Neutron capture cross section measurements of 238U, 241Am and 243Am at n_TOF

Proposal: Neutron capture cross section measurements of 238U, 241Am and 243Am at n_TOFThe increase of the world energy demand and the need of low carbon energy sources have triggered the renaissance and/or enhancement of nuclear energy in many countries. Fundamental nuclear physics can contribute in a practical way to the sustainability and safety of the nuclear energy production and the management of the nuclear waste. There exists a series of recent studies which address the most relevant isotopes, decay data, nuclear reaction channels and energy ranges which have to be investigated in more detail for improving the design of different advanced nuclear systems [1] and nuclear fuel cycles [2]. In this proposal, we aim at the measurement of the neutron capture cross sections of 238U, 241Am and 243Am. All three isotopes are listed in the NEA High Priority Request List [37], are recommended for measurements [1] and play an important role in the nuclear energy production and fuel cycle scenarios. The measurements will provide as well valuable nuclear structure data necessary for the improvement of nuclear models and the statistical interpretation of the nuclear propertiesPostprint (author's final draft

New Developments in the Field of Radiochemical Ageing of Aromatic Polymers

Polymers having an aromatic backbone polymers have a high mechanical strength and a high modulus. Their aromaticity increases their resistance for use in relatively severe conditions especially in aerospace and nuclear industry for which lifetime prediction is a key issue. For example, a challenge for nuclear plants is to extend lifetime from the initially planned 40 years duration to 50 or 60 years, which makes necessary to determine lifetime by a non-empirical method. Since polymers mechanical failure originates from chain scission or crosslinking of the backbone, the ideal method of lifetime prediction would first involve the elaboration of a kinetic model for chain scission and crosslinking. Then, the changes of molecular mass would be related to the changes of mechanical properties using the available laws of polymers physics. Lifetime would be then determined using a pertinent lifetime criterion. A noticeable difficulty comes here from the fact that oxidation, which plays a key major role in chain scission, is diffusion controlled and thus heterogeneously distributed in sample thickness. It is crucial, indeed, to determine experimentally and to predict this depth distribution of chain scission and crosslinking because it will play a key role on fracture properties. This chapter will be henceforward devoted to the effect of aromaticity on radiostability, the effect on temperature on the chain scission/crosslinking competition, the diffusion limited oxidation (which will be illustrated by the effect of dose rate, atmosphere and sample thickness), then some concluding remarks on oxidative stability of aromatic polymers and the possible link with the absence of macromolecular mobility below Tg. We will start by some basics of radiochemistry which are necessary for the good understanding of this paper, and especially the quantitative treatment for crosslinking and chain scission

Reactions of antioxidants with molecular oxygen. Part III: Influence of phenolic stabiliser structures on their oxidation in an inert matrix

The oxidation of five different phenolic antioxidants in inert substrates has been investigated varying the temperature and oxygen pressure conditions. The stabiliser consumption in this reaction has been quantified by steric exclusion chromatography. The tendency of the variation of the residual antioxidant concentration with exposure time in the presence of oxygen shows a simple apparent first order process in all cases. The kinetic parameters were determined applying this simple kinetic model. The influence of structural characteristics of stabilisers under study on kinetic parameters of the direct reaction with the oxygen has been analysed. On the other hand, the information obtained about reaction products generated for each antioxidant helped us to explain the results obtained

Reactions of antioxidants with molecular oxygen. Part I. 2,2′-methylene-bis(4-methyl-6-tert-butylphenol) in silicone matrix

The reaction of 2,2′-methylene-bis(4-methyl-6-tert-butylphenol) stabiliser with oxygen was studied in an inert substrate at 80-120°C temperature under 0.02-3.0 MPa oxygen pressure ranges. UV/VIS spectrophotometry and Gel Permeation Chromatography were used to follow the antioxidant consumption and the formation of oxidation products. A simplified mechanistic model of stabiliser oxidative transformation was proposed and corresponding kinetic parameters were determined and compared with the kinetic values obtained by other authors

Reactions of antioxidants with molecular oxygen. Part II. Isooctyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate in silicone matrix

The study of oxidation kinetics of isooctyl-3-(3,5-di-tert-butyl-4- hydroxyphenyl)propionate (Irganox 1135) stabiliser was carried out using silicone oil as an inert substrate. The stabiliser was exposed at 80-120 °C under 0.02-3.0 MPa oxygen pressure. UV/VIS spectrophotometry, gel permeation chromatography and high pressure liquid chromatography were used to follow the stabiliser consumption, whose kinetic parameters were determined by applying a simple kinetic model

Can polymer thermal oxidative ageing be modelled?

It has been supposed, for a long time, that kinetic modelling of polymer ageing for nonempirical lifetime prediction was out of reach for two main reasons: hypercomplexity of mechanisms and heterogeneity of reactions. The arguments relative to both aspects are examined here. It is concluded that, thanks to recent advances, especially the introduction of numerical methods, kinetic modelling is possible in various important practical cases

Polymères en ambiance nucléaire : comportement à long terme

Ce livre présente un certain nombre d’outils théoriques originaux, indispensables pour la prédiction de la durée de vie des matériaux polymères en ambiance nucléaire. Le problème de vieillissement des polymères est avant tout un problème d’ingénieur, dont la préoccupation majeure est la prédiction de durée de vie selon des critères pertinents du point de vue de l’application. Partant de ce constat, les auteurs ont focalisé leur intérêt sur les aspects les plus souvent négligés dans les ouvrages classiques mais cruciaux : la modélisation cinétique de l’oxydation radio-amorcée à faible débit de dose et les conséquences de l’irradiation sur les propriétés thermomécaniques. Ces deux aspects font l’objet de développements qui confèrent à l’ouvrage son originalité, lui permettant d’être un complément utile aux ouvrages classiques. Présenté de manière claire et pédagogique, cet ouvrage permettra à l’étudiant de Master, au jeune chercheur comme à l’ingénieur de rejoindre un courant de recherche vivace et inspiré, et d’apporter sa propre contribution au développement ainsi ouvert d’une véritable science des matériaux polymères en ambiance nucléaire. Les auteurs du présent ouvrage sont membres du groupe de recherche sur le Vieillissement des Matériaux Organiques au Laboratoire PIMM d’Arts et Métiers ParisTech. Ce groupe s’intéresse plus particulièrement à l’analyse et la modélisation cinétique des processus de vieillissement des polymères, en lien étroit avec l’industrie. (Extrait distribué par l'éditeur , en ligne

Study of the photon strength function of 152SM in resonance neutron capture at n-TOF

The Photon Strength Function of 152Sm has been investigated at nTOF by studying the ¿-ray spectra from resonance neutron capture of 151Sm. The experimental apparatus consisted of two C6D6 liquid scintillator detectors. The measured spectra were compared with the predictions of the DICEBOX code, for different assumptions on the Photon Stregth Functions and on the Nuclear Level Density. For a meaningful comparison, the model calculations were filtered through a detailed software replica of the experimental apparatus, performed by means of three different Monte Carlo simulations. Preliminary results indicate that a reasonable reproduction of the experimental ¿-ray spectrum is obtained by postulating the presence of a Scissors Resonance. Some hints on the most suitable models, developed in the most recent studies of the Photon Strength Functions and Nuclear Level Density, are also obtained. © 2007 Sissa Medialab Srl. All rights reserved.Postprint (published version

Integral cross section measurement of the12C(n,p)12B reaction

The integral cross section of the12C(n, p)12B reaction was measured at the neutron time of flight facility nTOF at CERN, from the reaction threshold at 13.6 MeV up to 10 GeV, by means of the combined activation and a timeofflight technique. The integral result is expressed as the number of12B nuclei produced per single pulse of the neutron beam. A simple integral expression is given for calculating the number of produced12B nuclei from any given evaluated cross section and/or model prediction. © 2015, CERN. All rights reserved.Postprint (author's final draft

Measurement of the240Pu(n,f) cross-section at the CERN n-TOF facility: First results from EAR-2

The accurate knowledge of neutron cross-sections of a variety of plutonium isotopes and other minor actinides, such as neptunium, americium and curium, is crucial for feasibility and performance studies of advanced nuclear systems (Generation-IV reactors, Accelerator Driven Systems). In this context, the240Pu(n,f) cross-section was measured with the time-of-flight technique at the CERN n-TOF facility at incident neutron energies ranging from thermal to several MeV. The present measurement is the first to have been performed at n-TOF's newly commissioned Experimental Area II (EAR-2), which is located at the end of an 18 m neutron beam-line and features a neutron fluence that is 25-30 times higher with respect to the existing 185 m flight-path (EAR-1), as well as stronger suppression of sample-induced backgrounds, due to the shorter times-of-flight involved. Preliminary results are presented. © 2015, CERN. All rights reserved.Postprint (published version