV applying the Reich-Moore approximation of the R-Matrix theory. Discrepancies between the experimental data and calculations based on the neutron resonance parameters recommended in the main neutron cross section libraries (JEFF, ENDF/B, JENDL) were observed. Improved resonance parameters were determined by a resonance shape analysis using the REFIT code. The resonance energy, neutron (Γ n) and radiation (Γγ) width were adjusted in a simultaneous fit to transmission and capture yield spectra below 100 eV. Above 100 eV fixed average radiation widths ( Γ γ 107 =140 meV, Γ γ 109 = 130 meV) were used and the neutron width Γ n was adjusted to only the capture yield data. Capture resonance integral I 0 were calculated from the parameters derived in this work (I 0,107 = 101.20 b, I 0,109 = 1515.24 b) and compared with those calculated using the cross sections recommended in the main libraries. Discrepancies in I 0 for 107Ag are mainly due to difference in the parameters of the resonances at 16.4 eV, 41.6 eV, 173.9 eV and 202.8 eV. In case of 109Ag differences are mainly due to the difference in parameters of the resonance at 5.2 eV. [ABSTRACT FROM AUTHOR]

Resonance energies Eλ, neutron widths Γn,λ, and radiation widths Γγ,λ for the compound system 175Lu + n were determined up to 1 keV from time-of-flight data reported in literature and recently measured at the GELINA facility of JRC-Geel (Belgium). The statistical analysis of the obtained resonance parameters provides an s-wave neutron strength function [S 0 = 1.96 (8)], mean level spacing [D 0 = 3.24 (9) eV], and average radiation width (⟨ Γγ0 ⟩ = 61.3 (59) meV) which are substantially different from those compiled in libraries dedicated to statistical calculations. The largest difference lies on the average radiation width, for which a value of 77(5) meV is recommended. 175 Lu neutron cross sections were calculated with the talys code by using our s-wave average parameters as constraints. At k T = 30 keV, we obtain a total neutron capture cross section equal to 1125(62) mbarns, confirming the lower values reported in the 1990s. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract A novel MicroMegas detector based on microbulk technology with an embedded XY strip structure was developed, obtained by segmenting both the mesh and the anode in perpendicular directions. This results in a very low-mass device with good energy and spatial resolution capabilities. Such a detector is practically “transparent” to neutrons, being ideal for in-beam neutron measurements and can be used as a quasi-online neutron beam profiler at neutron time-of-flight facilities. A dedicated front end electronics and acquisition system has been developed and used. The first studies of this new detection system are presented and discussed. [ABSTRACT FROM AUTHOR]

The absolute neutron-induced fission cross section of 242Pu was measured at five energies between 1 and 2.5 MeV at the low-scatter neutron measurement facility of the National Physical Laboratory, UK. The measurements are part of an effort to reduce uncertainties of nuclear data related to fast spectrum reactors. The neutron-induced fission results are in good agreement with the Evaluated Nuclear Data File/B-VII.1 but disagree with several recent measurements near the resonance-like structure around 1.1 MeV. Within the same experimental campaign, the spontaneous fission half-life of 242Pu was measured and it is in good agreement with previous results. [ABSTRACT FROM AUTHOR]

A sensitivity and uncertainty analysis was carried out to estimate the uncertainty in the neutron multiplication factor k eff and to identify the most important nuclear data for neutron induced reactions for criticality calculations of the latest MYRRHA designs. Sensitivity profiles, i.e. sensitivity to the nuclear data as a function of incoming neutron energy, were derived for both a critical and sub-critical core. They were calculated using codes that are based on different methodologies including stochastic and deterministic calculations (i.e. SCALE, MCNP and XSUN). The neutron induced nuclear data sensitivity analysis outlined the following quantities to be of special importance for the MYRRHA reactor concept: 239 Pu(n,γ) both in resonance and fast energy region, (n,f) fast, χ and ν fast; 238 U(n,n′) fast, (n,γ) resonance and fast, (n,n) resonance and fast; 240 Pu ν fast; 238 Pu(n,f) both resonance and fast; 56 Fe(n,γ) both resonance and fast. Differences of less than 4% between codes were obtained for these quantities, with few exceptions ( 238 Pu(n,f), 238 U(n,n) and 56 Fe(n,γ) reactions). Nuclear data covariance matrices of different libraries (SCALE-6, COMMARA-2 and JENDL-4.0m) were used to derive the uncertainty in k eff based on the calculated sensitivities. This study reveals that the largest contributions to k eff uncertainty result from the uncertainty in the average prompt neutron fission multiplicity of 239 Pu, in the 238 U inelastic scattering cross section and 239 Pu fission cross section, using the covariances from SCALE-6, COMMARA-2 and JENDL-4.0m, respectively. [ABSTRACT FROM AUTHOR]

Responds to comments about the reactogenicity and immunogenicity of commercial Haemophilus influenzae type b conjugate vaccines. Absence of interference with the immune response with regard to the administration of Hib conjugate vaccines; Error in the use of statistical analysis based on diary cards; Limitation of the statistical evaluation of immunogenicity.

Pu and Pu targets were prepared by the so-called 'molecular plating' on an Al backing for cross-section measurements. The total activity of the actinide layer was determined by low-geometry alpha-particle counting. The atomic abundances of the two Pu materials were determined via thermal ionization mass spectrometry. A radiochemical separation was performed by anion exchange prior to the preparation of the layers to prevent interferences with the ingrown daughter nuclide during the characterization and cross-section measurements. The targets were prepared to be used in the project 'Metrology for New Generation Nuclear Power Plants' (MetroFission), within the frame of the European Metrology Research Programme, directed to improve the knowledge on neutron cross sections through metrological approaches. For measurements of the Pu( n, f) and Pu( n, f) cross sections Pu and Pu targets were produced and mounted in fission chambers. In parallel, Pu and Pu targets were prepared for the ANDES project (Accurate Nuclear Data for Nuclear Energy Sustainability) for cross-section measurements at the CERN neutron time-of-flight facility n_TOF, and the Van de Graaff laboratories of IRMM and CNRS/CENBG. [ABSTRACT FROM AUTHOR]

Highlights: [•] Review of the experimental and evaluated data for natC(n,γ) and 12C(n,γ). [•] Comparison of ENDF/B-VII.1 and JEFF-3.1.2 within BR1 criticality calculations. [•] The thermal capture cross section is of importance in large graphite-systems like BR1. [•] The 12C(n th ,γ) given by Firestone and Révay (2011) is recommended to be used. [•] The JENDL-4.0 evaluation takes the latest experimental data available. [ABSTRACT FROM AUTHOR]

Abstract: Cross section data in the resolved and unresolved resonance region are represented by nuclear reaction formalisms using parameters which are determined by fitting them to experimental data. Therefore, the quality of evaluated cross sections in the resonance region strongly depends on the experimental data used in the adjustment process and an assessment of the experimental covariance data is of primary importance in determining the accuracy of evaluated cross section data. In this contribution, uncertainty components of experimental observables resulting from total and reaction cross section experiments are quantified by identifying the metrological parameters involved in the measurement, data reduction and analysis process. In addition, different methods that can be applied to propagate the covariance of the experimental observables (i.e. transmission and reaction yields) to the covariance of the resonance parameters are discussed and compared. The methods being discussed are: conventional uncertainty propagation, Monte Carlo sampling and marginalization. It is demonstrated that the final covariance matrix of the resonance parameters not only strongly depends on the type of experimental observables used in the adjustment process, the experimental conditions and the characteristics of the resonance structure, but also on the method that is used to propagate the covariances. Finally, a special data reduction concept and format is presented, which offers the possibility to store the full covariance information of experimental data in the EXFOR library and provides the information required to perform a full covariance evaluation. [Copyright &y& Elsevier]

Abstract: The emission probabilities and the energy distributions of tritons, α and 6He particles emitted in the spontaneous ternary fission (zero excitation energy) of 250Cf and 252Cf and in the cold neutron induced fission (excitation energy ) of 249Cf and 251Cf are determined. The particle identification was done with suited telescope detectors, at the IRMM (Geel, Belgium) for the spontaneous fission and at the ILL (Grenoble, France) for the neutron induced fission measurements. Hence particle emission characteristics of the fissioning systems 250Cf and 252Cf are obtained at zero and at about 6.5 MeV excitation energies. While the triton emission probability is hardly influenced by the excitation energy, the 4He and 6He emission probability in spontaneous fission is higher than for neutron induced fission. This can be explained by the strong influence of the cluster preformation probability on the ternary particle emission probability. [Copyright &y& Elsevier]

The emission probabilities and the energy distributions of tritons and α particles emitted in the spontaneous ternary fission (zero excitation energy) of 244Cm, 246Cm and 248Cm and in the cold neutron induced fission (excitation energy ≈ 605MeV) of 243Cm, 245Cm and 247Cm are determined. The particle identification was done with suited ΔE -E telescope detectors, at the IRMM (Geel, Belgium) for the spontaneous fission and at the ILL (Grenoble, France) for the neutron induced fission measurements. Hence particle emission characteristics of the fissioning systems 244Cm, 246Cm and 248Cm are obtained at zero excitation energy and at an excitation energy around 6.5 MeV. Whilst the triton emission probability is hardly influenced by the excitation energy, the 4He emission probability in spontaneous fission is about 20% higher than for neutron induced fission. This could be explained by the influence of the cluster preformation probability on the ternary α emission. [Copyright &y& Elsevier]

Abstract: The inclusive and exclusive reactions have been studied with a beam energy of 171 MeV and scattering angles for the reaction and 3°. The studies focused on the separation of the isovector spin-dipole resonance (IVSGDR) into its components by measuring tensor-analysing powers and observing the direct neutron decay to the low-lying proton-hole states in 11B. Merging the information obtained from both measurements resulted in the first-time verification of model-independent predictions of tensor-analysing powers at extreme forward angles and the experimental decomposition of the IVSGDR into its components. The experimental results are in reasonable agreement with theoretical estimates based on shell-model calculations. [Copyright &y& Elsevier]

This paper reports on the results of measurements of the (n,p) and (n,α) reactions on 26Al and 36Cl, in the neutron energy region up to 140 keV and 350 keV, respectively. The experiments were carried out at the GELINA neutron facility of the IRMM (Geel, Belgium). For both reactions several resonances could be identified which were never observed before. Using the obtained cross section data, reaction rates were calculated and compared with other experimental and theoretical values. [Copyright &y& Elsevier]

We are investigating the feasibility of nuclear physics experiments designed to overcome the loopholes of observer-dependent reality and satisfying the counterfactuality condition. In a first approach, we have measured polarization correlations of 1S0 proton pairs produced in 12C(d, 2He) and 1H(d, 2He) reactions in one setting. The results of these measurements are used to test the Bell and Wigner–Belinfante inequalities against the predictions of quantum mechanics. [Copyright &y& Elsevier]

Spin–isospin excitations of the medium-mass nucleus 58Co were studied using the (n,p)-type (d,2He) charge-exchange reaction at an incident energy Ed=170 MeV and small scattering angles. The achieved energy resolution of 130 keV, full width at half maximum, allowed the extraction of Gamow–Teller strength to 13 peaks at excitation energies lower than 4.1 MeV in the residual nucleus 58Co and is consistent with the results of a multipole-decomposition analysis. The identification of Gamow–Teller transitions is possible by comparison of the measured cross sections with DWBA calculations. The results are used to discuss the relevance of the Gamow–Teller strength distribution at low excitation energy with regard to electron-capture rates used in calculations for the final stage of a massive star. [Copyright &y& Elsevier]

For proton-induced reactions, a formalism is presented to determine polarization observables using a focal-plane polarimeter in combination with a large-acceptance spectrometer, where also the effect of the scattering in the non-dispersive plane of the spectrometer is taken into account. The inclusive proton-carbon analyzing power needed for the determination of spin observables was studied over a wide angular range and a new parameterization for this quantity was deduced. [Copyright &y& Elsevier]

At intermediate energies, the (d,2He) charge-exchange reaction can be used to observe Gamow–Teller strength in the β+ direction. 2He denotes the two-proton system being in the singlet 1S0 state. In the present experiment the two protons, which in the laboratory frame are emitted into the forward direction, have been momentum analyzed and detected in coincidence by the same spectrometer and detector. Protons from deuteron breakup processes can induce a large accidental coincidence background because of the much larger breakup cross-section as compared to the (d,2He) cross-section. Nevertheless, background-free 2He spectra with a resolution of 145 keV at an incident energy of 170 MeV are obtained, allowing the identification of many levels with high precision in the residual nuclei. The essential features of the detection system and the data-acquisition and analysis techniques which make our (d,2He) experiments possible are described. Two nuclei, 12C and 24Mg, have been used as a test case. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]