A new experimental area, the NEAR station, has recently been built at the CERN n TOF facility, at a short distance from the spallation target (1.5 m). The new area, characterized by a neutron beam of very high flux, has been designed with the purpose of performing activation measurements of interest for astrophysics and various applications. The beam is transported from the spallation target to the NEAR station through a hole in the shielding wall of the target, inside which a collimator is inserted. The new area is complemented with a γ-ray spectroscopy laboratory, the GEAR station, equipped with a high efficiency HPGe detector, for the measurement of the activity resulting from irradiation of a sample in the NEAR station. The use of a moderator/filter assembly is envisaged, in order to produce a neutron beam of Maxwellian shape at different thermal energies, necessary for the measurement of Maxwellian Averaged Cross Sections of astrophysical interest. A new fast-cycling activation technique is also being investigated, for measurements of reactions leading to isotopes of very short half life.

One of the critical aspects for the accurate determination of neutron capture cross sections when combining time-of-flight and total energy detector techniques is the characterization and control of systematic uncertainties associated to the measuring devices. In this work we explore the most conspicuous effects associated to harsh count rate conditions: dead-time and pile-up effects. Both effects, when not properly treated, can lead to large systematic uncertainties and bias in the determination of neutron cross sections. In the majority of neutron capture measurements carried out at the CERN n_TOF facility, the detectors of choice are the C6D6 liquid-based either in form of large-volume cells or recently commissioned sTED detector array, consisting of much smaller-volume modules. To account for the aforementioned effects, we introduce a Monte Carlo model for these detectors mimicking harsh count rate conditions similar to those happening at the CERN n_TOF 20 m fligth path vertical measuring station. The model parameters are extracted by comparison with the experimental data taken at the same facility during 2022 experimental campaign. We propose a novel methodology to consider both, dead-time and pile-up effects simultaneously for these fast detectors and check the applicability to experimental data from 197Au(n, γ), including the saturated 4.9 eV resonance which is an important component of normalization for neutron cross section measurements.

The enhancement of the parity-violating asymmetry in the vicinity of p-wave compound nuclear resonances was observed for a variety of medium-heavy nuclei. The enhanced parity-violating asymmetry can be understood using the s-p mixing model. The s-p mixing model predicts several neutron energy-dependent angular correlations between the neutron momentum k⃗_n, neutron spin σ⃗_n, γ-ray momentum k⃗_γ, and γ-ray polarization σ⃗_γ in the (n,γ) reaction. In this paper, the improved value of the transverse asymmetry of γ-ray emissions, corresponding to a correlation term σ⃗_n·(k⃗_n×k⃗_γ) in the ^139La(n⃗,γ)^140La reaction, and the transverse asymmetries in the transitions to several low excited states of ^140La are reported.

Asymptotic giant branch stars are responsible for the production of most of the heavy isotopes beyond Sr observed in the solar system. Among them, isotopes shielded from the r-process contribution by their stable isobars are defined as s-only nuclei. For a long time the abundance of ^{204}Pb, the heaviest s-only isotope, has been a topic of debate because state-of-the-art stellar models appeared to systematically underestimate its solar abundance. Besides the impact of uncertainties from stellar models and galactic chemical evolution simulations, this discrepancy was further obscured by rather divergent theoretical estimates for the neutron capture cross section of its radioactive precursor in the neutron-capture flow, ^{204}Tl (t_{1/2}=3.78  yr), and by the lack of experimental data on this reaction. We present the first ever neutron capture measurement on ^{204}Tl, conducted at the CERN neutron time-of-flight facility n_TOF, employing a sample of only 9 mg of ^{204}Tl produced at the Institute Laue Langevin high flux reactor. By complementing our new results with semiempirical calculations we obtained, at the s-process temperatures of kT≈8  keV and kT≈30  keV, Maxwellian-averaged cross sections (MACS) of 580(168) mb and 260(90) mb, respectively. These figures are about 3% lower and 20% higher than the corresponding values widely used in astrophysical calculations, which were based only on theoretical calculations. By using the new ^{204}Tl MACS, the uncertainty arising from the ^{204}Tl(n,γ) cross section on the s-process abundance of ^{204}Pb has been reduced from ∼30% down to +8%/-6%, and the s-process calculations are in agreement with the latest solar system abundance of ^{204}Pb reported by K. Lodders in 2021.

The average energy and multiplicity of prompt γ -rays from slow neutron-induced fission of ^235 U 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 E̅_γ of 1.71(5) MeV and multiplicity ν̅_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 E̅_γ and smaller ν̅_γ than other recent measurements, however the product of the two is in agreement within quoted uncertainties.

The design of fast reactors burning MOX fuels requires accurate capture and fission cross sections. For the particular case of neutron capture on 242Pu, the NEA recommends that an accuracy of 8-12 energy region (2 keV-500 keV) compared to their estimation of 35 current uncertainty. Integral irradiation experiments suggest that the evaluated cross section of the JEFF-3.1 library overestimates the 242Pu(n,γ) cross section by 14 addition, the last measurement at LANSCE reported a systematic reduction of 20-30 data sets. In the present work this cross section has been determined up to 600 keV in order to solve the mentioned discrepancies. A 242Pu target of 95(4) mg enriched to 99.959 capture cross section of 242Pu has been obtained between 1 and 600 keV with a systematic uncertainty (dominated by background subtraction) between 8 and 12 reducing the current uncertainties of 35 by the NEA in a large energy range. The shape of the cross section has been analyzed in terms of average resonance parameters using the FITACS code as implemented in SAMMY, yielding results compatible with our recent analysis of the resolved resonance region.The results are in good agreement with the data of Wisshak and Käppeler and on average 10-14 keV, which helps to achieve consistency between integral experiments and cross section data. At higher energies our results show a reasonable agreement within uncertainties with both ENDF/B-VII.1 and JEFF-3.2. Our results indicate that the last experiment from DANCE underestimates the capture cross section of 242Pu by as much as 40

The Pu-239(n, gamma) reaction cross section is very important for operation of both thermal and fast reactors, when loaded with MOX fuels. According to the NEA/OECD High Priority Request List the precision of cross section data for this reaction should be improved. The cross section of (n, f) reaction is much higher compared to (n, gamma) for this isotope. In such conditions the fission tagging technique could be applied to identify the fission background. In the past, this technique was successfully used for capture measurements at the n_TOF facility at CERN. The multi-section fission ionization chamber was constructed and used in the combination with Total Absorption Calorimeter (TAC) for detecting gamma rays for the precise measurement of Pu-239(n, gamma) reaction cross section at the n_TOF facility.

^{140}Ce(n,γ) is a key reaction for slow neutron-capture (s-process) nucleosynthesis due to being a bottleneck in the reaction flow. For this reason, it was measured with high accuracy (uncertainty ≈5%) at the n_TOF facility, with an unprecedented combination of a high purity sample and low neutron-sensitivity detectors. The measured Maxwellian averaged cross section is up to 40% higher than previously accepted values. Stellar model calculations indicate a reduction around 20% of the s-process contribution to the Galactic cerium abundance and smaller sizeable differences for most of the heavier elements. No variations are found in the nucleosynthesis from massive stars.

Chromium is a very relevant element regarding criticality safety in nuclear reactors because of its presence in stainless steel, an important structural material. Currently, there are serious discrepancies between the different evaluations regarding the neutron capture cross sections of 50Cr and 53Cr, most probably related to the difficulty of reducing and then estimating the very large neutron scattering effects on the shape of the resonances. In this context, there is a recent entry in the Nuclear Energy Agency (NEA) High Priority Request List (HPRL) to measure these reactions between 1 and 100 keV with an accuracy of 8-10%. In response to this request, we have performed a time-of-flight experiment at CERN n_TOF (Switzerland) and a complementary activation experimenton 50Crat30and90keVatCNAHiSPANoS(Spain).Theexperiments are presented herein, together with a discussion on the quality of the preliminary data and the results to be expected.

The Se-78(n, gamma)Se-79 cross section has a high impact on the abundances of Se-78 produced during the slow neutron capture process (s process) in massive stars. A measurement of the Se-78 radiative neutron capture cross section has been performed at the Neutron Time-of-Flight facility at CERN using a set of liquid scintillation detectors that have been optimized for a low sensitivity to neutrons. We present resonance capture kernels up to 70 keV and cross section from 70 to 600 keV. Maxwellian-averaged cross section (MACS) values were calculated for stellar temperatures between kT = 5 and 100 keV, with uncertainties between 4.6% and 5.8%. The new MACS values result in substantial decreases of 20-30% of Se-78 abundances produced in the s process in massive stars and AGB stars. Massive stars are now predicted to produce subsolar Se-78/Se-76 ratios, which is expected since Se-76 is an s-only isotope, while solar Se-78 abundances have also contributions from other nucleosynthesis processes.

In JMTR, irradiation tests of structural materials simulating fast reactor conditions were studied. The ratio of helium production to displacement damage (dpa) was used as an index of the irradiation effect, and the method was adopted to simulate the value in a fast reactor. It was thought to be possible to simulate fast reactor irradiation in JMTR, a light water reactor, by placing a component inside the capsule that shields thermal neutrons. As a result of the study, cadmium was found to be an appropriate material for shielding thermal neutrons. Therefore, the effect of the capsule containing cadmium on the reactor was evaluated, and it was confirmed that there were no safety issues. The results of tests on the loss of cadmium in the primary cooling water of the reactor confirmed that there was no corrosion effect on the reactor structural materials due to cadmium leakage. Although there were some problems in the molding of the cadmium, these problems could be solved by improving the casting method. By shield capsules, irradiation tests of stainless steel under less thermal neutron spectra were carried out. According to the analysis, we confirmed that thermal neutron shielding by cadmium enabled to simulate of the He/dpa ratio of the fast reactor.

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.

The neutron time-of-flight facility n_TOF at CERN is a spallation source dedicated to measurements of neutron-induced reaction cross-sections of interest in nuclear technologies, astrophysics, and other applications. Since 2014, Experimental ARea 2 (EAR2) is operational and delivers a neutron fluence of ∼4⋅107 neutrons per nominal proton pulse, which is ∼50 times higher than the one of Experimental ARea 1 (EAR1) of ∼8⋅105 neutrons per pulse. The high neutron flux at EAR2 results in high counting rates in the detectors that challenged the previously existing capture detection systems. For this reason, a Segmented Total Energy Detector (sTED) has been developed to overcome the limitations in the detector’s response, by reducing the active volume per module and by using a photo-multiplier (PMT) optimized for high counting rates. This paper presents the main characteristics of the sTED, including energy and time resolution, response to γ-rays, and provides as well details of the use of the Pulse Height Weighting Technique (PHWT) with this detector. The sTED has been validated to perform neutron-capture cross-section measurements in EAR2 in the neutron energy range from thermal up to at least 400 keV. The detector has already been successfully used in several measurements at n_TOF EAR2.

The ^246 Cm(n, γ ) and ^248 Cm(n, γ ) cross-sections have been measured at the Experimental Area 2 (EAR2) of the n_TOF facility at CERN with three C _6 D _6 detectors. This measurement is part of a collective effort to improve the capture cross-section data for Minor Actinides (MAs), which are required to estimate the production and transmutation rates of these isotopes in light water reactors and innovative reactor systems. In particular, the neutron capture in ^246 Cm and ^248 Cm open the path for the formation of other Cm isotopes and heavier elements such as Bk and Cf and the knowledge of (n, γ ) cross-sections of these Cm isotopes plays an important role in the transport, transmutation and storage of the spent nuclear fuel. The reactions ^246 Cm(n, γ ) and ^248 Cm(n, γ ) have been the two first capture measurements analyzed at n_TOF EAR2. Until this experiment and two recent measurements performed at J-PARC, there was only one set of data of the capture cross-sections of ^246 Cm and ^248 Cm, that was obtained in 1969 in an underground nuclear explosion experiment. In the measurement at n_TOF a total of 13 resonances of ^246 Cm between 4 and 400 eV and 5 of ^248 Cm between 7 and 100 eV have been identified and fitted. The radiative kernels obtained for ^246 Cm are compatible with JENDL-5, but some of them are not with JENDL-4, which has been adopted by JEFF-3.3 and ENDF/B-VIII.0. The radiative kernels obtained for the first three ^248 Cm resonances are compatible with JENDL-5, however, the other two are not compatible with any other evaluation and are 20 and 60

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.

Neutron capture cross section measurements of isotopes close to s -process branching-points are of fundamental importance for the understanding of this nucleosynthesis mechanism through which about 50% of the elements heavier than iron are produced. We present in this contribution the results corresponding to the high resolution measurement, for first time ever, of the 80 Se( n, γ ) cross section, in which 98 resonances never measured before have been reported. As a consequence, ten times more precise values for the MACS have been obtained compared to previous accepted value adopted in the astrophysical KADoNiS data base.

One of the crucial ingredients for the improvement of stellar models is the accurate knowledge of neutron capture cross-sections for the different isotopes involved in the s-,r- and i- processes. These measurements can shed light on existing discrepancies between observed and predicted isotopic abundances and help to constrain the physical conditions where these reactions take place along different stages of stellar evolution. In the particular case of the radioactive 94Nb, the 94Nb(n,γ) cross-section could play a role in the determination of the s-process production of 94Mo in AGB stars, which presently cannot be reproduced by state-of-the-art stellar models. There are no previous 94Nb(n,γ) experimental data for the resolved and unresolved resonance regions mainly due to the difficulties in producing highquality samples and also due to limitations in conventional detection systems commonly used in time-of-flight experiments. Motivated by this situation, a first measurement of the 94Nb(n,γ) reaction was carried out at CERN n_TOF, thereby exploiting the high luminosity of the EAR2 area in combination with a new detection system of small-volume C6D6-detectors and a high quality 94Nb-sample. The latter was based on hyper-pure 93Nb material activated at the high-flux reactor of ILL-Grenoble. An innovative ring-configuration detection system in close geometry around the capture sample allowed us to significantly enhance the signal-to-background ratio. This set-up was supplemented with two conventional C6D6-detectors and a highresolution LaCl3(Ce)-detector, which will be employed for addressing reliably systematic effects and uncertainties. At the current status of the data analysis, 18 resonance in 94Nb+n have been observed for the first time in the neutron energy range from thermal up to 10 keV.

The n_TOF neutron time-of-flight facility at CERN is used for nuclear data measurements. The n_TOF Collaboration works closely with the Nuclear Reaction Data Centres (NRDC) network to disseminate the experimental data through the international EXFOR library. In addition, the Collaboration helps integrate the results in the evaluated library projects. The present contribution describes the dissemination status of n_TOF results, their impact on evaluated libraries and ongoing efforts to provide n_TOF resonance parameters in ENDF-6 format for further use by evaluation projects.

Neutron-capture reactions on gadolinium isotopes play an important role in several fields of physics,in particular in nuclear Astrophysics for the understanding of the nucleosynthesis of heavy elements (beyond iron) in stars via the s- and r-processes [1] and in nuclear technology. Another important application of gadolinium is linked to the production of terbium, that offers a set of clinically interesting isotopes for theranostics, characterized by complementary physical decay characteristics. In particular, the low-energy β −emitter terbium-161 is very similar to lutetium-177 in terms of half-life (6.89 d), β − energy and chemical properties. Being a significant emitter of conversion/Auger electrons, greater therapeutic effect can therefore be expected in comparison to Lu-177 [2, 3]. For this reason, in the last decade, the study of the neutron capture reaction 160Gd(n,γ)161 Gd and the subsequent β − decay in terbium-161 is getting particular attention. As the nuclear data on the Gd-160 neutron capture reaction are quite scarce and inconsistent, a new measurement of the capture cross section of Gd-160 at the CERN neutron Time-Of-Flight facilty was performed in order to provide high resolution, high-accuracy data on this important reaction, in the energy range from thermal to hundreds of keV. In this contribution, the preliminary results of the n_TOF measurement are presented.

The neutron capture cross section of 241 Am is an important quantity for nuclear energy production and fuel cycle scenarios. Several measurements have been performed in recent years with the aim to reduce existing uncertainties in evaluated data. Two previous measurements, performed at the 185 m flight-path station EAR1 of the neutron time-of-flight facility n_TOF at CERN, have permitted to substantially extend the resolved resonance region, but suffered in the near-thermal energy range from the unfavorable signal-to-background ratio resulting from the combination of the high radioactivity of 241 Am and the rather low thermal neutron flux. The here presented 241 Am(n,γ) measurement, performed with C 6 D 6 liquid scintillator gamma detectors at the 20 m flight-path station EAR2 of the n_TOF facility, took advantage of the much higher neutron flux. The current status of the analysis of the data, focussed on the low-energy region, will be described here.