摘要:

For many years, thin‐window, single‐wire gas proportional counters were the only general‐purpose detectors available for nondispersive spectroscopy of low energy X‐rays. Their large area, low background, and coarse energy resolving capabilities, combined with their low cost, long lifetime, and ease of operation, mae them the workhorse instrument. During the last decade, solid state detectors and, more recently, gas scintillation proportional counters, have slowly replaced the standard gas proportional counter in many applications. Small are (0.2 cm2) Si(Li) detectors with 150 eV of FWHM noise have been used for fluorescence specctroscopy above 1 keV. However, their small area and cryogenic operation make these detectors less than ideal. Moreover, the nose in the associated electronics make these detectors useless below 0.4 keV. Gas sintillation proportional counters have now been developed to the point where they are the instrument of choice below 1 keV. Large are (≳100 cm2) counters with high sensitivity and low noise may be made relatively easily and inexpensively. Resolution sufficient to separate the nitrogen and oxygen K‐fluorescence lines have been achievd. Used with micron thin polypropylene windows, these counters have achieved 57% (FWHM) resolution at 149 eV sulfur L line. In addition, we have demonstrated that submillimeter imaging is possible with the gas scintillation proportional counter attached to a multiwire proportional counter. This paper will concentrate on a discussion of the principle of operation and design, and achieved levels of performance for the gas scintillation proportional counter. Where appropriate, their operation and performance will be compared to standard gas proportional counters and solid state detectors.

ISSN:0094-243X    

DOI:10.1063/1.33148

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The moleular and sputtered/evaporated multilayers and the acid phthalate crystals can be applied for relatively fast, high effiiency spectral analysis of constant and pulsed low energy x‐ray sources in the 100 to 2000 eV region. Limits of resolution are about 1 eV. Reviewed here are the basic methods for the theoretical and the experimental characterization of these analyzers as required for absolute x‐ray spectometry. The design and absolute calibration of spectrographs for pulsed low energy x‐ray source diagnostics are described.

ISSN:0094-243X    

DOI:10.1063/1.33149

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The utilization of reflection and transmission gratings as active elements for analyzing X‐rays in the wavelength region of 10‐250A˚ is discussed. Three approaches in a focussing reflection geometry are considered which all offer possibilities to enhance the experimental sensitivity or the resolution in a region of special interest. An experimental analysis of a standard grazing incidence instrument is presented. Transmission grating geometries are examined using results from planar transmission gratings with prefocussing mirrors.

ISSN:0094-243X    

DOI:10.1063/1.33151

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Both crystal despersion and diffraction grating instruments are routinely used for soft X‐ray dispersion in the fusion programme at the Culham Laboratory where the keV plasmas studied range from highly transient, high density ne≳1021cm−3, laser‐produced plasmas to relatively low density, ne≳ 1013cm tokamak plasmas. In this paper the soft X‐ray spetral features from these plasmas are discussed and the design parameters of appropriate instruments for X‐ray studies are considered.Useful spectral surveys of laser‐processed plasmas have been obtained using crystals bent convex in the de Broglie mode; higher aperture concave Johann configurations have been designed and constructed with multichannel read out for tokamak studies. Grazing incidence diffraction grating instruments have been operated in the photographic survey mode and as double channel monochromators. Operating experience with existing instruments is assessed. Examples of spectral information in the wavelength region ∼4 A˚ to ;∼400 A˚ are presented and their use in plasma diagnostic studies is discussed.

ISSN:0094-243X    

DOI:10.1063/1.33157

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

Quantitative diagnostis of fusion and astrophysial plasmas require knowledge of crystal spectrometric properties. To provide more reliable and verstile diagnostics of plasma conditions, increasingly accurate knowledge of crystal spectrometric properties is becoming necessary. We provide here a summary of the following accurately measured parameters for the crystals KAP, RbAP, TlAP, NH4AP, NaAP, ADP, and EDDT: 1) 2d∞‐the interplanar spacing of atoms 2) &Dgr;‐the angle correction or normal and anomalous dispersion that is required for application of the Bragg formula 3) &agr;‐the thermal expansion coefficient near room temperatures for commonly used planes 4) Rc‐the integrated coefficient of reflection Measured data on Rc are compared to theory with good agreement.

ISSN:0094-243X    

DOI:10.1063/1.33158

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The design possibilities and limitations of multilayer structures for soft x‐ray spetroscopy are summarized. Near grazing incidence structures can have a large integrated reflectivity and a large relative bandwidth close to one. The smallest possible bandwidth or highest possible resolution is obtained ner normal incidence, and is determined by the absorption index k of the most transparent material available; the maximum resolution in Nmax&bartil;1/2&pgr;k. Depending on the wavelength, values for Nmaxcan be between 10 and 104in the soft x‐ray region. The practical realization of a design requires good thickness control and sharp, smooth boundaries between the layers. Sufficient thickness control has been obtained byin situmonitoring of the x‐ray reflectivities. Within the uncertainties of the optical constant the measured performance of the best multilayer systems is in agreement with theory for multilayer periods larger than 30A˚. For smaller period lengths, the peak reflectivity is smaller than the theoretical values. The lower reflectivity can be explained by an effective roughness of the multilayer system in the order of 3A˚.

ISSN:0094-243X    

DOI:10.1063/1.33159

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

The opportunities offered by engineered synthetic multilayer dispersion elements for x‐rays have been recognized since the earliest days of x‐ray diffraction analysis. In this paper, application of sputter deposition tehnology to the synthesis of Layered Synthetic Microstructure (LSM’s) of sufficient quality or use as x‐ray dispersion elements is discussed. It will be shown that high efficiency, controllble bandwidth dispersion elements, with d spacings varying from 15 A˚ to 180 A˚, may be synthesized onto both mechanically stiff and flexible substrtes. Multilayer component materials include tungten, niobium, molybdenum, titanium, vanadium, and silicon layers separated by carbon layers.Experimental observations of peak reflectivity in first order, integrated reflectivity in first order, and diffraction performance at selected photon energies in the range, 100 to 15000 eV, will be reported and compared to theory. Emphasis is placed on results giving information concerning limiting structural characteristics of these LSM’s. It will be shown that the observed behavior is in accord with theory, both kinematic and dynamic regimes being clearly observed. In addition, the mosaic spread of these LSM’s is not detectable, indicatig that they are perfect structures. A consistent explanation of these experimental results indicates that roughness at the interfaces between constituent layers is the structural characteristic currently limiting diffracting behavior.

ISSN:0094-243X    

DOI:10.1063/1.33160

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

For the low energy x‐ray region of 100‐2000 eV, the complete atomic interaction, coherent scattering and photoelectric absorption can be desribed by a complex scattering amplitude which may be given through the atomic scattering factor, f1+if2. For this low photon energy region, it is shown by the relativistic quantum dispersion theory that the atomic scattering factors can be uniquely determined from simple relations involving only the atomic photoionization cross section dependence upon photon energy. We have compiled ‘‘state of the art’’ tables for the photoionization cross sections for 94 elements and for the photon energy region of 30−100,000 eV. With this compilation, we have established atomic scattering factor tables for the 100−2000 eV region. By a summing of the complex, atomic scattering amplitudes, a low energy x‐ray interaction can be determined. Even for atoms in the molecular or solid state the scattering cross sections remain atomic‐like except for photon energies very near the thresholds. Using practival examples, the methods of calculation, with the atomic scattering factors, are reviewed here for the followig: 1) x‐ray energy deposition within materials (energy response of x‐ray photocathodes); 2) transmission through a homogeneous medium: refraction; 3) transmission through a random collection of uniform spheres: low angle scattering in an inhomogeneous medium; 4) specular, Fresnel reflection (total and large angle reflection) at smooth boundry; and 5) Bragg reflection from a periodic, layered system‐(reflection by crystals and multilayers).

ISSN:0094-243X    

DOI:10.1063/1.33161

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

An overview of the calculation o photoionization cross sections for H&ngr;<1 keV is presented with partiular emphasis on providing a guide for evaluating the accuracy of theoretical work. An attempt is made to focus upon the various approximations made in each level of calculation and point out in which ranges they should be good. Central‐field, Hartree‐Fock, and more sophisticated methods are reviewed, particularly as they apply to free atoms and ions. In addition, the striking similarity of such calculated cross sections to core level photoemission in solids is pointed out.

ISSN:0094-243X    

DOI:10.1063/1.33162

出版商:AIP    

年代:1981

数据来源: AIP

摘要:

A review of grazing‐incidence optical design fundamentals is presented with special emphasis on mirror material and surface roughness considerations. Angle‐resolved scattering results on polished and diamond‐turned soft x‐ray mirrors are reviewed, along with the elements of optical scattering theory applied to soft x‐rays. Reflective filtering of higher‐order radiation in monochromator output beams is presented, comparing the transmission and rejection characteristics of one‐, two‐, and three‐reflection filters.

ISSN:0094-243X    

DOI:10.1063/1.33163

出版商:AIP    

年代:1981

数据来源: AIP