摘要:

Scientific investigations involving the use of neutron beams have been centered at reactor sources for the last 35 years. Recently, there has been considerable interest in using the neutrons produced by accelerator driven (pulsed) sources. Such installations are in operation in England, Japan, and the United States. In this article a brief survey is given of how the neutron beams are produced and how they can be optimized for neutron scattering experiments. A detailed description is then given of the various types of instruments that have been, or are planned, at pulsed sources. Numerous examples of the scientific results that are emerging are given. An attempt is made throughout the article to compare the scientific opportunities at pulsed sources with the proven performance of reactor installations, and some familiarity with the latter and the general field of neutron scattering is assumed. New areas are being opened up by pulsed sources, particularly with the intense epithermal neutron beams, which promise to be several orders of magnitude more intense than can be obtained from a thermal reactor.

ISSN:0034-6748    

DOI:10.1063/1.1137897

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The trajectory of an electrically charged droplet falling in air and electrostatically deflected is analyzed for the influence of droplet size, air frictional drag, and electrical charge. An analytical solution for the trajectory was obtained (assuming a linear velocity component) and programmed into a computer to generate graphs of the variation in trajectory. The experimental work verified that the droplet deflection is proportional to charge and the loss of velocity in the direction of deflection is predicted from the equations obtained here. These studies were used in designing a cell sorting device which places biological cells in defined locations on a microscope slide.

ISSN:0034-6748    

DOI:10.1063/1.1137898

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The design, construction, and evaluation of a computer‐controlled electronic cell sorting device is described; the computer performs all cell data analysis and sorting functions. The primary advantage is that the functions are programmable and, hence, any data analysis or sorting format can be implemented (within the constraints of the physical system). The software that has been developed is highly modular and can be manipulated to perform different functions. In our present configuration, the device analyzes data from each cell on a cell‐by‐cell basis, performs the sorting function, stores the cell data for off‐line analysis, and provides a real‐time display (histogram) of cell data.

ISSN:0034-6748    

DOI:10.1063/1.1137899

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

In order to measure respiration rates in rats irradiated to the whole thorax, a plethysmograph involving a microphone with extended low‐frequency response and an airtight, whole‐body chamber has been constructed. The microphone response to the respiration pressure waves created by the rats placed in the chamber is markedly greater in amplitude than the response to laboratory sounds and animal noises; thereby filtering complexities are avoided. The output from the microphone went to a frequency counter for measurement of the number of pressure waves per unit time. Control, unirradiated rats, between the ages of 3 and 18 months, demonstrated a respiration rate in the range of 130–160 breaths per minute. Rats that received thoracic radiation doses greater than 12 Gy displayed increased respiration rates and occasional abnormal respiration patterns. These results demonstrate that this whole‐body plethysmograph incorporating a sensitive microphone and simple electronics can be used for the measurement of respiration functions in rats with lung damage.

ISSN:0034-6748    

DOI:10.1063/1.1137900

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The determination of contrast thresholds for a human observer was performed by a new method. To the observer targets having increasing contrasts from left to right are presented. The luminances of the targets are chosen such that some of the targets are invisible to the observer. The observer counts the number of visible targets. From this number the contrast threshold can be derived. This method is objective, faster than traditional methods, and gives comparable results. The photometry for the determination of the contrasts is described.

ISSN:0034-6748    

DOI:10.1063/1.1137901

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Some physical properties of lanthanum hexaboride filaments, when operated as cathodes in a gas discharge, are presented. These directly heated hairpin‐shaped filaments have been tested in different types of ion sources and are shown to be capable of long‐pulse or cw discharge operations. The design of a shaped lanthanum hexaboride filament for the purpose of further extension of lifetime is also described.

ISSN:0034-6748    

DOI:10.1063/1.1137902

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

An ion source with a hollow cathode set at a position where no backstreaming electrons can arrive has been proposed and fabricated. The arc chamber is a magnetically line‐cusped semicylinder (i.e., semicircular cross section) whose axis is perpendicular to the ion beam axis and the hollow cathode is positioned on the extended line of the cylinder axis. Preliminary experiments were made on this source. The highest arc and gas efficiencies obtained were 0.64 A/kW and about 70%, respectively, and a proton ratio of 85% was attained. In addition, the fraction of metal impurities in the beam was measured to be negligibly small. These source performances are comparable to those of the conventional tungsten‐filament magnetic multipole line‐cusp sources for neutral beam injectors.

ISSN:0034-6748    

DOI:10.1063/1.1137903

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A new mechanism capable of strongly modulating an intense relativistic electron beam using two cavities was found recently. The frequency of the modulated intense relativistic electron beam (IREB) depends on the time it takes an electron to transit the distance between the two cavities. This transit time can be varied by changing the distance between the two cavities or by changing the propagation velocity of the electron beam. It is shown, in this paper, that by varying the intensity of a magnetic field located between the two cavities the drift velocity of the electrons in the IREB is changed, influencing the frequency of the IREB modulation. In a typical experiment a modulated IREB with power ∼5×109W was generated. The frequency of modulation was varied by ∼34% using an auxiliary small magnetic field coil.

ISSN:0034-6748    

DOI:10.1063/1.1137904

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

The soft x‐ray absorber‐foil technique for electron‐temperature measurements is considered. The idea is introduced to compare the signals of a surface‐barrier diode and an x‐ray‐sensitive photodiode rather than those of two identical detectors. The contrasting characteristics of the two detector types gives rise to an improvement of the temperature resolution by a factor 2 (at 0.4 keV) to 10 (at 10 keV).

ISSN:0034-6748    

DOI:10.1063/1.1137885

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

It is shown that the energy‐transfer efficiencies of opening switch and closing switch Ohmic heating transformers differ significantly, and that the efficiency of an opening switch transformer can be optimized by using an iron core with a substantial air gap (gap comparable to the plasma minor radius). A demonstration on the Caltech Encore gapped iron core tokamak is cited.

ISSN:0034-6748    

DOI:10.1063/1.1137886

出版商:AIP    

年代:1984

数据来源: AIP