The electromagnetic counterpart of the binary neutron star merger LIGO/Virgo GW170817. I. Discovery of the optical counterpart using the Dark Energy Camera

We present the Dark Energy Camera (DECam) discovery of the optical counterpart of the first binary neutron star merger detected through gravitational wave emission, GW170817. Our observations commenced 10.5 hours post-merger, as soon as the localization region became accessible from Chile. We imaged 70 deg2 in the i and z bands, covering 93% of the initial integrated localization probability, to a depth necessary to identify likely optical counterparts (e.g., a kilonova). At 11.4 hours post-merger we detected a bright optical transient located 10:600 from the nucleus of NGC4993 at redshift z = 0:0098, consistent (for H0 = 70 km s-1 Mpc-1) with the distance of 40±8 Mpc reported by the LIGO Scientific Collaboration and the Virgo Collaboration (LVC). At detection the transient had magnitudes i=17.3 and z=17.4, and thus an absolute magnitude of Mi = -15.7, in the luminosity range expected for a kilonova. We identified 1,500 potential transient candidates. Applying simple selection criteria aimed at rejecting background events such as supernovae, we find the transient associated with NGC4993 as the only remaining plausible counterpart, and reject chance coincidence at the 99.5% confidence level. We therefore conclude that the optical counterpart we have identified near NGC4993 is associated with GW170817. This discovery ushers in the era of multi-messenger astronomy with gravitational waves, and demonstrates the power of DECam to identify the optical counterparts of gravitational-wave sources

The Salt Cycle Process

The Salt Cycle Process is a nuclear fuel processing approach designed for application in compact facilities located at the reactor sites. Irradiated UO/sub 2/ fuels would be processed through a brief sequence of steps and partially purified UO/sub 2/ or UO/sub 2/--PuO/sub 2/ powders recovered, suitable for refabrication into fuel elements. The major steps of the process are the dissolution of uranium oxides in molten NaCl--KCl eutectic by chlorination to form soluble uranyl chloride and the reduction of uranyl chloride to UO/sub 2/, which separates as a solid. The preferred method of reduction is the electrolytic method, which yields UO/sub 2/ as a conveniently handled, adherent deposit on the cathode. Means are described for separation of Pu from U and for co-deposition of the Uo. Also included are discussions of the probable nature of the U and Pu species present in the molten salt, side reactions in which uranyl chloride may participate, and the influence of certain variables on the properties of the UO/sub 2/ produced. (auth