(106) Stein, R. A., Slawson, V., Zbid., 35, 1008 11963). (107) Stephenson, W. H., Anal. Chim. Acta 28, 597 (1963). (108) Svehla, G., Pall, A., Erdey, L., Talanta 10, 719 (1963). (109) Thomuson. H. W.. “Advances in Spectroscdpy,” Vol. 11, pp. 429-472, Interscience, New York, 1961. (110) Trudell, L., Boltz, D. F., ANAL. CHEM.35, 2122 (1963). (111) Tweet, A. G., Rev. Sci. Instr. 34, 1412 (1963). (112) Ulrich, W. F., “Developments in Applied Spectroscopy,” Ferraro, J. R., Ziomek, J. S eds., pp. 130-141, Plenum Press, kew York, 1963. ( 13) Ungnade, H. E., “Organic Electronic Spectral Data,” Vol. 11, 1953-5, Interscience, Kew York, 1960. ( 14) Vandenbelt, J. M., J . Opt. SOC. Am. 52, 284 (1962). ~
(115) Vandenbelt. J. M.. Avvl. .. Svectros. copy 17, 120 (1963). (116) Vandenbelt, J. M., ANAL.CHEM 35, No. 7, 69A (1963). (117) Van Es, W. L., Wisse, J. H., Anal. Biochem. 6, 115 (1963). (118) Wagener, G. N., Grand, C. G., Rev. Sa’.Instr. 34, 540 (1963). (119) Walker, P. ?VI. B., Leonard, J., Gibb, D., Chamberlain, P. J., J. Sci. Instr. 40, 166 (1963). (120) Weaver, W. J., Reschke, R. F., J . Pharmaceu. Sci. 52, 363 (1963). (121) Weber, C. W., Howard, 0. H., ANAL.CHEM.35, 1002 (1963). (122) Weber, W. J., Morris, J. C., Stumm, W., Zbid., 34, 1844 (1962). (123) Wexler, A. S., Ztrid., 35, 1936 (1963). (124) White, J. C., “Progress in Nuclear Energy,” Series IX, “Analytical Chemistry,” Vol. 2, Crouthamel, E. E., ed., I
~
Chap. 6, pp. 257-312, Pergamon Press, n’ew York. 1961. (125) Williams, D. M., Photochem. and Photobiology 1, 273 (1962). (126) Winefordner, J. D., St. John, P. A., ANAL.CHEM.35, 2211 (1963). (127) Wolken, J. J., Strother, G. K., App2. Optics 2, 899 (1963). (128) Wood, W. A., Gilford, S. R.,>Anal. Biochem. 2, 589 (1961). 1129) Wood. W. A.. Gilford. S. R.. Ibzd., 2, 601 (1961): (130) Yakovlev, S. A,, Optics and Svectroscopy 14, No. 5, 378 (1963). (131) Yankeelov, J. A., Anal. Biochem. 6 , 287 (1963). (132) Zimmerman, N., ANAL.CHEM.34, 710 (1962). (133) Zscheile, F. P., Jr., Murray, H. C., Baker, G. A., Peddicord, R. G., Zbid., 34, 1776 (1962). ~
X-Ray Absorption and Emission William 1. Campbell and James D. Brown, Bureau o f Mines, College Park Metallurgy Research Center, Ihterior, College Park, Md.
F
over a decade Liebhafsky, more recently in collaboration with Winslow and Pfeiffer, has prepared fundamental reviews on x-ray absorption and emission (676-278). These reviews have provided excellent milestones to gauge the rapid progress of x-ray analysis. The present review uses their format of a critical review of fundamental developments and tabular summaries of applications of x-ray spectrography and electron probe microanalysis. Progress in x-ray analysis over a similar period was summarized a t an ASTM Symposium on X-Ray Spectrography and Electron Probe Microanalysis held in June 1963 (426). The most significant advances have been to extend the range of application to include elements of atomic numbers 11 to 92, to lower the limits of detection from parts per thousand to parts per million, to increase the usage of automation including sample presentation and data readout, and to provide reliable commercially available electron probe microanalyzers. All of these advances are discussed in this review, which covers the period from December 1961 to Kovember 1963. I n this review, the authors have emphasized the fundamental advances achieved in x-ray spectrography and electron probe microanalysis. h s a result, approximately 15y0of the papers listed were published prior to 1961 but were not included in the earlier reviews. The tremendous volume of x-ray literature falls into two principal categories: fundamental papers on excitation, dispersion, and general analytical OR
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theory, and applications for specific elements in specific classes of samples. These papers on specific applications account for the majority of the current literature. Unfortunately, many of them are repetitious. One should no longer be surprised to find that general analytical procedures can be applied to a number of elements in various types of samples. In most instances, the description of the chemical and physical treatment of the sample is the author’s only worthwhile contribution to x-ray analysis. Recent textbooks, symposia, and conference proceedings are listed in Table I. These textbooks are recommended additions to the personal library of all x-ray analysts. The “Encyclopedia of X-Rays and Gamma-Rays” (101) is an indexed compilation of papers rather than a true encyclopedia. As expected from such multiple authorship, the quality of papers ranges from excellent to mediocre. The publication of conference proceedings is strongly encouraged. However, in some instances only a small fraction of the papers &re related to x-ray analysis. Also, there is an increasing tendency to include in these proceedings papers that have already been published in technical journals or as government reports. This duplication of publications is of questionable value. The training of personnel is mainly the function of individual laboratories. Most univer3ities devote little time to a discussion of even rudimentary aspects of x-ray spectrography. The best introduction to this subject is provided by the instrument manufacturers. As part
U. S .
Department o f the
of their sales promotion, these manufacturers conduct excellent training coursein x-ray theory and techniques. Works shops on x-ray analysis held as part of general conferences on spectroscopy also are valuable training aids. ABSORPTION
There have been no significant fundamental advances in absorption analysis during the past two years. X-ray instrumentation developments are discussed under emission. -4discussion of x-ray mass absorption coefficients is included in the section on electron probe microanalysis. Previous reviews (276art?), recent general papers (13.9, 1B.5, 198-201, 207, 473) , and the following analytical applications adequately summarize x-ray absorption: sulfur in oil (163, 154, 185, 373), chlorine in organic compounds (192), cobalt in hydrocarbons (373) and in aqueous solutions (198), plutonium in metal castings (267), T B P in kerosine-base solvents (146), composition of solders (339), lead and barium in glass (339), and evaluation of column-chromatographic separation of iodine- and bromine-containing compounds (340). Instrument development includes single-crystal (653) and double-crystal spectrometers ( 2 @ ) , the latter having a multisample changer. Absorption methods for control analyses, using radioactive isotopes as the x-ray source, will continue to increase in popularity because of their low cost and high reliability. However, x-ray absorption is not as satisfactory as emission for use as a general analytical tool. Emission has the advantages of
spectral line specificity, sensitivity of one or two orders of magnitude greater than absorption, and app1i:ability to a wide range of elements without changing any instrumental parrtmeter other than Bragg angle. These advantages account for the much more rapid growth of emission analyses. X-RAY SCAlTERING
Originally, scattered x-rays were considered to be principa ly undesired radiation; thus the analyst strived to reduce scattering to a minimum. illthough low backgrounds (scattered x-rays are the principal contributors) are required for trace element determinations (89), a number of new applications have recently developed f x which intense scattering is essential. There are two types of x-ray scattering-Rayleigh or unmodified and Compton or modified. T h e wavelength shift in Compton scattering is equal to 0.0243 (1 - cos #) A, where # is the angle between the incident and scattered x-ray beam. The ratio of Compton to Rayleigh scattering is a function of the “average” atomic number of the scatterer. T h e relationship was exploited by Dwiggins (142) in developing a method for determining the carbonhydrogen ratio in hydrocarbons. This method is adaptable to other classes of organic compounds, provided corrections are applied for Dther elements of low atomic number such as oxygen and nitrogen. Scattered primary x-rays are also used for monitoring x-ray tube voltage and current. T h e monitor may be incorporated into a feedback circuit for automatically adjLsting voltage and current or set to accumulate a preselected number of counts. The principal anakitical application of scattering is to co-rect for interelement and solvent effects (110, 236, 315). Since both scattering, and absorption are functions of composition, differences in absorption characteristics of standard and unknown are minimized by ratioing the emitted to scattered intensities. However, this method, although used very successfully by numerous investigators, is still empiricttl. Fundamental studies on x-ray sca ,tering would be welcome additions to the field of x-ray analysis. Both Rayleigh scattering and backscattered electrons are being used for determining high 2 atoms in low 2 media (302, 303, 3 2 ‘ , 322). McCue and coworkers (302, 303) employed Rayleigh scattering for determining uranium in alloys of low atomic number. They concluded t h a ; high precision analyses can be acccmplished in less time by scattering tecLhniques than by conventional wet chcmmistry or x-ray absorptiometry. Applications of back-
Table
I.
Summary of Recent Books
Author
Title
Birks, L. S. Birks, L. S. Blokhin, M. A. Bull. Acad. Sci. USSR Clark, G. L., ed. Kaeble, E. F., ed. Liebhafsky, H. A,, Pfeiffer. H. G.. Winslow, E. H., Zemany, P. D. Mueller, W. M., ed. Mueller, W. M., Fay, M., eds. Sagel, K.
Electron Probe Microanalysis X-Ray Spectrochemical Analysis The Physics of X-Rays Transactions, Fifth Conference on X-Ray Spectroscopy, Kharkov, 1961 Encyclopedia of X-Rays and Gamma Rays Handbook of X-Rays X-Ray Absorption and Emission in Analytical Chemistry
Smith, R. W., ed. Vainshtein, E. E.
Advances in X-Ray Analysis, Vol. 5 Advances in X-Ray Analysis, Vol. 6 Tables for X-Ray Emission and Absorption (in German) ASTM Symposium on X-Ray and Electron Probe Analysis, STP 349 Methods of Qualitative X-Ray Spectral Analysis (in Russian) SECTIONS ON X-RAYS
Ashby, W. D., ed. ASTM
Developments in Applied Spectroscopy, Vol. 1 Symposium on Advances in Electron Metallography and Electron Probe Microanalysis, STP 317 Spectroscopy in the Metallurgical Industry Developments in Applied Spectroscopy, Vol. 2 Proceedings, Xth Colloquium Spectroscopicum Internationale
Bovey, L., ed. Ferraro, J. R., ed. Lippincott, E. R., Margoshes, M., eds. Pattee, H. H., X-Ray Optics and X-Ray Microanalysis Cosslett, V. E., Engstrom, A., eds. Von Koch, H., Instruments and Measurements, Vol. 1 L’ungberg, G., e&.
scattered electrons are discussed in the section on electron probe microanalysis. CHEMICAL EFFECTS ON X-RAY SPECTRA
Much of our information regarding the inner electron shells of the atom was derived by x-ray emission and absorption techniques. These same methods are still being used to obtain additional knowledge on the electronic structure of crystals, bond character in molecules, and valence electron states (328, 333, 4lV9, 475, 480-482). These studies are predominantly the domain of the physicist, but there are areas of interest to the analytical chemist, particularly in the determination of coordination number and valence. The review papers by Faessler (158) and Jossem (232) are recommended as a n introduction to these applications. “The Physics of X-Rays” by Blokhin (64),a n outstanding work on theoretical and experimental x-ray physics, containing a section on fine x-ray structure, has recently been translated into English by the U. S. Joint Publications Research Service. Another valuable addition to the literature is an annotated bibliography on soft x-ray spectroscopy by Yakowitz and Cuthill (616). This bibliography lists approximately 550
references, covering the period 1950 to 1960, with emphasis on the application of soft x-ray spectroscopy to studies of valence band electronic states in metals and alloys. The transactions of the USSR Fifth Conference on X-Ray Spectroscopy related in most part to fine structure x-ray analysis are now available in English (83). Wavelength shifts as a function of chemical bonding and valence will be an increasing problem in fluorescent x-ray spectrography (274). r n t i l the late 1950’s, fluorescent x-ray spectrography was limited to the wavelength range of 0.5 to 3.0 A. Applications now extend into the 5- to 10-A. region, and are expected to reach 50 A . within a few years. Since analytical applications of long wavelength x-rays are rapidly increasing, the problem of wavelength dependence on chemical state will merit further attention in future reviews. INSTRUMENTATION
General. T h e Union Internationale de Cristallographie has issued a second edition of the “Index of Crystallographic Supplies” (378), which lists manufacturers and suppliers of x-ray generating and measuring equipment, goniometers, and crystals. -4 compilaVOL. 36, NO. 5, APRIL 1964
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tion of this type, but with emphasis on x-ray absorption and emission instrumentation, would be very helpful to the x-ray analyst. The two current trends in instrumentation are increased automation and extension into the soft x-ray region. These developments are a result of industry’s needs for rapid low-cost analyses of a wide range of elements. There are two types of automatic x-ray spectrographs : the sequential singlechannel spectrometer (Autrometer, Solartron); and the fixed multichannel spectrometers (Quantometer). The sequential spectrograph has the advantage of flexibility and lower cost, whereas the multichannel units accumulate d a t a more rapidly and the response for each element can be optimized. Increased automation includes automatic sample changers and digital readouts combined with computer facilities for direct conversion of intensity to concentration. For example, General Electric has developed a n unmanned program-controlled spectrometer with a n automatic sample changer and loader. Siemens recently released a description of its seven-channel unit, in which concentrations are computed and printed out with the optional d a t a processor. Soft x-ray spectrometers have been described for the wavelength ranges 10 to 30 A. (192, 217, 218, 386, 393), 30 to 200 A. (305,307), and wavelengths greater than 200 A. (10). Jarrell-Ash is developing a soft x-ray spectrograph with a 5 kv.-200-ma. power supply for emission, absorption, and scattering studies. Philips Electronics has adapted the Henke tube (208-210), a very efficient source of excitation for soft x-rays, for use with its vacuum spectrometer. Picker X-ray is now marketing a combined spectrometer-diffractometer assembly of two permanently mounted x-ray tubes. The change-over time from diffractometry to spectrography, or the reverse, is only a few minutes. Various instrumental modifications to aid the analyst have been described (43, 187, 230, 260, 376, 454, 476). Other developments in x-ray spectrometers include curved crystal optics with a constant take-off angle (32, 117, 382), curved crystal optics with a variable sample position (3.37), and the use of roller bearings in place of gears (389). Eastman (145) reported on maintenance problems for a n x-ray spectrograph over a 3-year period. A table of common symptoms and remedies was incaluded in his paper. Manufacturers could perform a valuable service by providing facilities to collect and distribute this kind of information. A study of stray x-rays around a commercially available x-ray spectrograph conducted by Gomberg et al. (182) showed that the radiation level at the
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ANALYTICAL CHEMISTRY
operator’s position meets safety requirements. However, radiation hazards must be minimized because of the increased use of nonprofessional employees. I n particular, x-ray power supplies should be automatically inoperative when the x-ray tube housing is removed for cleaning or for replacing the tube. Excitation. I n t h e mid-1940’s x-ray tubes with a n intense o u t p u t of 0.5 to 3.0 A. radiation became commercially available. These x-ray tubes, used in conjunction with the gas-filled ionization detectors also developed a t that time, made possible the phenomenal growth of fluorescent x-ray spectrography from 1950 to 1960. Since then, the most significant improvement in manufactured x-ray tubes has been the reduction of the beryllium window thickness from 1.0 to 0.25 mm. This thinner window when used with a chromium target has improved the sensitivity for period 3 elements by a factor of 5 to 10 (27, 92). Sensitivity for these elements can also be improved by the use of beryllium with a low impurity content. Zhukovskaya and Ioffe (518) found that ~ / values p for Machlett’s beryllium was 2 to 21/2 times greater than Soviet beryllium in the wavelength range 0.7 to 2.3 .A. There are two contrasting philosophies for achieving increased sensitivity in the soft x-ray region. Zemany (616, 51 7 ) presents some rather convincing arguments for a continual modification of conventional instrumentation. He emphasizes that fluorescent x-ray spectrography has been extended from titanium, atomic number 22, down to sodium, atomic number 11 (27, 7’2, 463), without any drastic change in the instrumentation. Furthermore, he states that analytical procedures devised for elements of medium and high atomic number are applicable to the elements of low atomic number. Other researchers advocate drastic changes in the excitation parameters by use of demountable, windowless (or ultrathin window) selectable target tubes which can be used for either primary or secondary excitation (36, 36, 132, 166, 208, 209, 218, 219, 431, 432, 459, 509). Marked improvement in the excitation parameters will not only increase the sensitivity for period 3 elements but more importantly will extend the range of x-ray spectrography to period 2 elements such as carbon, nitrogen, and oxygen. The design of demountable x-ray tubes varies from a simple modification of commercially available sealed tubes (36, 431, 509) to completely new concepts (35, 132, 166, 208, 209, 217, 218, 459). The Henke-type tube (208, 20@ has been adapted as the excitation source for the Philips inverted vacuum spectrograph, whereas the demountable x-ray tube designed by Thatcher and
Campbell (459) is an integral part of a high vacuum spectrometer. Their demountable tube has provisions for primary, secondary, or both types of excitation simultaneously, and samples can be inserted without breaking the main vacuum. Fox (166) described a very simple compact x-ray spectrograph which uses a low voltage primary source of excitation. Studies using secondary excitation sholv that the low energy portion of the continuum from a high atomic number target can efficiently excite soft x-ray spectra (459). I n addition, these studies show that characteristic K , L, or M spectral lines become the dominant excitation factor when their energy just exceeds the critical absorption energy of the secondary emitter. Of the six targets investigated, the most efficient target element for the excitation of aluminum K a is silicon, followed by tungsten, molybdenum, silver, chromium, and copper. The efficiency of a conventional thick window tungsten x-ray tube for exciting aluminum K a is about 0.7 count per second per watt (c/s/w) as compared to 70 c/s/w with the windowless demountable x-ray tube having a tungsten target. There is considerable disagreement as to the optimum excitation voltage, particularly in the soft x-ray region. This voltage is dependent on the primary and secondary emitter, window thickness, x-ray tube take-off angle, and type of excitation (primary or secondary). Distribution of wavelengths in the long wavelength continuum has not been quantitatively established. For example, Peterson (3.49) reported the distribution varied as l / X a , where a ranges from 1.8 for low 2 elements to 3.0 for high 2 elements. The intensity of the continuum is also a function of take-off angle, voltage, and window material (84, 144). Using a windowless x-ray tube, Thatcher and Campbell (459) found the optimum voltage for excitation of aluminum was 15 to 20 kv. Spielberg (432) concluded that the optimum voltage for exciting the aluminum K series is 20 and 35 kv. for 50- and 1050-micron-thick beryllium windows, respectively. Henke (220) used copper L a lines a t 13.3 A. to excite the K a lines of fluorine through boron; the copper anode was operated a t 6 kv. and 330 ma. .Use, he observed that carbon K a is a very efficient source of excitation for boron. Henke used 1-micron-thick aluminum foil as the x-ray tube window. The port of his x-ray tube is sealed by a gate until the spectrometer is evacuated, then the aluminum is slid into position. In this manner, the thin window does not support any pressure but merely serves to isolate the high vacuum in the x-ray tube from the mechanical pump pressure of the spectrometer.
Science, like women’s fashions, seems to run in cycles. Cp until the mid1940’s primary excitation was used almost exclusively. However, primary x-ray spectrography was not suitable as a general analytical method because of problems in instiwmentation and sample preparation. Since then, most of these earlier limitations on the use of primary excitation h a f e been removed. The use of electron excitation is now being re-evaluated in light of the improved vacuum systems and x-ray generating circuits (36, 166, 459, 509). Wyckoff and Davidson (509) observed a 100-fold increase in A1 K a intensity simply by removing the x-ray tube window. They attributed most of this increase to primary excitation by backscattered electrons. The Bureau of Mines’ demountable x-ray tube was converted into a heterogeneous x-ray source (electrons plus photons) by removing the cathode skirt and allowing backscattered electrons to reach the sample (469). Aluminum K a and magnesium K a intensities of 1000 and 500 c/s/w, respectively, were obtained. The rate of excitation of aluminum K a by the backscattere(j electrons was estimated to be 3000 :/s/pa. of sample current. Since backsvattered electrons give such a large increase in intensity, the next step was to irradiate the sample directly with electrons from the filament. Fox (166) measured an aluminum K a intensity of 7100 c/s/w and a peak-to-background ratio of 1000 to 1 using a 4-kv. source cif electrons. Unpublished studies by the reviewers on electron probe microanalysis indicate t h a t excellent peak-to-background ratios can be achieved with electron excitation by a judicious use of low excitation voltage, pulse-height discrimination, and, in particular, high resolution reflection-type curved crys:al optics. Also, the detailed intensity-to-concentration relationships derived for micro electron excitation are equally suited for macro electron excitation of large homogeneous samples. I n the medium and short wavelength regions there has beer little significant progress. Although 100-kv. power supplies have been available for several years, they were generally restricted to operation at 50 kv. because of excessive x-ray tube failures. Salmon (391A) found that the x-ray t J b e voltage readings were approximatsly 15 kv. lower than the correct values; therefore operation in excess of the specified voltage is the probable reason for these failures. Recommendations f x improving the stability of x-ray generators were given by Torkildsen (467) rind optimization of excitation parameters by Kopineck (257). Schreiber (39ti) compared the efficiency of W, Mo, and Cr targets using constant potent a1 and full wave rectification. Molybdenum and tung-
sten targets were compared by M.iiller (323). The spectral purity of the x-ray tube is very important in the determination of trace and minor constituents. Ladell and Parrish (163)described methods for qualitative and quantitative analyses of the spectral purity of diffraction tubes; their procedures are equally applicable to spectrographic tubes. One way to reduce impurity lines in the primary spectrum is to use selective filters (391). The choice of filter and filter thickness is determined by the degree of attenuation of undesired radiation, the residual intensity, and the excitation of the filter element. Gomberg et al. (183) summarized various methods for preparing thin x-ray filters. One recommended technique is to use Mallinckrodt photopurified rubber solution, type 7249, to which the elements are added as finely divided solids. Applications of radioactive isotopes continue to increase wherever nondispersive techniques are feasible (131,156, 455). Kuehn (261) presented an excellent summary on application of isotopes to fluorescent x-ray spectrography. Beta sources for x-ray production are described by Enomoto (152, 156, 157). Kastner, Parks, and Dickerson (8%) designed a fine focal spot self-powered x-ray generator using beta-rays as the power supply and field emission for x-ray generation. h portable x-ray spectrometer with a Tmli0 radioactive source was constructed by Xarbutt (327). A two-channel nondispersive spectrograph was evaluated by Seibel and Le Traon (404), in which calcium and iron in drill cores were excited by the bremsstrahlung from a radioactive tritium source encased in titanium. The detector-source head moved along the drill core a t a rate of 3 meters per hour. Dispersion. One of t h e more fruit-
Table II.
Compound Half K salt cyclohexane 1,2-diacetic acid Dioctadecyl adipate Dioctadecyl terephthalate
Crystals Showing Exceptional Promise (385)
Formula -CH2COOH
Melting P;int, C.
Minimum 2dSpacing, A.
...
31 2
Very strong
64
90
Extremely Excellent strong
85
84
Strong
54
Extremely Good strong
-CHzCOOK CH3(CHz)1700C, CH3(CHz)1,OOC/
(CH2)4
-COO(CHz)iiCH, ()-COO(
Tetradecanoamide
ful areas of research has been t h e development of new analyzing crystals for use in t h e long wavelength region, Crystals to be used as three-dimensional diffraction gratings for soft x-rays should have the following characteristics (163): stability to the atmosphere, low vapor pressure, melting point greater than 5OoC., 2d spacing of 15 to 50 A , good reflectivity and mechanical strength, cleavage parallel to the plane of interest, and suitable crystal growth characteristics. Isomet (60, 385) found four classes of crystals that warrant further evaluation : compounds analogous to KAP, amides of long-chain aliphatic acids, half K-salts of dibasic acids, and diesters of dibasic acids. Properties of the four most promising crystals are listed in Table 11. Baun and Fischer (33) investigated the UOZ, Zn, and TI salts of aliphatic acids. They concluded any desired spacing can be obtained with the correct combination of aliphatic acid and metal; however, large single crystals are difficult to grow. One method they considered is to use solution techniques and induce thin platelike crystals to grow along the (001) direction on a suitable substrate which can be bent if desired. ;isecond possibility is to use the Blodgett-Langmuir method of building up a crystal one layer a t a time. These “layered crystals” have greater perfection, based on rocking curves, than some single crystals of comparable spacings. The alkali metal salts of phthalic acid also have been investigated intensively (33, 60, 163, 385). Phthalic acid and its lithium salt form monoclinic crystals; all of its other salts-Na, K, Rb, Cs; T1, and SH4-are orthorhombic. An outstanding property of these crystals is the excellent cleavage along the (001) face. The principal 2d spacing of the
Reflectivity
Crystallinity Good
Excellent
CH2),7CH,
CHa(CH2)12COSH,
103.4
VOL. 36, NO. 5 , APRIL 1964
315 R
Table 111.
Applications to a Specific Class of Samples Alloys, general (466) Aluminum (146, 279)
Botanv (293) Ceramics (284) Clinical chemistry ( 1 1 , 177, 178, 179, 330) Coal (461) Copper-base alloys (160, 191) Ferrous allovs (256. 666) Geochemistiy (184,’371,’ 579, 407) Glass (130,269, 270) Iron and steel (73, 197, 2.21, 686, 406) Lime and cement (394,477) Nickel-base alloys (48, 233) Organic chemistry (346) Oxide catalysts (474) Paint (675) Petroleum (86, 143, 2.?, 384, 499) Pharmaceutical chemistry (410) Radioactive materials (91, 96) Rocket propellants (668) Soils (483) Uranium-base alloys (238) Wood and paper (608)
commercially available K A P (K acid phthalate) is 26.626 A. a t 27°C. (163). Sawyer and coworkers reported a 2d value of 26.60 f 0.01 X., but did not state the temperature (393). One of the more promising developments is a new commercially available crystal, pentaerythritol tetraacetate (PET). This crystal has twice the reflectivity of E D d T with approximately the same line width. Gypsum plates (26) have a higher reflectivity for M g K a than K A P ; however, there is some question as to the stability of gypsum, CaS04.2H20, in a vacuum. The reviewers found that the surface of gypsum crystals deteriorated rapidly in a high vacuum, 2 X 10-6 mm. of Hg. In a mechanical pump vacuum this deterioration required several days. Other studies on crystals include beryl and K A P (393)) bent single crystals of quartz and germanium (67, @ l ) , and rules for .electing and aligning monochromators (97,98,108,395). Methods for preparing bent LiF and mica crystals are given by Riggs (375). Priestley (366) improved the reflectivity of LiF by factors of 2.5 and 7.0 a t 2.0 and 0.7 A., respectively, by application of ultrasonics plus abrasion of the surface layers. A detailed procedure for preparing oriented soap films is described by Beard and Furnas (35). Kirn and Curlis (247) employed 70 to 240 layers of oriented behanate and hgnocerate films as diffraction gratings for 25- to loo-.\. radiation. Other applications for oriented soap films are described by Henke (210) and by Dowell and I3erwaldt (132).
Conditions under which extraneous diffraction lines occur in x-ray spectrochemical analysis nere wmmarized by Spielberg and Ladell (433). They point out that a crystal monochromator will not only “reflect” incident radiation 316 R
ANALYTICAL CHEMISTRY
from planes parallel to the principal planes ( h k I ) but in addition, there may be other reflections due to other sets of planes slightly tilted with respect to the principal plane. Quartz and topaz are used as specific examples in their paper. Several years ago, the reviewers had the opportunity to compare eight topaz crystals. Only one was found to be suitable for use as a monochromator when a single 0.005by 4-inch collimator was employed. However, the use of tRo fine collimators eliminated these extraneous reflections. Use of the Laue diffraction technique as a multichannel x-ray spectrometer was proposed by Ladell and Spielberg (264). This technique requires a single analyzing crystal to be used with a number of detectors for simultaneous registration of various spectral lines. Advantages of the Laue method are: The reflectivities of the various planes are internally calibrated, the source geometry is optimized, and superfluous lines are eliminated. R y t z e s (511) prepared a dual monochromator which has sections of two different crystals; each section is independently aligned. Two properly oriented detectors allow the simultaneous measurement of two spectral lines. Carson (91) proposed a similar device for the simultaneous measurement of gold and silver spectral lines from plated samples. Still another approach is to use a single crystal for both transmission- and reflection-type diffraction. Selection rules for this type of dualpurpose crystal were derived by Suoninen (449). Various instrumental parameters for optimizing line intensities and line-tobackground ratios are summarized by Spielberg, Parrish, and Lowitzsch (434). Detection. Reliable detectors with low dcad time and high q u a n t u m counting efficiency in t h e 0.3- to 5.0-.\. rrgion arc commercially available. Operation paramcters of these detectors are reviewed in recent papers (24, 180, 231, 329, 341, 403, 430, 498). The old problem of coincidence losses is the subject of additional discussion ( 4 1 , 411, 416, 427) because of the very high counting rates achieved with advanced instrumentation. I3ernstein and Canon (41) show that coincidence losses are directly related to counting rates and detertor dead time and, more complexly, to excitation voltage of the element, x-ray tube voltage, and type of x-ray power supply. At counting rates of 10,000 counts per second and a detector dead time of 1.2 microseconds the theoretical counting losses are 4, 2, and 1.2% for half-wave, full-wave, and constant potential operation, respectively. The low transmission of conventional window materials such as mica, beryllium, and Mylar imposes the principal
limitation to spectral sensitivity in the soft x-ray region (208-210, 266, 291, 292). Recently D u Pont has provided experimental amounts of 1/6-mil Mylar which can be stretched an additional 50%. Various organic films such as nitrocellulose and Formvar supported on a wire grid have been used extensively (87, 132, 208-210, 217). Campbell (87) reported 50% transmission of B e K a and greater than 65% transmission of all higher energy radiation using a very thin nitrocellulose window. One way to reduce the pressure differential on the detector window is to evacuate the spectrometer chamber and the detector simultaneously, and then operate the detector at less than atmospheric pressure. A new windowless soft x-ray detector (Bendix M-304 electron multiplier) has the following advantages (35) : windowless operation in a vacuum, a stable detecting surface which may be cleaned with conventional solvents, and low electronic noise. However, its output is not suitable for pulse-amplitude discrimination. The M-304 is a single dynode having a continuous surface of high resistance semiconductive material. Electrons, produced by impingement of photons on the cathode, gain energy from the electric field produced by the potential drop along the high resistive semiconductor surface. A magnetic field perpendicular to the electric field forces the released electrons to travel on a cycloidal path, striking the surface a t regular intervals. Each electron yields additional secondary electrons, thus giving a n amplification factor of 10. A novel narrowband x-ray detector designed for outer space research merits consideration for nonroutine applications (76). Operation of this detector .i based on the principle that the selective transmission and reflectance of neighboring 2 atoms can provide a narrow energy band of x-rays that fall between the x-ray absorption edges of the two elements. X discrimination ratio of 400 to 1 was obtained with a band \+idth of 1.2 k.e.v. for x-rays centered at 25 k.e.v. Since x-ray detectors and their associated electronics are the most developed component of x-ray analyzers, only minor improvements are anticipated. Activity is expected to be directed towards the soft x-ray region, in particular, further development of thin rvindow and windowless detectors. EMISSION
General. Applications of emission x-ray spectrography continue to grow a t a n increasing rate each year. This technique is now used worldwide for research and industrial control analyses of major, minor, and trace elements. This increasing interest in
emission methods pesults from t h e wide applicability oi x-rays for rapid quantitative analysis. For example, during the first two years that automated x-ray emission was applied to steel and ferroalloy production (23) 14 people were withdrawn from routine analysis; a t the same time, the workload n a s increased 5(l%. Furnace test specimens were analyzed for Cr, Ni, Mo, M n , P, Si, and S in 12 minutes, including qample prc.paration and reporting of results. An index to the literature on x-ray spectrography from 1913 to 1957 was compiled by .ishby (19). Over one hundred papers on emission applications u p to 1961 Y ere reviewed by Blokhin and Losev 165). There have been a large number of recent papers deicribing practices in European laboratories (31, 47, 235, 266, 288, 552, 360, 367, 457, 468, 506). Emission applications to specific classes of samples are summarized in Table 111. Deterniinations of specific elements are listed in Table IV. Readers’ comments are requested as to whether these tables :,hould be included in future reviews. As a result of the increased automation in emission analysis there is a renewed interest in tl-e more theoretical aspects of the intensity-concentration relationship (297). The earlier mathematical studies by Sherman (277) are receiving more attention as the need of high speed computational inethods increases. Of the theoretical papers, those by Suoninen (448, 450) are particularly noteworthy. hlathematirs for equating intensity to concentration in three- and four-component syste ns were developed by Losev (286,287). Il’in (225) derived general rules relating intensity to concentration, using simple correction factors based on emp rical parameters. Hirokawa (215) proposed mathematical corrections for interelement effects, whereas other investigators used a large number of standards :37, 191). Changes in line intensities resulting from variations in voldme, temperature, and type of acid were 3orrected by ratioing the intensities of the desired element to that of a n addec control element (316). Momoki (317) used a nomographic procedure to correct for daily variations in x-ray power, goniometer alignment, and analyzer settings. Taylor, Kagle, and Ileiter (456) proposed a geometrical method for relating intensity to concentration rind for converting weight per cent to atomic per cent. Reynolds (371j used mass absorption coefficients experimeritally determined for the sample to correct for interelement effects. These coefficients were determined by measui.ing the Compton scattered intensity for Mo K a ; over-all errors are estimated to be + 3%. Claisse (100) presented additional dis-
Table IV. Specific X-Ray Spectrographic Analysis Aluminum In alloys and metals (92, 166, 488) In cement materials (133, 221, 464, 477) In minerals and ores (25, 133, 379, 484) In miscellaneous materials (226, 269, 284, 379, 423, 424, 426, 451, 466, 606) Antimony (17, COO, 606) Arsenic (191, 228, 269, 342, 493) Barium (133, 269, $84, 293, 397, 486, 499, 506) Bismuth (456, 496) Boron (210) Bromine (109, 332, 342! 606) Cadmium (392) Calcium In cement materials and slags (36, 133, 221, 454, 477) In minerals and ores (25)379, 404, 484) In miscellaneous materials (86, 133, 145, 269, 284, 293, 379, 461, 499, 506) Carbon (142, 210) Chlorine (86, 133, 229, 397, 423, 424, 451, 506, 508) Chromium In alloys” and metals (37,81, 159, 191,233,319, 343, 374, 487) In miscellaneous materials (99, 221, 236, 269,293, 315, 346, 364, 410, 455,474, 485, 6061 In steels (23, 221, 285, 406) Cobalt In alloysa ( 170, 233) In miscellaneous materials (99, 269, 293, 357, 373, 429, 606) In steels (286, 435) Copper In alloyso (34, 37, 81, 112, 169, 191, 320, 343) In metals (176, 213, 487) In miscellaneous materials (11, 110, 236, 293, 342, 367, 384, 506) In steels (286, 318, 406) . Fluorine (209, 210) Gallium (487) Germanium (365, 456) Hafnium (193) Hydrogen (142) Iodine (331 506) Iron In alloysa (37, 162, 170, 191, 220, 290, 320, 343) In biological and medicinal materials ( 11, 109, 293, 299) In cement materials (36, 133, 221, 464, 477) In metals (176, 213, 487) In minerals and ores (25, 66, 116, 133, 379, 383, 404, 440, 486) In miscellaneous materials (17, 99, 143, 146, 229, 268, 269, 284, 316, 338, 342, 379, 423, ~
424,461,455, 485,506,607)
In oils (384) In slags (316) In steels (221, 285) Lead In alloys (112, 166, 171, 191) In minerals and ores ( 8 2 ) In miscellaneous materials (103, 293, 294, 342, 346, 496, 606, 613) In oils (86, 133, 229, 499) Magnesium In cement materials (221, 394, 477) In glass (269) In miscellaneous materials (26, 115, 209, 284, 379) In alloysa (37, 81, 159, 171, 191, 319, 320, 343) In metals (176, 487) In minerals and ores (383, 486) In miscellaneous materials (99, 146, 221, 269, 293, 316, 316, 379, 410, 6061 In steels (23, 145, 286, 406) Mercury (410, 495) Molybdenum In alloysa (37, 81, 159, 233, 238, 289) In miscellaneous materials (293, 367, 474) In steels (23, 221, 286, 289, 318, 406) (Continued)
VOL. 36, NO. 5 , APRIL 1964
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Table IV.
(Continued)
Nickel In alloys" (37, 112, 159, 162, 169, 220, 281, 290, 343) In metals (429, 487) In miscellaneous materials (17, 99, 145, 229, 236, 293, 342, 357, 455, 474, 485, 506) In oils (143, 384) In steels (63,285, 406) Niobium In alloys (81, 289, 466) In minerals and ores (295, 296, 386, 486, 490) In miscellaneous materials (289, 364) Kitrogen (300) Oxygen (210) Palladium (238) Phosphorus (23, 133, 145, 166, 209, 221, 229, 379, 397, 506) Platinum (34) Plutonium (294, 312) Potassium (25, 145, 269, 284, 299, 379, 451, 484, 506) Rare! earth elements In minerals and ores (202, 458) In miscellaneous materials (202, 281, 443) In rare earth mixtures (168, 202) 405, 458) Rhodium (158) Ruthenium (238) Scandium (293) Selenium (119, 410) Silicon In alloysa and metals (92, 166, 279) In cement materials (133, 454, 477) In glass and slags (221, 269) In minerals and ores (25, 115, 133, 279, 484) In miscellaneous materials (209, 284, 379, 451, 455, 506) In steels (23, 145, 435) Sodium (26, 209) Strontium (269, 428, 441, 486, 495, 506) Sulfur (23, 26, 86, 133, 145, 209, 221, 229, 269, 397, 477, 506) Tantalum (81, 289, 383, 466, 490) Tellurium (456) Thallium (381) Thorium (82, 443, 4-91) Tin In alloys ( 112, 191, 392) In miscellaneous materials (293, 383) Transuranium elements (255) Titanium In alloysa (159, 343) In metals ($2, 176, 457, 487) In minerals and ores (25, 133, 379, 484) In miscellaneous materials (221, 269,284, 293, 916, 357, 379,'423, 424, 451, 506) In steels (285) Tungsten In alloys" 137, XI, 289, 466) In steels (285, 289) Uranium In alloys (226, 302, 319, 326) In minerals and ores (82, 133, 408, 491, 492) In mi~cellaneousmaterials (103, 214, 255, ,904, 312) Vanadium In alloys and steels (37, 231, 285, 406) In miscellaneous materials (145, 176. 289. 236. 293. 3.42. L87) In oils (86, 143, 384) Yttrium (168, 295, 296, 417, 418) Zinc In alloys (112, 171, 191, 320, 343, 392, 443) In biological and medicinal materials (11, 62, 109, 299) In metals (176, 487) In miscellaneous materials (17, 86, 133, 236, 293, 342, 397, 486, 499, 506) Zirconium In alloys (238,259,443,466) In metals (63, 457) In minerals and ores (195, 296) In miscellaneous materials (99, 193, 269) a Exclusive of steels.
31 8 R
ANALYTICAL CHEMISTRY
cussion on the borax fusion technique, while absorption effects in petroleum were covered by Gunn (195); both of these papers merit attention. Another noteworthy paper (85) gives detailed instructions for the determination of elements of low atomic number. -1lley and Higgins (13) developed a n empirical method to correct for the variable thickness of 1/4-mil Mylar. This variable thickness results in systematic errors in the determination of low atomic numbers elements unless each sample holder is independently calibrated. Effect of variations in ambient temperature upon the optical alignment of an x-ray spectrometer is discussed by Davies (118). This temperature-dependent effect increases with increasing Bragg angle, degree of resolution, and expansion coefficient of the analyzing crystal. These shifts in spectral line position result in systematic analytical errors when using calibration .curve techniques rather than analyzing standard and unknown sequentially. Quantitative studies on crystal alignment as a function of temperature are being conducted a t the reviewers' laboratory; both organic and inorganic crystals have been investigated. Counting techniques are the subject of several papers (65, 190, 498). Spectral line interferences are summarized by I3ertin and Longobucco (44). Michaelis (313) made a significant contribution to x-ray analysis by compiling a list of 3400 standard samples, reference materials, and high purity chemicals, Moorehead (320) describes standards suitable for the analysis of aluminum and magnesium alloys. Sample Preparation. Sample preparation is a very important variable in emission analysis because of the small d e p t h of sample being examined (465). Kilday and Michaelis (243, 314 ) found that surface preparation must be carefully controlled for the determination of lead in free-cutting steel. A metallographic polish with 0.25-micron diamond abrasive was required to eliminate systematic errors due to the tearing away or smearing of lead particles. However, fine polishing will not eliminate systematic errors if the element being determined exists in two or more phases and these phases have significant differences in their x-ray absorption characteristics. For example, the silicon Kcu intensity in hypereutectic hl-Si alloys is dependent on the composition of the -%l-Sieutectic and the size of the primary silicon crystals in the hypereutectic. Lihl (279) employed this intensity dependence on phase composition in his studies of the hl-Si eutectic formation. .1 wide range of alloy steel samples and standards were prepared as buttons by use of a small arc-melting furnace
(159). Approximately 40 to 50 grams of alloy steel were placed in a watercooled copper melting pot, then arcmelted under argon using carbon electrodes. Excellent sample homogeneity was achieved by the violent stirring action produced by the arc. Bernstein (39, 40) concluded from his studies on particle size effect that to achieve quantitative results with-powdered samples either the particle size or the particle size distribution must be constant or extremely fine grinding must be employed. Although it may be necessary to use powdered samples for process control, other methods of sample preparation s.nh as fusion or solution are recommended by the reviewers for most analytical applications. The objective of fiision or solution methods is to achieve a homogeneous material in which the x-ray intensities are independent of in ierelement effects (68, 111-113, 290, 81ter. This avoids the need for t h e correction of take-off angle (79) required for the normal type of rotating curved crystal spectrometer. Il'in (664) and Dorovskil (7'0) described curved crystal spect,rometers built in Russia. Ditsman (12.$,165) and Cowley (108) investigated the regions of diffraction from curved crystals and showed that these regions form roughly a n X shape on the c r y t a l for Johannsontype spectrometers. Simanov and Trunov (4.21) have reported the suc-
Table VI. Applications of Electron Probe Microanalysis Analysis of meteoritic phases ( 7 , 76, 160, 181, 249, 368) Corrosion studies (141, 504) Determinations of solid state solubility 1129, 151) Electron beam scanning (106, 248, 355) Examination of biological specimens (77, 106, 107, 272, 283, 311 , 377, 453, 469-472, 614 ) General metallurgical (YO, 114, 175 282, 298, 308, 309, 344,351 , 552,501 ) Identification of inclusions and particles (61, 222, 251, 262, 308, 368, 398, 399, $02, 460, 478,494)
Identification of mineral phases (106, 282, 344, 409, 436, 446) Segregation studies ( 1 , 14, 28, 102, 164, 262, 246, 660, 252, 273, 308, 310) Semiconductors and synthetic inorganic crystals (122, 301 ) Semiquantitative and quantitative analysie of phases (3,58, 242, 245, 401, 452, 460, 461, 471, 510)
Solid state diffusion (2-5, 21, 22, 45, 59, 129, 149, 196, 306, 347, 348, 40%)' Surface and thin layers (49, 308, 462, 504, 505)
cessful bending of germanium crystals for use in curved crystal spectrometers. Miscellaneous. Normally, contamination of t h e target by a carbonaceous layer has been no problem in measuring x-ray intensities in the wavelength range from 0.5 to 5 A. Adler, Dwornik, and Rose ( 8 ) report a rapid change in intensity when using a diffusion pump oil containing sulfur. The same condition could conceivably arise if silicone oils or greases were used in the vacuum system. The unique problems associated with the preparation of fragile biological materials for examination in an electron probe microanalyzer are discussed by Boyde and Switsur ( 7 4 ) . T o obtain flat surfaces, they have developed a method of producing amorphous surface layers. Little advantage has been taken of some of the other possible effects of the interaction of x-rays or electrons with matter in electron probes, such as electron or x-ray diffraction. The universal analyzer described by Elion, Shapiro, and Bennett (148) would have provided such facilities. Some work has been done by Heise (206) on the use of the Kossel line technique. Ichinokawa and Uyeda (223) utilized the electron probe for selected area diffraction in the back-reflection region of areas 15 microns in diameter. The next few years should see a rapid development of the use of electron probe microanalyzers for these associated techniques. Applications. Applications of the electron probe to various fields are given in Table V I . T h e measurem e n t of extremely low concentrations in high-purity samples is possible if the impurity can be concentrated into localized areas (16; p. 53, 57). This application was suggested by the fact that in preparing diffusion couples between pure iron and other metals it was observed that the impuritie-: in the iron, though small in concentration, precipitated out in the form of small inclusionsin the diffusionzone. Further, the composition of these inclusions depended on the types of metals forming the diffusion zone. This suggests the
possibility of using selected metals to localize specific impurities so they may be analyzed. If there is any single field of application in which the electron probe has advanced most rapidly, it is the study of solid-state diffusion. Studies ( 2 , 4) on the effect of pressure on diffusion have shown a n unsuspected pressure dependence of the composition of phases in the diffusion zone. Diffusion at atmospheric pressure yields compounds whose composition varies with distance in the diffusion zone. The same diffusion process a t higher pressures yields compounds of constant composition. These facts have been advanced as the cause for certain discrepancies which appear in the literature on the composition of phases determined by diffusion. ACKNOWLEDGMENT
The reviewers thank Mary Ann Conway for her extensive editorial assistance and Donna Dotson for typing the manuscript and references. They also acknowledge the kindness of the many authors who forwarded copies of their papers. For future reviews, a brief summary in English plus two copies of the paper would be appreciated. LITERATURE CITED
(1) Adda, Y., Aaam, N . , Donze, G., Mallen, J., Maurice, F., Weisz. AI. 31.. Corn 1. R e d . 254, 1052 (1962).' ( 2 ) *&a, Y., Beyeler, AI., Kirianenko,
A , , I b i d . , 250, 115 (1960). (3) Adda, Y., Gewler, hl., Kirianenko, A . , Maurice, F., X e m . Sci. Rev. &fet. 18, 716 (1061). (4) Adda, Y., Reyeler, AI., Kirianenko, A , , Pernot, R., Ibid., 17, 423 (1960). (5) Adda, Y., Philibert, ,J.) Acta M e t . 8, 700 (1960). ( 6 ) Addink, S . If'. H., J . Iron Steel Inst. 194, 199 (February 1960). ( 7 ) Adler, I., Dnornik, E. J., C . S. Geol. Survey, Prof. Paper 424-B,263 (1961). (8) Adler, I., Dwornik, E. J., Rose, H. J., Brit. J . A p p l . Phys. 13, 245 (1!362), (9) Adler, I., llassoni, C. J., Rev. Sci. Instr. 33, 247 (1962). (10) Alexander, E., Fraenkel, F. P., A F EOAR Grant 62-33, ATR, Technical VOL. 36, NO. 5, APRIL 1964
323 R
Ilept. No. 1, Hebrew Univ., Jerusalem, Israel. 1962. (11) A Lexander, G. V., ANAL.CHEM.34, 951 ( 1962). (12) AIllenden, - - - - D., Mulvey, T., A . E . I .
Eng.
~
2 , lau (1962).
(13) Alley, B. J., Higgins, J. H., U. S.
Army Missile Command, Redstone Arsenal. Ala.. ASTIA Rent. RK-TR-
63-7 ( 1863). ---, ’ (14) Alm, S., Kiessling, R., J . Inst. Metals 91, 190 (1963). (15) Am. SOC. Testing Materials, Spec. Tech. Publ. 308 (1962). (16) Ihzd., 317 (1962). (17) Ankner, D., thesis, Johannes Gutenberg Universitat, Mainz, 1961. (18) Archard, G. D., Mulvey, T., “X-Ray \
Optics and X-Ray Microanalysis,” p. 393, Academic Press, New York, 1963. (19) Ashby, G. E., “Index to the Litera-
ture on X-Ray Spectrographic Analysis,” Part I, 1913-1957; .4m. SOC. Testing Materials, Spec. Tech. Publ.
292 (1361). (20) Ashby, W. D., ed., “Developments in Applied Spectroscopy,” Vol. 1, Plenum Press, New York, 1962. (21) Austin, A. E., Richard, S . A,, J . Appl. Phys. 32, 1462 (1961). (22) Austin, A. E., Richard, S . A,,
Schwartz, C. M., Battelle Memorial Institute Contract S o . AF 33(616) 6265 (June 15, 1960). (23) Raecklund, J., Advan. X - R a y Anal.
6, 328-38 (1963). (24) Bailey, L. E., J . Appl. Phys. 32, 3008 (1963). (25) Baird. A. K.. MacColl. R. S..
ityre, D. B., Advan. X - R a y Anal:
5,412 (1962). (26) Baird, A. K., McIntyre, D. B., Welday, E. E., Ihid., 6, 377 (1963). (27) %lis, E. W., Bronk, L: B., Pfeiffer,
H. G., Welbon, W. W., Winslow, E. H., Zemany, P. D., ANAL.CHEM.34, 1731
( 1962). (28) Ballinger, J., Hughes, I. C. H.,
Alulvey, T., Brit. Cast Iron Res. Assoc.
(29, (1961). (30) Banerjee, B. R., Bingle, W. D., Blake, N. S., Ihid., 15, 769 (1963). (31) Baron, G., Favre, J., Rimbault, C., Cham. Anal. 42 (8) 388 (1960). (32) Batyrev, V. A , , Bogdanov, V. G., Izv. Akad. N a u k SSSR, Ser. Faz. 25, 933 (1961). (33) Baun, W. L., Fischer, D. W., Wright Patterson Air Force Base, Ohio, ASDTDR-310 (May 1963). (34) Baun, W. L., Renton, J. J., Wright-
Patterson .4ir Force Base, Ohio, Tech. Doc. Rept. ASD-TDR-62-926 (December 1962). (3.51 Beard. - - - ~ - D. W . Furnas. T . C.. WrightPatterson Air Fbrce B h e , Ohio,. Ript. ASD-TDR-62-519 (August 1962). (36) Bens. J.. Silicates Ind. 26, 526 (1961) ~, (in Frenchj. (37) Beraer. R., Deceuleneer, P., Rev. ‘ Univerielle Mines 4, 207 (1961); Trans. KO. CRL/T. 1159. (38) Bernard, A . , Brvson-Haynes, D., ’ Mulvev. T.. J . Sb. In&.- 36. 438 \--,
~
(1959):‘ ‘ (39) Bernstein, F., Advan. X - R a v Anal. 5, 486 (1962). (40) Ihid., 6, 436 (1963). (41) Bernstein, S., Canon, AI., Rev. Sci. Instr. 33, 112 (1962). (42) Bertin, E. P., ~ A L CHEM. . 34, 804 (1962). (43) Bertin, E. P., Longobucco, R. J., Advan. X - R a y Anal. 5, 447 (1962). (44) Rertin, E. P., Longobucco, R. J., Norelco Reptr. 9, 64 ( 1962).
324 R
ANALYTICAL CHEMISTRY
(45) Beyeler, M., Adda, Y . , Compt. Rend. 253. 2967 (l9S1). (46) Beyeimann, k., Cretius, K., Klzn. Wochschr. 40, 86 (1962). (47) Bills, K. M., BNF Analytical Conf., Malvern, 1961, p. 103, British Son-
Waltham, Mass., RADC-TN-61-125 (AD260478) (1961). (77) Brooks, E. J., Tousimis, A. J., Birks, L. S., J . Cltrastruct. Res. 7, 56 (1962). (78) Brown, J. D., Thatcher, J. W.,
Ferrous lletals Research Association, London, 1962. (48) Bills, K. M., “Spectroscopy in the Metallurgical Industry,” p. 16, Hilger and Watts, London, 1963. (49) Bird, R. J., J . Inst. Petrol. 465,
5, 527 (1962). (79) Brown, J. D., Thatcher, J . W., Campbell, W. J., Norelco Reptr. 10, 85 ( 1963). (80) Brown, J . D., Thatcher, J. W.,
297 (1962). (50) Birks, L. S., ANAL.CHEM.32, S o . 9, 19A (1960). (51) Birks, L. S., “Electron Probe Micro-
analysis,” Vol. XVII, Interscience, New York, 1963. (52) Birks, L. S., J . Appl. Phys. 33, 233 (1962). (53) Birks, L. S., “X-Ray Spectrochem-
ical Analysis,” Interscience, S e w York,
19.59. (54) Birks, L. S., Batt, A . P., ASAL. CHEM.35, 778 (1963). (55) Birks, L. S., Brown, D. hl., Zbid., 34, 240 (1962). (56) Birks. L. S.. Harris. D. L.. Zhid.. 34, 943 (1962) (57) Birks, L. S., Seebold, R. E., Am. ~
SOC. Testing Materials, Spec. Tech. Publ. 308, 53 (1962). (58) Birks, L. S., Seebold, R. E., Fall Meeting Met. Soc. AIME, Xew York,
1962. (59) Birks, L. S., Seebold, R. E., C . S.
Saval Research Lab., NRL Rept.
5461 (1960). (60) Birks, L. S., Siomkajlo, J. M., Spectrochzm. Acta 18, 363 (1962). (61) Birks, L. S., Siomknjlo, J . hZ., Koh, P. K., Trans. Met. SOC. A I M E 218, 806 (1960). (62) B‘irnbaum, D., Hall, T., Lee, R., Pro. SOC. Ezptl. Bid. Med. 108, 321 (1961). (63) Blank, G. R., Heller, H. A., Norelco Reptr. 9, 23 (1962). (64) Blokhin, M. A,, “Physics of
X-Rays,” 2nd rev. ed., Trans. Ser. AEC-tr-4502, Phys. Office of Technical Services, Dept. Commerce, 1961. (65) Blokhin, hl. A,, Losev, 5 . F., Zavodsk. Lab. 27, 1091 (1961) (in English). (66) Blokhin, M. A., Volkov, V. F., Ihid., 27, 1110 (1961). (67) Boehm, F., DuMond, J . W. M., Henrikson, H. E., Seppi, E. J., “Electromagnetic Lifetimes and Properties of Nuclear States.” Katl. Res. Council, Committee on Nuclear Science, p. 106, 1962. (68) Boinck, J., Chem. Weekhlad 58, 482 (1962). (69) Bondar’, A. D., Karev, V. N.,Klyucharev, A. P., Sikolaychuk, A. D., Zavodsk. Lab. 28, 1446 (1962). (70) Borovskii, I. B., Ditsman, S. A., Bogdanov, V. G., I z v . Akad. Nauk S S S R , Ser. Fzz. 25, No. 8, 919 (1961). (71) Bovey, L., “Spectroscopy in the
Metallurgical Industry,” Buxton Symp., July 1962, Hilger and Watts, London, 1963. (72) Boyd, B. R., Dryer, H. T., “De-
velopments in Applied Spectroscopy,” Vol. 11, p. 335, Plenum Press, Sew York, 1963. (73) Boyd, B.
