Measurement of w values of low-energy electrons in several gases.

The W value, the mean energy required to form an ion pair, was measured for monoenergetic electrons in the energy range from 5 to about 500 eV in air, N2, O2, CO2, tissue-equivalent gases (Rossi-Failla and Srdoc mixtures), methane, ethane propane, n-butane, i-butane, pentane, hexane, nonane, ethylene, acetylene, ethanol, acetone, H2O, D2O, H2, D2, C6H6, C6D6, argon, krypton, and xenon. The W values of all gases increase continuously with decreasing electron energy; they approach infinity asymptotically at the ionization threshold and the well-known energy-independent high-energy W values at high electron energies. A comparison between the results and newer experimental and theoretical works of other authors sometimes shows very good agreement. The experimental error is estimated to be less than 2%

The measurement of electron spectra in the track of protons in water vapour.

The spectra of the electrons in the track of 1 MeV protons passing through water vapour were measured with a retarding field spectrometer mounted in a movable evacuated probe. About 50,000 measurements were performed in the energy range from 0 to 3000 eV at more than 1300 different radial and angular positions relative to the proton path. The radial distances, reduced to density 1g.cm-3, range from 0.25 nm, where the primary electron spectrum is predominant, to 30 nm, where the electrons are slowed down by collisions with water molecules. From the dense net of data the following were calculated: (i) The dependency of the energy fluence on the solid angle at different distances; (ii)The energy flux vectors for different energy ranges as a function of the radial distance from the proton path; (iii) The spectral fluences at different distances from the proton path; (iv) The degradation spectrum

Measurement of average energy required to produce an ion pair (W value) for low-energy ions in several gases.

The W value, the mean energy required to form an ion pair, was measured for monoenergetic positive H, He, C, N, O, and Ar ions in the energy range from 1 to 50 keV in air, N2, CH4, CO2, and a tissue-equivalent gas (Rossi-Failla mixture). The W values of ions increase, in general, with decreasing energy; only those of H ions show a minimum at an energy of about 25 keV for some gases. The estimated standard deviation of the measurements is about 2% in most cases

Determination of Selenium in Biological Materials by Stable Isotope Dilution Gas Chromatography-Mass Spectrometry

Selenium can be determined quantitatively in biological samples after digestion using nitric acid, orthophosphoric acid, and hydrogen peroxide and the formation of 5-nitropiazselenol. Samples are spiked with enriched 82Se and lsotoplc ratio of 80Se to 82Se is measured by combined gas chromatographymass spectrometry using dual ion monitoring. Precise determination at the parts-per-billion level is possible. The accuracy of the method Is verlfied by using standard reference materials