摘要:

Mass spectrometer investigations have been made of rare gas fission products extracted from uranium irradiated with thermal neutrons. The irradiated uranium rods were allowed to stand for various periods of time after irradiation to permit the decay of most fission product chains to stable isotopes. Four stable isotopes of xenon were found having mass numbers 131, 132, 134, and 136, and three stable isotopes of krypton with mass numbers 83, 84, and 86. Kr86, the most abundant of the latter group, is probably formed directly in fission. In addition a long lived krypton with mass 85 was discovered which is isomeric with a 4.0 hr. Kr85reported previously.The relative abundances of these isotopes which are related directly to fission yields of the corresponding mass chains have been determined with an accuracy of 1% or better. The mass numbers of these fission chains can now be identified with certainty by comparing mass spectrometer abundance data with known yield values of the active chain members. Finally, the half-life of krypton 85 was determined by comparing its concentration to that of a stable isotope over a period of time.

ISSN:1923-4287    

DOI:10.1139/cjr47a-001

出版商:NRC Research Press    

年代:1947

数据来源: NRC

摘要:

The theory and method of measuring the diffusion length of thermal neutrons in graphite are discussed in detail. The graphite pile was a rectangular parallelepiped, 185.8 cm. square and 153.6 cm. high. The source was 1.2 gm. of radium mixed with beryllium. Part of the pile was used to slow down the neutrons to thermal velocities, and the density distribution of thermal neutrons was explored in the remainder of the pile with detectors of dysprosium oxide. The diffusion length of thermal neutrons in this graphite of average pile density 1.55 gm. per cc. was found to be 51 cm., with a probable error of 3 cm.

ISSN:1923-4287    

DOI:10.1139/cjr47a-002

出版商:NRC Research Press    

年代:1947

数据来源: NRC

摘要:

The density distribution of thermal neutrons was measured with a small boron trifluoride chamber in a cylindrical tank containing 113 litres of heavy water in which lithium carbonate was dissolved. The diffusion length was found to be 22.7 cm. in this solution containing 7.70 × 10−4atoms of lithium per molecule of heavy water (99.4 atom % D). After corrections were applied for the capture of neutrons in the heavy water and light hydrogen, the capture cross-section of lithium was found to be 59 × 10−24cm.2per atom for neutrons of standard velocity 2200 m. per sec. from the measured diffusion length and known transport mean free path.

ISSN:1923-4287    

DOI:10.1139/cjr47a-003

出版商:NRC Research Press    

年代:1947

数据来源: NRC

摘要:

A. S. King has made extensive intensity estimates of spectral lines in furnace and are spectra, and these data provide useful material for determining line strengths. The estimates have been made for many elements of astrophysical interest, and are reduced to line strengths for FeI, TiI, and TiII.

ISSN:1923-4287    

DOI:10.1139/cjr47a-004

出版商:NRC Research Press    

年代:1947

数据来源: NRC

摘要:

Various opinions have been expressed regarding the importance of such factors as a 'diffusing effect' due to small angle scattering in determining the visual range in a cloud. If a reduction of apparent contrast and an influence on brightness level are the only important factors, conditions at the obscuration point should be described by,whereBtdenotes the brightness of an object which has a contrastCwith its background,Bcand μDrepresent respectively the cloud brightness and optical density in the line of sight, andPdenotes the contrast limen value. Experiments to test this relation have been performed with an ammonium chloride smoke in a chamber 1.8 m. long. The results indicate that the equation is adequate and that factors not taken into consideration in it play a negligible role in total obscuration under laboratory conditions. The experiments were performed at various brightness levels within the 1 to 100 millilambert range.

ISSN:1923-4287    

DOI:10.1139/cjr47a-005

出版商:NRC Research Press    

年代:1947

数据来源: NRC

摘要:

As the apparent contrast of a square test object situated behind a smoke layer is decreased in laboratory experiments a point is reached at which the object appears as a light patch of unrecognizable shape. On decreasing the apparent contrast a little further the object becomes completely invisible. A study of the conditions under which the apparent loss of definition occurs was carried on simultaneously with the study of total obscuration described in the preceding paper. The optical density of smoke required to produce loss of definition was found to be linearly related to the logarithm of the ratio of object to cloud brightness, in close correspondence with the relation found for total obscuration. Over the range of our experiments the minimum optical density of smoke associated with loss of definition was from 12 to 23% less than that associated with total obscuration, the magnitude of the difference depending on brightness conditions. Since the phenomenon of loss of definition is observable in the presence of a veiling glare without smoke, it is probably of physiological origin.

ISSN:1923-4287    

DOI:10.1139/cjr47a-006

出版商:NRC Research Press    

年代:1947

数据来源: NRC

摘要:

Difficulties were encountered in smoke chamber experiments in obtaining reliable extinction coefficient data by methods based on brightness measurements of bright and 'black' surfaces seen through the smoke. These difficulties led to an investigation of the reliability of a commonly used method employing a parallel light beam and a photoelectric cell. The results indicate that the method is capable of yielding extinction coefficient data with an accuracy of 1 to 2% under the conditions of our experiments.

ISSN:1923-4287    

DOI:10.1139/cjr47a-007

出版商:NRC Research Press    

年代:1947

数据来源: NRC

摘要:

The standard method of correcting the phase characteristic of low-pass networks by introducing mutual inductance between the coils is extended. By means of mutual inductance between the coils and a capacity across them, it is possible to eliminate the third and fifth order terms in the variation of the phase shift with frequency. The relation required between the circuit constants for this result is given, and is found to be very simple.

ISSN:1923-4287    

DOI:10.1139/cjr47a-008

出版商:NRC Research Press    

年代:1947

数据来源: NRC