Spectral Distribution of a Thin Window Rhodium Target X-Ray Spectrographic Tube J. V. Gilfrich, P. G. Burkhalter, R. R. Whitlock, E. S. Warden,’ and L. S. Birks Naval Research Laboratory, Washington, D . C. 20390
PREVIOUSLY(I, 2) we have published the spectral distribution for W-, Mo-, Cu-, and Cr-target X-ray spectrographic tubes for use by analysts in the “Fundamental Parameter” technique (3) for X-ray fluorescence analysis. The present note gives similar information on the new Rh target SEG-SOH tube. Rh is one of the best targets for general use because the atomic number is moderately high, yielding good continuum intensity as well as both the K- and L-series characteristic lines which can be used for exciting the specimens. In 1
Present address, University of Maryland, College Park, Md.
(1) J. V. Gilfrich and L. S. Birks, ANAL.CHEM., 40, 1077 (1968). (2) L. S. Birks, “X-Ray Spectrochemical Analysis,” 2nd ed., Interscience Publishers, New York, 1969, pp 121-8. (3) J. W. Criss and L. S. Birks, ANAL.CHEM., 40, 1080 (1968).
addition, the new thinner window transmits more primary radiation of long wavelength which greatly improves the excitation of low atomic number elements. EXPERIMENTAL The measurements were made in a modified single crystal X-ray spectrometer in much the same manner as reported previously (1) and as shown in Figure 1 of Reference 1. However, because the intent was to extend the spectral measurements to relatively long wavelengths, it was necessary to use a vacuum spectrometer. It was also necessary to use several different crystals to diffract in different portions of the wavelength range of interest because the LiF (200) used in the preyious work is limited to wavelengths shorter than about 3.8 A; a crystal with large enough d spacing to diffract the longest wavelengths would have poor dispersion at the shorter wavelengths.
Table I. Integrated Intensity (in Arbitrary Units) in the Spectrum of a Thin-Window Rh-Target SEG-SOHTube
A0
(A)
0.29 0.31 0.33 0.35 0.37 0.39 0.41 0.43 0.45 0.47 0.49 0.51 0.53b 0.55 0.57 0.59 0.61 0.63 0.65 0.67 0.69 0.71 0.73 0.75 0.77 0.79 0.81 0.83 0.85 0.87 0.89 0.91 0.93 0.95 0.97 0.99 1.01 1.03 1.05 1.07
934
Ix AA 8.00 25.0 33.6 38.2 41.2 43.4 44.4 44.8 45.2 44.8 44.4 43.6 46.0 52.2 52.0 51.8 51.6 51.4 51 .O 50.8 50.4 50.2 50.0 49.8 49.6 49.2 48.8 48.6 48.2 47.8 47.6 47.2 46.8 46.4 46.0 45.6 45.2 44.8 44.4 43.6
A“(A) 1.09 1.11 1.13 1.15 1.17 1.19 1.21 1.23 1.25 1.27 1.29 1.31 1.33 1.35 1.37 1.39 1.41 1.43 1.45 1.47 1.49 1.51 1.53 1.55 1.57 1.59 1.61 1.63 1.65 1.67 1.69 1.71 1.73 1.75 1.77 1.79 1.81 1.83 1.85 1.87
(Rh Target, SEGdOH, 45 KV (c.P.), Ah = 0.02 A) Continuum A“ (A) A 4 (A) I A AA I x AX Ix AA 43.2 1.89 18.4 2.69 5.40 5.26 42.4 1.91 18.0 2.71 41.6 1.93 5.10 17.4 2.73 1.95 5.00 17.0 2.75 40.8 4.80 16.4 2.77 40.0 1.97 4.70 39.2 16.0 2.79 1.99 4.54 38.4 2.81 2.01 15.7 37.6 4.40 15.5 2.83 2.03 4.30 36.8 14.8 2.85 2.05 4.16 36.0 14.4 2.87 2.07 4.04 35.4 13.9 2.89 2.09 3.94 34.6 2.11 13.4 2.91 3.80 34.0 13.0 2.93 2.13 3.70 33.2 2.95 2.15 12.6 3.60 32.4 12.2 2.97 2.17 2.99 2.19 3.50 31.8 11.8 3.40 31.2 11.4 3.01 2.21 3.30 3.03 30.4 11.1 2.23 3.05 3.20 29.8 2.25 10.8 3.07 3.12 29.4 2.27 10.4 3.04 3.09 28.8 10.1 2.29 3.11 2.96 9.80 28.4 2.31 3.13 9.46 2.88 27.8 2.33 9.20 3.15 2.80 27.2 2.35 2.74 8.92 3.17 26.6 2.37 2.66 3.19 2.39 8.60 26.0 3.21 2.60 8.34 25.4 2.41 2.52 3.23 2.43 8.06 25.0 2.46 3.25 2.45 7.80 24.6 3.27 2.40 2.47 7.60 24.0 2.34 7.34 3.29 23.6 2.49 2.28 7.10 3.31 23.0 2.51 2.22 6.80 3.33 22.4 2.53 2.16 6.70 3.35 2.55 22.0 2.10 6.50 3.37 21.6 2.57 3.39 2.04 21.0 6.30 2.59 3.41 6.10 2.00 20.4 2.61 1.94 3.43 6.00 20.0 2.63 1.90 3.45 5.80 19.4 2.65 3.47 1.84 5.60 18.8 2.67
ANALYTICAL CHEMISTRY, VOL. 43, NO. 7, JUNE 1971
A” (A) 3.49 3.51 3.53 3.55 3.57 3.59 3.61 3.63b 3.65 3.67 3.69 3.71 3.73 3.75 3.77 3.79 3.81 3.83 3.85 3.87 3.89 3.91 3.93 3.95* 3.97 3.99 4.01 4.03 4.05 4.07 4.09 4.11 4 . 13b 4.15 4.17 4.19 4.21 4.23 4.25 4.27
Ix AA 1.80 1.76 1.72 1.68 1.64 1.60 1.56 1.68 1.77 1.74 1.72 1.68 1.65 1.62 1.60 1.57 1.54 1.51 1.48 1.46 1.42 1.41 1.38 2.07 2.08 2.04 2.02 2.00 1.96 1.93 1.90 1.87 3.92 5.88 5.76 5.60 5.48 5.34 5.20 5.06
istics from the spectra). As before, the absorption edge jumps in the continuum can be observed; in this case both the K edge and the L edges are observed. At first glance, the intensities of the L lines seem unusually high compared to the intensity of the K lines. However when one considers that the overvoltage of the K lines is only a factor of two, while for the L lines it is greater than thirteen, the relative intensities of the two series do not seem unreasonable. The fraction of the total radiation contributed by the K lines is 10 while the L lines make up 25 % of the total. The spectral distribution which has been measured represents the actual spectrum available to excite the specimen in X-ray fluorescence analysis-that is, the spectrum outside the tube window, not that generated with the target. Simple absorption calculations indicate that the 0.12-mm Be window will transmit only a small fraction (less than 2073 of any radiation of wavelength longer than 6 A emerging from the target. Thus one observes in the data herein presented that the intensity at 7 A is about three orders of magnitude lower than that at 1 p\ near the peak of the continuum. It is also
The diffraction efficiency of the various crystals was determined as the single-crystal integral reflection coefficient ( R J and this parameter was measured for each crystal over its diffracticg range. Four crystals owere used: LiF (220), 2d = 2.85 A ; LiF (200), 2d ,= 4.03 A ; Graphite, 2d = 6.71 A; and KAP, 2d = 26.6 A. Their single-crystal integral reflection coefficients are shown in Figure 1. Each of the crystals has a usable range of wavelength which overlaps the crystal with the next larger (or smaller) d spacing. This overlapping was used to ensure that the measurements with all the crystals were consistent. Effectively, three different detectors were used. As before ( I ) , a 2.3-cm 90% Ar, 10% CHI flow proportional counter was used for most of the wavelength range. However, at short wavelengths, the quantum efficiency of the flow detector was very low and a 2.0-cm sealed Xe proportional counter was used in:tead. In the region of the Ar K absorption edge (3.87 A), the same 2.3-cm flow proportional counter was used but with pure CH4as the counting gas. RESULTS AND DISCUSSION
The spectral distribution measured for this Machlett Rh target SEG-50H X-ray tube at 45 kV (c.P.) is shown in Figure 2 and is tabulated in Table I. In the figure, the measured integrated intensity of each characteristic line has been corrected to the proper natural line breadth (#) and the height adjusted accordingly (this removes spectrometer character-
(4) M. A. Blokhin, “The Physics of X-rays,” 2nd ed., State Publishing House of Technical Theoretical Literature, Moscow, 1957, AEC-tr-4502, p 404-6. (5) J. A. Bearden, U.S. Atomic Etrergy Comm. Rept., NYO-10586 (1964).
Table I. (Continued)
A=
(A)
4.29 4.31 4.33 4.35 4.37 4.39 4.41 4.43 4.45 4.47 4.49 4.51 4.53 4.55 4.57 4.59 4.61 4.63 4.65 4.67 4.69 4.71 4.73 4.75 4.77 4.79 4.81 4.83 4.85 4.87 4.89 4.91
(Rh Target, SEG-SOH, 45 KV (c.P.), AA Continuum
(A)
Zx AA
A”
4.94 4.80 4.68 4.56 4.42 4.30, 4.16 4.04 3.94 3.80 3.70 3.58 3.46 3.36 3.26 3.14 3.04 2.94 2.86 2.76 2.66 2.58 2.50 2.42 2.34 2.26 2.16 2.08 2.02 1.94 1.88 1.80
4.93 4.95 4.97 4.99 5.01 5.03 5.05 5.07 5.09 5.11 5.13 5.15 5.17 5.19 5.21 5.23 5.25 5.27 5.29 5.31 5.33 5.35 5.37 5.39 5.41 5.43 5.45 5.47 5.49 5.51 5.53 5.55
(A)
Zx AA
Aa
1.74 1.68 1.62 1.56 1.50 1.45 1.40 1.35 1.30 1.26 1.21 1.17 1.13 1.08 1.05 1.01 0,980 0.924 0.908 0.876 0 844 0.816 0.788 0.760 0.730 0.702 0.680 0.656 0.634 0.610 0.590 0.568
5.57 5.59 5.61 5.63 5.65 5.67 5.69 5.71 5.73 5.75 5.77 5.79 5.81 5.83 5.85 5.87 5.89 5.91 5.93 5.95 5.97 5.99 6.01 6.03 6.05 6.07 6.09 6.11 6.13 6.15 6.17 6.19
~
(A)
Zx AA
xu
0.546 0.528 0.510 0,494 0.476 0.458 0.440 0.426 0.412 0.396 0.382 0.368 0.356 0.342 0.332 0.320 0.306 0.296 0.286 0.276 0.266 0.256 0.248 0.240 0.232 0.224 0.214 0.208 0.202 0.196 0.188 0.182
6.21 6.23 6.25 6.27 6.29 6.31 6.33 6.35 6.37 6.39 6.41 6.43 6.45 6.47 6.49 6.51 6.53 6.55 6.57 6.59 6.61 6.63 6.65 6.67 6.69 6.71 6.73 6.75 6.77 6.79 6.81 6.83
= 0.02
A)
Zx AA 0.177 0.172 0.166 0.162 0.157 0.152 0.148 0.144 0.140 0.136 0.133 0.130 0.126 0.123 0.120 0.117 0.114 0.112 0.109 0.106 0.104 0.102 0.100 0.098 0.096 0,094 0.092 0.090 0.088 0.086 0.085 0.083
A”
(A)
Ix AA
6.85 6.87 6.89 6.91 6.93 6.95 6.97 6.99 7.01 7.03 7.05 7.07 7.09
0.082 0.080 0 .p79 0.078 0.076 0.075 0.074 0.072 0.071 0.070 0.069 0.068 0.067
Characteristic lines.
(A) KLY
KO L-y2,3
L,1 Lpz,i~, LP 3 LP4
LP 1 Lrrl,~ L, Lz
0.61473 0.54397 3.6855 3,9431 4.1310 4.2522 4.2888 4.37414 4.59835 4.9217 5.2169
Zx AA 445 105 4.52 12.5 42.6 76.0 39.8 47 1 790 5.34 12.8
* A for Continuum is tke middle of the Ah interval. Edges: K @ 0.534 A (Zx AA is 30.3 from 0.520 to 0.534 and 15.7 from 0.534 to 0.540) LI @ 3.629 A (Zx AA is 0.69 from 3.620 to 3.629 and 0.99 from 3.629 to 3.640) LII @ 3.942 A (Zx AA is 0.14 from 3.940 to 3.942 and 1.93 from 3.942 t o 3.960) LIII @ 4.130 A (Zx AA is 0.92 from 4.120 to 4.130 and 3.00 from 4.130 to 4.140) A for lines is from Bearden ( 5 ) (weighted average for doublets). AA for lines is natural line breadth [from Blokhin, (4)].
b
ANALYTICAL CHEMISTRY, VOL. 43, NO. 7, JUNE 1971
935
Rh SEG-SOH
K Lines
45 kV(cp)
5-
L Lines
5-
L Graphite
-{
a t I0-’ 25 :
LiF
-0) Y
>. 4 m t
z W
t-
z
3-
(3
0
2-
I-
%Figure 2. X-ray spectrum from thin-window Rhtarget X-ray tube I
I
I
I
2 3 4 WAVELENGTH (%)
I
I
5
6
Figure 1. Single crystal integral reflection coefficients of Graphite, LiF (200), LiF (220), and KAP
interesting to note that over 90 Z of the total measured continuum radiation occurs at wavelengths shorter than 2.7 A.
RECEIVED for review February 1, 1971. Accepted March 1, 1971. This work was supported in part by the Defense Atomic Support Agency.
Atomic Absorption Characteristics of Rhenium Resonance Lines below 2500 A B. W. Bailey and J. M. Rankin Division of Laboratories and Research, New York State Department of Health, Albany, N . Y . 12201 IN 1967, MARGOSHES ( I ) showed that the optimum wavelengths for use in atomic absorption can be predicted with reasonable accuracy by the use of the published values of the for the transitions involved. These oscillator strengths, y-‘, values are related to the observed absorption either through the integrated absorption coefficient s k v d v , or the absorption coefficient at the center of the line, k,, depending on whether a continuum or a line source is utilized in the excitation process. The relevant relationships are : ae j k y d y = - Naf j - i mc
for a continuum source and
for a line source assuming only Doppler broadening (2-5). (1) M. Margoshes, ANAL.CHEM.,39, 1093 (1967). (2) G. Herzberg, “Molecular Spectra and Molecular Structure,” Vol. I, 2nd ed., Van Nostrand-Reinhold Company, New York, N. Y., 1950. (3) A. C. G. Mitchell and M. W. Zemansky, “Resonance Radiation and Excited Atoms,” Cambridge University Press, London, 1961. 936
ANALYTICAL CHEMISTRY, VOL. 43, NO. 7, JUNE 1971
m and e are the mass and charge of the electron, A”, is the Doppler breadth and Niis the atom population of the lower level. Previous studies (6) have shown that the values for the oscillator strengths quoted in the literature are of coasiderable uncertainty in the wavelength region below 2500 A and are probably one to three orders of magnitude below their true value.. In view of this uncertainty Corliss (7) has determined corrected intensity values for many of the transitions below 2500 and has derived correction factors for the oscillator strengths of lines in this region of the spectrum. Earlier investigations of the atomic absorption characteristics of rhenium (8, 9) have established the resonance line at 3460.46 A as the analytical line of choice. Other lines
A
(4) A. Walsh, “Physical Aspects of Atomic Absorption”: “Atomic Absorption Spectroscopy,” ASTM STP 443; American Society for Testing and Materials, Philadelphia, Pa., 1969. (5) E. Pungor, “Flame Photometry Theory,” D. Van Nostrand Company, Ltd., London, 1967. (6) N. P. Perkin and I. Y . Y . Slavenar, Opt. Spectrosc., 15, 83 (1963). (7) C. H. Corliss, Specfrochimica Acfa,23B, 117 (1967). (8) V. A. Fassel and V. G. Mossotti, ANAL.CHEM., 35, 252 (1963). (9) W. G. Schrenk, D. A. Lehman, and Lorin Heufeld, Appl. Specfrosc.,20, 389 (1966).
