Papers by Alberto Mengoni
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2016
The newly built second experimental area EAR2 of the n_TOF spallation neutron source at CERN allo... more The newly built second experimental area EAR2 of the n_TOF spallation neutron source at CERN allows to perform (n, charged particles) experiments on short-lived highly radioactive targets. This paper describes a detection apparatus and the experimental procedure for the determination of the cross-section of the 7 Be(n,α) reaction, which represents one of the focal points toward the solution of the cosmological Lithium abundance problem, and whose only measurement, at thermal energy, dates back to 1963. The apparently unsurmountable experimental difficulties stemming from the huge 7 Be γ-activity, along with the lack of a suitable neutron beam facility, had so far prevented further measurements. The detection system is subject to considerable radiation damage, but is capable of disentangling the rare reaction signals from the very high background. This newly developed setup could likely be useful also to study other challenging reactions requiring the detectors to be installed directly in the neutron beam.
Nucleation and Atmospheric Aerosols, 2005
The method for an experimental determination of the stellar enhancement factor for the cross sect... more The method for an experimental determination of the stellar enhancement factor for the cross section of the 151 Sm(n, γ) reaction process is proposed. This study offered the pretext for an excursus on the interconnections between capture and dissociation reactions and the interplay between theory and experiments in the determination of neutron capture cross sections.
Implementation of a cross section evaluation methodology for safety margins analysis: Post processing and data analysis for the capture cross section measurements of odd Gadolinium isotopes
The Astrophysical Journal, 2021
Recent models for evolved Low Mass Stars (with M 3 M), undergoing the AGB phase assume that magne... more Recent models for evolved Low Mass Stars (with M 3 M), undergoing the AGB phase assume that magnetic flux-tube buoyancy drives the formation of 13 C reservoirs in He-rich layers. We illustrate their crucial properties, showing how the low abundance of 13 C generated below the convective envelope hampers the formation of primary 14 N and the ensuing synthesis of intermediate-mass nuclei, like 19 F and 22 Ne. In the mentioned models, their production is therefore of a purely secondary nature. Shortage of primary 22 Ne has also important effects in reducing the neutron density. Another property concerns AGB winds, which are likely to preserve C-rich subcomponents, isolated by magnetic tension, even when the envelope composition is O-rich. Conditions for the formation of C-rich compounds are therefore found in stages earlier than previously envisaged. These issues, together with the uncertainties related to several nuclear physics quantities, are discussed in the light of the isotopic admixtures of s-process elements in presolar SiC grains of stellar origin, which provide important and precise constraints to the otherwise uncertain parameters. By comparing nucleosynthesis results with measured SiC data, it is argued that such a detailed series of constraints indicates the need for
EPJ Web of Conferences, 2017
The accurate knowledge of the neutron-induced fission cross-sections of actinides and other isoto... more The accurate knowledge of the neutron-induced fission cross-sections of actinides and other isotopes involved in the nuclear fuel cycle is essential for the design of advanced nuclear systems, such as Generation-IV nuclear reactors. Such experimental data can also provide the necessary feedback for the adjustment of nuclear model parameters used in the evaluation process, resulting in the further development of nuclear fission models. In the present work, the 240 Pu(n,f) cross-section was measured at CERN's n TOF facility relative to the well-known 235 U(n,f) cross section, over a wide range of neutron energies, from meV to almost MeV, using the time-of-flight technique and a setup based on Micromegas detectors. This measurement was the first experiment to be performed at n TOF's new experimental area (EAR-2), which offers a significantly higher neutron flux compared to the already existing experimental area (EAR-1). Preliminary results as well as the experimental procedure, including a description of the facility and the data handling and analysis, are presented.
Neutron capture rates in the r-process-The role of direct radiative capture
... to be shorter than the mean beta decay lifetime, r~. The (n, -y) equilibration NEUTRON CAPTUR... more ... to be shorter than the mean beta decay lifetime, r~. The (n, -y) equilibration NEUTRON CAPTURE RATES IN r-PROCESS 744 MATHEWS ETAL ... and Cameron (1978) but exceeds by one to two orders of magnitude the neutron exposure calculated in the stellar model of Blake et a ...
HNPS Advances in Nuclear Physics
The n_TOF facility at CERN is a neutron Time-Of-Flight facility based on a spallation neutron sou... more The n_TOF facility at CERN is a neutron Time-Of-Flight facility based on a spallation neutron source. During the Second Long Shutdown (LS2) , a new experimental zone was designed and delivered. This new experimental area -the NEAR station - is located very close to the lead spallation target, at a distance of just ~3m. In this way, the high luminosity of the n_TOF neutron spallation source can be fully exploited. Towards the characterization of the new experimental area as well for the benchmarking of the performed simulations, the multi-foil activation measurement will be implemented. Eleven threshold and seven capture reference reactions will be utilized for the unfolding of the NEAR neutron beam energy spectrum that stretches from the meV to the GeV region.
The European Physical Journal A
The 235U(n,f) cross section was measured in a wide energy range (18 meV–170 keV) at the n_TOF fac... more The 235U(n,f) cross section was measured in a wide energy range (18 meV–170 keV) at the n_TOF facility at CERN, relative to 6Li(n,t) and 10B(n,α) standard reactions, with high resolution and accuracy, with a setup based on a stack of six samples and six silicon detectors placed in the neutron beam. In this paper we report on the results in the region between 18 meV and 10 keV neutron energy. A resonance analysis has been performed up to 200 eV, with the code SAMMY. The resulting fission kernels are compared with the ones extracted on the basis of the resonance parameters of the most recent major evaluated data libraries. A comparison of the n_TOF data with the evaluated cross sections is also performed from thermal to 10 keV neutron energy for the energy-averaged cross section in energy groups of suitably chosen width. A good agreement, within 0.5%, is found on average between the new results and the latest evaluated data files ENDF/B-VIII.0 and JEFF-3.3, as well as with respect to ...
25p-ZK-8 Algebraic-eikonal approach to the electron-molecule scattering
Selenium-79 is a branching point in the slow neutron capture process (s-process) with relevant im... more Selenium-79 is a branching point in the slow neutron capture process (s-process) with relevant implications in nucleosynthesis and in stellar models. The products of the s-process nucleosynthesis after 79 Se are the s-only isotopes 80,82 Kr, whose solar system abundances are accurately known. This information, in conjunction with the experimental cross section of 79 Se(n,γ) will allow one to extract reliable conditions for the temperature and neutron density, as well as the role of the main and weak s-process contributions to the
A bulk micromegas detector with the anode segmented in 2 orthogonal directions and equipped with ... more A bulk micromegas detector with the anode segmented in 2 orthogonal directions and equipped with a neutron/charged particle converter is employed at the neutron time-of-flight (nTOF) facility at CERN to determine the incident neutron beam profile and beam interception factor as a function of the neutron energy determined by the time of flight. Discrepancies between experimental results and simulations in the values of the beam interception factor range up to 12 % and are to be ascribed to a defect in the mesh of the bulk. Nevertheless the detector proved to be really useful for checking the alignment of the neutron beam optics of the facility. Measurements with a new pixelized bulk detector for the determination of the beam interception factor are forseen before the end of 2012.
Electron—Molecule Collision Process: Review and Perspective of Algebraic Approaches
Symmetries in Science VII, 1994
The calculation of the scattering cross section for the electron molecule collision process can b... more The calculation of the scattering cross section for the electron molecule collision process can be a formidable and not rarely an untreatable task using conventional methods based on integro—differential techniques. Recently, an alternative procedure has been proposed (Bijker et al., 1986) which makes use of an algebraic description of the molecular structure, the Vibron Model (Iachello, 1981), in conjunction with the Glauber diffractive theory for the dynamic of the collision process. This approach, named algebraic—eikonal, has been applied to the calculation of scattering cross sections for several dipolar diatomic targets. The long—range dipole interaction, certainly dominant for the vibrationally elastic process, has been included in the formalism and the relative scattering amplitudes derived.
/sup 148,150/Sm: A test for s-process nucleosynthesis
ABSTRACT We have measured to a precision of approx.4.5% the neutron capture cross sections of /su... more ABSTRACT We have measured to a precision of approx.4.5% the neutron capture cross sections of /sup 148,149,150/Sm over the neutron energy range 4<E<250 keV. These data, in conjunction with calculated cross sections for /sup 147/Nd and /sup 147,148/Pm, are used to establish a set of Maxwellian-averaged cross sections useful for investigation of branchings in the s-process of stellar nucleosynthesis. The ratio of the values of the s-process current N/sub s/ (Maxwellian-averaged neutron cross section times s-process abundance) for the s-only isotopes /sup 148,150/Sm is 0.91 +- 0.03 rather than unity as predicted by the local approximation. We interpret this result as due to an s-process branching which partly bypasses /sup 148/Sm. Since the ..beta..-decay rates at the branching points are expected to be almost independent of temperature, we are able to obtain an estimate of the s-process neutron density of n/sub n/ = 1.0 +- 0.4 x 10/sup 8/ cm/sup -3/. The new results have also served to considerably improve the N/sub s/-systematics in the mass region Aroughly-equal145.
Coulomb dissociation of C
Sm-148,150-A test for s-process nucleosynthesis
... For example, near E = 30 keY the cross sections are modified by - 16% (' by + 1.6 ... Si... more ... For example, near E = 30 keY the cross sections are modified by - 16% (' by + 1.6 ... Since the Maxwell-Boltzmann distribution extends with significant area below the minimum energy ( 4 keV ... local systematics for the level density parameter a was determined by a careful statistical ...
Coulomb excitation of< sup> 11</sup> Be
Low-lying intruder 1< sup>−</sup> state in< sup> 12</sup> Be and the melting of the< i> N</i>= 8 shell closure
Physical review letters, Jan 27, 2018
We report on the measurement of the ^{7}Be(n,p)^{7}Li cross section from thermal to approximately... more We report on the measurement of the ^{7}Be(n,p)^{7}Li cross section from thermal to approximately 325 keV neutron energy, performed in the high-flux experimental area (EAR2) of the n_TOF facility at CERN. This reaction plays a key role in the lithium yield of the big bang nucleosynthesis (BBN) for standard cosmology. The only two previous time-of-flight measurements performed on this reaction did not cover the energy window of interest for BBN, and they showed a large discrepancy between each other. The measurement was performed with a Si telescope and a high-purity sample produced by implantation of a ^{7}Be ion beam at the ISOLDE facility at CERN. While a significantly higher cross section is found at low energy, relative to current evaluations, in the region of BBN interest, the present results are consistent with the values inferred from the time-reversal ^{7}Li(p,n)^{7}Be reaction, thus yielding only a relatively minor improvement on the so-called cosmological lithium problem. ...
Uploads
Papers by Alberto Mengoni