Potential U.S. contributions to in-reactor experiments for fast reactor surveillance systems

It is maintained that special features of FFTF make it an ideal system to test sodium boiling detection techniques by acoustic/neutronic methods and to test the response of acoustic/neutronic sensors to vibrations. It is shown that accumulated research results indicate that such tests in FFTF are feasible, predictable, promising and safe.     

Chromatin proteins of large and small brain nuclei

A simple fluorometric assay for monoamine oxidase (MAO) [EC 1.4.3.4] activity towards beta-phenylethylamine (PEA) was devised. The procedure consists in measuring the disappearance of PEA fluorometrically. The disappearance of PEA was completely inhibited by pargyline, a potent inhibitor of MAO. MAO activity for PEA was linear with 10 mg to 100 mg of liver tissue in 3 ml of reaction mixture for up to 90 min of incubation. Using this method, the V max values and the apparent Km values of MAO for PEA in several rat tissues were determined, and compared with those for benzylamine and 5-hydroxytryptamine (5-HT).     

Are all photon radiations similar in large absorbers?--a comparison of electron spectra

Conventional X rays, i.e. X rays generating voltage between roughly 150 and 300 kV, are used in many radio-diagnostic procedures and also in radiobiological experiments. They release less energetic and, therefore, more densely ionising electrons than the high-energy gamma rays from 60Co or from the A bombs. Accordingly, they are considered to be somewhat more effective, especially at low doses. Various radiobiological studies, especially studies on chromosome aberrations have confirmed this assumption, but epidemiological investigations, e.g. the comparison of the excess relative risk for mammary cancer in the X-ray exposed patients and in the gamma-ray exposed A bomb survivors, have not demonstrated a similar difference. In view of the missing epidemiological evidence and largely for the reasons of practicality in radiation protection, the ICRP has recommended the radiation weighting factor unity equally for all photon radiations. However, in the discussion preceding the 2005 Recommendations of the ICRP, the issue remains controversial. In a recent paper, Harder et al. argue--with reference to an assessment by the German Radiation Protection Commission (SSK)--that the use of the same weighting factor for different photon energies can be justified more directly. For high-energy incident photons, they present the degraded photon spectra at different depths in a phantom, and they conclude that much of the difference between high-energy gamma rays and conventional X rays disappears in a large phantom. The present assessment, which is more direct, compares the spectra of electrons released (through pair production, Compton effect and photo effect) in a small and in a very large receptor for the incident photons of 150 keV, 1 MeV and 6 MeV. For the 1 Mev and 6 MeV photons, there is a substantial shift towards smaller electron energies in the large receptor, but the electron spectra remain much harder than those from the 150 keV incident photons. Furthermore, it is seen--in agreement with earlier conclusions by Straume--that for the broad gamma-ray spectrum from the A bombs there is no shift at all to lower energies within the body, but rather some degree of hardening of the radiation. The assumption that distinct differences between high-energy gamma rays and conventional X rays are restricted to small samples must, thus, be rejected. The attribution of the same effective quality factor or radiation weighting factor to all photon energies remains, therefore, an issue that is based on the considerations beyond dosimetry.     

Optical frequency measurements with the global positioning system: tests with an iodine-stabilized He-Ne laser

Global positioning system- (GPS-) referenced optical frequency combs based on mode-locked lasers offer calibrations for length metrology traceable to international length standards through the SI second and the speed of light. The absolute frequency of an iodine-stabilized He-Ne laser [127I2 R(127) 11-5 f component] was measured with a femtosecond comb referenced to a multichannel GPS timing receiver. The expected performance and limitations of GPS-referenced comb measurements are discussed.     

Transistor-like behavior of transition metal complexes

Electron transport through semiconductor and metallic nanoscale structures, molecular monolayers, and single molecules connected to external electrodes display rectification, switch, and staircase functionality of potential importance in future miniaturization of electronic devices. Common to most reported systems is, however, ultrahigh vacuum and/or cryogenic working conditions. Here we introduce a single-molecule device concept based on a class of robust redox active transition metal (Os(II)/(III)) complexes inserted between the working electrode and tip in an electrochemical scanning tunneling microscope (in situ STM). This configuration resembles a single-molecule transistor, where the reference electrode corresponds to the gate electrode. It operates at room temperature in a condensed matter (here aqueous) environment. Amplification on-off ratios up to 50 are found when the redox level is brought into the energy window between the Fermi levels of the electrodes by the overpotential ("gate voltage"). The current-voltage characteristics for two Os(II)/(III) complexes have been characterized systematically and supported by theoretical frames based on molecular charge transport theory.