摘要:

A qualitative theory of the nature of high frequency discharges, with special reference to those developed by the use of external sleeve electrodes, is advanced on the assumption that the discharge is largely determined by its d-c. wall and space charges, and that the chief function of the high frequency field is to maintain the electron temperature. This theory leads to the conclusion that there must be a high negative wall charge under the electrodes, and a high radial field tending to drive positive ions to the walls. Thus each electrode has many of the characteristics of a cathode in a d-c. discharge. This conclusion is verified by the appearance of the high frequency discharge and by a careful examination of deposits resulting from the removal, by positive ion bombardment of the tube wall, of thin metallic films and of materials of which the discharge tube itself is composed.

ISSN:1923-4287    

DOI:10.1139/cjr48a-019

出版商:NRC Research Press    

年代:1948

数据来源: NRC

摘要:

The index of refraction of thin films deposited on an optical flat is obtained by comparison of the fringe system set up in the film with that in the air gap between the film and another optical flat. The use of the method is illustrated by application to films produced in high frequency discharge tubes. Films produced in Pyrex glass and quartz tubes are shown to be silica in the form of cristobalite. Films produced in polystyrene tubes prove to have an index of refraction that is very low and is a function of the thickness.

ISSN:1923-4287    

DOI:10.1139/cjr48a-020

出版商:NRC Research Press    

年代:1948

数据来源: NRC

摘要:

The surface areas, as determined from X-ray diffraction and low temperature nitrogen adsorption data, were compared for a number of carbon blacks and activated charcoals. Comparative data were also obtained on samples of charcoal at various stages of activation and after calcination. The X-ray diffraction data indicated that all the samples examined were composed of small graphitelike crystallites of the same order of magnitude, which had specific surfaces of about 2500 to 3000 sq. m. per cc. The nitrogen adsorption surface of a highly activated charcoal was found to be about equal to the X-ray surface. It is suggested that the crystallite surface represents the potential adsorption surface of a carbonaceous material and, providing that crystal growth does not occur during activation, the activation process makes these surfaces available to external adsorbate.

ISSN:1923-4287    

DOI:10.1139/cjr48a-021

出版商:NRC Research Press    

年代:1948

数据来源: NRC

摘要:

The energies of the α-particles from weak preparations of several new radioactive substances were measured in a grid ionization chamber filled with argon. The accurately known energies of α-particles from several well known sources were used for calibration. The voltage pulses produced by electron collection from the tracks were amplified in a linear amplifier of high stability and converted into flat-topped pulses. An accurately known voltage was subtracted, and the small residual pulses were further amplified. The frequency distribution of pulse sizes was recorded on an electronic pulse analyzer.The final values of the energies are as follows:92U233, 4.823 ± 0.003;89Ac225, 5.801 ± 0.010;87Fr221, 6.298 ± 0.010;85At217, 7.023 ± 0.010;84Po213, 8.336 ± 0.005; and94Pu239, 5.159 ± 0.005 Mev.The ionization–energy curve in argon was found to be linear within experimental error for α-particles of energy 5 to 9 Mev. Extrapolation of this line determines an intercept of 85 kev. at zero ionization.

ISSN:1923-4287    

DOI:10.1139/cjr48a-022

出版商:NRC Research Press    

年代:1948

数据来源: NRC

摘要:

In the recently discovered (4n + 1) radioactive series, bismuth 213 transforms to polonium 213 by β-emission. The latter rapidly transforms by α-emission to lead 209. The present paper describes a measurement of the half-period of polonium 213. A preparation of radium 225 was placed between two Geiger–Müller counters. One detected β-particles while the other detected α and β-particles. Coincidences were counted with a modified Rossi circuit. The pulse-width on the grid of one of the tubes of the coincidence unit was made variable, while the pulse-width on the other remained fixed. The pulse-width associated with the counter that responded only to β-particles was chosen to be variable. Coincidences were counted as a function of the pulse-width. Corrections were made for accidental coincidences and exact coincidences arising from other causes. The final value for the half-periodTof polonium 213 isT = 4.2 ± 0.8 μsec. A subsidiary experiment to determine the half-period of thorium C′ gave the valueT = 0.34 ± 0.06 μsec. in reasonable agreement with measurements by other workers.

ISSN:1923-4287    

DOI:10.1139/cjr48a-023

出版商:NRC Research Press    

年代:1948

数据来源: NRC

摘要:

These experiments were undertaken to investigate the transfer of heat from solid surfaces to flowing water. The bulk temperature of the cooling water was below the boiling point, and the surface temperature of the heat transfer tube went to about 100 °C. above the boiling point. Water velocities ranged up to 10 ft. sec.−1and heat fluxes up to 720 w. cm.−2. The non-dimensionless heat transfer constantain the Dittus and Boelter formula (Nu) = a(Re)0.8(Pr)0.4, which under normal forced convection has a value of 2.30 × 10−2, increased to four times the normal value under the surface boiling conditions. It is shown graphically that the constantabears a simple relation to the heat flux and the length–diameter ratio for surface temperatures below a certain value. For constant heat flux and volume flow rate, the surface temperature rises with rising bulk liquid temperature until it reaches the certain value of the surface temperature referred to above. The surface temperature then remains constant with further rise in the bulk liquid temperature until conditions become too unstable for measurements.

ISSN:1923-4287    

DOI:10.1139/cjr48a-024

出版商:NRC Research Press    

年代:1948

数据来源: NRC