Solid-state effects on thermal-neutron cross sections and on low-energy resonances

The neutron total cross sections of several single crystals (Si, Cu, sapphire), several polycrystalline samples (Cu, Fe, Be, C, Bi, Ta), and a fine-powder copper sample have been measured from 0.002 to 5 eV. The Cu powder and polycrystalline Fe, Be and C data exhibit the expected abrupt changes in cross section. The cross section of the single crystal of Si is smooth with only small broad fluctuations. The data on two single Cu crystals, the sapphire crystal, cast Bi, and rolled samples of Ta and Cu have many narrow peaks approx. 10/sup -3/ eV wide. High resolution (0.3%) transmission measurements were made on the 1.057-eV resonance in /sup 240/Pu and the 0.433-eV resonance in /sup 180/Ta, both at room and low temperatures to study the effects of crystal binding. Although the changes in Doppler broadening with temperature were apparent, no asymmetries due to a recoilless contribution were observed

First operation of the Israeli Tandem Electrostatic Accelerator Free-Electron Laser

Abstract Results of first operation of the Israeli Electrostatic-Accelerator Tandem Free-Electron Laser (EA-FEL) are reported. This EA-FEL utilizes a 1.4 A electron beam obtained from a parallel flow Pierce-type electron gun. The e-beam is transported into a resonator located inside a planar Halbach configuration wiggler, which is at a potential of 1.4 MeV with respect to the cathode. A resonator utilizing two curved parallel plates as a waveguide and two Talbot effect quasioptical reflectors (wave splitters) provides a quality factor Q + 30 000. Millimeter wave radiation pulses of 2 s duration were obtained at a frequency of 100.5 GHz, as predicted, at a power level above 1 kW. 1998 Elsevier Science B.V. All rights reserved