Measurement of the N 14 (n,p) C 14 cross section at the CERN n_TOF facility from subthermal energy to 800 keV

© 2023 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0. https://creativecommons.org/licenses/by/4.0/Background: The N14(n,p)C14 reaction is of interest in neutron capture therapy, where nitrogen-related dose is the main component due to low-energy neutrons, and in astrophysics, where N14 acts as a neutron poison in the s process. Several discrepancies remain between the existing data obtained in partial energy ranges: thermal energy, keV region, and resonance region.Purpose: We aim to measure the N14(n,p)C14 cross section from thermal to the resonance region in a single measurement for the first time, including characterization of the first resonances, and provide calculations of Maxwellian averaged cross sections (MACS). Method: We apply the time-of-flight technique at Experimental Area 2 (EAR-2) of the neutron time-of-flight (n_TOF) facility at CERN. B10(n,α)Li7 and U235(n,f) reactions are used as references. Two detection systems are run simultaneously, one on beam and another off beam. Resonances are described with the R-matrix code sammy.Results: The cross section was measured from subthermal energy to 800 keV, resolving the first two resonances (at 492.7 and 644 keV). A thermal cross section was obtained (1.809±0.045 b) that is lower than the two most recent measurements by slightly more than one standard deviation, but in line with the ENDF/B-VIII.0 and JEFF-3.3 evaluations. A 1/v energy dependence of the cross section was confirmed up to tens of keV neutron energy. The low energy tail of the first resonance at 492.7 keV is lower than suggested by evaluated values, while the overall resonance strength agrees with evaluations. Conclusions: Our measurement has allowed determination of the N14(n,p) cross section over a wide energy range for the first time. We have obtained cross sections with high accuracy (2.5%) from subthermal energy to 800 keV and used these data to calculate the MACS for kT=5 to kT=100 keV.Peer reviewe

Design study for a new spallation target of the n_TOF facility at CERN

The n_TOF facility is a time of flight spectrometer dedicated to measuring neutron capture and fission cross sections. The neutron source consists on a lead target bombarded by a high energetic proton beam. After finishing a successful period of data taking by the end of 2004, it has been decided to upgrade the neutron spallation source with a cladded target. In this study, Monte Carlo simulations are reported for the assessment and comparison of the neutron and gamma fluxes from different target configurations. In addition, the plans for a second vertical measuring station with a flight path of 20 m above the spallation target have been considered in the simulations as well. Results for the energy deposition and the target heating are also presented

First tests of the applicability of γ\gamma-ray imaging for background discrimination in time-of-flight neutron capture measurements

In this work we explore for the first time the applicability of using $\gamma$-ray imaging in neutron capture measurements to identify and suppress spatially localized background. For this aim, a pinhole gamma camera is assembled, tested and characterized in terms of energy and spatial performance. It consists of a monolithic CeBr$_3$ scintillating crystal coupled to a position-sensitive photomultiplier and readout through an integrated circuit AMIC2GR. The pinhole collimator is a massive carven block of lead. A series of dedicated measurements with calibrated sources and with a neutron beam incident on a $^{197}$Au sample have been carried out at n_TOF, achieving an enhancement of a factor of two in the signal-to-background ratio when selecting only those events coming from the direction of the sample.Comment: Preprint submitted to Nucl. Instr. and Meth.

Recent highlights and prospects on (n,γ\gamma) measurements at the CERN n_TOF facility

Neutron capture cross-section measurements are fundamental in the study of the slow neutron capture (s-) process of nucleosynthesis and for the development of innovative nuclear technologies. One of the best suited methods to measure radiative neutron capture (n,$\gamma$) cross sections over the full stellar range of interest for all the applications is the time-of-flight (TOF) technique. Overcoming the current experimental limitations for TOF measurements, in particular on low mass unstable samples, requires the combination of facilities with high instantaneous flux, such as the CERN n_TOF facility, with detection systems with an enhanced detection sensitivity and high counting rate capabilities. This contribution presents a summary about the recent highlights in the field of (n,$\gamma$) measurements at n_TOF. The recent upgrades in the facility and in new detector concepts for (n,\g) measurements are described. Last, an overview is given on the existing limitations and prospects for TOF measurements involving unstable targets and the outlook for activation measurements at the brand new high-flux n_TOF-NEAR station.Comment: 7 pages, 5 figures (8 panels). Proceedings of the CGS-17 conference. To be published in EPJ Web of Conference

Neutron induced fission cross-section of 240Pu(n,f): first results from n_TOF (CERN) Experimental Area II

The accurate knowledge of neutron cross-sections of a variety of plutonium isotopes and other minor actinides, such as neptunium, americium and curium, is crucial for feasibility and performance studies of advanced nuclear systems (Generation-IV reactors, Accelerator Driven Systems). In this context, the 240Pu(n,f) cross-section was measured with the time-of-flight technique at the CERN n_TOF facility at incident neutron energies ranging from thermal to several MeV. The present measurement is the first to have been performed at n_TOF's newly commissioned Experimental Area II (EAR-2), which is located at the end of an 18m neutron beam-line and features a neutron fluence that is 25-30 times higher with respect to the existing 185m flight-path (EAR-1), as well as stronger suppression of sample-induced backgrounds, due to the shorter times-of-flight involved. Preliminary results are presented

Measurement of the prompt fission γ -rays from slow neutron-induced fission of 235 U with STEFF

© 2024 The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/The average energy and multiplicity of prompt γ-rays from slow neutron-induced fission of 235U have been measured using the STEFF spectrometer at the neutron time-of-flight facility n_TOF. The individual responses from 11 NaI scintillators were corrected for multiple γ-ray interactions, prompt fission neutrons and background counts before being deconvolved to estimate the emitted spectrum of prompt fission γ-rays. The results give an average γ-ray energy E¯γ of 1.71(5) MeV and multiplicity ν¯γ of 2.66(18) considering γ-rays emitted within the energy range 0.8–6.8 MeV. The n_TOF data has a slightly larger E¯γ and smaller ν¯γ than other recent measurements, however the product of the two is in agreement within quoted uncertainties.Peer reviewe

Nuclear data activities at the n_TOF facility at CERN

Nuclear data in general, and neutron-induced reaction cross sections in particular, are important for a wide variety of research fields. They play a key role in the safety and criticality assessment of nuclear technology, not only for existing power reactors but also for radiation dosimetry, medical applications, the transmutation of nuclear waste, accelerator-driven systems, fuel cycle investigations and future reactor systems as in Generation IV. Applications of nuclear data are also related to research fields as the study of nuclear level densities and stellar nucleosynthesis. Simulations and calculations of nuclear technology applications largely rely on evaluated nuclear data libraries. The evaluations in these libraries are based both on experimental data and theoretical models. Experimental nuclear reaction data are compiled on a worldwide basis by the international network of Nuclear Reaction Data Centres (NRDC) in the EXFOR database. The EXFOR database forms an important link between nuclear data measurements and the evaluated data libraries. CERN's neutron time-of-flight facility n_TOF has produced a considerable amount of experimental data since it has become fully operational with the start of the scientific measurement programme in 2001. While for a long period a single measurement station (EAR1) located at 185 m from the neutron production target was available, the construction of a second beam line at 20 m (EAR2) in 2014 has substantially increased the measurement capabilities of the facility. An outline of the experimental nuclear data activities at CERN's neutron time-of-flight facility n_TOF will be presented

Review and new concepts for neutron-capture measurements of astrophysical interest

The idea of slow-neutron capture nucleosynthesis formulated in 1957 triggered a tremendous experimental effort in different laboratories worldwide to measure the relevant nuclear physics input quantities, namely (n, γ) cross sections over the stellar temperature range (from few eV up to several hundred keV) for most of the isotopes involved from Fe up to Bi. A brief historical review focused on total energy detectors will be presented to illustrate how advances in instrumentation have led to the assessment of new aspects of s-process nucleosynthesis and to the progressive refinement of stellar models. A summary will be presented on current efforts to develop new detection concepts, such as the Total-Energy Detector with γ-ray imaging capability (i-TED). The latter is based on the simultaneous combination of Compton imaging with neutron time-of-flight (TOF) techniques, in order to achieve a superior level of sensitivity and selectivity in the measurement of stellar neutron capture rates.European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (ERC Consolidator Grant project HYMNS) 681740Instituto de Salud Carlos III Spanish Government FPA2014-52823-C2-1-P FPA2017-83946-C2-1-PConsejo Superior de Investigaciones Cientificas (CSIC) PIE-201750I26Program Severo Ochoa SEV-2014-039

Erratum: Measurement of the Ge 70 (n,γ) cross section up to 300 keV at the CERN n_TOF facility (Physical Review C (2019) 100 (045804) DOI: 10.1103/PhysRevC.100.045804)

© 2023 Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. https://creativecommons.org/licenses/by/4.0/An error was discovered in the neutron flux used to normalize the 70Ge(n, γ) data. The same error affects data in Ref. [1] and a separate correction will be published. Updated resonance kernels are printed in Tables I and II. Systematic uncertainties in the capture kernels are 3.2% below and 5.1% above 10 keV neutron energy. Analysis of the (updated) resonance parameters under the same assumptions as in Ref. [1] yield the average resonance parameters [Γγ = 200(12) meV with σGamma;γ = 62(8) and D0 = 1400(200) eV, where «Γγ»,σΓγ and D0 are expectation value of s-wave radiation width, standard deviation of the distribution of Γγ and s-wave resonance spacing, respectively. The difference in D0 does not come from use of correct flux. We found a bug in the code used for determination of D0 of 70Ge. The corrected unresolved cross section from 25-300 keV is shown in Fig. 1. The correction of the flux mainly affects the data at high neutron energy above 100 keV where now our data are in better agreement with the ENDF/B-VIII evaluation [3] and previous results from Walter and Beer [2]. Systematic uncertainties of the unresolved cross section are 6.7%. The Maxwellian averaged cross sections (MACS) are shown in Table III. Above the experimental limit of 300 keV, we used the ENDF/B-VIII cross section for our MACS calculations, assuming a 20% uncertainty. Changes in the MACS values remain below 6%, therefore, our astrophysical considerations remain largely unchanged. It should be noted that the agreement between our results and Kadonis-1.0 [4] is now excellent. We apologize for any inconvenience this caused. The corrected results will be provided to the EXFOR database. (Figure Presented).Peer reviewe