摘要:

New equipment designed to measure the effect of pressure and isotopic substitution on liquid/liquid equilibria in polymer/solvent systems is described. The phase separation is detected by monitoring low‐angle forward scattered light, together with simultaneous loss in transmitted light, from an He–Ne laser shining through the sample. Phase transitions can be induced by varying temperature/time and/or pressure/time profiles or by a combination of such changes. The system operates at high precision (±0.001 K, ±0.002 MPa), and over wide temperature and pressure ranges (240≤T/K≤600, 0.01≤P/Mpa≤35). The temperature, pressure, and transmitted and scattered light intensities are digitally recorded, and the rate of change of the temperature and/or pressure used to induce the phase transition is under computer control. The system is being used to study the temperature, pressure, polymer molecular weight, and molecular weight distribution, and H/D dependences of phase equilibria for polystyrene (PS)/(CH3)2CO and PS/(CD3)2CO solutions. Sample results are reported. The pressure and molecular weight dependences of the coexistence curve, and their isotope effects, are large.  

ISSN:0034-6748    

DOI:10.1063/1.1143329

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We will present a method of chromaticity correction for a high brilliant SR ring. This method has been successfully applied to a low emittance ring, the VUV and soft x‐ray ring, which is one of the future plans of the Photon Factory. As a result, we have obtained a sufficiently wide dynamic aperture, more than 40 mm in both transverse directions.  

ISSN:0034-6748    

DOI:10.1063/1.1143330

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The vertical acceptance of the Photon Factory storage ring had been limited by a narrow vacuum chamber at an insertion device. To increase the acceptance, the vertical betatron function at the device was reduced. This modification resulted in an increase of the beam lifetime by a factor of 1.5 and enabled one to operate the ring continuously for 24 h without a beam injection. The effects of the optics modification on the beam lifetime, beam injection, betatron tune shifts produced by the insertion devices, and the brilliance of the synchrotron light are presented.

ISSN:0034-6748    

DOI:10.1063/1.1143331

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A versatile small‐angle x‐ray diffraction/scattering system has been developed at Stanford Synchrotron Radiation Laboratory for studies of biological and other materials. The system includes two sets of collimation slits separated by an ionization chamber, a sample holder cooled by a circulation bath, a vacuum/He scattering path after the sample holder and a detector, either a linear one‐dimensional position‐sensitive proportional counter or a position‐sensitive quadrant detector. Data aquisition is controlled by a VAXstation through a CAMAC interface. Menu‐driven data acquisition and on‐line analysis software has been developed. The system can be used to collect small‐ to intermediate‐angle x‐ray scattering and diffraction data. Monochromatic, anomalous, and time‐resolved scattering/diffraction experiments are possible. A time‐resolved spectrophotometer using photodiode arrays has also been developed for simultaneous measurements of optical absorption spectra and x‐ray scattering/diffraction.

ISSN:0034-6748    

DOI:10.1063/1.1143332

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Ultrasmall‐angle x‐ray scattering (USAXS) using the Bonse–Hart twin‐crystal diffractometer system1on a synchrotron radiation source (SRS) is being developed as a technique for studying the structure of colloidal dispersions and other inhomogeneous materials with features in the size range 500 A˚ to 1 &mgr;m. The use of well‐characterized colloidal samples in this range highlights the problems which must be resolved in order to obtain reliable data from the system. This paper addresses the specific problems of attenuation, absorption, detector dead time, and smearing for the USAXS configuration. The system has been used to study a variety of materials and some previously unobserved features have been found in the scattering profile of a colloidal latex. This serves to indicate the value of the improved system in the field of colloidal science.  

ISSN:0034-6748    

DOI:10.1063/1.1143333

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The x‐ray beams for the next generation of synchrotrons will contain much more power (1–10 kW) than is available at present day facilities. Cooling the first optical components in these beam lines will require the best cooling technology that one can bring to bear. Argonne continues to pioneer the use of liquid metals as the cooling fluid and has adopted liquid gallium as the liquid metal of choice. Its low melting point, 29.7 °C and its very low vapor pressure make it an easy fluid to handle and its high thermal conductivity and heat capacity make it an excellent cooling fluid. A series of experiments were performed during April 1991 with the wiggler beam at the F2 station of the CHESS facility at Cornell to investigate the cooling of large areas of high power. Two types of cooling crystal geometries were tested. One where the cooling channels were core drilled just below the surface of the crystal and a second where slots were cut into the crystal just below the surface with a diamond saw. Both crystals performed well with photon beam powers up to 1050 W and power densities of up to 14.5 W/mm2at normal incidence. An infrared camera was used to measure the variation in the temperature of the top layer of the silicon crystals. For the core‐drilled crystal the peak temperature measured at the center of the beam at a power density of 12.3 W/mm2was 15 °C hotter than the crystal surface outside of the beam with a flow of liquid gallium of 2 gpm (gallons per minute) and was 10 °C with a flow of 4 gpm. The maximum distortion of the crystal surface distortion of the core‐drilled crystal was about ±2.0 arcsec for the 2 gpm case with a maximum power density of 10.9 W/mm2and about 5% of the expected beam intensity was lost at peak power of 14.5 W/mm2. For the slotted crystal the peak temperature difference for a peak power of 10.9 W/mm2was 3.5 °C and 2.0 °C for liquid gallium flows of 1 gpm and 2 gpm, respectively. No intensity loss was measured for the maximum power density of 14.5 W/mm2. The fact that the peak temperature difference on the surface of both crystals was decreasing with increased flow of liquid gallium suggests that even higher power densities can be accommodated with higher flows of liquid gallium.

ISSN:0034-6748    

DOI:10.1063/1.1143334

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A variable‐metric (VM) crystal is one in which the spacing between the crystalline planes changes with position in the crystal. This variation can be either parallel to the crystalline planes or perpendicular to the crystalline planes of interest and can be produced by either introducing a thermal gradient in the crystal or by growing a crystal made of two or more elements and changing the relative percentages of the two elements as the crystal is grown. A series of experiments were performed in the laboratory to demonstrate the principle of the variable‐metric crystal and its potential use in synchrotron beam lines. One of the most useful applications of the VM crystal is to increase the number of photons per unit bandwidth in a diffracted beam without losing any of the overall intensity. In a normal synchrotron beam line that uses a two‐crystal monochromator, the bandwidth of the diffracted photon beam is determined by the vertical opening angle of the beam which is typically 0.10–0.30 mrad or 20–60 arcsec. When the VM crystal approach is applied, the bandwidth of the beam can be made as narrow as the rocking curve of the diffracting crystal, which is typically 0.005–0.050 mrad or 1–10 arcsec. Thus a very large increase of photons per unit bandwidth (or per unit energy) can be achieved through the use of VM crystals. When the VM principle is used with bent crystals, new kinds of x‐ray optical elements can be generated that can focus and defocus x‐ray beams much like simple lenses where the focal length of the lens can be changed to match its application. Thus both large magnifications and large demagnifications can be achieved as well as parallel beams with narrow bandwidths.

ISSN:0034-6748    

DOI:10.1063/1.1143335

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A system for performing x‐ray diffraction on biological samples as a function of pressure and temperature is described. It is capable of operating in a pressure range of 1 bar–3 kbar (0.1–300 MPa) and in a temperature range of −30 to 80 °C. The system incorporates microprocessor‐based pressure and temperature controllers which provide automated control with excellent stability characteristics: Fluctuations in pressure and temperature can be maintained within ±1 bar (0.1 MPa) and ±0.05 °C, respectively. Use of the apparatus is illustrated by application to a pressure‐induced phase transition in a lipid‐water liquid crystal.

ISSN:0034-6748    

DOI:10.1063/1.1143336

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Supersonic beams of atomic nitrogen and oxygen are produced by an electrodeless rf discharge within a ceramic nozzle. Mixtures of N2or O2seeded in He are heated by 100 W at 38 MHz with a stagnation pressure of 200–250 Torr. The flux of reactive atoms is 1–3×1018sr−1 s−1with stream velocities of 3.2–3.6 km/s and a velocity spread of 20% FWHM. The source is relatively simple to construct, because it requires only passive cooling for operation in vacuum.

ISSN:0034-6748    

DOI:10.1063/1.1143811

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

H−/D−current and emittance scaling is measured in a magnetic multipole negative ion source. The gas in the source is the only difference as no reoptimization of the source is carried out, thus giving a direct comparison of the performance for the two isotopes. It is found that the H−current is greater than the D−current by approximately a factor of 2 under the same discharge conditions. The extracted electron to ion ratio is commensurately higher in deuterium than in hydrogen. Finally, the emittance in deuterium at the higher arc currents is found to be lower than that in hydrogen. Some comments are made on the scaling within the context of the accepted model of negative ion production.    

ISSN:0034-6748    

DOI:10.1063/1.1143337

出版商:AIP    

年代:1992

数据来源: AIP