摘要:

Simple techniques and easily constructed equipment are described for a small cryogenics laboratory utilizing a commercial helium liquefier. Emphasis is placed on simplicity and availability rather than on high accuracy and efficiency in low‐temperature work. Accessories for a Collins liquefier and a commercial liquid‐helium storage container are described. Techniques used for reaching and measuring intermediate temperatures are outlined, along with a description of two portable cryostats. A small mica and Pyrex platinum resistance thermometer has been developed, and its relatively simple fabrication is described.

ISSN:0034-6748    

DOI:10.1063/1.1771053

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

An examination of the theoretical relationship between absorption and crystal response in a Stark‐effect microwave spectrograph indicates that a direct proportionality exists between the absorption coefficient and the component of crystal current at the modulation frequency, provided that certain reasonable conditions are fulfilled.An experimental method is described which utilizes this principle to obtain measurements of the ratio of one absorption coefficient to another. This method involves a matching of the modulation frequency component of crystal current against an adjustable reference signal. These measurements may be used to determine the energy separation of the lower states of the lines observed, thus yielding microwave data on vibrational or torsional energy levels. Line breadth and saturation can be measured equally well with minor modifications in method.This experimental method was tested by measuring the known ratios of absorption coefficients of the carbonyl sulfide lines near 24 000 mc which are assigned to various isotopic species. The range of deviation of measured ratio from known ratio was 25 percent, and this discrepancy is attributed to reflections in the microwave transmission line, particularly at the ends of the Stark electrode. The determination of molecular vibrational or torsional energy levels is discussed.

ISSN:0034-6748    

DOI:10.1063/1.1771054

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The method developed by Baird and Bird for the measurement of relative absorption intensities has been extended to the estimation of absolute absorption intensities. The estimation of absolute intensity is based on the measurement of the ratio of modulation‐frequency component to direct component of crystal current at low microwave power levels.A preliminary test of the method has been conducted by making measurements on the intensity of the line CH3Cl35,J=0→1,F=32→52over a range of crystal currents. Measured intensities less than the calculated intensity by 15 percent to 25 percent were observed over a range of nine in crystal current, indicating that the method is at least feasible for the estimation of intensities. Even crude estimates can be extremely useful in the identification of spectral lines, and it seems likely that the method admits of much refinement in accuracy.

ISSN:0034-6748    

DOI:10.1063/1.1771055

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

In order to answer a number of specific questions, thickness and density measurements were made on Ilford nuclear track emulsions before and after processing. Measurements were made as equilibrium was approached under various conditions of ambient relative humidity. Thickness measurements were made with a modified dial micrometer. Volume measurements were made by weighing plates immersed in carbon tetrachloride. A special study of plates stored in a vacuum was carried out. The washing time was found to have an important effect on the shrinkage factor. The data obtained are presented in a number of tables and graphs. The theory of water diffusion in emulsion has been appended by W. H. Barkas, and the emulsion constants evaluated from the experimental data. Attention is directed to the very long characteristic diffusion times implied for thick emulsions.

ISSN:0034-6748    

DOI:10.1063/1.1771056

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Equipment to carry out recrystallization and zone melting of silicon from a floating liquid zone is described. In the first design, silicon was melted by a tungsten ring. In an improved apparatus, no heater element inside the melting chamber is necessary, since the silicon is melted by induction heating. The system is capable of producing crystals of extreme purity. Silicon single crystals of resistivities up to several hundred ohm cm have been grown with the described equipment.

ISSN:0034-6748    

DOI:10.1063/1.1771057

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The response of the long counter has been investigated with calibrated neutron sources having average energies up to 5 Mev and has been found to be flat down to a low energy limit that is determined by the construction of the counter. A closer examination reveals fluctuations in the sensitivity of about 5 percent which occur at resonances for neutron scattering by carbon. One can account qualitatively for these fluctuations in terms of the scattering properties of the carbon present in the paraffin moderator of the counter.

ISSN:0034-6748    

DOI:10.1063/1.1771058

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

A device is described by which the stopping power for polonium alpha particles of thin solid or liquid films can be compared with that of gases. An optical system measures film thickness, and the relative stopping power is inferred from the decrease of range which results when a thin film is inserted across a beam of alpha particles.The device has been used with polystyrene and acetylene and a relative stopping power of 0.99±0.02 is observed.

ISSN:0034-6748    

DOI:10.1063/1.1771059

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Techniques are described for the ``eradication'' and processing of thick electron‐sensitive nuclear emulsions, and for handling ``pellicles.'' 400‐micron and 600‐micron emulsions, eradicated by a method which preserves their sensitivity to minimum‐ionization particles, exhibit marked reduction in track distortion, as well as in background. A modified procedure for uniform development of thick emulsions by the temperature‐cycling method gives a favorable ratio of grain density to background. Countermeasures against stripping of thick emulsions from their glass base have proved efficacious over a 3‐year period.A stack of emulsions without glass support (``pellicles'') provides a large sensitive volume in which tracks can be readily followed from one layer to the next. The lateral swelling (∼25 percent) during processing, which discouraged the application of this technique, was overcome by the authors [Phys. Rev.85, 712 (1952)] in 1951. They evolved a successful method for mounting thick, stripped emulsions onto glass after exposure, butprior to processing, so that the pellicles can be developed as ordinary plates. Since then, additional experience has been gained in the application of pellicle stacks to high‐energy physics. Our procedures lead to emulsions free from lateral swelling, free from blistering, and characterized by a level of distortion sufficiently low to permit multiple scattering measurement even on fairly ``stiff'' tracks. The advantages and limitations of this technique, its possible applications, details of the mounting procedure, and methods of following tracks from layer to layer are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1771060

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Some formulas for the calculation of the solid angle subtended by a circular aperture at an isotropically emitting point or spread source are presented as well as three tables of solid‐angle values.

ISSN:0034-6748    

DOI:10.1063/1.1771061

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The type 6218 tube provides a simple means of obtaining pulses with very fast rise time, unlimited, as heretofore, to 150 pps as in mercury‐switch pulsers. It also provides a means of generating double ornpulses of variable separation at repetition rates limited only by the separation of the pulses. Circuits permitting the use of the tube, as well as wave forms produced are given.

ISSN:0034-6748    

DOI:10.1063/1.1771062

出版商:AIP    

年代:1954

数据来源: AIP