摘要:

A pulsed beam of alpha particles from a 5.5 MV Van de Graaff accelerator has been used to study radiative capture reactions. Time‐of‐flight techniques are used to discriminate against neutrons produced when the beam interacts with collimator‐target contaminants, as well as against beam independent background due to cosmic rays. With a beam pulse of less than 4 nsec (FWHM) duration and a repetition rate of 2 MHz, a portion of the34S(&agr;,&ggr;)38Ar excitation function was examined nearE&agr;=3.6 MeV and the background found to be an approximate factor of 15 below that of the effective dc excitation function. In addition it is demonstrated that an angular distribution taken on resonance by this method requires substantially less background subtraction. The method has also been successfully applied to radiative capture studies in which the incident beam energy is above the neutron threshold for the target nuclei.

ISSN:0034-6748    

DOI:10.1063/1.1684874

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

An instrument permitting the study of ionization processes caused by ion and electron impact on solid surfaces under well defined conditions is described. It consists functionally of a single focusing mass spectrometer providing a monoisotopic and monoenergetic primary beam and a quadrupole mass spectrometer for the analysis of secondary ions released from a target surface. Low primary ion current densities and ultrahigh vacuum conditions allow investigations without essential alterations of the target surface during experiment. Some results demonstrating instrument performance are presented.

ISSN:0034-6748    

DOI:10.1063/1.1684875

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The display system developed is capable of storing and displaying a computer generated display on standard TV monitors. The system is relatively inexpensive (≈ $11 000 including four monitors), has medium resolution (≈ 490×250 points), and has the capability for displaying both graphics and alphanumerics. This paper describes the operation of an interface which converts the computer output into a TV signal stored on a magnetic disk recorder. Also described is a circuit used for improving the high frequency response of the disk recorder, and thereby the resolution of the display system.

ISSN:0034-6748    

DOI:10.1063/1.1684876

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Experiments and theoretical calculations are carried out to determine the accuracy attainable by intensity modulation and wavelength modulation optical monitoring techniques used to specify film thickness. Experimental results show that film thickness errors of 5% are typical in deposition thickness monitoring based on intensity modulation techniques. It is demonstrated by calculation that an appreciable improvement of film thickness accuracy can be obtained by wavelength modulation techniques, and that variable wavelength dielectric filters may conveniently be used as spectral filters for wavelength modulation devices to provide a film thickness accuracy between 0.5 and 1%. Results obtained may be used for the design of optical thickness monitoring systems.

ISSN:0034-6748    

DOI:10.1063/1.1684877

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The effect of the measurement system is usually ignored in the interpretation of LEED patterns. This effect can, however, be treated analytically through the use of the instrument response function, which represents the intensity function the instrument would record for a perfect surface. We have measured the response function for a particular LEED system using a double aperture Faraday collector and have identified the various experimental factors which determine its detailed functional form. The Fourier transform of the response function defines the range over which the instrument behaves as an interference detector. The effect of long range correlations on the pattern is suppressed by this finite range, with the result that fairly untidy surfaces may not be easily distinguished from those which are nearly perfect.

ISSN:0034-6748    

DOI:10.1063/1.1684878

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A study of the instability in surface composition of reduced lead oxide glass surfaces is described which suggests a possible mechanism for the observed gain degradation of channel electron multipliers in high vacuum environments. In particular, the depletion of surface oxygen from initial levels which were up to 10 times the stoichiometric concentration was observed, using the method of Auger electron spectroscopy. A model incorporating surface oxygen as a possible donor species in the secondary emission process is discussed, which qualitatively predicts the observed pressure dependence of multiplier gain and the onset of fatigue at about 10−7Torr.

ISSN:0034-6748    

DOI:10.1063/1.1684879

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

An EPR system for use at liquid helium temperatures is described. The design of this system is such that one can interchange samples and adjust the cavity coupling when operating at liquid helium temperatures. Samples can be interchanged when operating below the lambda point without disturbing the helium bath. Also, the system includes a goniometer for angular dependence studies.

ISSN:0034-6748    

DOI:10.1063/1.1684880

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The energy measurement of high peak power CO2laser pulses is generally accompanied by permanent damage to the surface of the detecting element. The use of appropriate optics simultaneously reducing the field density and enlarging the detection area appears to be a successful mean to bypass this difficulty. The instrument described in this paper combines diverging optics with a large sensing sheet made of pyroelectric material in order to provide fast response. The device is capable of detecting a 10 J, 10 MW peak power pulse at a repetition rate of 10 pulses/sec. Its spectral response is flat from 0.36 to 12 &mgr;.

ISSN:0034-6748    

DOI:10.1063/1.1684881

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Measurements of the reversible and total magnetothermal effects together with relevant magnetic quantities of annealed nickel using a new measuring equipment have been made. It is shown that the reversible magnetothermal components measured by the direct and indirect method are in reasonable agreement in the field range applied. The numerical value of the constantb″is evaluated and it is concluded that in moderate fields, reversible changes in intrinsic magnetization and rotation of the magnetization vectors predominate.

ISSN:0034-6748    

DOI:10.1063/1.1684882

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A system is presented for controlling the frequency sweep of a cw self‐oscillating magnetic resonance spectrometer. The system incorporates a Hewlett‐Packard synchronizer, model 8708A, which covers a total range of 50 kHz–430 MHz. The frequency control is sufficiently precise that, when the linewidth to frequency ratio is 10−5or more, averaging may extend over several hours. Details are given for applying the system to quadrupole resonance of chlorine.

ISSN:0034-6748    

DOI:10.1063/1.1684883

出版商:AIP    

年代:1971

数据来源: AIP