End-point energy measurements of field emission current in a continuous-wave normal-conducting rf injector

The LANL/AES normal-conducting radio-frequency injector has been tested at cw cathode gradients up to 10  MV/m. Field-emission electrons from a roughened copper cathode are accelerated to beam energy as high as 2.5 MeV and impinge on a stainless steel target. The energies of the resulting bremsstrahlung photons are measured at varying levels of injector cavity rf power corresponding to different accelerating gradients. At low cavity power, the bremsstrahlung spectra exhibit well-defined end-point energies at the positions where the number of single-photon events decreases to one (S/N ratio=1). Increasing the cavity power raises the probability of two-photon events in which two photons simultaneously arrive at the detector and register counts at twice the photon energy. The end-point energies at high cavity power are recorded at positions where the single-photon events transition to two-photon events. The measured end-point energies using this method are in excellent agreement with PARMELA calculations based on the cavity gradients deduced from the cavity rf power measurements

Acceptorless dehydrogenation of small molecules through cooperative base metal catalysis

The dehydrogenation of unactivated alkanes is an important transformation both in industrial and biological systems. Recent efforts towards this reaction have revolved around high temperature, organometallic C–H activation by noble metal catalysts that produce alkenes and hydrogen gas as the sole products. Conversely, natural desaturase systems proceed through stepwise hydrogen atom transfer at physiological temperature; however, these transformations require a terminal oxidant. Here we show combining tetra-n-butylammonium decatungstate (TBADT) and cobaloxime pyridine chloride (COPC) can catalytically dehydrogenate unactivated alkanes and alcohols under near-UV irradiation at room temperature with hydrogen as the sole by-product. This noble metal-free process follows a nature-inspired pathway of high- and low-energy hydrogen atom abstractions. The hydrogen evolution ability of cobaloximes is leveraged to render the system catalytic, with cooperative turnover numbers up to 48 and yields up to 83%. Our results demonstrate how cooperative base metal catalysis can achieve transformations previously restricted to precious metal catalysts