Characterization of the n-TOF EAR-2 neutron beam

The experimental area 2 (EAR-2) at CERNs neutron time-of-flight facility (n-TOF), which is operational since 2014, is designed and built as a short-distance complement to the experimental area 1 (EAR-1). The Parallel Plate Avalanche Counter (PPAC) monitor experiment was performed to characterize the beam prole and the shape of the neutron 'ux at EAR-2. The prompt γ-flash which is used for calibrating the time-of-flight at EAR-1 is not seen by PPAC at EAR-2, shedding light on the physical origin of this γ-flash

The measurement programme at the neutron time-of-flight facility n-TOF at CERN

Neutron-induced reaction cross sections are important for a wide variety of research fields ranging from the study of nuclear level densities, nucleosynthesis to applications of nuclear technology like design, and criticality and safety assessment of existing and future nuclear reactors, radiation dosimetry, medical applications, nuclear waste transmutation, accelerator-driven systems and fuel cycle investigations. Simulations and calculations of nuclear technology applications largely rely on evaluated nuclear data libraries. The evaluations in these libraries are based both on experimental data and theoretical models. CERN's neutron time-of-flight facility n-TOF has produced a considerable amount of experimental data since it has become fully operational with the start of its scientific measurement programme in 2001. While for a long period a single measurement station (EAR1) located at 185 m from the neutron production target was available, the construction of a second beam line at 20 m (EAR2) in 2014 has substantially increased the measurement capabilities of the facility. An outline of the experimental nuclear data activities at n-TOF will be presented

Cross section measurements of 155,157Gd(n, γ) induced by thermal and epithermal neutrons

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 185 m from the neutron source, with an array of 4 CD 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 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 181 eV and 307 eV, respectively for Gd and Gd, 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) × 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

Neutron spectroscopy of 26Mg states : Constraining the stellar neutron source 22Ne(α,n)25Mg

This work reports on accurate, high-resolution measurements of the 25Mg(n,γ)26Mg and 25Mg(n,tot) cross sections in the neutron energy range from thermal to about 300 keV, leading to a significantly improved 25Mg(n,γ)26Mg parametrization. The relevant resonances for n+25Mg 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 26Mg. With this information experimental upper limits of the reaction rates for 22Ne(α,n)25Mg and 22Ne(α,γ)26Mg were established, potentially leading to a significantly higher (α,n)/(α,γ) ratio than previously evaluated. The impact of these results has been studied for stellar models in the mass range 2 to 25 M⊙

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

Radiative Neutron Capture Cross-Section Measurement of Ge Isotopes at n_TOF CERN Facility and Its Importance for Stellar Nucleosynthesis

This work was supported by the Austrian Science Fund FWF (J3503), the Adolf Messer Foundation (Germany), the UK Science and Facilities Council (ST/M006085/1), and the European Research Council ERC-2015-StG No. 677497. We also acknowledge the support of the National Science Centre, Poland, under the grant UMO-2016/22/M/ST2/00183, the MSMT of the Czech Republic and the Croatian Science Foundation under the project IP-2018-01-8570.This manuscript summarizes the results of radiative neutron capture cross-section measurements on two stable germanium isotopes, Ge-70 and Ge-73. Experiments were performed at the n_TOF facility at CERN via the time-of-flight technique, over a wide neutron energy range, for all stable germanium isotopes (70,72,73,74, and 76). Results for Ge-70 [Phys. Rev. C 100, 045804 (2019)] and Ge-73 [Phys. Lett. B 790, 458 (2019)] are already published. In the field of nuclear structure, such measurements allow to study excited levels close to the neutron binding energy and to obtain information on nuclear properties. In stellar nucleosynthesis research, neutron induced reactions on germanium are of importance for nucleosynthesis in the weak component of the slow neutron capture processes.Austrian Science Fund (FWF) J3503Adolf Messer Foundation (Germany)UK Science and Facilities Council ST/M006085/1European Research Council (ERC)European Commission 677497National Science Centre, Poland UMO-2016/22/M/ST2/00183Ministry of Education, Youth & Sports - Czech RepublicCroatian Science Foundation IP-2018-01-857

Neutron spectroscopy of ²⁶Mg states: Constraining the stellar neutron source ²²Ne(α,n)²⁵Mg

This work reports on accurate, high-resolution measurements of the 25Mg(n,γ)26Mg and 25Mg(n,tot) cross sections in the neutron energy range from thermal to about 300 keV, leading to a significantly improved 25Mg(n,γ)26Mg parametrization. The relevant resonances for n+25Mg 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 26Mg. With this information experimental upper limits of the reaction rates for 22Ne(α,n)25Mg and 22Ne(α,γ)26Mg were established, potentially leading to a significantly higher (α,n)/(α,γ) ratio than previously evaluated. The impact of these results has been studied for stellar models in the mass range 2 to 25 M⊙

The effect of scattering by water on the irradiation of cell cultures for the dosimetric characterization of a new prototype of IORT (Intra-Operative Radiation Therapy) device: Monte Carlo simulation and experimental validation

The electron beam emitted backward by Plasma Focus devices is being considered as a radiation source for IORT applications. Radiobiological investigations have been conducted to assess the potential of this new prototype of IORT device. A standard Xray beam ISO-H60 was used for comparison, irradiating cell cultures in a holder filled with an aqueous solution. The influence of scattering by the culture water and by the walls of the holder was investigated to determine its influence on the dose delivered to the cell culture. MCNPX simulations were run and experimental measurements conducted. The effect of scattering by the holder was found to be negligible; scattering by the culture water was determined to give an increase in dose of the order of 10%

First results of an eye lens dosimetry survey in an interventional cardiology department

The eye lens annual dose limit for exposed personnel to ionizing radiation has recently been revised by the ICRP - International Commission on Radiological Protection and the proposed new limit has been accepted by European legislation through the Council Directive 2013/59/EURATOM 2013. Among medical exposed personnel, the staff performing interventional cardiology are usually affected by relevant doses. For this reason a survey, employing dosemeters characterized in terms of Hp(3), was performed in order to get the order of magnitude of the doses received by the eye lens, at least as a first guess. The survey showed that the annual dose limit can easily be reached if a proper radiation protection approach is not implemented

Impact of new results of the neutron capture cross section measurements for odd gadolinium isotopes on thermal-spectrum systems

International audienceLight Water Reactors (LWRs) are frequently equipped with fuel pins in which UO2 is mixed with Gd2O3. Gd odd isotopes have extremely high neutron capture cross sections at very low energies and are currently used as burnable poisons. For this reason, ENEA put forward a research proposal for an improvement of the Gd nuclear data accuracy by means of new experiments to be done in the framework of the n TOF Collaboration. In 2016, new measurements were performed at the CERN, and subsequently ENEA in collaboration with IRSN, started to reevaluate the neutron capture cross sections (XSs) of Gd odd isotopes. This paper presents the results of Monte Carlo simulations performed with the new measured data to estimate their impact on the criticality of a thermal-spectrum benchmark for which the value of keff is known. The outcomes demonstrate that the new data can produce a keff which is closer to the experimental one than that obtained using the currently available Gd evaluations