Mastromarco, M.*; Amaducci, S.*; Colonna, N.*; 木村 敦; 他118名*
European Physical Journal A, 58(8), p.147_1 - 147_13, 2022/08
The U(n,f) cross section was measured in a wide energy range (18 meV - 170 keV) at the n_TOF facility at CERN, relative to Li(n,t) and B(n,) standard reactions, with a setup based on a stack of six samples and six silicon detectors placed in the neutron beam. A resonance analysis has been performed up to 200 eV, with the code SAMMY. 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 the broad group average fission cross section established in the framework of the standard working group of IAEA. However, some discrepancies, of up to 4 %, are still present in some specific energy regions.
Chiaveri, E.*; Aberle, O.*; Alcayne, V.*; 木村 敦; 他124名*
EPJ Web of Conferences, 239, p.17001_1 - 17001_8, 2020/09
Since the start of its operation in 2001, the neutron time of-flight facility of CERN, n_TOF, has become one of the most forefront neutron facilities in the world for wide-energy spectrum neutron cross section measurements. Thanks to the combination of excellent neutron energy resolution and high instantaneous neutron flux available in the two experimental areas, the second of which has been constructed in 2014, n_TOF is providing a wealth of new data on neutron-induced reactions of interest for nuclear astrophysics, advanced nuclear technologies and medical applications. In this document the main characteristics of the n_TOF facility and their relevance for neutron studies in the different areas of research will be outlined. In addition, the future perspectives of the facility will be described including the upgrade of the spallation target, the setup of an imaging installation and the construction of a new irradiation area.
Terranova, N.*; Aberle, O.*; Alcayne, V.*; 木村 敦; 他125名*
EPJ Web of Conferences, 239, p.01024_1 - 01024_5, 2020/09
The U(n,f) cross section from 20 MeV up to about 1 GeV has been measured relative to the H(n,n)H reaction. The neutron flux impinging on the U sample has been obtained by detecting recoil protons originating from n-p scattering in a CH sample. Two Proton Recoil Telescopes (PRT), consisting of several layers of solid-state detectors and fast plastic scintillators, have been set at proton scattering angles of 25.07 and 20.32. Extensive Monte Carlo simulations were performed to characterize proton transport through the PRTs. In this work we compare measured data collected with the PRTs with a full Monte Carlo simulation based on the Geant-4 toolkit.
Manna, A.*; Aberle, O.*; Alcayne, V.*; 木村 敦; 他125名*
EPJ Web of Conferences, 239, p.01008_1 - 01008_5, 2020/09
The neutron induced fission of U is extensively used as a reference for neutron fluence measurements in various applications. However, no data exist on neutron induced fission of U above 200 MeV. The neutron facility n_TOF offers the possibility to improve the situation. The measurement of U(n,f) relative to the differential n-p scattering cross-section, was carried out with the aim of providing accurate and precise cross section data in the energy range from 10 MeV up to 1 GeV. In this measurements, recoil proton telescopes are used to measure the neutron flux while the fission events are detected and counted with dedicated detectors. In this paper the measurement campaign and the experimental set-up are illustrated.
Amaducci, S.*; 原田 秀郎; 木村 敦; 他118名*
European Physical Journal A, 55(7), p.120_1 - 120_19, 2019/07
n_TOF施設にて、熱から170keVの中性子エネルギー領域において、U(n, f)断面積を測定した。Li(n, t)およびB(n, )標準断面積に対する相対測定により、1.5%という系統的不確かさで測定値を得た。本測定には、6層からなるサンプルと6台のSi検出器を用いた。918keVエネルギー領域において、本測定結果は、最近の評価済み核データであるENDF/B-VIII.0およびJEFF3.3の評価値が、約5%過大評価であることを示した。高分解能測定の結果、keV領域で、共鳴構造を観測した。本測定より、7.811eVのエネルギー範囲の断面積の積分値について、249.71.4(統計的不確かさ)0.94(系統的不確かさ)beVという結果を得た。この結果は、最近確立された標準値247.53beVを支持するものである。
Lederer-Woods, C.*; Battino, U.*; Ferreira, P.*; Gawlik, A.*; 木村 敦; n_TOF Collaboration*; 他128名*
Physics Letters B, 790, p.458 - 465, 2019/03
cross sections were measured at the neutron time-of-flight facility n_TOF at CERN up to neutron energies of 300 keV, providing for the first time experimental data above 8 keV. Results indicate that the stellar cross section at =30 keV is 1.5 to 1.7 times higher than most theoretical predictions. The new cross sections result in a substantial decrease of Ge produced in stars, which would explain the low isotopic abundance of Ge in the solar system.
Mastromarco, M.*; Manna, A.*; Aberle, O.*; Andrzejewski, J.*; 原田 秀郎; 木村 敦; n_TOF Collaboration*; 他116名*
European Physical Journal A, 55(1), p.9_1 - 9_20, 2019/01
Neutron capture cross section measurements on Gd and Gd were performed using the time-of-flight technique at the n_TOF facility at CERN on isotopically enriched samples. The measurements were carried out in the n TOF experimental area EAR1, at 185m from the neutron source, with an array of 4 CD liquid scintillation detectors. At a neutron kinetic energy of 0.0253eV, capture cross sections of 62.2(2.2) and 239.8(8.4) kilobarn have been derived for Gd and Gd, respectively, with up to 6% deviation relative to values presently reported in nuclear data libraries, but consistent with those values within 1.6 standard deviations. A resonance shape analysis has been performed in the resolved resonance region up to 181eV and 307eV, respectively for Gd and Gd, where on average, resonance parameters have been found in good agreement with evaluations. Above these energies and up to 1keV, the observed resonance-like structure of the cross section has been analysed and characterised. From a statistical analysis of the observed neutron resonances we deduced: neutron strength function of 2.01(28) 10 and 2.17(41) 10; average total radiative width of 106.8(14)meV and 101.1(20)meV and s-wave resonance spacing 1.6(2)eV and 4.8(5)eV for n + Gd and n + Gd systems, respectively.
佐藤 哲也; 浅井 雅人; Borschevsky, A.*; Beerwerth, R.*; 金谷 佑亮*; 牧井 宏之; 水飼 秋菜*; 永目 諭一郎; 長 明彦; 豊嶋 厚史; et al.
Journal of the American Chemical Society, 140(44), p.14609 - 14613, 2018/11
Damone, L.*; Barbagallo, M.*; Mastromarco, M.*; Cosentino, L.*; 原田 秀郎; 木村 敦; n_TOF Collaboration*; 他152名*
Physical Review Letters, 121(4), p.042701_1 - 042701_7, 2018/07
We report on the measurement of the Be(n,p)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 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 Li(p,n)Be reaction, thus yielding only a relatively minor improvement on the so-called cosmological lithium problem. The relevance of these results on the near threshold neutron production in the p+Li reaction is also discussed.
Barbagallo, M.*; Andrzejewski, J.*; Mastromarco, M.*; Perkowski, J.*; Damone, L. A.*; Gawlik, A.*; 木村 敦; n_TOF Collaboration*; 他122名*
Nuclear Instruments and Methods in Physics Research A, 887, p.27 - 33, 2018/04
Following the completion of the second neutron beam line and the related experimental area (EAR2) at the n_TOF spallation neutron source at CERN, several experiments were planned and performed. The high instantaneous neutron flux available in EAR2 allows to investigate neutron induced reactions with charged particles in the exit channel even employing targets made out of small amounts of short-lived radioactive isotopes. After the successful measurement of the Be(n,)cross section, the Be(n,p)Li reaction was studied in order to provide still missing cross section data of relevance for Big Bang Nucleosynthesis (BBN), in an attempt to find a solution to the cosmological Lithium abundance problem. This paper describes the experimental setup employed in such a measurement and its characterization.
Lerendegui-Marco, J.*; Guerrero, C.*; Mendoza, E.*; Quesada, J. M.*; Eberhardt, K.*; Junghans, A. R.*; 木村 敦; n_TOF Collaboration*; 他126名*
Physical Review C, 97(2), p.024605_1 - 024605_21, 2018/02
This paper presents a new time-of-flight capture measurement on Pu carried out at n_TOF-EAR1(CERN), focusing on the analysis and statistical properties of the resonance region, below 4 keV. The Pu(n,)reaction on a sample containing 95(4) mg enriched to 99.959% was measured with an array of four CD detectors and applying the total energy detection technique. The high neutron energy resolution of n_TOF-EAR1 and the good statistics accumulated have allowed us to extend the resonance analysis up to 4 keV, obtaining new individual and average resonance parameters from a capture cross section featuring a systematic uncertainty of 5%, fulfilling the request of the NEA.