Cross-section measurements of radiative proton-capture reactions in 112^{112}Cd at energies of astrophysical interest

Reactions involving the group of nuclei commonly known as p nuclei are part of the nucleosynthetic mechanisms at astrophysical sites. The $^{113}$In nucleus is such a case with several open questions regarding its origin at extreme stellar environments. In this work, the experimental study of the cross sections of the radiative proton-capture reaction $^{112}$Cd(p,$\gamma$)$^{113}$In is attempted for the first time at energies lying inside the Gamow window with an isotopically enriched $^{112}$Cd target. Two different techniques, the in-beam $\gamma$-ray spectroscopy and the activation method, have been applied. The latter method is required to account for the presence of a low-lying $^{113}$In isomer at 392 keV having a halflife of $\approx 100$ min. From the cross sections, the astrophysical S factors and the isomeric ratios have been additionally deduced. The experimental results are compared to detailed Hauser-Feshbach theoretical calculations using TALYS, and discussed in terms of their significance to the optical model potential involved.Comment: 12 pages, 13 Figures, Accepted for publication to Phys. Rev.

It’s all about diffusion: Measurements and modeling of particle morphologies in dispersed-phase polymerization

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Contrasting acrylate versus methacrylate crosslinking reactions and the impact of temperature

Divinyl monomers containing multiple vinyl groups are commonly used in polymerization reactions to introduce crosslinked networks. The reactivity of the second vinyl group in a crosslinker monomer decreases once it becomes incorporated in a polymer chain. This Reduced Reactivity Parameter (Ψ) depends on the monomer-crosslinker pair. To date, our group has developed this concept exclusively from methacrylate-based copolymerization systems1,2. Acrylate co-monomers introduce another level of complexity from a competing mechanism toward gel content and macromolecular network development; long chain branching from chain transfer to polymer. The later form networks via α-hydrogen abstraction, which is a prominent reaction with acrylates. Moreover, the differences in reactivity ratio between acrylates and methacrylates add another layer of heterogeneity through the polymerization which also impacts the kinetics and ultimate network structure. In this work, we compare the network formation reaction and the Ψ-parameters for 1,4 butanediol dimethacrylate (BDDMA, containing methacrylate groups) with its acrylate-based counterpart (BDDA, containing acrylate groups) in copolymerization reactions with either n-butyl methacrylate (nBMA) or n-butyl acrylate (nBA). The Ψ-parameter for all systems is estimated by comparing the experimental results with Monte Carlo simulations of the polymerization reactions. The goal of the work is to decouple the contributions of pendent-vinyl based crosslinking and long-chain branching (α-hydrogen abstraction) from the resulting kinetic profile that the Ψ parameter is determined from. Moreover, we contrast the balance of contributions from propagation, chain transfer, reactivity ratios, and utility of the pendent vinyl groups for crosslinking between reactions at either 60 or 70 °C. Even this seemingly small shift in temperature has a marked impact on the kinetics and resulting network for the different pairs of (meth)acrylate comonomers. Tripathi, A.K.; Neenan, M.L.; Sundberg, D.C.; Tsavalas, J.G., Influence of n-Alkyl Ester Groups on Efficiency of Crosslinking for Methacrylate Monomers Copolymerized with EGDMA: Experiments and Monte Carlo Simulations of Reaction Kinetics and Sol-Gel Structure , Polymer (2016), 96, 130–145, DOI:10.1016/j.polymer.2016.04.017 Tripathi, A.K.; Tsavalas, J.G.; Sundberg, D.C., “Monte Carlo Simulations of Free Radical Polymerizations with Divinyl Crosslinker: Pre- and Post-Gel Simulations of Reaction Kinetics and Molecular Structure , Macromolecules (2015) 48, 184−197, DOI: 10.1021/ma502085

Mechanistic insights into topological network formation in free radical co-polymerization

The first part of the talk will discuss reaction kinetics and molecular architecture development during free-radical, bulk copolymerizations of a homologous series of methacrylate monomers with a series of dimethacrylate crosslinkers of varying alkyl spacer lengths. The overall objective of this work was to determine the extent to which the ester side chains of the methacrylate monomers hinder chain-end radical propagation reactions through the pendent vinyl groups of the crosslinking monomer. We have determined that this steric hindrance is quite significant and increases to the point where the sweeping radius of the pendent vinyl can be obstructed by the neighboring monomer ester side groups. The effective sweeping radius of the pendent vinyl can be equivalently expressed by various combinations of dimethacrylate and methacrylate. Please download the file below for full content

Modelling of the effect of ELMs on fuel retention at the bulk W divertor of JET

Effect of ELMs on fuel retention at the bulk W target of JET ITER-Like Wall was studied with multi-scale calculations. Plasma input parameters were taken from ELMy H-mode plasma experiment. The energetic intra-ELM fuel particles get implanted and create near-surface defects up to depths of few tens of nm, which act as the main fuel trapping sites during ELMs. Clustering of implantation-induced vacancies were found to take place. The incoming flux of inter-ELM plasma particles increases the different filling levels of trapped fuel in defects. The temperature increase of the W target during the pulse increases the fuel detrapping rate. The inter-ELM fuel particle flux refills the partially emptied trapping sites and fills new sites. This leads to a competing effect on the retention and release rates of the implanted particles. At high temperatures the main retention appeared in larger vacancy clusters due to increased clustering rate

Be ITER-like wall at the JET tokamak under plasma

The JET tokamak is operated with beryllium and tungsten plasma-facing components to prepare for the exploitation of ITER. To determine beryllium erosion and migration in JET a set of markers were installed. Specimens from different beryllium marker tiles of the main wall of the ITER-like wall (ILW) JET tokamak from the first and the second D-D campaign were analyzed with nuclear reaction analysis, x-ray fluorescence spectroscopy, scanning electron microscopy and x-ray diffraction (XRD). Emphasis was on the determination of carbon plasma impurities deposited on beryllium surfaces. The C-12(d, p(0))C-13 reaction was used to quantify carbon deposition and to determine depth profiles. Carbon quantities on the surface of the Be tiles are low, varying from (0.35 +/- 0.07) x 10(17) to (11.8 +/- 0.6) x 10(17) at cm(-2) in the deposition depth from 0.4 to 6.7 mu m, respectively. In the 0.4-0.5 mm wide grooves of castellation sides the carbon content is found up to (14.3 +/- 2.5) x 10(17) at cm(-2) while it is higher (up to (38 +/- 4) x 10(17) at cm(-2)) in wider gaps (0.8 mm) separating tile segments. Oxygen (O), titanium (Ti), chromium (Cr), manganese (Mn), iron (Fe), nickel (Ni) and tungsten (W) were detected in all samples exposed to plasma and the reference one but at lower quantities at the latter. In the central part of the Inner Wall Guard Limiter from the first ILW campaign and in the Outer Poloidal Limiter from the second ILW campaign the Ni interlayer has been completely eroded. XRD shows the formation of BeNi in most specimens