One of the most puzzling problems in Nuclear Astrophysics is the "Cosmological Lithium Problem", i.e the discrepancy between the primordial abundance of
7
Li observed in metal poor halo stars 1, and ...the one predicted by Big Bang Nucleosynthesis (BBN). One of the reactions that could have an impact on the problem is
7
Be(n,p)
7
Li. Despite of the importance of this reaction in BBN, the cross-section has never been directly measured at the energies of interest for BBN. Taking advantage of the innovative features of the second experimental area at the n_TOF facility at CERN, an accurate measurement of
7
Be(n,p) cross section has been recently performed at n_TOF, with a pure
7
Be target produced by implantation of a
7
Be beam at ISOLDE. The experimental procedure, the setup used in the measurement and the results obtained so far will be here presented.
One of the most puzzling problems in Nuclear Astrophysics is the "Cosmological Lithium Problem", i.e the discrepancy between the primordial abundance of 7Li observed in metal poor halo stars 1, and ...the one predicted by Big Bang Nucleosynthesis (BBN). One of the reactions that could have an impact on the problem is 7Be(n,p)7Li. Despite of the importance of this reaction in BBN, the cross-section has never been directly measured at the energies of interest for BBN. Taking advantage of the innovative features of the second experimental area at the n_TOF facility at CERN, an accurate measurement of 7Be(n,p) cross section has been recently performed at n_TOF, with a pure 7Be target produced by implantation of a 7Be beam at ISOLDE. The experimental procedure, the setup used in the measurement and the results obtained so far will be here presented.
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 flight 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.
Ce 140 ( 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. Published by the American Physical Society 2024
This manuscript describes the production of three targets obtained by implantation of different activities of 7Be into thin aluminium disks. Two of the produced targets were used to measure ...the 7Be(n, p)7Li cross section in the energy range of interest for the Big-Bang Nucleosynthesis. A third target was used to measure the cross sections of 7Be(n, p)7Li and 7Be(n, α)7Li nuclear reactions with cold and thermal neutrons, respectively. This paper describes also the characterization of the first two targets, performed after the neutron irradiation, in terms of implanted 7Be activities and spatial distributions.
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
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.
Abstract The average energy and multiplicity of prompt $$\gamma $$ γ -rays from slow neutron-induced fission of $$^{235}$$ 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 $$\gamma $$ γ -ray interactions, prompt fission neutrons and background counts before being deconvolved to estimate the emitted spectrum of prompt fission $$\gamma $$ γ -rays. The results give an average $$\gamma $$ γ -ray energy $${\bar{E}}_{\gamma }$$ E ¯ γ of 1.71(5) MeV and multiplicity $$\bar{\nu }_{\gamma }$$ ν ¯ γ of 2.66(18) considering $$\gamma $$ γ -rays emitted within the energy range 0.8–6.8 MeV. The n_TOF data has a slightly larger $${\bar{E}}_{\gamma }$$ E ¯ γ and smaller $$\bar{\nu }_{\gamma }$$ ν ¯ γ than other recent measurements, however the product of the two is in agreement within quoted uncertainties.
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