摘要:

A number of improvements in a facility developed over the past three years at the Stanford Synchrotron Radiation Laboratory for the study of pressure and/or temperature effects on materials are described. These include improved beam collimation to both reduce background and eliminate gasket scatter, a remote, pneumatically operated pressurizer, and introduction of a variety of electronics hardware to allow both computer control of experiments and on-line data analyses. Considerations are given to the possible effects of heating of the pressure cavity by the incident beam and to possible fluctuations of the incident beam intensity/energy profile. In both cases, there was no evidence to indicate that these phenomena warranted any further consideration, i.e., they are not considered to be problems in terms of analyzing the data. Extended measurements of a well-defined diffraction peak indicated that a considerable improvement over our earlier work has been realized in terms of the precision in the determination of the energy of the peak, viz., a precision of better than 0.04% for measurement periods as short as 10 s; the estimated precision in the net peak area is less than 3%. The system was used to examine the kinetics of the B1-to-B2 pressure-induced phase transition in KBr. The volume change in the two-phase region is measured to be 10.41%±0.10%, in excellent agreement with most of the previous measurements. A plot of the time dependence of the growth rate of the high-pressure phase indicates that the phase transformation can be described by the Avrami equation. Constants for the phase transition kinetics are given.

ISSN:0034-6748    

DOI:10.1063/1.1137405

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Some techniques are given for the design, construction, and chemical surface treatment of niobium uhf reentrant cavities. These techniques ensure that when these cavities are operated at helium temperatures they will consistently display unloadedQvalues above 107.

ISSN:0034-6748    

DOI:10.1063/1.1137406

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An unusually rugged highly sensitive and inexpensive bubble tiltmeter has been designed, tested, and built in quantity. These tiltmeters are presently used on two volcanoes and an Alaskan glacier, where they continuously monitor surface tilts of geological interest. This paper discusses the mechanical, thermal, and electric details of the meter, and illustrates its performance characteristics in both large (>10−4radian) and small (<10−6radian) tilt environments. The meter’s ultimate sensitivity is better than 2×10−8radians rms for short periods (hours), and its useful dynamic range is greater than 104. Included is a short description of field use of the instrument for volcano monitoring.

ISSN:0034-6748    

DOI:10.1063/1.1137408

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A vapor furnace producing stable atomic and molecular beams for photoionization experiments is described. During operation the furnace causes no detectable magnetic stray field because it is heated by a stream of hot air. Thus angle‐ and energy‐resolved measurements of photoelectron spin polarization could be done at a kinetic energy as low as 0.5 eV. The high temporal stability of the target beam is demonstrated by means of an angular distribution measurement with mercury atoms.

ISSN:0034-6748    

DOI:10.1063/1.1137409

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An intracavity, cw, dye‐laser photothermal deflection (PTD) technique has been developed for gas‐phase vibrational overtone spectroscopy. This new technique has a similar S/N ratio and significantly lower window noise than the intracavity photoacoustic technique under identical conditions.

ISSN:0034-6748    

DOI:10.1063/1.1137410

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A new system has been developed for calibration of space plasma analyzers, in particular ion mass spectrometers. The system provides a large‐area (∼250 cm2), highly parallel (±0.5°), and spatially uniform (±5%) beam of ions over the energy per charge range from 5 eV/charge to 100 keV/charge. Other special features include variable energy spread from &Dgr;E∼1 eV to ∼3 keV/charge and multiple charge state ions such as He2+or Xe9+. Among several key ion optical elements are a high‐efficiency electron bombardment ion source capable of delivering ∼10−8A, a 90° crossed electric and magnetic field mass spectrometer designed to produce either a mixed or a mass‐selected beam, and a unique beam expansion system which produces the uniform large‐area beam. The system also includes automatic beam monitoring and control via a feedback loop, as well as provisions for semiautomatic control of angle and energy analysis. Use of the calibration system during its development phases has made possible the rapid calibration of five complex satellite ion mass spectrometers already flown. Data from one of these calibrations are discussed here.

ISSN:0034-6748    

DOI:10.1063/1.1137411

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The sample size for conventional double collector isotope mass spectrometry has been reduced more than three orders of magnitude by using a ‘‘pushing’’ gas for precise stabilization of sample pressure. The sample is stored in a long microcontainer (50 cm, 0.5 mm i.d.) to moderate the effect of diffusive mixing of sample with the pushing gas. If the analysis is sufficiently rapid (e.g., a run of 1 min for the unknown sample between two runs on the standard), then almost total sample consumption is possible. This method retains the high precision and simplicity of dynamic flow, yet possesses the high sensitivity of static mass spectrometry.

ISSN:0034-6748    

DOI:10.1063/1.1137412

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Time‐of‐flight methods are valuable in measurements of the velocity distribution of low‐energy atoms and molecules whose energies are difficult to measure directly. A system is described which uses pseudorandom beam chopping and a CAMAC compatible computer interface to provide energy resolution as good as conventional time‐of‐flight techniques, but with a duty factor of 50%. This system was designed for ice sputtering experiments.

ISSN:0034-6748    

DOI:10.1063/1.1137413

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A system to measure the temporal behavior of atomic or molecular fluorescence, which is disturbed by large noise background, has been developed. This system uses the pseudorandom modulation technique of length up to 1023, temporal resolution of approximately 83 ns, and a photon counting capacity of 107counts/s. Data processing by a minicomputer and a hardware demodulation circuit enable quick analysis of a large volume of data. The signal‐to‐noise ratio of this measurement system is discussed with some experimental comparisons. The system is tested in the decay time measurement of I2fluorescence.

ISSN:0034-6748    

DOI:10.1063/1.1137414

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A high optical power‐density excimer laser pumped by an electron‐beam‐sustained discharge has been developed. The electron‐beam generator comprised a 200‐kV pulse transformer‐driven power supply and an electrostatically focused electron‐beam diode. The careful design and optimization of this generator has allowed very reliable, reproducible operation of the complete laser system with a high enhancement ratio of 4.8. An average output power density of 0.63 MW cm−2in a 250‐ns (FWHM) pulse has been obtained from ane‐beam‐sustained discharge XeCl* laser with an extraction efficiency of 1.5%.

ISSN:0034-6748    

DOI:10.1063/1.1137390

出版商:AIP    

年代:1983

数据来源: AIP