n_TOF Collaboration(Mazzone, A. et al), Babiano-Suarez, V., Caballero, L., Domingo-Pardo, C., Ladarescu, I., & Tain, J. L. (2020). Measurement of the Gd-154(n, gamma) cross section and its astrophysical implications. Phys. Lett. B, 804, 135405–6pp.
Abstract: The neutron capture cross section of Gd-154 was measured from 1 eV to 300 keV in the experimental area located 185 m from the CERN n_TOF neutron spallation source, using a metallic sample of gadolinium, enriched to 67% in Gd-154. The capture measurement, performed with four C6D6 scintillation detectors, has been complemented by a transmission measurement performed at the GELINA time-of-flight facility (JRC-Geel), thus minimising the uncertainty related to sample composition. An accurate Maxwellian averaged capture cross section (MACS) was deduced over the temperature range of interest for s process nucleosynthesis modelling. We report a value of 880(50) mb for the MACS at kT = 30 keV, significantly lower compared to values available in literature. The new adopted Gd-154(n, gamma) cross section reduces the discrepancy between observed and calculated solar s-only isotopic abundances predicted by s-process nucleosynthesis models.
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n_TOF Collaboration(Mastromarco, M. et al), Domingo-Pardo, C., & Tain, J. L. (2022). High accuracy, high resolution U-235(n,f) cross section from n_TOF (CERN) from 18 meV to 10 keV. Eur. Phys. J. A, 58(8), 147–13pp.
Abstract: The U-235(n,f) cross section was measured in a wide energy range (18 meV-170 keV) at the nTOF facility at CERN, relative to Li-6(n,t) and B-10(n,alpha) 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 nTOF 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 the broad group average fission cross section established in the framework of the standard working group of IAEA (the so-called reference file). However, some discrepancies, of up to 4%, are still present in some specific energy regions. The new dataset here presented, characterized by a unique combination of high resolution and accuracy, low background and wide energy range, can help to improve the evaluations from the Resolved Resonance Region up to 10 keV, also reducing the uncertainties that affect this region.
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n_TOF Collaboration(Mastromarco, M. et al), Domingo-Pardo, C., & Tain, J. L. (2019). Cross section measurements of Gd-155,Gd-157(n,) induced by thermal and epithermal neutrons. Eur. Phys. J. A, 55(1), 9–20pp.
Abstract: Neutron capture cross section measurements on Gd-155 and Gd-157 were performed using the time-of-flight technique at the nTOF facility at CERN on isotopically enriched samples. The measurements were carried out in the nTOF experimental area EAR1, at 185 m from the neutron source, with an array of 4 C6D6 liquid scintillation detectors. At a neutron kinetic energy of 0.0253 eV, capture cross sections of 62.2(2.2) and 239.8(8.4) kilobarn have been derived for Gd-155 and Gd-157, 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 181 eV and 307 eV, respectively for Gd-155 and Gd-157, where on average, resonance parameters have been found in good agreement with evaluations. Above these energies and up to 1 keV, 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)x10-4 and 2.17(41)x10-4; 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-155 and n + Gd-157 systems, respectively.
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n_TOF Collaboration(Massimi, C. et al), Domingo-Pardo, C., & Tain, J. L. (2012). Resonance neutron-capture cross sections of stable magnesium isotopes and their astrophysical implications. Phys. Rev. C, 85(4), 044615–15pp.
Abstract: We have measured the neutron capture cross sections of the stable magnesium isotopes Mg-24,Mg-25,Mg-26 in the energy range of interest to the s process using the neutron time-of-flight facility n_TOF at CERN. Capture events from a natural metal sample and from samples enriched in Mg-25 and Mg-26 were recorded using the total energy method based on (C6H6)-H-2 detectors. Neutron resonance parameters were extracted by a simultaneous resonance shape analysis of the present capture data and existing transmission data on a natural isotopic sample. Maxwellian-averaged capture cross sections for the three isotopes were calculated up to thermal energies of 100 keV and their impact on s-process analyses was investigated. At 30 keV the new values of the stellar cross section for Mg-24, Mg-25, and Mg-26 are 3.8 +/- 0.2 mb, 4.1 +/- 0.6 mb, and 0.14 +/- 0.01 mb, respectively.
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n_TOF Collaboration(Massimi, C. et al.), Domingo-Pardo, C., Giubrone, G., & Tain, J. L. (2017). Neutron spectroscopy of Mg-26 states: Constraining the stellar neutron source Ne-22(alpha, n)Mg-25. Phys. Lett. B, 768, 1–6.
Abstract: This work reports on accurate, high-resolution measurements of the Mg-25(n, gamma)Mg-26 and Mg-25(n, tot) cross sections in the neutron energy range from thermal to about 300 keV, leading to a significantly improved Mg-25(n, gamma)Mg-26 parametrization. The relevant resonances for n+Mg-25 were characterized from a combined R-matrix analysis of the experimental data. This resulted in an unambiguous spin/parity assignment of the corresponding excited states in Mg-26. With this information experimental upper limits of the reaction rates for Ne-22(alpha, n)Mg-25 and Ne-22(alpha, gamma)Mg-26 were established, potentially leading to a significantly higher (alpha, n)/(alpha, gamma) ratio than previously evaluated. The impact of these results has been studied for stellar models in the mass range 2 to 25 M-circle dot. (C) 2017 The Author(s). Published by Elsevier B.V.
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Martinez, T. et al, Agramunt, J., Algora, A., Domingo-Pardo, C., Jordan, M. D., Rubio, B., et al. (2014). MONSTER: a TOF Spectrometer for beta-delayed Neutron Spectroscopy. Nucl. Data Sheets, 120, 78–80.
Abstract: beta-delayed neutron (DN) data, including emission probabilities, P-n, and energy spectrum, play an important role in our understanding of nuclear structure, nuclear astrophysics and nuclear technologies. A MOdular Neutron time-of-flight SpectromeTER (MONSTER) is being built for the measurement of the neutron energy spectra and branching ratios. The TOF spectrometer will consist of one hundred liquid scintillator cells covering a significant solid angle. The MONSTER design has been optimized by using Monte Carlo (MC) techniques. The response function of the MONSTER cell has been characterized with mono-energetic neutron beams and compared to dedicated MC simulations.
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Mach, H., Lindroth, A., Ruchowska, E., Kvasil, J., Fogelberg, B., Gulda, K., et al. (2016). On the enhanced E1 transitions in the K=3/2 parity doublet band in Ra-223. Eur. Phys. J. A, 52(6), 172–10pp.
Abstract: We have applied the fast timing beta gamma gamma(t) technique to remeasure lifetimes of selected states in Ra-223 populated in the beta(-) decay of Fr-223. T-1/2 = 587(12) ps and 210(13) ps have been obtained for the 3/2(-) and 5/2(-) states at 50.1 and 79.7 keV, that are more accurate than the previous values of 630(70) ps and 166(55) ps, respectively. Our vertical bar D0 vertical bar value of 0.155(10) e.fm obtained for the K = 3/2 configuration together with the available values of vertical bar D0 vertical bar for the K = 1/2 and K = 5/2 parity doublet bands establish the configuration dependence of vertical bar D0 vertical bar at low spins in this nucleus. Results of theoretical calculations performed for Ra-223, using the quasiparticle-phonon model (QPM) with inclusion of the Coriolis coupling, reasonably well reproduce octupole correlations in this nucleus.
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n_TOF Collaboration(Lerendegui-Marco, J. et al.), Domingo-Pardo, C., Tain, J. L., & Tarifeño-Saldivia, A. (2018). Radiative neutron capture on Pu-242 in the resonance region at the CERN n_TOF-EAR1 facility. Phys. Rev. C, 97(2), 024605–21pp.
Abstract: The spent fuel of current nuclear reactors contains fissile plutonium isotopes that can be combined with uranium to make mixed oxide (MOX) fuel. In this way the Pu from spent fuel is used in a new reactor cycle, contributing to the long-term sustainability of nuclear energy. However, an extensive use of MOX fuels, in particular in fast reactors, requires more accurate capture and fission cross sections for some Pu isotopes. In the case of Pu-242 there are sizable discrepancies among the existing capture cross-section measurements included in the evaluations (all from the 1970s) resulting in an uncertainty as high as 35% in the fast energy region. Moreover, postirradiation experiments evaluated with JEFF-3.1 indicate an overestimation of 14% in the capture cross section in the fast neutron energy region. In this context, the Nuclear Energy Agency (NEA) requested an accuracy of 8% in this cross section in the energy region between 500 meV and 500 keV. This paper presents a new time-of-flight capture measurement on Pu-242 carried out at nTOF-EAR1 (CERN), focusing on the analysis and statistical properties of the resonance region, below 4 keV. The Pu-242(n, gamma) reaction on a sample containing 95(4) mg enriched to 99.959% was measured with an array of four C6D6 detectors and applying the total energy detection technique. The high neutron energy resolution of nTOF-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.
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n_TOF Collaboration(Lederer-Woods, C. et al.), Domingo-Pardo, C., & Tain, J. L. (2021). Destruction of the cosmic gamma-ray emitter Al-26 in massive stars: Study of the key Al-26(n, p) reaction. Phys. Rev. C, 104(2), L022803–7pp.
Abstract: The Al-26(n, p) Mg-26 reaction is the key reaction impacting on the abundances of the cosmic gamma-ray emitter Al-26 produced in massive stars and impacts on the potential pollution of the early solar system with Al-26 by asymptotic giant branch stars. We performed a measurement of the Al-26(n, p) Mg-26 cross section at the high-flux beam line EAR-2 at the n_TOF facility (CERN). We report resonance strengths for eleven resonances, nine being measured for the first time, while there is only one previous measurement for the other two. Our resonance strengths are significantly lower than the only previous values available. Our cross-section data range to 150 keV neutron energy, which is sufficient for a reliable determination of astrophysical reactivities up to 0.5 GK stellar temperature.
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n_TOF Collaboration(Lederer-Woods, C. et al.), Domingo-Pardo, C., & Tain, J. L. (2021). Destruction of the cosmic gamma-ray emitter Al-26 in massive stars: Study of the key Al-26(n, alpha) reaction. Phys. Rev. C, 104(3), L032803–6pp.
Abstract: Neutron destruction reactions of the cosmic gamma-ray emitter Al-26 are of importance to determine the amount of Al-26 ejected into our galaxy by supernova explosions and for Al-26 production in asymptotic giant branch stars. We performed a new measurement of the Al-26(n, alpha) reaction up to 160-keV neutron energy at the neutron time-of-flight facilities n_TOF at CERN and GELINA at EC-JRC. We provide strengths for ten resonances, six of them for the first time. We use our data to calculate astrophysical reactivities for stellar temperatures up to 0.7 GK. Our results resolve a discrepancy between the two previous direct measurements of this reaction, and indicate higher stellar destruction rates than the most recently recommended reactivity.
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