We developed inexpensive and disposable gas sensors with a low environmental footprint. This approach is based on a biodegradable substrate, paper, and features safe and nontoxic electronic materials. We show that abrasion-induced deposited WS₂ nanoplatelets on paper can be employed as a successful sensing layer to develop high-sensitivity and selective sensors, which operate even at room temperature. Its performance is investigated, at room temperature, against NO₂ exposure, finding that the electrical resistance of the device drops dramatically upon NO₂ adsorption, decreasing by ~42% (~31% half a year later) for 0.8 ppm concentration, and establishing a detection limit around~2 ppb (~3 ppb half a year later). The sensor is highly selective towards NO₂ gas with respect to the interferents NH₃ and CO, whose responses were only 1.8% (obtained for 30 ppm) and 1.5% (obtained for 8 ppm), respectively. Interestingly, an improved response of the developed sensor under humid conditions was observed (tested for 25% relative humidity at 23 °C). The high-performance, in conjunction with its small dimensions, low cost, operation at room temperature, and the possibility of using it as a portable system, makes this sensor a promising candidate for continuous monitoring of NO₂ on-site.

Dramatic differences in the elastic scattering of the neutron rich nuclei ${}^6\mathrm{He}$ and ${}^8\mathrm{He}$ are found when new high quality data for the ${}^8\mathrm{He}+{}^{208}\mathrm{Pb}$ system are compared with previously published ${}^6\mathrm{He}+{}^{208}\mathrm{Pb}$ data at the same laboratory frame incident energy. The new ${}^8\mathrm{He}$ data are of the same level of detail as for stable beams. When comparing them with those previously obtained for ${}^6\mathrm{He}+{}^{208}\mathrm{Pb}$ at the same energy, it is possible to determine from the data alone that ${}^6\mathrm{He}$ has a much longer range absorption than ${}^8\mathrm{He}$. However, both nuclei show significant absorption beyond their strong absorption radii. While it has been known for a long time that elastic scattering at energies around the barrier only determines the optical potential over a small distance in radial space, typically $\pm 0.5$ fm or so, both the ${}^6\mathrm{He}$ and the ${}^8\mathrm{He}$ imaginary potentials obtained from various optical model fits to these data are the same over a much wider range of $\pm 1.5$ fm.