V O L U M E 28, NO. 4, A P R I L 1 9 5 6 (75) Klingman, D. W., Hooker, D. T., Banks, C. V., ANAL.CHEnr. 27, 572 (1955). (76) Kress, K. E., llees, F. G. S.,ANAL.CHEM.27, 528 (1955). (77) Lemhke, A., Kaufmann, W., Milchwissenschaft 9, 113 (1954); J . Am. Oil Chemists’ SOC.32, 115 (1955). (78) Long, D. R., Keuzel, R. W., A N A L . CHEM.27, 1110 (1955). (79) Lord, J. W., Bradley, P. ll.,Analyst 80, 429 (1955). (80) Lothe, J. J., ASAL. CHEW27, 1546 (1955). (81) Malm, C. J., Tanghe, L. J., Laird, B. C., Smith, G. D., Ibid., 26, 188 (1954). (82) llalmstadt, H. V., Gohrbandt, E. C., Ibid., p. 442. (83) Xlarkle, G. E., Boltz, D. F., Ibid., p. 447. (84) Xlarzys, A. E. O., Analyst 80, 194 (1955). (85) Xlehler, A. H., Science 120, 1043 (1954). (86) llellon, hl. G., .4N.4L. CHEM.26, 181 (1954). (87) l k y e r , A. S., J . Org. Chem. 20, 1240 (1955). (88) llitzner, B. lf.,J . Opt. SOC.A m e r . 45, 997 (1955). (89) Mitzner, B. AI., Lewin, S. Z., Ibid., 44, 499 (1954). (90) Kielsch, W., and Boltr, G., Microchim. Acta 1954, 481. (91) Nielsen, S. O., Rev. Sci. Instr. 26, 516 (1955). (92) Norris, XI. S.,Fleck, S. A, Lichtenfels, D. H., ANAL.CHEM., 27, 1565 (1955). (93) O’Connor, R. T., Goldhlatt, L. A., Ibid., 26, 1726 (1954). (94) Odeen, XI., Beckman Instruments, Inc., Fullerton, Calif., Beckman Bull. 222-C (1955). (95) Orgel, L. E., Quart. Revs. (London) 8 , 422 (1954). (96) Ovenston, T. C. J., Photoelectric Spectrometry Group Bull., S o . 6, 132 (1953). (97) Ovenston, T. C. J., Watson, J. H. E., Analyst 79, 383 (3954). ANAL. CHEM.26, 642 (1954). (98) Parke, T. V., Davis, W. W., (99) Pearson, R. Xl.. Analyst 80, 656 (1955). (100) Pepe, J. J., Kniel, I., Czuha, AI., ANAL. CHEY.27, 755 (1955). (101) Photoelectric Spectrometry Group. Bull., KO.7, 168 (1954). (102) Prescott, B. E., A p p l . Spectroscopy 7, 200 (1953); 8, 46, 96, 146 (1954); 9, 49 (1955). (103) Price, T . D., Hudson, P. B., ANAL.CHEY.26, 1127 (1954). (104) Reilley, C. N.,Crawford, C. ll.,Ibid., 27, 717 (1955). (105) Reilley, C. N., Schweizer, B., Ibid., 26, 1124 (1954). (106) Rosenhaum, E. J., Ibid., p. 20. (107) Rosenblatt, D. H., J . Phys. Chem. 58, 40 (1954). (108) Ross, I. G., J . Opt. SOC.A m e r . 44, 40 (1954). (109) Royer, G. L., Lawrence, H. C., Kodama, S. P., and Warren, C. W., ANAL.CHEY.27, 501 (1955). (110) Schmauch, L. J., and Gruhh, H. ll.,Ibid., 26, 308 (1954).
583 (111) Scott, J. F., Sinsheimer, R. L., in “Radiation Biology,” -4. Hollaender, ed., Vol. 11,Chaps. 4,5, AlcGraw-Hill, Kew Tork, 1955. (112) Scott, L. Leonard, G. ITr.., ANAL.CHEY.26, 445 (1954). (113) Sharpe, L. H., Ibid., p. 1528. (114) Sponer, H., in “Annual Review of Physical Chemistry,” G. K. Rollefson and R. E. Powell, eds., Vol. 6, pp. 193-216, Annual Reviews, Inc., Stanford, Calif., 1955. (115) Stafford, R. W., Shay, J. F., Francel, R. J., ANAL.CHEY.26, 656 (1954). (116) Swann, 31. H., Adams, 11. L., Esposito, G. G., Ibid., 27, 1426 (1955). (117) Sweetser, P. B., Bricker, C. E., Ibid., 26, 195 (1954). (118) Tarrant, -4. W. S.,Photoelectric Spectrometry Group Bull., S o . 6, 143 (1953). (119) Taylor, K. W., Smith, 31. J. H., Analyst 80, 607 (1955). (120) Tepe, J. B., St. John, C. V., A N ~ LCHEM. . 27, 744 (1955). (121) Thamer, B. J., J . Phys. Chem. 59, 450 (1955). (122) Thornburg, W., J . Opt. SOC.A m e r . 45, 740 (1955). (123) Troy, D. J., -4NAL. CHEM.27, 1217 (1955). (124) Tunnicliff, D. D., J . Opt. SOC.A m e r . 45, 963 (1955). (125) Underwood, -4.L., . ~ N A L . CHEW26, 1322 (1954). (126) Uzumasa, Y., Kishimura, AI., Bull. Chem. SOC.J a p a n 28, 88 (1955). (127) Vandenhelt, J. AI., J . Opt. SOC.A m e r . 44, 641 (1954). (128) Vandenhelt, J. 11., Childs, C. E., Lundquist, D., Saladonis, J., Science 119, 514 (1954). (129) Vandenhelt, J. AI., Henrich, C., April. Spectroscopy 7, 171 (1953). (130) Vandenhelt, J. JI., Henrich, C., Yandenberg, S. G., A N . ~ L . CHEY.26, 726 (1954). (131) Vandenbelt, J. AI., Spurlock, C. H., J . Opt. S o t . A m e r . 45, 967 (1955). (132) Walsh, A. D., and Duncan, A . B. F., in “Annual Review of
w-.,
Physical Chemistry,” G. K. Rollefson and R. E. Powell, eds., Vol. 5, pp. 163-98, Annual Reviews, Inc., Stanford, Calif., 1954. (133) (134) (135) (136) (137) (138)
Wedgewood, P., Cooper, R. L., Analyst 80, 652 (1955). West, P. W., Coll, H., ANAL.CHEY.27, 1221 (1955). Wilkinson, P. G., J . Opt. SOC. Amer. 45, 862 (1955). Wilkinson, P. G., Tanaka, Y., Ibid., 45, 344 (1955). Wyman, G. AI., Ibid., 45, 965 (1955). Yarhorough, V. s l . , Haskin, J. F., Lambkin, \V. J., .INAL. CHEM.26, 1576 (1954).
I REVIEW OF FUNDAMENTAL DEVELOPMENTS IN
I I
I
I
I
X-Ray Absorption and Emission
I
I
T
HERMAN A. LIEBHAFSKY and EARL General Electric Co., Schenoctady, N. Y.
HE popularity of analytical methods based upon x-ray emis-
sion and absorption, and upon t h e analogous ?-ray processes, continues t o grow. T h e meetings during t h e past 2 years at which such methods were discussed are too numerous t o list. Abstracts of the Pittsburgh Conference papers (6-8)provide a fair index t o progress in this field and t o the material presented a t other conferences. T h e present revieF will be easier t o follow n-ith these abstracts arid the earlier reviews (88-93) a t hand; references t o the individual abstracts are not in general made here. An event of first importance t o all those interested in using x-rays is the appearance, considerably expanded in its fourth edition, of Clark’s “Applied 9-Rays” (31 ). I n the present review, two important topics-detectors and histochemical analysis-have been given more extended treatment than the others. -in attempt has been made t o present enough about t h e absorption and emission of -/-rays t o inform
H. WINSLOW
the analytical chemist usually concerned with what happens outside the nucleus. T h e bibliography falls far short of including all t h e references, especially all the ?-ray references, compiled in preparing t h e review. * DETECTORS
T h e subject of x-ray and ?-ray detection belongs primarilj- to the physicist. T h e analytical chemist must take notice of it, however, because the detectors concerned are now among the tools of his profession. Were it not for the great improvements t h a t have occurred in these detectors during the past 15 years, there would be little or no occasion for these reviews. T h e information about detectors in Table I is perhaps a reasonable minimum for the analytical chemist; further information is available (14, 46, 50, 75, 131, 143). T h e photographic plate, though invaluable for specialized
ANALYTICAL CHEMISTRY
584
proportional counter is capable. Fortunately, however, the analytical chemist in general reCounting Energy Kame Type Quantitative (Time Resolution) Resolution quires only t h a t the resolution Ionization chamber (current) Gas-filled (low field) Yes S O N O be good enough not t o decrease I’roportional counter Gas-filled (intermediate Yes Yes Good field) the reliability of his results. (iciger counter Gas-filled (t?igh field) Tes Yes NO The proportional counter, and Scintillation counter Photoelectric (phototube Yes Tes Moderate rnult iplier) on occasion even the scintillaPl~itoelectricdetector Pliotoelectric (phototube Yes Ko s o multiplier) tion counter, can sometimes Cliidiiiiiiiii 6:ilfide Photuconducting S O h-0 h-0 meet this usually modest requirement. T h e modern scintillation Table 11. Data for X-Ray Detectors in Figure 1 (131) counter (46, 77, f O O ) , which C‘tiiintt.r Absorbing Medium Birks in his monograph ( 1 4 ) Suiiiber Counter Type Pressure. Cin. H g Active Length, Ciii. Window Thickness, Cin. calls “the most important and 1 Geiger, e n d - r n i n d o ~ ~ A , 55 10.2 Mica 0.0013 2 Proportional, side-window Xe, 30 2., Re 0 . 0 1 2 i versatile instrument in nuclear 3 Proportjonal, sjde-window Xe, 30 MicaO.0013 + R e 0 . 0 1 2 7 physicsresearch,” uses a photo4 Proportional, side-window Kr. 50 Mica 0 , 0 0 1 3 - B e 0 . 0 1 2 7 J Scintillation NaIST1 0.70 Be 0.0127 multiplier tube t o count t h e G Scintillation NaI.Tl 0.10 Be 0.0127 7 Scintillation SaI.TI 0.05 Be 0 , 0 1 2 7 scintillations produced when xrays or ?-rays are absorbed b y a Sorelco. Type G2019, has inactire length about 0.3 em. included in calculations. a phosphor such as a thalliumactivated sodium-iodide crystal. Its energy resolution is applications ( $ 7 ) , has not been included because it will scarcely about 2.5 times lower than t h a t of the proportional counter, b u t be used n-heii another detector will serve. it has important compensating advant,ages (13’1). Perhaps its The first three detectors ( 1 4 s ) all depend upon ionization by most serious disadvantage is t h a t unavoidable presence of photophotons absorbed by a gas in a n electric field. The field may be multiplier tube noise limits its usefulness in the region of wave between a positively charged central wire and a coaxial metal lengths longer than about 3;1. cylinder. the field is increased, there orcurs first a region in An excellent comparative study of Geiger counters, proporwliicah the charged particles produced are collected without tional counters, and scintillation detectors has recently been multiplication (ionization chamber); then a region in which carried out by Taylor and Parrish (131). there is sigiiificant, multiplication, and the number of particles Since the detector used has a marked effect on the quality and collected is proportional under proper conditions to the energy precision of the x-ray patterns, the x-ray analyst must have a of the photons (proportional counter); and finally a region of working knowledge of the detector characteristics in order t o choose t h e detector best suited for the problem. There are complete gaseous breakdown in which there is enormous multimany factors, such as the linearity of response, quantumplication t h a t bears no relation to the energy of the incident counting efficiency, st,ability, background, possibility of pulsephotons (Geiger counter). K i t h the improved means of exheight discrimination, etc., v-hich must he considered in choosing teriial amplification now available, the current ionization chama detector for a particular problem for no one detector is ideal for all x-ray problems. I)er ( a s distinct from the connting: or pulse ionization chamber) I n this paper one of t’he most iinportant factors, the quant,umd i ‘ s c ~ w st o be considered by thra unalytical chemist for measuring counting efficiency, will be discussed. The following example the intenFity of relatively strong polychromatic beams ( 4 8 ) . will illustrate its importance. Frequently LIoKci radiation is Geiger counters, though well known and easy to use, are subused to obtain single-crystal dift‘raction patterns. Since t h e quantum counting efficiency of a Xa1,Tl scintillation counter jc’i‘t to one limitation (f.$3), sometirncs serious, which does not is about 99% and an argon-filled Geiger counter only 1 3 % , a t hamper proportional and scintillation counters. I n Geiger 0.71.4.$ a gain of more t,han a factor of 7 in the measured intensity coilritere, the act of ionization bj- a single photon produces a ~vould I)e realized without incre;ising the power input t o t,he s1ic:cth of positive ions that reduces the field a t the central x - ~ i ytulle siiiiply by using the former. This is ne:irly the same wire 1)elow the potential required t o start a discharge by a subsequent photon. This condition \rill continue for a time-called 75 the .,dead time” of the counter-until the positive ion sheath hay drifted far enough from the wire to raise the field a t the wire , t o the pheabove the starting potential. In other ~ o r d s on-ing nomenon of dead time, Geiger counter readings will inrrease less than proportionally t o the intensity of the x-ray beam, and the counter n-ill “choke” if the intensity becomes high enough. In addition to the loss of counts by the mechaiiism just described, d l (Aounters are of course subjecat to additional losses if the resulving power of the recording equipment is inadequate. Counting: losses in analytic:il n o r k are more likely t o cause concern with x- than with ?-rays because the former are likely to be used :it tlir higher intensities. Proportional counters (63, 118) hold promise of great future development in analytical chemistry because they are capable of energy resolution, or “pulse height discrimination” as it is often called, pulse height and energy being proportional in the idenl case. As a consequence, the proportional counter offers a highly convenient means of spectral analysis t h a t does not entail the great sacrifice of intensity concomitant with the use of crystal monochromators for this purpose. T o be sure, the resoFigure 1, Calculated counting efficiencies of detectors listed in Table 11 (731) lntion possible with crystals greatl). exceeds t h a t of which the Table I.
Characteristics of Electrical Detectors
;:;
~~
V O L U M E 28, N O . 4, A P R I L 1 9 5 6 gain in inteiisity that would be realized in practice by using a high-power rotating-anode x-ray tube, with its additional cost a n d maintenance difficultiep, instead of a stat,ion:try-anode wat’ercooled tube. T h e point made above regarding quantum-counting efficiency is clear from Figure 1 and Table 11, which contain some of the more important data given b). Taylor and Parrish. Inasmuch as the properties of the window on the counter help determine the efficiencj-, the type of windox is given for eavh dtatector. For example, growing absorption by the beryllium window is responsible for the gradual reduction in efficiency of the scintillation counter with increasing wave length. D a t a foi, such counters are given for three thicknesses (0.70, 0.10, a n d 0.05 em.) of sodium iodide; t,he figure shows that only the thicakcst crystal escapes a reduction of efficiency a t 0.375 A. owing t o the presence of the K absorption edge of iodine. h (75) have used some of the counters of Figure 1 in the x-ray diffrac-tometry of radioactive samples. Though radioactive samples are gro\ving rapidly in importance, the point of principd immediate interest here is the use of energy resolution (pnlse-height discrimination) t o separate the radioactive background from the x-ray lines under investigation. T h e follo\ving quotation describes the detection Pystem, which has the important and desiral,le property of conveniently accomnlodating any one of several detectors. Thcl photomultiplier tube, rryst,al, and cat,hode follon-er coiiiprise a unit which may be called t,he scintillation head. I t is used as a unit and is mounted on the goniometer a r m in place of the usual Geiger t,ube. T h e cathode follower feeds a linear amplifier with a gain adjustable up to 2500. T h e amplifier in t u r n feeds a pulse height, di,scrimirlator n-hich may be set to pass all pulses greater than a given amplit.ude (base) or only those pulses being nit,hin a specified amplitude range (windon.). From the discriminat,or the signal goes to standard scaling and counting equipment. Il-hen making measurements such as are shown i n Figure 1 ( 7 6 ) , it is convenient to use a recording count,ingrate meter synchronized x i t h a motor-driven base line on the discriminator. -411 oscilloscope showing the out>put, of the amplifier is useful for monitoring purposes. IThen using the proportional count,er, the same equipment was used by simply replacing the scintillation head 11-ith an equivalent proportional counter head. The Geiger counter fed the counting equipment d i r e d y witho u t the intervening additional amplifier and discriminator. From the discussion of -;-ray absorptiometry (below), it is clear that the mass a h o r p t i o n coefficients involved are oftc~n much smaller than thope of thr usnal x-rays. Consequently, a -pray detector to be efFic>irritmust often w n t a i n a relativrly large absorbing mass. , Only the scintillation counter, which (-an accommodate a massive crystal, can conveniently provide such a mass (49). I t is therefore a powerful -,-ray detector. ICarlier discussions of the phot,oelectrir detector (88) auffic~ for the present. A previous discussion of the cadmium sulfide detector (93) needs supplementing in one respect. The small size of this detector makes it v,-cll adapted to dosimetric nieasiirements in radiotherapy, and the rpsults obtained have been rather more r e h b l e than might have heen anticipated (20, 51, 124). ABSORPTIOR
583 monochromatic beanis” is operational, as is desirable, and it connotes “spectrometry.” Absorptiometry with Monochromatic Beams. I n thc abeorptiometry of gases, x-rays of long-rvave length must often be used to ensure appreciable absorption. The filtering effect of the sample on a polychromatic beam then often leads t o a pronounced decrease in effective wave length (Q6)-an undesirable complication. T h e development of a gas analyzer that employs a monochromatic beam and a Geiger counter is therefore welcome (117).
.\nother development that is welcome for this and other r m sons is the use of radioactive isotopes as x-ray sources (86, 1 2 4 ) . These must not be confused w-ith */-ray sources (discussed later), n-hich are also radioactive but in which the transformation leading to radiation occurs within the nucleus. T h e x-rays from ratlioactive sources may for present purposes be regarded as monochromatic. I n the radioactive x-ray sources of interest here, the foIIo\viiig sequence of events may he thought to occur. T h e nuc~lens captures an electron from the K - shell, and this transmutes the element into the one next nearer hydrogen in the periodic t:ihlp. T h e K- shell vacancy in the new element is now filled by : ~ i i L- electron, whereupon a K line of the new element is radiated. ;2lthough the intensity of this K line is usually low, it is no different for purposes of analysis from t’he same line generated :tt the same intensity in any other way, but the use of radioactive x-ray sources can nevertheless bring important advantages. Hughes and ITilczeu-aki ( 6 4 )capitalize on these advant:rges liy using iron-55 as a source for the K-lines of manganese for the determination of sulfur in hydrocarbons. T h e folloivirig quotation, of value as a genwal guide, explains their selection of t,his radioactive isotope. Of the more than 100 isotopes engaged in this process, only iron-55) nickel-59, rhodium-] 02, and cadmium-109 showed any promise of being useful for s-ray absorption analysis a t the time this work \vas st’arted. T h e criteria are: T h e half life should be reasonably long, so that the source does not decay too rapidly, yet not so long that, the specific activity is low; no other competing radiation should be emitt’ed (positive and negative p-ravs being easily absorbed are excepted); and it, should tie avafiable and readily processed into a useful, easily handled source. Iron-55 was chosen as the isotope most nearly meeting these requirements. T h e experimental met’hod consists essentially of using a Geiger counter to measure the attenuation by the sample of x-rays (wave length 2 A.) from the radioactive source. T h e usual ( ~ ) i i siderations apply, and the (slow) decay of the radioactive sourc’e must be taken into account. T h e great value of the method is clear from Table 111. T h e over-all reliability of the method is estimated a t 2u, or 0.05% sulfur. Xn important application of t h e method of Glocker and Frohnmayer ( 5 3 ) is discussed in the section captioned “Histochcmical .Inalysis.” Absorptiometry with Polychromatic Beams. Titus (134) gives i n comprehensive detail the quantitative analysis, by absorptiometry with polychromatic beams, of treated carbon brushps usrd in aircraft, this being the “point-to-point exploration of
For the sake of simplicity, ”x-ray absorption spectrometry” h a s been abandoned as a subdivision in these reviews. T h e term was used mainly t o deTable 111. Comparison of Speed, qccuracj-,and Cost of Determination of Sulfur i n scribe the method of Glocker Petroleum Products (64) and Frohnmayer (531, kvhich Speed can logically be included under Relative Cost Elapsed Operator Samples .iccuracy time, time, per Sulfur, EquipOperator “absorptiometry with monoMethod hours inin. day 70 inent tirne c h r o m a t i c b e a m s ” because Bomb-sulfur 24 36 13 0.03-0.14 5 i . 2 Lamp-sulfur 3 29 1G 0.03 1 5.8 the method is usually a difOld x-ray method (66) n.. 1._ 2 7 48 0.09 20 1.4 ferential measurement of this K-capture 0.08 5 GO 0.05 6 1.0 kind. “.ibsorptiometry with ~~
ANALYTICAL CHEMISTRY
586
beams to study detonation waves ( 7 4 )and boundary layers (14Z), as is the general subject of x-ray flash photography (47). ?-Ray Absorptiometry. Because y-rays are formed in nuclear processes, which generally involve high energies, one might eypect their wave lengths to be shorter than those of the usual x-rays, which result from electron transitions within atoms. One might espect further, considering the pronounced decrease of x-ray mass absorption coefficients with decreasing wave length, that mass absorption coefficients for ?-rays will be appreciably smaller than those ordinarily met with in x-ray absorptiometry. Table Is’, which has been constructed from data in standard references (60, 114), shows that both expectations are realized. Further, y-ray coefficients show markedly the smaller variation from element to element, and this gives x-rays an advantage for applications other than simple thickness gaging. Of course, the situation is considerably more complex than the simple statements above might indicate. For example, it is well known that scattering and photoelectric absorption both contribute to x-ray absorption coefficients, and that the photoelectric contribution tends t o increase with atomic number. As the wave length decreases, the photoelectric contribution becomes markedly less important, and this is the main reason why -pray coefficients are so much the smaller. On the other hand, these coefficients include y-rays consumed in the production ( a t energies above 1 m.e.v. ) of positron-electron pairs, a process impossible with ordinary x-rays. An excellent discussion of -pray absorption is given by Bethe and Ashkin (121). Extensive values of y-ray absorption coefficients are available from both theoretical (44, 125) and experimental work, much of the latter being necessary in connection with the shielding problems that have arisen in this atomic age (9, 45, 54, 57, 85, 107). As Table I V makes clear, samples for y-ray absorptiometry will generally have to be thicker than were x-rays being used. Accordingly, it is not surprising to find that the */-ray technique is making rapid progress in nondestructive testing, particularly in thickness gaging and in radiography (5, 18, 22, 52, 67, 140). The exceedingly high precision (0.01%) attained by Berman and Harris ( 1 2 ) in thickness measurements with a cobalt-60 source makes their work worthy of special mention. Many more references could be cited. ilebersold ( 5 ) lists as in Table V the radioactive isotopes most useful as y-ray sources in radiographv. - _ . These are likely also to be the most useful of the isotopes now available for ahsorptiometry in general. Leboeuf, Miller, a n d Table IV. Absorption of X-Rags and G a m m a - R a g s Connallj- ( 8 7 ) have carried out Energy, Wave Length, Mass Absorption Coefficienta -4. Carbon Water Aluminum Copper Lead h1.e Y a n extensive investigation of 1.24 2.5 5.2 ?-ray absorptiometry with 0.01 27 0.31 0.51 1.9 0.025 0.496 several sources (notably an 0.37 0.218 0.18 0.29 0.05 0.18 0.10 0.124 0.15 0.17 americium-plutonium mixture) 0.107 0.121 0.25 0,050 0.116 not listed in Table V. These 0.089 0.095 0.081 0.50 0,025 0.076 0.070 0.75 0.017 authors were in an exception0.067 0,059 0 : 069 0.012 1.00 ally favorable position to comFor definition of mass absorption coefficient, see, for example, (81, 84.88). pare y-ray and x-ray absorptiometry on highly absorbing samples (usually high both in mass and in atomic numTable V. Isotopes for Radiography (5) ber). The following quotaPrincipal 4pprox. y-Ray tion summarizes their comGamma R a y Approximate Output/Cu;ie. Isotope Half Life Energies, 1ZI.e.v. Specific Activity R/Hr./Ft. Type of Use parison.
impregnated materials” of an earlier review (136). The treatment consists usually of impregnating the brush stock with a solution of a salt-e.g., lead chloride, cadmium chloride, barium fluoride, barium bromide-to an extent that will leave the desired amount, usually a few per cent, of salt in the brush when the water has been removed. The purpose of the treatment is to reduce or eliminate excessive wear of brushes used on motors and generators operating a t high altitudes. The speed and nondestructive character of the method, and its adaptability to pointto-point exploration, were exceptionally useful in this application. Grohse (65) has found absorptiometry with polychromatic beams to be a unique method for studying the “fluidization” of a finely divided solid by a gas, as in beds of silicon fluidized by air. Bed density profiles, which reveal the character and effectiveness of fluidization, could be readily determined without disturbing the bed-impossible when internal probes are used. The usefulness of absorptiometry with polychromatic beams in the atomic energy program (93) has been extended by Lambert (30, 79-8S, 87), who applied this method to aqueous solutions of 35 compounds and ions of 25 elements tyidely distributed in the periodic table. K i t h elements of atomic numbers 42 to 65, Lambert encountered the “deviations from linearity” (96) to be expected under certain conditions when an absorption edge falls within the wave-length range of a polychromatic beam. Lambert’s extensive and precise absorbance data greatly facilitate x-ray absorptiometry with polychromatic beams. Terrell and Davidson (132) have corroborated published favorable experience (21, 108, 1 4 1 ) with the General Electric x-ray photometer in the petroleum industry, and have emphasized particularly the increase in operating efficiency that results because the speed of this x-ray method reduces the time during which the product being tested must remain in compounding facilities or in storage. Cranston, M a t t h e w , and Evans ( 3 5 ) have published the results of an extensive British study of the determination of sulfur in hydrocarbons. The method in principle closely resembles that of the previous paragraph but the equipment is different. The extensive analytical results in general show that the Sunbury method is highly reliable. Esceptionally interesting, b u t outside conventional analytical chemistry, is the use of absorptiometry with polychromatic
Cobalt 60
5.3 years
1.1,1.3
35 c/g-1954
14.4
Tantalum 182
117 days
1.1,1.2
1 . 5 C/g
6.7
Cesium 137 Iridium 192
37 years 75 days
0 66 0 3,O S
20 C/g-l955 30 C/g-l951
3.5 3.0
Thulium 170
127 days
0.088
a
Service irradiation
Roentgens in 1 hour a t 1-foot distance from source.
Heavy castings, thick weldments Heavy castings, thick weldments Pipe lines, light alloys. thin sections Light alloys, thin sections
The principal advantages of using radioisotopes as gamma photon sources are the following: 1. Extreme stability of source intensity 2. D e c r e a s e d i n s t r u m e n t complexity 3. Compact size
V O L U M E 2 8 , NO. 4, A P R I L 1 9 5 6 4. More nearly monoenergetic characteristic of the emitted photons. 5. Much wider range of photon energies available, about 202,000 k.e.v. 6. Lower over-all cost of the instrument.
The principal limitation is the low intensity generally available compared to the extremely high intensities from x-ray tubes. Because of this, these sources cannot effectively compete with x-ray photometry in the energy range u p to 50 k.e.v. I n tlie range 50 to 400 k.e.v., however, these sources offer attract,ive Iiossibilities. Berrihard and Chasek (13) applied y-ray absorptiometry to the measurement of soil density with encouraging results. Further applications should be forthcoming soon. ERIISSIOZ
X-Ray Emission Spectrography. A brief review of this rapidly developing field cannot do justice t o all the good work that. is being done. It is unfortunately necessary to call attention to the continuing confusion in nomenclature, which is obvious among the 35 papers on the subject given a t the recent Pittsburgh Conferences (6-8)-especially among those in 1955. “X-ray emission spectrography” was chosen as a name here because it is operational ( a spectroyiaph, not a spectroscope is used), and because i t includes characteristic x-ray s p x t r a excited by any means whatever-not “fluorescent” x-rays alone. Especially with x-ray excitation, pronounced “deviations due to absorption” (19) can occur, and the intensity of an emitted line consequently cannot be regarded as proportional to the concentration of an element in a sample. These deviations can be duc to one or more of the folloiving causes. “Filtering” effect on an incident polychromatic beam, absorption of the incident beam, absorption of the analytical (charact.eristic) line, and enhancement of the analytical line owing to escitation by the characteristic line of another element in the sample. Sherman (IB), who has investigated these deviations theoretically and experimentally for several years, has recently (8) treated the difficult cnlianrement problem with highly encouraging results. I n solving the comples mathematical problem of enhancement with monochromatic excitation, Sherman takes into account the varioils absorption and emission coefficients and derives equations that yield results in satisfactory agreemrrit with observed value?. H e further indicates hon- the problem of polychromatic excitation may be solved. Beattie and Brissey ( 1 0 ) have given a satisfactory, semiempirical treatment of deviations due to absorption in quaternary high-temperature alloys. Several other matters of general interest remain. I t has been shoivn experimentally (94)that an s-raj- emission spectrograph operating under ideal conditions may, as concerns precision, be reguded as a random system in which the predictable standard deviation ( S C = is realized. Conversely, if the actual standard deviation exceeds the predictable, operating conditions are not ideal. The latest in a series of investigations concerned with the (small) effect of chemical combination of x-ray spectra is dwcribed by Cauchois ( 6 7 ) . The increasing use of x-ray emission spectrography for the determination of elements in small aniounts ( 9 3 ) received particular attention a t the 1955 Pittsburgh Conference (8) and is evident in many of the references cited below. Rhodin (8) analyzed thin films, and Pfeiffer and Zemany ( 113)showed t h a t x-ray emission spectrography is adaptal)le to spot test techniques. Gruhb and Zenianj- (56) moved further in the same direction by using an ion-exchange membrane to concentrate traces of ions for subsequent determination in the x-ray spectrograph. The usefulness of x-ray emission in the petroleum industry is evident (17,28,56,37‘, 76, 78, 91, 135); three different examples will be cited. Lamb, Siebylski, and Kiefer (18)extended earlier work of Birks, Brooks, Friedman, and Roe ( 17) to show t h a t x-ray emission spectrography could compete successfully with x-ray absorptiometry in the determination of tetraethyllead in gasoline
4s)
587 (91) and that variations in the composition of the matrix (everything not being determined-e.g., sulfur, other impurities, and organic halides) were easier to deal with in the emission method. Davis and Van Nordstrand ( 3 6 ) used the method for barium, calcium, and zinc in lubricating oils. Determination of the first two elements required the use of a helium path, and certain deviations due to absorption were treated mathematically to give results in accord with experiment. Dyroff and Skiba ( 3 7 ) have done murh to solve another prolilem that has recently vexed the petroleum industry-the determination of traces of iron, nickel, and vanadium in cracking catalysts-it being well known that the latter two elements are especially objectionable even when present in minute amounts. The application of x-ray spectrography to the analysis of minerals generally has progressed rapidly during the past 2 years ( 2 , 3, 4, 1, 8, 24, 58, 69, 73, 84,206, 120, 163, 130, 139). I n part, this progress has come because x-ray emission can, with miiiinium trouble and preferably by use of a helium path, reveal which of the important metals are present in a n untreated ore and give a fair indication of their amounts even when these amounts are small. Further impetus derives from the fact that the x-ray method escapes the complexities of w-et chemical analysis-e.g., in determinations of elements such as tungsten, tantalum, or the rare earths. Thus, hdler and Axelrod a t the U. S. Geological Survey have determined thoria iu rock samples with thallium as an internal standard (2). Tournay (138), using electron escitation, has found the intensity ratio of an L line of uranium to an L line of thorium to be a simple function of composition, so that the addition of a standard was unnecessary; Tournay (136, 137) also applied this method to the determination of niobium and tantalum in cassiterite slags. Campbell and Carl ( 2 3 ) at the Eastern Esperinient Station of the Bureau of 3Iines have for several years been investigating x-ray emission techniques for thia determination, three of which (establishing niobium-tantalum ratio in separated oxide mistures; internal standards techniques; use of an additivp) gave results believed by them to be more reliable than those bj- existing chemical methods. These authors (8) have carried out a similar study of the determination of germanium in coal and coal ashes. X-ray emission spectrograph:- continues useful in the deterniination of major constituents in alloj,s, as is clear from the papers presented at, the Pittsburgh Conferences (6-8)and from other references cited in t’his section. The number of recently published papers dealing exclusively with this application (19, 61, 62. 101, 102) is not large, perhaps because the method is proving to be relatively trouble-free. Nihalisin (102) reports the saving of time usually realized when x-ray emission spectr ography is used in combination with established w t methods in the analysis of high-temperature alloys and cites data showing the x-ray results to be sufficiently reliable for quality control. Clark, Loranger, Bodnar, and Terford (32, 3.3) combined x-ray emission spectrography with x-ray diffraction and with radiography in a comprehensive analysis of foundry dusts, which sometimes constitute health hazards. The development of apparatus for x-ray emission spectrography goes forward rapidlj-. The trends are toward curved crystals to increase intensity and simplify optics (1.5, 7 l ) , toward increasing use of the proportional and the scintillation counter (14, 29, 46>50, 76, 103, 131, I @ ) , and of course toward more completely automatic equipment (66, 70, 78, 116, 129). The large spectrographs cannot be adequately described here. Several smaller instruments are of particular interest. Birks and Brooks (15) describe a curved-crystal spectrograph for which intensity, resolution, and line-background ratio were as favorable for a 1-mg. sample as for a 10-gram sample in a commercial flat-crystal spectrograph. These authors ( 1 6 ) also describe a miniature spectrograph without moving parts that is used on ordinary diffraction equipment with a photographic plate. Cas-
588 taing and Guinier (26) have published a n English description of their “electronic microanalyzer,” discussed in a n earlier review (91). Macdonald and Harwood (99) have developed equipment unusual in several respects. It combines a spectrograph employing electron excitation with an electron diffraction unit so t h a t an x-ray spectrogram and an electron diffraction pattern could be photographed for the same sample, which gives information a t once about ultimate composition and about the compounds present. iZ plane glass optical diffraction grating was used to disperse characteristic lines ranging from 5 to 200 A%. T h e equipment should prove pal ticularly valuable in the studv of surface films. Another vacuum spectrograph, described by llorlet (104), provides for velocity selection of the exciting electron beam and is capable of handling K- and L-spectra in the range 2 to 20 A. Xdler and Axelrod ( 3 )have designed a “multiwave-length‘ ’ spectrograph that provides for the simultaneous measurement of as many as four characteristic lines. Four channels, each containing a detector, a goniometer, an analyzing crystal, and a collimator, converge on a single x-ray tube and sample holder. One of the goniometers doubles as a scanning goniometer. A two-goniometer prototype has been built and applied successfully to the determination of niobium in bauxite ores. Three valuable techniques related to x-ray emission spectrography employ unusually interesting equipment. Steinhardt and Serfass (126, 127) use a n “x-ray photoelectron spectrometer” for the study of surfaces. The process studied may be regarded as electron excitation in reveise-here an x-ray beam is used to produce a characteristic electron spectrum in which the variation of photoelectron intensity with photoelectron energy characterizes the sample surface. H&mos (39)has built a n “x-ray microanalyzer camera,” in which a single cylindrically bent crystal is used to reflect onto a photographic plate all the characteristic x-rays evcited by an x-ray beam incident upon a very small sample area. The applications tested, which follow, show why this instrument is of great potential value: precise thickness measurements on surface layers between 2 X 10-5 and 3 X cm. thick; microanalysis of alloys on volumes near cc.; concentration variations in surface layers-e.g., determination of microscopic segregations. Finally, though Lindstrom (97) is concerned primarily with ahsorptiometry (see “Histochemical A4nalysis’’ below), his techniques and equipment are of interest t o anyone concerned with v-raj- emission spectrography a t the longer wave lengths. ?-Ray Spectrometry. This technique (8, 68, 111) is restricted t o radioactive isotopes and to elements that can be made t o yield radioactive isotopes. It is related to x-ray emission spectrography, the principal differences stemming from the fact that nuclei-not atoms-are the sources of ?-rays. .4s ordinarily practiced, ?-ray spectrometry involves the measurement of the intensity of radiant energy as a function of wave length, and thus goes beyond spectrometry as usually defined--/-ray spectrography might be a hetter name. Kahn and Lyon ( 6 8 ) have this to say: This method simplifies radiochemical analysis, but does not, of course, replace it. The energies of the -prays from any one radioisotope are characteristic, but by no means unique; hence, identification by this method may have to be augmented by determination of half life and maximum beta energy, or by chemical separation. While chemical similarity presents no problem, similarity in the gamma energies of two substances in the sample may give misleading results. Pure beta emitters cannot be identified by this method, but their maximum beta energy may be obtained with the spectrometer. T h e gamma spectrometer goes beyond radiochemical analysis in t h a t a particular radioisotope, rather than just a n element, is identified. A plications of the method are numerous. T h e spectrometer is o f use in the solution of many problems in the radiochemical laboratory, in checking procedures, and in analyzing unknown substances.
ANALYTICAL CHEMISTRY For reasons given in the section entitled “Detectors,” a arintillation rounter with pulse-height discrimination is ordinarily the most, desirable detector for -/-ray spectrometry. The identification and study of radioactive isotopes in t h r atomic energy program and their monitoring in tracer esperiments are two important applications of y-ray spectrometr!.. I n necessarily simple form, the technique is also used in aerixl prospecting for radioactive minerals (112, 119, 128) and oil (115). Peirson and Franklin (112) have estimated that uranium can Iw just detected above background so long as the factor (per (wit Us08 times area in square yards) exceeds 100, the 0bservatio:is being made from a plane traveling 120 miles per hour a t an altitude of 500 feet. Finally, -/-ray spectrometry is doing much to simplify and to increase the reliability of neut’ron activation analysis, a n example being the determination of impurities in nixterials of semiconductor grade purity such as silicon (10.5). HISTOCIiER.IIChL ANALYSIS
The interesting and important work on s-ray methods of histochemical analysis being carried on by Engstrom and his collaborators has had only brief mention in earlier reviews (88, SO-93). Airecent comprehensive publication by Lindstrom ( 9 7 ) emphasizw anew t h a t this research is making a major contribution not only to our knowledge of the living cell but also to the difficult terhnique of using long-Tyave-length ( 2 . 5 h. and above) x-rays i n microanalysis. The two major kinds of analytical prohlenis solved are consequently desrribetl here in some detail.
METAL DISC WITH WPPORTlNO SPECIMEN AN0 REFERENCE SYSTEM
FOIL,
Figure 2. Schematic diagram of apparatus for determining dry weight of li\ing tissues (97) Thc following general ol)swv:Ltioris apply to both kinds of prolilems. The scde of operations is fixed by the necessity of ?omparing adjacent sections of tissue only microns in width, which makes i t advisable to use the photographic plate as detector, in order that the necessary measurements of x-ray intensity can he made on greatly enlarged areas. Inasmuch as lighter elements are principally involved, long-wave-length x-rays must be employed. This in turn requires thin samples and a vacuum path. Finally, for work in vacuum, the samples must be dry. Determination of Dry Weight. The first problem is that of finding the dry weight per unit area, and the variations therein, of various cytologic structures. This problem is solved by means of absorptiometry with a filtered, continuous polychromatic heam of 1.5-kv. peak or 8.3 A. minimum wave length. The ana,lysis is done by the comparative method with a carefully prepared step gage of nitrocellulose foils as standard (see schematic Figure 2). The reliability of the results depends in large measure on how well deviations from the (ideal) linear relationship between log Z and dry weight per unit area can be eliminated or allowed for. It is Fell known, this can be accomplished by the comparative method (144), provided that standard (reference system) and unknown, identical in mass, shape, and elementary composition, are exposed to the same x-ray beam. I n the cytological investigations, these conditions arr difficault to meet, not only because
V O L U M E 2 8 , NO. 4, A P R I L 1 9 5 6
589
the samples are comples in composition, h u t also because they are very small, as is clear from the units employed (mioromicrograms per square micron or lo-'? gram per 10-8 sq. cm.). Fortunately, some simplifmtions are possible. Carbon, nitrogen, and oxygen in tissue proteins are the elements principally responsible for the ahsorption of x-rays by the different biological structures. Furthermore, the elementary composition of proteins varies little even though they are made up of various amino acids in greatly different proportions. Nitrocellulose foils therefore make satisfactory standard step gages. T h e elementary compositions of these standards and of the unknowns are similar enough so t h a t differences in x-ray ahsorption can he alloaed for on the b a a s of the systematic "errors" (some positive, Some negative) t h a t can he approximated in advance. Lindstram ( 9 7 ) has computed such systematic errors not only for the important constituents of biological materials a t six wave lengths in the range 2.5 to 22 A,, but also for the polychromatic beam actually employed. (Only polychromatic beams can meet the high intensity requirements imposed by the low sensitivities of the fine-grained emulsions employed to ensure sufficiently high resolution.)
Table VI. Data on 20 Cells Cell No.
nd,,
mr, Mi010miclogrsms
An impressive demonstration of what can he done with thc method is provided by Figure 3, which shows a microradiogram of a section of striated muscle, a n excellent test object. I n the figure, anisotropic bands (white, 0.5 t o 0.7 micron wide) of high dry-weight per unit area alternate with broader (dark, 1.3 to 1.5 microns wide) isotropic hands whose dry weight per unit area is lower in the ratio 1 to 1.41 + 0.05. The ratio is the mean of ten values obtained by photometering ilreas of ahout 1.5 square microns (1.5 X 10-8 sq. em.) each, and the small uncertainty in the mean includes the natural variations in the tissue! The kind of detailed quantitative information the method can yield is well illustrated by the determination of the total dry nreight of individual ascites tumor cells, the volume of each cell being less than 4 X 10-g cc. The total dry weight, m, of a cell is given by m, = 1.32 u,wma/6 (for units, see Table V I )
where number of standard foils equivalent in absorbance to the sample w = weight per unit area (1.775 micromicrograms per sq. micron) of one standard foil a = diameter of cell The data far twenty individual cells are given in TaMe VI. The mean value of the dry weight, (3.95 + 0.20) X tir =
of samples containing many cells. Such analyses cannot, of course, reveal the.individud variations t h a t appear in Table VI. Elementary Analyses on a Cytochemical Scale. Calcium, phosphorus, and sulfur have been quantitatively determined in biological samples comparable in volume with t h e living cell (97). The initid step in this direction was taken by Engstriim (411, who was the first to show t h a t the method of Gloeker and Frohnmayer (65),could he successfully applied to microtome sections of biological materiala At the long wave lengths necessary, the problem of obtaining high enough intensity in t h e monochromatic beam is especially acute. This makes i t desirable to modify the original method of Glocker and Frohnmayeyer whenever possible, by using characteristic lines of suitable elements to replace the usually less intense monochromatic x-rays diffracted by a crystal from a polychromatic beam. This modification, m d e by Moxnes (109, 110) and by EngstrBm (4$),will not be given a special name. T o carry out the analyses, i t was neeessay to design and build a high-vacuum x-ray spectrophotometer t h a t employed a curved crystal (nsually quartz with an approprinte radius of curvzture) to ensure sufficient intensity. The photographic plate served as deteotor, and exposure times ranged from 30 minutes to 4 hours. Only one wave length near each side of the ahsorption edge was used, and the distance of each wave length from the edge N&S appropriately allowed for. For the determination of calcium (absorption edge near 3.1 A,) the monochromatic beams had to be taken from a polychromatic beam of 7 kv., because suitable charaoteristic lines were unavaihhle. I n the case of phosphorus (absorption edge near 5.8 A,), the La, line of niobium and the LBLline of zirconium were used. The Lal line of ruthenium and the LgI line of molybdenum served for determining sulfur (absorption edg,
Figure 3. M i c r o r a d i o g r a m of 3-niieron thick section of fwrnalin-fixed striated r n u s z l z of Chironornics
The neeumcy and precision of the results may be Judged trom the following. I n sections of biological materials, about 10 microns thick, the ahsolute errors in tbe determination of calcium ranged between 1 0 . 1 5 and = t o 2 micromicrograms per square micron; those for phosphorus and sulfur between f0.06 and + O . l micromicrograms per square micron. These errors often corresponded to less than 5 % of the amount of element present in the sample. Although the accuracy and precision of the method are rcmsrkahle in light of the minute samples, the outstanding feature
ANALYTICAL CHEMISTRY
590 Table VII.
Research Results for Biological Materials
Sample Human bone tissue
Conclusions‘ Single Haversian systems differ significantly in calcium-phosphorus ratio. Arterial wall in arteriosclerosis Dense, homogeneous, calcified section of wall shows 3.3 times as much calcium a s phosphorus. Human kidney section Homogeneous section of renal calculus contains 5.3 + 0.2 micromicrograms calcium per square micron. Sucleolus contains about 4.4%. DhosSea urchin eze . phorus. R a t epidermii Corneal and spinous layers are roughly identical in sulfur concentration. Based on analytical results by new methods on necessarily restricted number of samples, may subsequently need to be modified.
__
of the work is this minuteness itself, which makes it possible t o discover how the chemical composition of biological materials varies from one small section to another. The data thus obtained can be combined XTith dry-weight data from absorptiometry with polychromatic beams to yield conclusions of the kind listed in Table VII. Owing to the complexity of living tissue, the x-ray techniques described above will often need to be supplemented with others. Recent work shows the progress t h a t can be expected to follow from such a concerted analytical approach (11, 26) 38-40, 43, 98). ACKKOWLEDGMEYT
For help in the preparation of this review, the authors wish Institutet, Stockholm, William Parrish, Philips Laboratories, and several of their colleagues, notably H. G. Pfeiffer and P. D. Zemany. t o thank Bo Lindstrom, Karolinska
LITERATURE CITED
(1) Adler, I., dxelrod, J. M.,ANAL.CHEM.26, 931 (1954). (2) Ibid., 27, 1002 (1955). (3) Adler, I., Axelrod, J. AI., J . Opt. SOC.Amer. 43, 769 (1953). (4) Adler, I., Axelrod, J. AI., Spectrochim. Acta 7, 91 (1955). (5) A4ebersold,P. C., AVondestructize Testing 12, No. 3, 19 (1954). ANAL.CHEY.25,358 (1953). Ibid., 26,423 (1954). Ibid., 27,308 (1965). Beach, L. A., Theus, R. B., Faust, TT’. R., Phys. Rev. 92, 355 (1963). Beattie, H. J., Brissey, R. XI., ANAL.CHEY.26, 980 (1954). Bergman, G., Engfeldt, B.. Beta Pathol. Microbial. Scand. 35, No. 6, 537 (1954). Berman, A. I., Harris, J. N., Rea. Sci. Instr. 25,21 (1954). Bernhard, R. K., Chasek, I f . , Sondestructice Testing 11, So. 8, 17 (1953). Birks, J. B., “Scintillation Counters,” LIcGraw-Hill, Xew York, 1953. Birks, L. S., Brooks, E. J., ANAL.CHEM.27, 437 (1955). Ibid., p. 1147. Birks, L. S., Brooks, E. J., Friedman, H., Roe, R. AI., Ibid., 22,1258 (1950). Brewer, D . E., Iron Age 172, S o . 27, 80 (1953). Brissey, R. AI.. Liebhafsky, H. A., Pfeiffer, H. G., .hi. SOC. Testing AIaterials, Spec. Tech. Pub. 157, 43 (1954). Broser, I., Oeser, H., Warminsky, R., Strahlentherapie 90, 399 (1953). Calingaert, G., Lamb, F. W.,lfiller, H. L., Koakes, G. E., ASAL.CHEY.22,1238 (1950). Calkins. G. D., Pobereskin, AI., Chem. Eng. Progr. Symposium Ser. 50, No. 11, 259 (1954). Campbell, 1%‘. J., Carl, H. F., ANAL.CHEM.26, 800 (1954). Carl, H. F., Campbell, IT. J., Am. SOC. Testing Materials, Spec. Tech. Pub. 157,63 (1954). Carlstrom, D., J . Histochem. and Cytochem. 2, S o . 2, 149 (Xlarch 1954). Castaing, R., Guinier, A , AKAL.CHEM.25, 724 (1953). Cauchois, Y., J . chtm. p h y s 51, KO.1, D76 (1954). Chem. Eng. S e w s 31,4781 (1953). Ibid., 32, 584 (1954). Ibid. p. 3833. Clark, G. L., “Applied X-Rays,” 4th ed., AIcGraw-Hill, S e w York. 1955.
Clark, G. L., Loranger, W.F., Bodnsr, 9. J., AIVAL. CHEY.26, 1413 (1954). Clark, G. L., Terford, H. C., Ibid., 26, 1416 (1954). Compton, A. H., Allison, S. K., “X-Rays in Theory and Experiment,” 2nd ed., Van Sostrand, Kew York, 1943. Cranston, R. W,, lfatthews, F. 1%‘. H., Evans, N., J . I m t . Petroleum 40, 55 (1954). Davis, E. N., Van Xordstrand, R. A,, ASAL. CHEW26, 973 (1954). Dyroff, G. V., Skiba, P., Ibid., 26, 1774 (1954). Engfeldt, B., Cancer 7, S o . 4, 815 (July 1954). Engfeldt, B., Engstrom, A., Datta, N., Ezptl. Cell Research, Suppl. 3, 110 (1955). Engfeldt, B., Engstrom, d.,Zetterstrom, R., J . Bone and J o i ~ t Surgery 36B, N o . 4, 654 (Xov. 1954). Engstrom, A , , Acta Radiol. Suppl. 63, (1946). Engstrom, A , , Rea. Sci. Instr. 18, 681 (1947). Engstrom, d.,Carlstrom, D., Scensk Kem. Tidskr. 67, 107 (1955). Fano, U., Sucleonics 11, S o . 8 , 8 (1953). Ibid., S o . 9, p. 55. Flugge, S., Trendelenburg, F., “Ergebnisse der exakten S a t u r wissenschaften.” 1’01. XXVII, p. 361 (A. Krebs), SpringerVerlag, Berlin, 1953. Ibid., 5’01. XXVIII,p. 1 (W. Schaaffs), 1955. Foody, F. B., personal communication, Oct. 10, 1955. Rea. Sci. Instr. 25, 746 (1954). Foote. R. S., Koch, H. W., Friedman, H., Birks, L. S.,Brooks, E. J., Am. SOC.Testing Materials, Spec. Tech. Pub. 157, 3 (1954). Gahlen, W., Strahlentherapie 96, 474 (1955) Garrett, C., Morrison, A,, Rice, G., Am. SOC.Testing Naterials, Spec. Tech. Pub. 145,9 (1953). Glocker, R., Frohnmayer, W., A n n . Physik 76, 369 (1925). Goldstein, H., Wilkins, J. E., Jr., U. S. Atomic Energy Commission, Rept. NYO-3075 (1954). Grohse, E. IT., A.I.Ch.E. Journal 1,358 (1955). Grubb, W ,T., Zemany, P. D., Suture 176, 221 (1955). Gueben, G., Bull. S O C . roy. sci. Liege 22, 11 (1953). Gulbransen, L. B., ANAL.CHEM.27, 1181 (1955). HBmos, L. v., “X-Ray Xcroanalyaer Camera,” Elanders Boktryckeri Aktiebolag, Goteborg, 1953; Trans. Roy. Inst. TechnoZ. Stockholm 68, (1953); Ceram. Abstr. 33, 36 (1954): A p p l . Mechanics Reo. 155 (April 1954). “Handbook of Chemistry and Physics,” 36th ed., p. 2398, Chemical Rubber Publishing Co., Cleveland, Ohio, 1954. Hasler, 11. F., Kemp, J. W..Am. SOC.Testing Materials, Spec. Tech. Pub. 157,34 (1954). Hasler. L l . F.. Rittenhouse. J.. Am. Inst. JIinine- and Met. Engrs., Electric Furnace Steel Conference, preprint, 1954. Hendee, C. H., Fine, S.,Phys. R e t . 95, 281 (1954). ANAL.CHEM.26,1889 (1954). Hughes, H. K.. ITilcsewski. J. W., Hughes, H . K., Wilcaewski, J. W., Proc. Bm. Petroleum I m t . 30 M(III), 11 (1950). Instr. Automat. 27, No. 1, 150 (1954). Johnston, J. E., Faires, R. -4.,hlillett, R. J., Proc. Second Radioisotope Conference, Atomic Energy Research Establishment, Oxford, July 1954; “Physical Sciences and Industrial ;Ipplications,” Vol 11, Butterworths Scientific Publirations. London, 1954. Kahn, B., Lyon, 77’. S., Sucleonics 11, S o . 11, 61 (1953). Kemp, J. W.,Andermann, G., 1st Ottawa Symposium on Applied Spectroscopy, Ottawa, Ont., (September 1954); . 4 ~ CHEY. . 26,1665 (1954). Kemp, J. W., Jones, J. L., Hasler, AI, F., Pittsburgh Conference on -4nalytiral Chemistry and .-ipplied Spectroscopy, Pittsburgh, Pa., March 1954. Kemp, J. W., Jones, J., Zeitx, L., Pittsburgh Conference on Analytical Chemistry and dpplied Spectroscopy, Pittsburgh, Pa., March 1955. Kemp, J. W., lIcCory, L. E., Hasler, A l , F., Pittsburgh Conference on dnalytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., Ilarch 1954. King, A. G., Dunton, P., Science 122, 72 (1955). Kistiakomsky, G. B., J . Chem. Phys. 19, 1611 (1951). Kohler, T. R., Parriah, W., Rev. Sci. Instr. 26, 374 (1955). Kokotailo, G. T., Damon, G. F., ASAL.CHEY.25, 1185 (1953). Krebs, A. T., Science 122, S o . 3157, 17 (1955). Lamb, F. IT., Kiebyljki, L. M,, Kiefer, E. W.,A N ~ LCHEM. . 27, 129 (1955). Lambert, I f . C., Xorthwest Regional Meeting, d C S , Richland, Wash., June 1950. Ibid., June 1954. Lambert, 11. C., U. S. .-itomic Energy Commission, Rept. HW-24717 (1952). Ibid., HW-30190 (1954). Ibid., HW-30634 (1954).
V O L U M E 28, NO. 4, A P R I L 1 9 5 6
591
Laning, S. H., Division of Analytical Chemistry, 128th Meeting, ACS, Minneapolis, hlinn., September 1955. Land, L. H., Skaggs, L. S., Pingel, J. H., Rose, J. E., Rea. Sci. Instr. 24,394 (1953). Lapp, R. E., Andrews, H. L., “Nuclear Radiation Physics,” Prentice-Hall, New York, 1948. Leboeuf, 31. B., Miller, D. G., Connally, R. E., Nucleonics 12. No. 8.18 (1954). Liebhafsky, H. A., A ~ A LCHEM. . 21, 17 (1949). Ibid., 22,15 (1950). Ibid., 23,14 (1951). Ibid., 24,16 (1952). Ibid., 25,689 (1953). Ibid.. 26.26 (1954). Liebhafsky, ‘H. +4., Pfeiffer, H. G., Zemany, P. D., Ibid., 27, 1257 (1955). LiebhaGky, H. A., Smith, H. ll.,Tanis, H. E., Winslow, E. H., Ibid., 19,861 (1947). Liebhafsky, H. A., Zemany, P. D., Ibid., 23, 970 (1951). Lindstrijm. B., Acta Radwl. Supp2. 125 (1955). Lindstrom, B., hloberger, G., Ezitl. Cell Research 9, 68 (1955). Macdonald, G. L., Harwood, -M. G., Brit. J . A p p l . Phys. 6, 168 (1955). LIaeder, D., Rev.s e i . Instr. 26,805 (1955). hIariC?e,Ll., Chim. I n d . 72, KO.3 bis, 156 (1954). Mihalisin, J. R.. Iron Age 174, No. 3, 108 (1954). Miller, D. C., il’orelco Reporter 2 [ l ] , 3 (1955). >lorlet, J., Bull. classe sci., Acad. roy. Belg. 39, 205 (1953). Xorrison. G. H.. Coserove. J. F.. Pittsburgh Conference on ilnalytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 1955. ;\lortimore, D. >I., Romans, P. A., Tews, J. L., Sorelco Reporter 1, [7], 107 (1954). lloteff, J., Nucleonics 13, KO.7 , 24 (1955). llottlau, -1.Y., Driesens, C. E., Jr., ASAL. CHEX 24, 1852 (1952). Aloxnes, N. H., 2. physik. Chem. A144, 134 (1929). Ibid., A 152,380 (1931). O’Kelley, G. D., U. S. Atomic Energy Commission, Tech. Inform. Service, Oak Ridge, Tenn., MTA-31, 5-17 (1952). Peirson, D. H., Franklin, E., Brit. J . A p p l . Phys. 2, 281 (1951). Pfeiffer, H. G., Zemany, P. D., Nature 174, 397 (1954). Pollard, E. C., Davidson, W. L., “Applied Xuclear Physics,” 2nd ed., Wiley. New York, 1951. Pringle, R. TV.. Roulston, K. I., Brownell, G. W.,Lundberg, H. T. F., Trans. Am. Inst. Mining M e t . Engrs. 196, Tech. Pub. 3642-L; Mining Eng. 5 , No. 12, 1255 (1953).
REVIEW OF FUNDAMENTAL
(116) (117) (118) (119) (120)
Rev.Sci.Instr. 26,94 (1955). Ibid., p. 630. Rowland, R. E., J . A p p l . Phys. 24, 811 (1953). Russell, W.L., Econ. Geol. 46,427 (1951). Salmon, A I . L., Blacklodge. J. P., 16th Midwest Regional
Meeting, ACS, Omaha, -Neb., November 1954. (121) Segr6, E., “Experimental Nuclear Physics,” Vol. 1, p. 304 (H. A. Bethe and J. Ashkin), Wiley, New York, 1953. (122) Sherman, J., Am. SOC.Testing Materials, Spec. Tech. Pub. 157,27 (1954). (123) Shurkus, A. A., I n d . Labs. 4, No. 2, 8 (1953). (124) Simon, H.. Ann Physik 12,45 (1953). (125) Spencer, L. V., Fano, U., Phys. Rev. 81, 464 (1951). (126) Steinhardt, R. G., Jr., Serfass, E. J., AKAL.CHELI.23, 1586 (1951). (127) Ibid., 25,697 (1953). (128) Steljes, J. F., Brit. J . A p p l . Phys. 3, 203 (1952). (129) Sterk, A. A., Pittsburgh Conference on rlnalytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 1955. (130) Stevenson, J. S., Am. Mineralogist 39, 436 (1954). (131) Taylor, J., Parrish, W., Rev.Sei. Instr. 26, 367 (1955). (132) Terrell, H. D., Davidson, J. C., Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., March 1955. (133) Thomas, B. W.,I n d . Eng. Chern. 46, S o . 3, 93.4 (1954). (134) Titus, A. C., Power Apparatus and Systems, No. 14, 1160 (October 1954). (135) Titus, A. C., Winslow, E. H., “Review of Control and Evaluation of Carbon Brush Impregnation Treatments Using X-Rav” (Photometer) iibsorution 3Iethod.” General Electric \ Co., Schenectady, ’ N. I !., Tech. Information Series R 53MG301. (136) Tournay, AI., BUZZ. SOC. franc. mineral et crist. 76, S o . 10-12, LXIII (1953). (137) Ibid., 77,725 (1954). (138) Tournay, M., Compt. rend. 234,2527 (1952). (139) Traill, R. J., Can. Mining J . 76, 55 (March 1955). (140) Untermyer, S., ivucleonics 12, KO.5, 35 (1954). (141) T’ollmar, R. C., Petterson, E. E., Petruzeelli, P. .4.,ANAL. CHEY.21, 1491 (1949). (142) Weltmann, R. N., Kuhns, P. TV., Ifatl. Advisory Conim. Beronaut., Tech. Tote 3098 (1954). (143) Wilkinson, D. H., “Ionization Chambers and Counters,” Cambridge hlonographs on Physics, Cambridge University Press, Cambridge, 1950. (144) Zemany, P. D., Winslow, E. H., Poellmitz, G. S., Liebhafsky, H. d.,ANAL.CHEM.21,493 (1949).
i Diffraction
I I I
BENJAMIN POST and ISIDOR FANKUCHEN Polytechnic Institute o f Brooklyn, Brooklyn 1, N. Y.
I
N THE present review no effort has been made t o comment on, or even t o list, all papers dealing with x-ray diffraction which have appeared during the past year. Rather, an effort has been made t o limit the discussion t o items which are believed t o be of general interest t o chemists; emphasis has been placed on analytical methods and crystallographic studies of organic and inorganic compounds. Several books dealing with various aspects of x-ray crystallography have appeared during the past year; two are especially noteworthy. Both deal with “powder” methods of x-ray difhaction-i.e., t h e x-ray studies of polycrystalline materials. ‘‘XR a y Diffraction Procedures” b y Klug and Alexander (44)is an excellent manual of techniques ; “X-Ray Diffraction b y Polycrystalline Materials” by Peiser, Rooksby, and Wilson (59) is a
collection of essays which deals extensively 11ith a n-ide variety of topics in x-ray diffraction. Both volumes present large amounts of material n o t readily available n-ithout a thorough search of the literature. Two journals are now devoted exclusiveiy t o publication of crystallographic papers: Acta Crystalloyraphica and Zeitschrifl f u r Kristallographie. T h e latter resumed publication in October 1954, after discontinuing publication during the war. APPARATUS AND TECHNIQUES
A goniometer has been described which is designed t o facilitate t h e investigation of diffraction intensities from single crystal8
using Geiger counters (30). T h e crystal m a y b e rotated about each of t h e Eulerian axes; each reciprocal lattice point may be
