r-Process Lanthanide Production and Heating Rates in Kilonovae

r-Process nucleosynthesis in material ejected during neutron star mergers may lead to radioactively powered transients called kilonovae. The timescale and peak luminosity of these transients depend on the composition of the ejecta, which determines the local heating rate from nuclear decays and the opacity. Kasen et al. (2013, ApJ, 774, 25) and Tanaka & Hotokezaka (2013, ApJ, 775, 113) pointed out that lanthanides can drastically increase the opacity in these outflows. We use the new general-purpose nuclear reaction network SkyNet to carry out a parameter study of r-process nucleosynthesis for a range of initial electron fractions $Y_e$, initial specific entropies $s$, and expansion timescales $\tau$. We find that the ejecta is lanthanide-free for $Y_e \gtrsim 0.22 - 0.30$, depending on $s$ and $\tau$. The heating rate is insensitive to $s$ and $\tau$, but certain, larger values of $Y_e$ lead to reduced heating rates, due to individual nuclides dominating the heating. We calculate approximate light curves with a simplified gray radiative transport scheme. The light curves peak at about a day (week) in the lanthanide-free (-rich) cases. The heating rate does not change much as the ejecta becomes lanthanide-free with increasing $Y_e$, but the light curve peak becomes about an order of magnitude brighter because it peaks much earlier when the heating rate is larger. We also provide parametric fits for the heating rates between 0.1 and $100\,\text{days}$, and we provide a simple fit in $Y_e$, $s$, and $\tau$ to estimate whether the ejecta is lanthanide-rich or not.Comment: 19 pages, 9 figure

Blockade of current through single calcium channels by trivalent lanthanide cations. Effect of ionic radius on the rates of ion entry and exit.

Currents flowing through single dihydropyridine-sensitive Ca2+ channels were recorded from cell-attached patches on C2 myotubes. In the presence of dihydropyridine agonist to prolong the duration of single-channel openings, adding micromolar concentrations of lanthanum (La), cerium (Ce), neodymium (Nd), gadolinium (Gd), dysprosium (Dy), or ytterbium (Yb) to patch electrodes containing 110 mM BaCl2 caused the unitary Ba2+ currents to fluctuate between fully open and shut states. The kinetics of channel blockade followed the predictions of a simple open channel block model in which the fluctuations of the single-channel current arose from the entry and exit of blocking ions from the pore. Entry rates for all the lanthanides tested were relatively insensitive to membrane potential, however, exit rates depended strongly on membrane potential increasing approximately e-fold per 23 mV with hyperpolarization. Individual lanthanide ions differed in both the absolute rates of ion entry and exit: entry rates decreased as cationic radius decreased; exit rates also decreased with cationic radius during the first part of the lanthanide series but then showed little change during the latter part of the series. Overall, the results support the idea that smaller ions enter the channel more slowly, presumably because they dehydrate more slowly; smaller ions also bind more tightly to a site within the channel pore, but lanthanide residence time within the channel approaches a maximum for the smaller cations with radii less than or equal to that of Ca2+

Development of highly selective ligands for separations of actinides from lanthanides in the nuclear fuel cycle

This account summarizes recent work by us and others on the development of ligands for the separation of actinides from lanthanides contained in nuclear waste streams in the context of a future European strategy for nuclear waste management. The current status of actinide/lanthanide separations worldwide is briefly discussed, and the synthesis, development, and testing of different classes of heterocyclic soft N- and S-donor ligands in Europe over the last 20 years is presented. This work has led to the current benchmark ligand that displays many of the desirable qualities for industrial use. The improvement of radiolytic stability through ligand design is also discussed

Selective Lanthanide Sensing with Gold Nanoparticles and Hydroxypyridinone Chelators.

The octadentate hydroxypyridinone chelator 3,4,3-LI(1,2-HOPO) is a promising therapeutic agent because of its high affinity for f-block elements and noncytotoxicity at medical dosages. The interaction between 3,4,3-LI(1,2-HOPO) and other biomedically relevant metals such as gold, however, has not been explored. Gold nanoparticles functionalized with chelators have demonstrated great potential in theranostics, yet thus far, no protocol that combines 3,4,3-LI(1,2-HOPO) and colloidal gold has been developed. Here, we characterize the solution thermodynamic properties of the complexes formed between 3,4,3-LI(1,2-HOPO) and Au3+ ions and demonstrate how under specific pH conditions the chelator promotes the growth of gold nanoparticles, acting as both reducing and stabilizing agent. 3,4,3-LI(1,2-HOPO) ligands on the nanoparticle surface remain active and selective toward f-block elements, as evidenced by gold nanoparticle selective aggregation. Finally, a new colorimetric assay capable of reaching the detection levels necessary for the quantification of lanthanides in waste from industrial processes is developed based on the inhibition of particle growth by lanthanides

Modification of the standard model for the lanthanides

We show that incorporation of strong electron correlations into the Kohn-Sham scheme of band structure calculations leads to a modification of the standard model of the lanthanides and that this procedure removes the existing discrepancy between theory and experiment concerning the ground state properties. Within the picture suggested, part of the upper Hubbard $f$-band is occupied due to conduction band-$f$-mixing interaction (that is renormalized due to correlations) and this contributes to the cohesive energy of the crystal. The lower Hubbard band has zero width and describes fermionic excitations in the shell of localized $f$-s. Fully self-consistent calculations (with respect to both charge density and many-electron population numbers of the $f$-shell) of the equilibrium volume $V_0$ and the bulk modulus of selected lanthanides have been performed and a good agreement is obtained.Comment: 1 fi

DFTB+ and lanthanides

DFTB+ is a recent general purpose implementation of density-functional based tight binding. One of the early motivators to develop this code was to investigate lanthanide impurities in nitride semiconductors, leading to a series of successful studies into structure and electrical properties of these systems. Here we describe our general framework to treat the physical effects needed for these problematic impurities within a tight-binding formalism, additionally discussing forces and stresses in DFTB. We also present an approach to evaluate the general case of Slater-Koster transforms and all of their derivatives in Cartesian coordinates. These developments are illustrated by simulating isolated Gd impurities in GaN