摘要:

The resistive (Coulter) method of counting and sizing particles in a conducting fluid has been extended to polystyrene spheres 900 Å in diameter, with a present detection limit near 600 Å, through the use of individual submicron pores etched in irradiated plastic sheet. The use of a nonionic surfactant and ultrasonic cleaning effectively relieves the problem of plugging. The particles may be driven through the pore by the electric field, without the use of pressure, to yield the vector sum of the electrophoretic and electro‐osmotic velocities. A new theory, yielding an upper limit to the resistive pulse on passage of a sphere, agrees well with data for spheres with diametersd<0.4D, whereDis the pore diameter, and complements a previous theory that gives a lower limit, valid ford>0.9D. We estimate that a detection limit near 250 Å will be attainable with the further development of current techniques.

ISSN:0034-6748    

DOI:10.1063/1.1684724

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The somewhat obvious but relatively unused technique for generating cold gas by bubbling room temperature N2directly into liquid nitrogen offers twice the cooling time of the conventional immersed heater or continuous gas flowthrough systems. An apparatus for implementing the technique is illustrated.

ISSN:0034-6748    

DOI:10.1063/1.1684725

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

We report the behavior of 24 different types of junction field effect transistors at 4.2 K, giving the characteristics (gain, bandwidth, and noise) of the six different types which make satisfactory amplifiers.

ISSN:0034-6748    

DOI:10.1063/1.1684726

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A technique using an optically modulated laser carrier beam has been developed for calibrating the streak speed, linearity, and orthogonality of an image converter streak camera while it simultaneously records experimental data.

ISSN:0034-6748    

DOI:10.1063/1.1684727

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A detailed description is given of an ion beam system and instrumentation used in studies of the ejection of electrons associated with the Auger neutralization of N2+, H2+, and N+ions in the energy range 10–30 eV under controlled surface conditions. Ions are generated in a low pressure discharge, electrostatically focused and mass analyzed by a refocusing magnetic spectrometer to remove undesired ion, neutral, and metastable species. The ion kinetic energy spread is low (approximately 0.4 eV at half‐maximum) and the beam intensity is as high as 10−8A. The combination of ultrahigh vacuum techniques to lengthen the time required to reach adsorption equilibrium after flashing, and special guarding and analog data reduction techniques to reduce instrumentation time response, permitted the study of transient adsorption effects as well as the more usual equilibrium studies.

ISSN:0034-6748    

DOI:10.1063/1.1684728

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Many commercially available net radiometers using polyethylene shields to protect their sensing surfaces have 5% of these surfaces covered with a highly reflective white paint. The purpose of this paint is to reduce the sensitivities of these instruments to short wave radiation and make them equal to a supposedly lower long wave radiation sensitivity. Theoretical considerations, however, yield no conclusive evidence for such a differential transmission of short and long wave radiation by thin films of polyethylene. Furthermore, rederivations of the net long wave radiation equations for the calibration chambers of J. P. Funk [J. Sci. Instrum.36, 267 (1959); J. Geophys. Res.67, 2753 (1962)] and L. J. Fritschen [J. Appl. Meteor.2, 165 (1963);4, 528 (1965)], who pioneered in the construction and evaluation of these instruments, indicate that certain approximations made in the original derivations completely account for the original 5% discrepancy. New experiments verify these findings and demonstrate the equality of short and long wave calibration constants for polyethylene shielded net radiometers without the customary 5% areal covering of white paint.

ISSN:0034-6748    

DOI:10.1063/1.1684729

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

A new type, long focal length, 600 keV, continuous high current density accelerator is described. Beam focus is obtained from a combination of five magnetic and electrostatic lenses. The construction and preliminary multimomentum operation are outlined, wherein a total current of 80 mA at a current density of approximately 40 mA/cm2was obtained. A simple theory for maximum focused beam current density is developed for semispace charge‐neutralized machines which compares favorably with the experimental results. Problems such as back‐streaming electrons and required vacuum conditions are discussed. Focus and beam optics are considered for simultaneous acceleration of a multicomponent beam composed of the several molecular ions of normal hydrogen and of a hydrogen‐deuterium mixture.

ISSN:0034-6748    

DOI:10.1063/1.1684730

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The fringing field effect of a deflecting magnet on a charged particle trajectory is examined through its strict analytical expression, and thus the limit of approximation to be applied is discussed. The slope and location of a particle trajectory in the median plane are given, and, forzfocusing, the focal length and the location of an assumed thin lens are derived showing how the lens concept can be introduced. The present analysis will give the procedure to obtain the higher order calculations if they are needed.

ISSN:0034-6748    

DOI:10.1063/1.1684731

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

We describe a shift register which is operated by a digital clock as usual, but shifts analog rather than binary signals. This system can be used, among other purposes, as a delay line, in which mode it overcomes many of the limitations of LC delay lines with extremely long delays. The circuit will operate as a digital filter when the delay is immaterial, and the clock rate is chosen to provide the proper folding frequency. Some applications to radio astronomy are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1684732

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

In high current linear accelerators there may be instability in the coherent lateral motion of the particles caused by the electrostatic image of the beam. Appropriate placement of focusing magnetic lenses (the type normally employed to prevent symmetric radial expansion of the beam) can be used to control the lateral motion. Criteria for stability are derived.

ISSN:0034-6748    

DOI:10.1063/1.1684733

出版商:AIP    

年代:1970

数据来源: AIP