摘要:

Time sampling techniques have been applied to the study of optical absorption transients. The method is described in terms of its use for the study of the decay of the concentration of metastable atoms following a pulsed discharge. Light from a capillary source is passed through the discharge tube. The transmitted intensity of one of the spectral lines which is absorbed by the metastable atoms is measured using an interference filter and a gated photomultiplier. The photomultiplier gate occurs at twice the discharge frequency so that alternate pulses of the photomultiplier output are reduced by absorption. The component of the photomultiplier output at the discharge frequency is proportional to the absorption and can be measured with a narrow band amplifier and synchronous detector. Since the time resolution of the system is determined by the width of the photomultiplier gate, the response of the synchronous detector can be made slow enough to average the absorption signal over many decay periods. Fluctuations in the number of electrons leaving the cathode of the photomultiplier limit the useful sensitivity of the present system to approximately two parts in 104. This represents a hundredfold improvement in sensitivity over that available with previous techniques. The results of some studies of helium metastables are presented in order to illustrate the detail which can be obtained with this technique.

ISSN:0034-6748    

DOI:10.1063/1.1771237

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The cryostat produces temperatures down to 0.74°K by pumping on a liquid helium bath with a large diffusion pump. A shielding pot containing liquid helium at 2°K reduces heat influxes to the main bath and plays a very important role in reducing the pressure drop arising from viscous flow of the gas up the helium Dewar. The low temperature region is visible and the experimental apparatus is easily accessible merely by removing two glass Dewars.

ISSN:0034-6748    

DOI:10.1063/1.1771238

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A versatile automatic scanner for paper strips which records directly optical density or radioactivity is built around a servo type recorder (Brown). Interference filters provide a narrow band light source. For scanning in the visible or ultraviolet where monochromatic light is desired the monochromator of a Beckman model DU spectrophotometer replaces the filters. The instrument incorporates positive synchronization of strip and recording paper, sequential scanning of strips to provide an optical density curve followed by superposition of the integral of this curve. Areas are easily calculated without the need for planimetry. The slits of varying size are interchangeable and are designed for either optical or radioactive scanning. For medium levels of activity a Geiger‐Mu¨ller tube is interchangeable with the photocell, while for low activities, optical scanning of autoradiographs may be performed.

ISSN:0034-6748    

DOI:10.1063/1.1771240

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The phenomenon of stick‐slip, which manifests itself in the squeaking of rubbing surfaces and is of considerable practical importance, can be advantageously studied at very low sliding speeds. An apparatus has been developed in which a flat surface is driven at speeds on the order of 10−7to 10−4cm/sec, the driving force being a weight. The speed is controlled by the viscous drag of a paddle in a bath of pitch. There is no appreciable elastic restraint in this drive, so that stick‐slip vibration of the moving surface does not occur. A stationary rider is pressed against the moving surface by a dead weight. The friction is measured by the elastic deflection of a ring, the stiffnessofwhich controls the tendency of the rider toward stick‐slip vibration. Results are briefly described.

ISSN:0034-6748    

DOI:10.1063/1.1771241

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A well‐localized target of hydrogen, deuterium, or helium has been developed for use with the University of Illinois 300‐Mev betatron. The liquefied target gas is contained in a thin‐walled brass cylinder in contact with a low‐temperature reservoir. For hydrogen and deuterium targets the reservoir contains hydrogen, while for a helium target the reservoir contains helium. Target cylinders of 1.25‐inch diameter with 0.0005‐inch walls and 2‐inch and 4‐inch diameter with 0.001‐inch walls have been used giving proton and meson backgrounds from the cylinder walls of less than 10 percent. A liquid nitrogen cooled radiation shield surrounds the target and reservoir. The nitrogen shield and the vacuum jacket enclosing it have thin windows allowing one to study the production of protons of energy >20 Mev and mesons of energy >7 Mev. From the 3 liter reservoir the loss rate of liquid hydrogen is 40 ml per hour and of liquid helium is 250 ml per hour.

ISSN:0034-6748    

DOI:10.1063/1.1771242

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The hot‐wire anemometer is principally used for turbulence investigations in both subsonic and supersonic flows. Its use has been extended to the observation of transient phenomena in shock tubes. Since its sensitivity to different phenomena varies, depending upon the operating conditions, the hot wire is quite well suited for timing very weak as well as strong travelling shock waves. A triggering and timing arrangement was developed pointing to further improvement. It was found that the hot‐wire trigger is a reliable instrument under widely varying shock tube operations.

ISSN:0034-6748    

DOI:10.1063/1.1771243

出版商:AIP    

年代:1955

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1771247

出版商:AIP    

年代:1955

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1771248

出版商:AIP    

年代:1955

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1771249

出版商:AIP    

年代:1955

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1771250

出版商:AIP    

年代:1955

数据来源: AIP