摘要:

The state of the art, and the principal problems of particle replication techniques have been reviewed. The objective was to obtain the highest reliability as well as the maximum geometrical and contrast resolution for the replication technique. To this end, further improvements and complementary developments of the now‐known techniques of particle replication were made. The essential stages consist of: (1) preshadowing of the sample by a refractory alloy (Pt:10%Rh) evaporated in high vacuum from a carbon rod; (2) utilizing a residual gas scattering evaporation technique (carbon in an argon atmosphere of 10−3mm Hg) at twice the mean free path of the carbon (this forms a thin uniform carbon coating layer as a supporting layer which gives a minimum of contrast in the electron microscope); (3) utilizing an auxiliary strengthening layer of a subliming material (sulfur) to protect effectively the replica from deformation or fracture during the preparation procedure (the auxiliary layer can later be removed by sublimation); (4) development of an easy to do partial‐particle replication technique, utilizing a thermoplastic embedding technique to restrict replication to only one side of a particle which will give superposition free images.

ISSN:0034-6748    

DOI:10.1063/1.1716846

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Philco 2N501, 2N502, and 2N504 transistors have been operated successfully in the avalanche mode as fast discriminators on photomultiplier tubes and as the pulse generating element in pulse generators. They exhibit the property of a fast rise time (≲1 nsec) and sharp discriminating characteristics but have the disadvantage of a long recovery time (∼80 nsec).

ISSN:0034-6748    

DOI:10.1063/1.1716847

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The Dauphinee and Mooser circuit [Rev. Sci. Instr.26, 660 (1955)] for the measurement of resistivity and the Hall effect is liable to certain systematic errors due to capacitive effects in the switches. The magnitude of these errors is estimated, and it is shown how they may be eliminated by the use of suitably placed trimming capacitors and by a suitable switching sequence. The sensitivity of the circuit is also calculated.

ISSN:0034-6748    

DOI:10.1063/1.1716848

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

``Low energy'' as used in this report means ionic and atomic beam velocities from approximately 5×107to 2×108cm/sec. In this velocity region an ion beam brought to charge equilibrium in helium gas has a much greater content of components of high positive charge than does the same beam charge equilibrated in other gases. To achieve this effect, however, the pressure of helium gas in a charge stripper or converter cell placed in the beam path must be much higher than in other gases. The predicted effect, calculated from the charge changing cross sections, is verified by experiments on the stripping of Li+to Li++in air and helium. In a qualitative experiment the proton beam of the Chicago synchrocyclotron was increased 100% by equilibrating the hydrogen constituent in a 90–10 HeH2mixture before issuing it from the ion source into the acceleration chamber.

ISSN:0034-6748    

DOI:10.1063/1.1716849

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Improvements are presented in the use of the ``twin'' scintillation detector described in an earlier paper. Conditions are specified under which the fluorescence yield is maximized and the proton to electron ratio equalized in both solutions. For a neutron energy of 2.19 Mev the instrumental line width is 23%. The estimated lower limit of its potential range is ¼ to ⅓ mev. Other improvements in sensitivity have permitted the measurement of background neutron fluxes of the order of those produced by cosmic rays.

ISSN:0034-6748    

DOI:10.1063/1.1716850

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

A General Electric analytical mass spectrometer, which was originally designed only for gaseous samples, has been modified so that the sample system can be converted for application to solid samples at elevated temperatures up to 1000°C. Conversion is accomplished by the complete replacement of the sample system by a magnetically operated device and a cavity furnace, the heater of which is thermally attached to the furnace body and servo‐controlled to keep to the predetermined temperature within a fraction of a degree. The furnace body is a silica tube, 5 mm i.d. Replacement of the sample can be done within 10 min without breaking the major vacuum. Advantages and disadvantages compared to the Knudsen cell are also discussed.

ISSN:0034-6748    

DOI:10.1063/1.1716851

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

A target for the production of neutrons by the D(d,n) He3reaction is described. The target gas is circulated to cool the foils used as entrance and exit windows for the incident deuteron beam. Low mass construction is employed to minimize the scattering of neutrons.

ISSN:0034-6748    

DOI:10.1063/1.1716852

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Direct measurements of the ratio of the surface absorptivity of sunlight to the thermal emissivity have been made, and the apparatus is described. A thin plate to be measured is suspended in a vacuum, surrounded by walls cooled by liquid nitrogen, and illuminated by an arc light, which simulates solar radiation. The desired ratio is determined from the equilibrium temperature, which ranged from 0° to 250°C for the samples measured. Possible errors in the procedure have been analyzed theoretically, and corrections introduced where necessary. Intensity fluctuations in the present light source have limited the accuracy to 10%, but this is not a fundamental limitation in the method. Values of the thermal emissivity are also obtained from the rate of change of sample temperature.

ISSN:0034-6748    

DOI:10.1063/1.1716853

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

A transistorized time‐to‐pulse‐height converter is described which has a timebase range of 0 to 15 nsec, and a stability of 10−10sec. The circuit has been used for the mass analysis of particle beams by time‐of‐flight. Time resolutions of 10−9sec were obtained using conventional scintillation counters. The circuit has a short dead time (3×10−7sec), contains a gating facility, but is of simple design. It has been in use at CERN for the previous six months, and functions satisfactorily under experimental conditions.

ISSN:0034-6748    

DOI:10.1063/1.1716854

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Apparatus has been developed for the measurement of shortening and tension of isolated muscle using variable capacitance methods. An isotonic transducer is described which will measure up to 2.5 cm of shortening with a minimum of inertial loading with 1% linearity. An isometric transducer is described which will measure tensions up to 100 g with not more than 5‐&mgr; displacement from 0 to 200 cycles/sec. Simple modifications provide other ranges of tension.

ISSN:0034-6748    

DOI:10.1063/1.1716855

出版商:AIP    

年代:1960

数据来源: AIP