An improved method for estimating the neutron background in measurements of neutron capture reactions

The relation between the neutron background in neutron capture measurements and the neutron sensitivity related to the experimental setup is examined. It is pointed out that a proper estimate of the neutron background may only be obtained by means of dedicated simulations taking into account the full framework of the neutron-induced reactions and their complete temporal evolution. No other presently available method seems to provide reliable results, in particular under the capture resonances. An improved neutron background estimation technique is proposed, the main improvement regarding the treatment of the neutron sensitivity, taking into account the temporal evolution of the neutron-induced reactions. The technique is complemented by an advanced data analysis procedure based on relativistic kinematics of neutron scattering. The analysis procedure allows for the calculation of the neutron background in capture measurements, without requiring the time-consuming simulations to be adapted to each particular sample. A suggestion is made on how to improve the neutron background estimates if neutron background simulations are not available.Comment: 11 pages, 9 figure

Pulse processing routines for neutron time-of-flight data

A pulse shape analysis framework is described, which was developed for n_TOF-Phase3, the third phase in the operation of the n_TOF facility at CERN. The most notable feature of this new framework is the adoption of generic pulse shape analysis routines, characterized by a minimal number of explicit assumptions about the nature of pulses. The aim of these routines is to be applicable to a wide variety of detectors, thus facilitating the introduction of the new detectors or types of detectors into the analysis framework. The operational details of the routines are suited to the specific requirements of particular detectors by adjusting the set of external input parameters. Pulse recognition, baseline calculation and the pulse shape fitting procedure are described. Special emphasis is put on their computational efficiency, since the most basic implementations of these conceptually simple methods are often computationally inefficient.Comment: 13 pages, 10 figures, 5 table

First Measurement of 72Ge(n,γ) at n_TOF

9th European Summer School on Experimental Nuclear AstrophysicsThe slow neutron capture process (s-process) is responsible for producing about half of the elemental abundances heavier than iron in the universo

Pulse processing routines for neutron time-of-flight data

A pulse shape analysis framework is described, which was developed for n_TOF-Phase3, the third phase in the operation of the n_TOF facility at CERN. The most notable feature of this new framework is the adoption of generic pulse shape analysis routines, characterized by a minimal number of explicit assumptions about the nature of pulses. The aim of these routines is to be applicable to a wide variety of detectors, thus facilitating the introduction of the new detectors or types of detectors into the analysis framework. The operational details of the routines are suited to the specific requirements of particular detectors by adjusting the set of external input parameters. Pulse recognition, baseline calculation and the pulse shape fitting procedure are described. Special emphasis is put on their computational efficiency, since the most basic implementations of these conceptually simple methods are often computationally inefficient.Croatian Science Foundation - Project No. 168

The new vertical neutron beam line at the CERN n_TOF facility design and outlook on the performance

At the neutron time-of-flight facility n_TOF at CERN a new vertical beam line was constructed in 2014, in order to extend the experimental possibilities at this facility to an even wider range of challenging cross-section measurements of interest in astrophysics, nuclear technology and medical physics. The design of the beam line and the experimental hall was based on FLUKA Monte Carlo simulations, aiming at maximizing the neutron flux, reducing the beam halo and minimizing the background from neutrons interacting with the collimator or back-scattered in the beam dump. The present paper gives an overview on the design of the beam line and the relevant elements and provides an outlook on the expected performance regarding the neutron beam intensity, shape and energy resolution, as well as the neutron and photon backgrounds

Experimental neutron capture data of 58 Ni from the CERN n_TOF facility

The 58 Ni( n , γ ) cross section has been measured at the neutron time of flight facility n_TOF at CERN, in the energy range from 27 meV up to 400 keV. In total, 51 resonances have been analyzed up to 122 keV. Maxwellian averaged cross sections (MACS) have been calculated for stellar temperatures of k T = 5 – 100 keV with uncertainties of less than 6%, showing fair agreement with recent experimental and evaluated data up to k T = 50 keV. The MACS extracted in the present work at 30 keV is 34.2 ± 0 . 6 stat ± 1 . 8 sys mb, in agreement with latest results and evaluations, but 12% lower relative to the recent KADoNIS compilation of astrophysical cross sections. When included in models of the s -process nucleosynthesis in massive stars, this change results in a 60% increase of the abundance of 58 Ni, with a negligible propagation on heavier isotopes. The reason is that, using both the old or the new MACS, 58 Ni is efficiently depleted by neutron captures.National Science Foundation (NSF) de los Estados Unidos. PHY 02-16783 y PHY 09-22648Joint Institute for Nuclear Astrophysics (JINA) de los Estados Unidos. EU MIRG-CT-2006-04652

Destruction of the cosmic γ -ray emitter 26 Al in massive stars: Study of the key 26 Al ( n , α ) reaction

Neutron destruction reactions of the cosmic γ -ray emitter 26Al are of importance to determine the amount of 26Al ejected into our galaxy by supernova explosions and for 26Al production in asymptotic giant branch stars. We performed a new measurement of the 26Al(n, α) 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.Austrian Science Fund (FWF). J3503The U.K. Science and Technologies Facilities Council (STFC) ST/L005824/1 y No. ST/M006085/1The European Research Council ERC-2015-STG. 677497European Cooperation in Science and Technology (Cost Action), programa Chemical Elements as Tracers of the Evolution of the Cosmos(ChETEC) CA1611

Measurement of the α ratio and (n, γ) cross section of 235U from 0.2 to 200 eV at n_TOF

We measured the neutron capture-to-fission cross-section ratio (α ratio) and the capture cross section of 235U between 0.2 and 200 eV at the n_TOF facility at CERN. The simultaneous measurement of neutron-induced capture and fission rates was performed by means of the n_TOF BaF2 Total Absorption Calorimeter (TAC), used for detection of γ rays, in combination with a set of micromegas detectors used as fission tagging detectors. The energy dependence of the capture cross section was obtained with help of the 6 Li(n,t) standard reaction determining the n_TOF neutron fluence; the well-known integral of the 235U(n, f ) cross section between 7.8 and 11 eV was then used for its absolute normalization. The α ratio, obtained with slightly higher statistical fluctuations, was determined directly, without need for any reference cross section. To perform the analysis of this measurement we developed a new methodology to correct the experimentally observed effect that the probabilities of detecting a fission reaction in the TAC and the micromegas detectors are not independent. The results of this work have been used in a new evaluation of 235U performed within the scope of the Collaborative International Evaluated Library Organisation (CIELO) Project, and are consistent with the ENDF/B-VIII.0 and JEFF-3.3 capture cross sections below 4 eV and above 100 eV. However, the measured capture cross section is on average 10% larger between 4 and 100 eV.Ministerio de Economía, Industria y Competitividad de España. FPA2014-53290-C2-1, FPA2016-76765- P y FPA2017-82647-P7º Programa Marco CHANDA de la Comisión Europea. FP7-60520