摘要:

We present a simple method for complete determination of the x‐ray polarization state, using just one Bragg reflection from a single‐crystal analyzer. For the linear polarization componentsP1andP2, we show that the usual method of using a 90° Bragg reflection can be extended to using any Bragg reflection with 2&thgr;≠90°. For circular componentP3, we use the intensity modulation profile in an azimuthal rotation caused by the phase‐sensitive interference around a multiple‐beam Bragg reflection. The combination of the two measurements allows a straightforward complete determination of x‐ray polarization, including an unpolarized component, in a broad applicable energy range.

ISSN:0034-6748    

DOI:10.1063/1.1144266

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have developed a Macintosh computer program to analyze Debye–Scherrer x‐ray powder diffraction films digitized with a conventional scanner. The program uses a fast derivatives‐free procedure to fit distorted ellipses corresponding to the diffraction rings on the film. These ellipses are collapsed into a one‐dimensional plot of intensity versus scattering angle, from which one can extract information about the diffraction pattern that would have been lost in visual reading. Moreover, uncertainties are decreased by a factor of ∼30 over visual reading, and the analysis of diffraction films is reduced to a matter of minutes.

ISSN:0034-6748    

DOI:10.1063/1.1144267

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

Microminiaturization of the diamond anvil tip is necessary in order to obtain multimegabar pressures. Because of this and the steep pressure gradients present tiny x‐ray beams are required. This paper describes the production and metrology of 5 &mgr;m x‐ray apertures for x‐ray diffraction studies to 100 keV in the diamond anvil cell. It is expected that this design will serve as the basis for 2 &mgr;m apertures.

ISSN:0034-6748    

DOI:10.1063/1.1144268

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

The diffraction and optical properties of several crystal concentrator configurations which could be adopted in hard x‐ray astrophysical observations are discussed and compared in terms of effective area, focusing characteristics, and overall dimensions. First, a concentrator consisting of a set of circular rings covered with asymmetric mosaic crystals in Laue geometry is considered; focusing is achieved by an appropriate choice of the geometrical parameters and the asymmetry angles. Specific effective areas larger than 600 cm2can be obtained in the energy range 120–190 keV by using Si (422) Bragg reflections in a device with a diameter of 2.5 m and a focal length of 13.5 m. Afterwards, a spherical‐zone crystal concentrator is analyzed where asymmetric Laue geometry leads to focusing. With a focal length of 8 m and Si (422) reflections, the mean effective area in the energy range 100–300 keV is about 6500 times larger than the focal spot while the separation power of the concentrator is of the order of 10 arcsec. Finally, a concentrator consisting of several coaxial focusing paraboloids is analyzed. The surfaces of the paraboloids are covered by mosaic crystal tiles with lattice planes disposed normally to the meridians. By using Ge crystals with a mosaic width of ≊350 &mgr;rad and assuming a focal lengthf=10 m with a total aperture 2&agr;=16 deg, it is possible to obtain effective areas larger than 1000 cm2for energies smaller than about 150 keV. On the other hand, the ratio between the mean effective area and the size of the focal spot in the energy range 200–500 keV is higher than 10 000.

ISSN:0034-6748    

DOI:10.1063/1.1144269

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A modified Rice University‐type compact Mott spin polarimeter operating at 20 kV is adapted to a large commerical hemispherical electron energy analyzer. Normal energy analyzer functions are preserved via a retractable channeltron in the polarimeter acceleration column. In the spin‐detection mode, the polarimeter permits analysis of two orthogonal transverse spin‐polarization components. Electron trajectory analysis is used to optimize polarimeter lens column voltages in both normal and spin‐detection modes. Performance levels are established by experiments and significantly improved spin‐detection efficiency is shown to be accessible by changes in the polarimeter collection solid angle.

ISSN:0034-6748    

DOI:10.1063/1.1144270

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We have built a simple and high performance inverse photoemission spectrometer using a BaF2window and a Cu–BeO electron multiplier with KBr as the photocathode for low‐ and high‐pass filters, respectively. It is found that using the BaF2low‐pass filter improves the resolution by 0.2 eV to compare with SrF2. The intensity was reduced to a quarter of that with SrF2, although it is enough to obtain good inverse photoemission spectra.

ISSN:0034-6748    

DOI:10.1063/1.1144271

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A technique for quantitative analysis of gas mixtures in a laser mass spectrometer is presented. It is based on the addition of two calibration gases with different orders of multiphoton ionization process to the sample gas. The ratio of the signals of these two internal standards serves as a sensor for the laser intensity within the ionization volume. Thus strongly fluctuating signals due to higher‐order multiphoton ionization can be normalized for every single laser shot. In addition, for such a relative measurement, effects of long‐term drifts of the apparatus are eliminated. Concentrations varying from a few ppm to several percent could be determined with an accuracy better than 10% at every single laser shot. Therefore this technique allows high time resolution.

ISSN:0034-6748    

DOI:10.1063/1.1144272

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A high‐resolution laser spectroscopy system for refractory elements with an argon‐ion‐ sputtering atomic beam source was constructed, and it has been demonstrated that the sputtering method is extremely useful as an atomic beam source for high‐resolution laser spectroscopy to measure hyperfine structures and isotope shifts for refractory elements, such as Hf, Ta, and W. This source produced intense neutral atomic beams of more than 1010atoms/s for these elements, and the yield was easily controlled by adjusting the argon‐ion current and the acceleration voltage. Resonance linewidths were 32, 66, and 48 MHz for Hf, Ta, and W, respectively, which are sufficient to measure the hyperfine structures and the isotope shifts in optical transitions. With this system, the signal‐to‐noise ratio reached more than 106. In addition, the temperature of the sputtered atoms found was rather low compared to the kinetic energy given to the atoms.

ISSN:0034-6748    

DOI:10.1063/1.1144457

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

A mathematical model for evaluating the molecular intensity produced by a solenoid‐actuated pulsed beam source is described. The particular source studied here is used to introduce reactant gas pulses at various user‐specified intervals into a fixed‐bed microreactor system for transient catalysis studies where quantification of the inlet pulse intensity is required for data analysis. The model equations which describe the beam source performance utilize relationships from one‐dimensional isentropic gas expansion, gas effusion through a small hole, and macroscopic mass balances around the valve orifice from which a closed‐form algebraic expression for the pulse intensity is obtained. The parameters in this expression represent observables which include the ideal gas specific heat capacity ratio, the stagnation properties of the gas in the supply chamber of the beam source, and the beam valve driver settings. Comparisons between experimental and predicted values for the pulse intensities, where the latter are of the order 1017molecules per pulse, show excellent agreement.

ISSN:0034-6748    

DOI:10.1063/1.1144273

出版商:AIP    

年代:1993

数据来源: AIP

摘要:

We present a new technique for selective, highly sensitive, absolute detection of different multiply charged ion species with equal charge‐to‐mass ratios in mixed multicharged ion beams. This is achieved by exploiting the statistics of potential electron emission as induced by the ion beams on a clean metal surface. The applicability of the method is illustrated by way of different practical examples.

ISSN:0034-6748    

DOI:10.1063/1.1144274

出版商:AIP    

年代:1993

数据来源: AIP