摘要:

An energy dispersive x‐ray absorption spectroscopy instrument has been built at the X6A beam port of the x‐ray ring at the National Synchrotron Light Source (NSLS). This instrument allows the collection of extended x‐ray‐absorption fine structure and/or x‐ray absorption near‐edge structure spectra for many elements on the millisecond time scale. The beamline employs a four‐point crystal bender and a rectangular Si 220 crystal to access incident energies between 6.5 and 21 keV. Because the polychromator focuses the synchrotron beam to a narrow 100‐&mgr;m line, this experimental apparatus is ideal for x‐ray absorption spectroscopy experiments in special environments such as at high pressures, forinsituexperiments, and/or for very small samples. In this manuscript we will describe the instrument design and present data with which to evaluate the instrument. This beamline is available through the NSLS user proposal system.

ISSN:0034-6748    

DOI:10.1063/1.1144778

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The x‐ray microbeam scanning facility in our laboratory at Chalmers University of Technology/Go¨teborg University is described in terms of optical and mechanical design, imaging capacity, spatial resolution, and sensitivity. Different types of visualization of the elemental distribution are demonstrated and application of image processing is discussed. Examples of applications in the field of single‐particle analysis as well as tree ring analysis are given. Future perspectives of the technique are also discussed.

ISSN:0034-6748    

DOI:10.1063/1.1144750

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A flat‐crystal spectrometer for analyzing ultrasoft x rays in the wavelength region 10–25 A˚ was constructed for use on an electron beam ion trap. The spectrometer employs a position‐sensitive proportional counter for detection and affords a nominal resolving power of 2000 at a Bragg angle of 45°. Measurements of theL‐shell spectra of Ne‐like Fe16+and of the 3s1/2–3p3/2transitions in near Na‐like Pb71+, which fall into the wavelength region from 13.5 to 17.5 A˚, are presented demonstrating high throughput and excellent signal‐to‐noise characteristics. The actual resolving power achieved was limited by the intrinsic resolution of the crystal to 500. A resolving power close to the nominal value was achieved in second order Bragg reflection.

ISSN:0034-6748    

DOI:10.1063/1.1144786

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We have constructed an in‐laboratory stopped‐flow extended x‐ray absorption fine structure (EXAFS) apparatus by combining laboratory EXAFS equipment in the dispersive mode and a stopped‐flow unit with two 150‐&mgr;m‐thick boron nitride windows. The rotating anode x‐ray generator with a Mo target was used as an x‐ray source. The self‐scanning photodiode array was adopted as a position sensitive‐linear x‐ray detector. In order to obtain a suitable x‐ray flux intensity, the accumulation of weak intensities during a short gate time was carried out by repeating the measurements. We have confirmed the performance of our apparatus by repeatedly measuring a number of static EXAFS spectra of 0.20 mol dm−3aqueous solution of copper(II) sulfate. By use of our newly developed apparatus, we have succeeded in the direct determination of the structure of the reaction intermediate, the heterodinuclear copper(II)/mercury(II) complex, formed in the copper(II) ion incorporation into the homodinuclear mercury(II) complex of 5,10,15,20‐tetrakis(4‐sulfonatophenyl)porphine.

ISSN:0034-6748    

DOI:10.1063/1.1144775

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A simple method has been proposed for the removal of diffraction peaks from x‐ray absorption fine structure spectra of a single crystal observed in the fluorescence mode (i.e., excitation spectrum), in which the diffraction peaks inevitably appear. With a patching up of the appropriate spectrum regions from the spectra having many diffraction peaks, it is shown that we can synthesize one spectrum without the diffraction peaks. Here, several spectra are observed in rotating the single crystal within small angles. As an example, this method is successfully applied in finding the local structure around the Cr3+ion in a single crystal of &agr;‐Al2O3:Cr3+. The bond distances of Cr3+–O2−have been determined asr1=2.04 A˚ andr2=1.95 A˚, those are closer to the bond distances in Cr2O3.

ISSN:0034-6748    

DOI:10.1063/1.1144793

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

An electric‐discharge‐pumped XeCl laser using phototriggering by x rays is reported. A consistent input of the stored energy into the pumping discharge plasma has been realized. An output pulsed energy of about 10 J has been achieved in a ∼3‐lactive volume with an efficiency ≳2%. High spatial uniformity of the laser radiation and a stable space discharge were observed. A stability analysis of the discharge pumping has been made for the XeCl laser in terms of the current‐voltage characteristic model. The method for parametric optimization of such systems is described.

ISSN:0034-6748    

DOI:10.1063/1.1144742

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We describe a stimulated Brillouin gain (SBG) spectrometer based on low power continuous‐wave frequency‐stabilized lasers. The high resolution and broad tuning range of this spectrometer are demonstrated through a SBG spectrum of glycerol in the glassy state (T=146 K). The narrow Brillouin linewidth (17 MHz half‐width at half‐maximum) and large Brillouin shift (17.31 GHz) in this spectrum illustrate the extremely high equivalent ‘‘finesse’’ of the instrument, a finesse that would be difficult to achieve through interferometric techniques. The accuracy and precision with which the Brillouin shift can be measured are demonstrated using SBG spectra of liquid methylene chloride as an example. Our Brillouin shift values obtained over the temperature range 178–300 K are in excellent agreement with values measured previously by others using spontaneous and stimulated Brillouin scattering.

ISSN:0034-6748    

DOI:10.1063/1.1144743

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A novel, simple, and inexpensive calibration scheme for a continuous‐wave difference frequency spectrometer is presented, based on the stabilization of an open transfer cavity by locking onto the output of a polarization stabilized HeNe laser. High frequency, acoustic fluctuations of the transfer cavity length are compensated with a piezoelectric transducer mounted mirror, while long term drift in cavity length is controlled by thermal feedback. A single mode Ar+laser, used with a single mode ring dye laser in the difference frequency generation of 2–4 &mgr;m light, is then locked onto a suitable fringe of this stable cavity, achieving a very small long term drift and furthermore reducing the free running Ar+linewidth to about 1 MHz. The dye laser scan provides tunability in the difference frequency mixing process, and is calibrated by marker fringes with the same stable cavity. Due to theabsolutestability of the marker cavity, precise frequency determination of near infrared molecular transitions is achieved via interpolation between these marker fringes. It is shown theoretically that the residual error of this scheme due to the dispersion of air in the transfer cavity is quite small, and experimentally that a frequency precision on the order of 1 MHz per hour is routinely obtained with respect to molecular transitions.  

ISSN:0034-6748    

DOI:10.1063/1.1144744

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A lab‐built personal computer‐based electron spin resonance (ESR) spectrometer is described which incorporates a wide range magnetic field/microwave frequency lock as part of its magnetic field control subsystem. Instrument operation is accomplished by keyboard commands, with important experimental variables logged automatically for reference during subsequent data analysis. The spectrometer features both narrowband field modulation and direct‐detection time‐resolved ESR modes. The data acquisition system and field/frequency lock operate such that spectrum recordings consisting of multiple magnetic field sweeps are undistorted by long‐term klystron frequency drift. The spectrometer features low noise microwave preamplification, balanced mixer detection, automatic reference arm phase control, and a fast automatic frequency control system requiring no klystron frequency modulation. Natural abundance13C and33S studies of the terephthalic acid radical trianion and sulfite radical anion are presented as proof of spectrometer performance.

ISSN:0034-6748    

DOI:10.1063/1.1144745

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The article presents a modification to the spline deconvolution technique. The method was developed within the framework of electron paramagnetic resonance imaging and is particularly useful in cases of low signal‐to‐noise ratio (S/N) and when the deconvolution kernel is a large fraction (about 50%) of the studied function. The modified spline deconvolution method works directly in the signal space and does not require a low‐pass filter that causes loss of information and limits the resolution as is the case of Fourier deconvolution. The comparison was done with Fourier deconvolution and was based on three parameters that account for resolution, noise, and proportion stability. Experimental tests were done using two nitroxide‐free radicals of different linewidths (0.05 and 0.16 mT, respectively) at different gradient values (between 0.05 and 0.2 mT/m). Modified spline deconvolution gave consistently better results in all the three parameters, particularly at the lower gradient values. For this reason the method is useful ininvivoexperiments where the low S/N does not permit use of high gradient values.

ISSN:0034-6748    

DOI:10.1063/1.1144746

出版商:AIP    

年代:1994

数据来源: AIP