We demonstrate the utility of gold nanoparticles (AuNPs) as the basis of a stand-alone, inexpensive, and sensitive mercury monitor. Gold nanoparticles absorb visible light due to localized surface plasmon resonance (LSPR), and the absorbance changes when mercury combines with the gold nanoparticles. The sensitivity of the peak absorbance is proportional to the surface-area-to-volume ratio. We chose 5 nm spheres, because they have the largest surface-area-to-volume ratio while still having a peak absorption in the visible. The adsorption of 15 atoms of Hg causes a 1 nm shift in the LSPR wavelength of these particles. Assembled into a film using the Langmuir-Blodgett method, the AuNP LSPR can be tracked with a simple UV-Vis spectrometer. The rate of shift in the peak absorbance is linear with mercury concentrations from 1 to 825 μg /m 3 Hg air . Increasing the flow velocity (and mass transfer rate) increases the peak shift rate, making this system a viable method for direct ambient mercury vapor measurements. Regeneration of the sensing films, done by heating to 160°C, allows for repeatable measurements on the same film.

We show that single gold nanorods can act as highly sensitive mercury vapor sensors with attogram resolution. We exposed assorted gold nanorods, with aspect ratios ranging from 2.8-4.1, to μg m(-3) concentrations of mercury vapor in air for 1 hour. Pre- and post-exposure, the nanorods were examined with a combination of dark field spectroscopy and transmission electron microscopy. Because we isolated individual particles, we can describe the shape and size effects distinctly rather than statistically (a constraint of studying heterogeneous nanoparticle films). No measurable changes occurred to the shape and size of the nanorods due to their saturation with mercury vapor. The localized surface plasmon resonance (LSPR) of the mercury-saturated nanorods blue shifted 2.6-3.8 nm; the magnitude of the shift depended on the initial shape and size of the nanorod. Larger aspect ratios and surface-area-to-volume ratios both enhance the LSPR shift seen in saturated nanoparticles. The predictions of a core-shell model mirrors the shape and size effects observed experimentally. These results increase our understanding of mercury-adsorption by gold surfaces, and help to optimize nanoparticle-based plasmonic mercury sensing.

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The 35 Cl(n,p) and 35 Cl(n,α) cross sections at incident neutron energies between 2.42-2.74 MeV, were measured using the Berkeley High Flux Neutron Generator. The cross sections for 35 Cl(n,p) were more than a factor of three to five less than all of the values in the neutron absorption data libraries, while the 35 Cl(n,α) cross sections are in reasonable agreement with the data libraries. The measured energy-differential cross section is consistent with a single resonance with a width of 293(46) keV. This result suggests that, despite the high incident neutron energy, any attempt to model (n,x) cross sections in the vicinity of the N = Z = 20 shell gap requires a resolved resonance approach rather than Hauser-Fesbach. I.

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