Electronegative Impurities Research Articles

Effects of quenching reactions on the breakdown voltage in Ar-Hg penning mixture

The influence of impurity gases on the breakdown voltage of the Penning mixture is investigated. To eliminate the electrode effects from the breakdown phenomena, high frequency (RF) breakdown field in Ar-Hg mixture with small amounts of impurity gases, such as H2, N2, Kr or Xe, is measured at room temperature, using a silica discharge tube. The breakdown field goes up with increasing quantities of admixed impurity gases; the order of effectiveness is Xe>H2>N2>Kr. Discussions are made on the infuence of impurity gases on the breakdown. It has become clear that, if quantities of impurity gases are expressed by the products of their partial pressures and the quenching rate constants of metastable Ar by them, the curves of the breakdown field versus impurity quantities are independent of the kind of impurity. From this result, it is concluded that, in Ar-Hg Penning mixture, the dominant cause for the increase in the breakdown voltage is the quenching of metastable Ar by those impurities. The effect of electronegative impurity HI was also measured. However, HI influence was not large.

Large multi-feedthrough vacuum seal for low temperature applications

An alumina-filled casting epoxy (trade name Stycast) was found to reliably seal to thin stainless steel edges and 1 mm diam stainless steel feedthrough pins. All seals retained their integrity after typically 50 cycles from −196 ° to 20 °C and 10 cycles from −196 ° to +100 °C. Several chambers were constructed using the epoxy both as a vacuum-tight wall and as an electrical insulator for a large number of multi-kV feedthroughs. The largest of these was 18 cm in diameter and contained 125 feedthrough pins. The chambers were immersed in a Freon-11 bath at −105 °C, filled with liquid xenon, and tested for the presence of electronegative impurities. After degassing, the contamination levels measured were slightly higher than those we commonly observe for chambers constructed only of glass and metal.

Slowly Diffusing Impurities in Lithium Metal

The diffusion of Sn, Pb, Sb, and Bi tracers in Li metal has been investigated, using a thin-film evaporating-sectioning technique. The results can be expressed by the Arrhenius relations ${D}_{\mathrm{Sn}}=0.62{e}^{\ensuremath{-}\frac{(15.0\ifmmode\pm\else\textpm\fi{}1.2)}{\mathrm{RT}}}$, ${\mathrm{D}}_{\mathrm{Pb}}=1.6\ifmmode\times\else\texttimes\fi{}{10}^{2}{e}^{\ensuremath{-}\frac{(25.2\ifmmode\pm\else\textpm\fi{}1.2)}{\mathrm{RT}}}$, ${D}_{\mathrm{Sb}}=1.6\ifmmode\times\else\texttimes\fi{}{10}^{10}{e}^{\ensuremath{-}\frac{(41.5\ifmmode\pm\else\textpm\fi{}4.5)}{\mathrm{RT}}}$, and ${D}_{\mathrm{Bi}}=5.3\ifmmode\times\else\texttimes\fi{}{10}^{13}{e}^{\ensuremath{-}\frac{(47.3\ifmmode\pm\else\textpm\fi{}3.4)}{\mathrm{RT}}}$. The data are not in agreement with established diffusion models based on attractions between vacancies and excess valency ions. Instead, diffusivity appears to decrease as the valency of the impurity increases. However, on the assumption that it is not probable for an impurity in a highly electropositive matrix to be more than singly ionized, the diffusive behavior of impurities in Li can be at least qualitatively understood in terms of two competing mechanisms, to the effect that relatively large and electropositive impurities should diffuse mainly via vacancies, small and electronegative impurities as interstitials.

Effect of electronegative impurities on electronic conduction in compressed nitrogen

Measurements of pulsed electron currents in compressed nitrogen show that appreciable attachment occurs to oxygen impurity of the order of 10 parts per million, and that the process depends on the partial pressure of oxygen, as well as on the ratio of electric field and gas density, E/p.

An electrochemical separation process for use in polarographiy

A simple electrochemical method is described whereby metals which are soluble in mercury can be analysed polarographically for traces of more electronegative impurities. The technique was specifically developed for the analysis of bismuth using a square wave polarograph and full details, both experimental and theoretical, are given in this case. Other possible uses of the method in the analysis of mercury-soluble metals employing both conventional and square wave polarographs and also in the analysis of aqueous salt solutions are suggested.

LXXIV. Columnar recombination in nitrogen

Abstract Under normal conditions of use, pulse ionization chambers function by virtue of the collection of free electrons liberated by the incident radiation. It is sometimes found, especially under conditions of high gas pressure, that the recorded pulse is smaller than the initial ionic burst and this loss of pulse height is generally attributed to capture of electrons by electronegative impurities in the gas resulting in the formation of negative ions which, owing to their much smaller mobility, are not collected within the short collection times used.

A Proportional Counter with Grid Control

Where accurate energy loss measurements are to be attempted, counter proportionality must be preserved over the entire active length of the anode wire. This may be endangered by attachment to electronegative impurities in the counter gas ; or by the counter end effect, which causes a serious loss of gas amplification at the wire terminations (Curran, Angus, and Cockroft 1949 ; Rossi and Staub 1949).

Radio-carbon dating by a proportional counter filled with carbondioxide

Synopsis A technique is described for the measurement of the natural activity of 14 carbon in a CO 2 -filled proportional counter. The following experimental details are discussed: The characteristics of the counter, the influence of gas pressure on the working voltages and on the counting rates, the effect of electronegative impurities, the background, the chemical procedure, the countertubes, the electronic apparatus and finally the possible sources of errors. The efficiency of the counter is 100 per cent in the sensitive part. The counting rate due to fresh carbon is 5.6/min, whereas the background is 3.9/min. At present the counter contains CO 2 at three atmospheres but the measurements indicate that it will be possible to increase the pressure at least up to about 15 atm. Up to now 30 samples have been dated.