Experimental setup and procedure for the measurement of the 7Be(n,α)α reaction at n-TOF

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 7Be(n,α)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 7Be 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

On the application of ICP-MS techniques for measuring uranium and plutonium: a Nordic inter-laboratory comparison exercise

Inductively coupled plasma mass spectrometry (ICP-MS) techniques are widely used for determination of long-lived radionuclides and their isotopic ratios in the nuclear fields. Uranium (U) and Pu (Pu) isotopes have been determined by many researchers with ICP-MS due to its relatively high sensitivity and short measurement time. In this work, an inter-laboratory comparison exercise among the Nordic countries was performed, focusing on the measurement of U and Pu isotopes in certified reference materials by ICP-MS. The performance and characters of different ICP-MS instruments are evaluated and discussed in this paper. <br/

Be 7 (n,α) He 4 Reaction and the Cosmological Lithium Problem : Measurement of the Cross Section in a Wide Energy Range at n-TOF at CERN

M. Barbagallo et al (n-TOF Collaboration), ‘7Be(n,α)4He Reaction and the Cosmological Lithium Problem: Measurement of the Cross Section in a Wide Energy Range at n_TOF at CERN’, Physical Review Letters, Vol 117(15): 152701, October 2016, DOI: https://doi.org/10.1103/PhysRevLett.117.152701 Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.The energy-dependent cross section of the Be7(n,α)He4 reaction, of interest for the so-called cosmological lithium problem in big bang nucleosynthesis, has been measured for the first time from 10 meV to 10 keV neutron energy. The challenges posed by the short half-life of Be7 and by the low reaction cross section have been overcome at n-TOF thanks to an unprecedented combination of the extremely high luminosity and good resolution of the neutron beam in the new experimental area (EAR2) of the n-TOF facility at CERN, the availability of a sufficient amount of chemically pure Be7, and a specifically designed experimental setup. Coincidences between the two alpha particles have been recorded in two Si-Be7-Si arrays placed directly in the neutron beam. The present results are consistent, at thermal neutron energy, with the only previous measurement performed in the 1960s at a nuclear reactor. The energy dependence reported here clearly indicates the inadequacy of the cross section estimates currently used in BBN calculations. Although new measurements at higher neutron energy may still be needed, the n-TOF results hint at a minor role of this reaction in BBN, leaving the long-standing cosmological lithium problem unsolved.Peer reviewe

Serpentine differentiation and polyploid evolution in \kur{Knautia arvensis} agg. (Dipsacaceae).

Evolutionary history of an intricate polyploid complex Knautia arvensis agg. in Central Europe has been studied using combined approach of molecular (AFLP, DNA-sequencing) and cytological (flow cytometry, karyology) techniques. Possible evolutionary scenario has been suggested for the whole complex and for the serpentine population in particular, based on critical assessment of results obtained from the different methods

7Be(n,p)7Li cross section measurement for the cosmological lithium problem at the n_TOF Facility at CERN

One of the most puzzling problems in Nuclear Astrophysics is the ldquoCosmological Lithium Problemrdquo, i.e the discrepancy between the primordial abundance of 7Li observed in metal poor halo stars (Asplund et al. in Astrophys J 644:229- 259, 2006, [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 (Sabate-Gilarte et al. in Eur Phys J A 53:210, 2017, [2]; Weiss et al. in NIMA 799:90, 2015, [3]), 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 mesurement started in April 2016 and lasted for two months. The experimental procedure, the setup used in the measurement and the results obtained so far will be here presented

7^{7} Be(n,p)7^{7} Li Cross Section Measurement for the Cosmological Lithium Problem at the n _\_ TOF Facility at CERN

International audienceOne 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 (Asplund et al. in Astrophys J 644:229–259, 2006, [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 (Sabate-Gilarte et al. in Eur Phys J A 53:210, 2017, [2], Weiss et al. in NIMA 799:90, 2015, [3]), 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 mesurement started in April 2016 and lasted for two months. The experimental procedure, the setup used in the measurement and the results obtained so far will be here presented