摘要:

A neutron crystal spectrometer is described which has the following features: (1) a useful range from 0.1 to 11.5 Å, (2) exceptional reproducibility for high precision experiments, (3) complete automatic control for measuring sample transmission as a function of wavelength, (4) a temperature regulated sample changer with range from −196 to 300°C, and (5) direct recording of data on punch cards, and a FORTRAN program for the statistical analysis of the data on a digital computer. Three alternate techniques were investigated and developed for extending the range of the spectrometer to wavelengths longer than 1 Å where the relative intensity of higher order Bragg reflections becomes large. In two of the methods, crystalline filters are used to attenuate shorter wavelength neutrons in the beam. In the third, a mechanical neutron velocity selector is used which transmits only the desired first order reflection. The residual higher order contamination in the spectrometer beam was measured to be less than 0.5% over the useful range of each technique. Examples of cross section measurements on V, Gd, and crystalline and fused quartz are presented. The total cross section of vanadium, which is used as a reference standard in many neutron scattering experiments, was determined to be &sgr;T=(4.93±0.02)+(2.78±0.01)&lgr;(Å) barns in the region from 0.1 to 4.0 eV (0.92 to 0.145 Å). The total cross section of normal gadolinium measured at thermal energy (0.0253 eV) is 50 400±500 b.

ISSN:0034-6748    

DOI:10.1063/1.1719779

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A simple focused‐beam electron bombardment evaporator was developed for the controlled vaporization of carbon and other refractory materials. An electrically isolated cylindrical shield deflects and focuses the electron beam, allowing a large anode to cathode distance. This avoids interference by gas conductance, resulting in a more efficient and stable bombardment process. A performance comparison is made between the described evaporator and a conventional carbon arc evaporator.

ISSN:0034-6748    

DOI:10.1063/1.1719780

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

Using a thermistor in a dc bridge configuration, a relationship is developed between the bridge open‐circuit output potential and the absolute temperature. This thermistor function accurately predicts temperature magnitudes and changes in temperature over large spans. The inflected shape of the bridge open‐circuit output potential versus absolute temperature allows for an excellent linearization of the output potential over an appreciable temperature range. The function is completely determined by the temperature coefficient of resistance of the thermistor, by a characteristic bridge resistance ratio, and by the absolute temperature. The function has been programmed satisfactorily in FORTRAN IV.

ISSN:0034-6748    

DOI:10.1063/1.1719781

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The concept of replacing each magnet edge by a suitably located thin lens is used to develop a set of design formulas for the transverse focusing properties of uniform‐field deflecting magnets. A brief comparison is given to recent work of Enge, who showed that the thin lens concept is a valid first order approximation. The formulas are applied to several examples, including a double focusing magnet with arbitrary deflection angle and ratio of gap to radius of curvature. Finally the method is used to study the transverse acceptance angle of a certain class of ``beam dump'' magnets.

ISSN:0034-6748    

DOI:10.1063/1.1719782

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

The electromagnetic transducer described here is simple and compact and capable of measuring displacements of 2.6×10−9cm with a signal‐to‐null ratio of 2:1.

ISSN:0034-6748    

DOI:10.1063/1.1719783

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A device for measuring complex permeabilities, called a magnetic flux sensor, has been constructed from ferrite. Tests of the sensor which involve the imaginary part of the complex permeability are described in this paper. With a signal‐to‐null ratio of 2:1, the sensor can detect a change of resistance per unit resistance in metallic samples of 1.1×10−7, an electrical power absorption of 3.4×10−10W, a radiant flux of 3.1×10−8W/cm2, and a temperature change of 4.9×10−5°K. Construction of the sensor is also described.

ISSN:0034-6748    

DOI:10.1063/1.1719784

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A mathematical model is proposed for calculating the steady state performance of a constant power dissipating thermistor in a laminar shear flow. It is assumed that the fluid is dissipationless and that forced convection is negligible. Explicit values of the excess temperature of a small thermistor, above that of the impinging fluid temperature, have been calculated for asymptotically small and large values of shear velocity.

ISSN:0034-6748    

DOI:10.1063/1.1719785

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A device similar to a hot wire anemometer has been developed in which the wire is replaced with a thermistor. Niiler has presented a theory of the response of the anemometer to velocity gradients. Experimental calibration curves are presented here to show that Niiler's model explains the operational characteristics quite satisfactorily. The associated electronic circuitry is described and the design considerations which determine the magnitudes of the various adjustable parameters are discussed. This anemometer has been used to detect the onset of the various modes of secondary flow, the amplitude of the disturbances, their wavelengths, and their drift velocities. Both velocity and temperature fields may be measured.

ISSN:0034-6748    

DOI:10.1063/1.1719786

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A method is described for measuring the pyroelectric coefficient, dc dielectric constant, and volume resistivity of a polar material over a broad temperature range. The technique is based on the observation of the capacitive charging of a pyroelectric sample by the pyroelectric current generated during a continuous temperature change. This method has the advantages of requiring neither a heat flux measurement nor the attaining of isothermal conditions and does not alter the domain structure of a ferroelectric material. Values of the above properties were measured for Clevite PZT‐5 (lead‐zirconate‐titanate ceramic) over the temperature range from −200 to 200°C. The pyroelectric coefficient of Clevite PZT‐4 (lead‐zirconate‐titanate ceramic) was measured by a simplified method over the temperature range of 25 to 75°C.

ISSN:0034-6748    

DOI:10.1063/1.1719787

出版商:AIP    

年代:1965

数据来源: AIP

摘要:

A metallic, horizontal disk mechanical velocity selector suitable for studying scattering at the intersection of two monoenergetic molecular beams has been constructed and tested. Principles of the design, construction, and operation are presented along with detailed calculations of the transmission characteristics for both narrow and divergent beams. The calculations are in good agreement with measurements of the transmitted intensities of beams of cesium atoms effusing from an oven at 405°K.

ISSN:0034-6748    

DOI:10.1063/1.1719788

出版商:AIP    

年代:1965

数据来源: AIP