crease in the &r1l2product with increasing current density will still be obtained; but attempts to correlate the data with various models (4, 6, 7, 9) will lead to erroneous conclusions. The existence of this effect is further evidence of the unreliability of chronopotentiometry for the study of adsorp tion (6). It should also be recognized that adsorption can occur during the double-layer-charging region and that this would also invalidate the application of the usual models. A detailed treatment of the desorp-
tion effect for chronopotentiometric and chronocoulometric conditions is in progress and will be published later, LITERATURE CITED
(1) Anson, F. C., ANAL. CHEM.38, 54 ( 1966). (2) Christie, J. H., Anson, F. C., Oster-
young, R. A., J . Electroanal. Chem., in press (1966). (3) Christie, J. H., Lauer, G., Osteryoung, R. A., Ibid., 7, 60 (1964). (4) Laitinen, H. A., Chambers, L. M., ANAL.CHEM.36, 5 (1964). (5) Lingane, P. J., unpublished data, 1966.
(6) Lorena, W., Z. Elektrochem. 59, 730 (19.55). - ~, (7) Murray, R. W., Gross, D. J., ANAL. CHEM.38, 392 (1066). (8) Osteryoung, It., unpublished data, 1966. (9) Tatwawadi, S. V., Bard, A. J., ANAL. CHEM.36, 2 (1964). \ - -
JOSEPH H. CHRISTIE ROBERTA. OSTERYOCNG North American Aviation Science Center Thousand Oaks, Calif. 91360 and Gates and Crellin Laboratories of Chemistry California Institute of Technology Pasadena, Calif. 91109
Application of Photoactivation to the Determination of Germanium in Titanium SIR: Techniques with photonuclear reactions are used for the determination of several elements (2-4). Lukens, Otvos, and Wagner ( 5 ) , in commenting on photoactivation with the 3-m.e.v. van de Graaff accelerator, suggest that photoactivation appears to be a useful supplement to neutron activation analysis. I n this case the (y,y') reaction is predominant. Photoproduction of neutron-deficient isotopes by the (y ,n) reaction is considered to be more effective with the use of a high-power linear accelerator. I n this paper, photoactivation of germanium and titanium is investigated with a 20-m.e.v. linear electron accelerator, Its application to the nondestructive determination of germanium in titanium is presented. Radioactivation analysis of germanium is generally based on the formation of G d 5 or Gen by irradiating samples with reactor neutrons. The ( y , n ) reaction of germanium yields Gees, which is a neutrondeficient isotope and has a half life of 40.4 hours. The production of Gees is of particular interest, because GeB9 has favorable nuclear properties as a tracer of germanium. The present work is based on counting the Gee9 photopeak activity. The available photon flux intensity is monitored by measuring the induced activity of Sc47,
Table 1. WGe/WTi
(=
1.992 x 9.851 X 4.982 X 2.456 x 1.284 X 0.648 X
1622
Rw)
10-1 lo-'
lo-'
IO-' lo-*
which is produced by the ( y , p ) reaction of titanium. This internal standard method has been applied to the analysis of zirconium in hafnium (6) and tantalum in niobium ( I ) . EXPERIMENTAL
Germanium and titanium oxides of high punty were used. Synthetic samples were prepared by mixing known weights of germanium oxides and titanium oxides. Samples of 50 mg. each were weighed and wrapped doubly in thin aluminum foil of approximately 5 mg./cm.2 These samples were irradia.ted for 1 hour with a 20-m.e.v bremsstrahlung generated from the electron linear accelerator at the Japan Atomic Energy Research Institute. The high energy electron beam from the accelerator was converted to bremsstrahlung by a platinum converter. In the forward direction, the photon flux intensity was estimated to be about 5 X 106 roentgens per minute with an average beam current of 40 pa. During irradiat,ion, the target assembly containing the samples was cooled by circulating water. After irradiation, the samples were transferred into polyethylene capsules and activity measurements were made using a Technical Measurements Corp. 256-channel pulse height analyzer with a 3-@ X 3-inch NaI-TI activated crystal.
Gamma-Ray Spectra of Germanium and Titanium. Gamma-ray spectra of irradiated germanium and titanium are shown in Figures l and 2, respectively. The spectrum of germanium, taken 96 hours after irradiation, exhibits prominent photopeaks a t 0.51, 0.88, 1.12, and 1.34 m.e.v. These photopeaks decay with 40.4 hours half life, indicating the presence of Ge69. The spectrum (Figure 1) has a shoulder on the high side of the 0.51m.e.v. photopeak and the activity has the same half life. As a result, of the inability of the spectrometer to resolve the two peaks, the combined area is used for the activity measurements. I n the photoactivated germanium samples, large amounts of the 82-minute G d 5 were also produced by the (7,n) reaction. It was identified by the short-lived contribution to the peak a t 0.26 m.e.v. and disappeared after about 10 hours. No other photopeaks were observed in the spectrum of irradiated germanium. The y-ray spectrum of photoactivated titanium shows intense photopeaks at 0.16 m.e.v. and 0.51 m.e.v. nnd weak ones at 1.02 m.e.v. and 1.32 m.e.v. The peaks at 0.51 m.e.v. and 0.16 m.e.v. decayed with a half life of 3.07
Relationship between WG,/WT~and AG,/AB, for GeOrTiO:, Mixtures
AG., c.p.m. (8.51, f 0.05,) x 104 (4.698 f 0.08,) X lo4
(2.04, f 0 . 0 ~ x) 104 (1.251 f 0.038) X lo4 (3.930 i 0.186) X lo3 (3.641 f 0.010) X lo3
ANALYTICAL CHEMISTRY
RESULTS AND DISCUSSION
Am, c.p.m. (1.203 f 0.020) X (1.362 f 0.006) X (1.18, i 0.01s) X (1.558 i 0.00s) X (8.578 f 0.16,) x (1.608 f 0.011) X
106 lo6 106 106 10' 106
Ao./Am ( = R A ) 7.07 X 10-1 3.44 x 10-1 1.72 x 10-1 8.05 x 10-2 4.58 X 10-2 2.27 x 10-2
RA/Rw 3.55 3.50 3.47 3.28 3.56 3.53 3.49 f 0.09,
t
All measured activities were normalized to the values of the end of irradiation by following the decay of the photopeaks. Table I lists the results of the analyses of synthetic samples. In Table I, Aoe and A h represent the photopeak activity of GeBgand Sc411respectively; WTi is the weight of titanium, and Woethe weight of germanium present in the sample. For the quantitative analyses of germanium] it is possible to use the linear relationship between the photopeak activity ratio of Ges9/S~47,(= RA) and the weight ratio of Ge/Til (= Rw). The values of RA/RTVare constant for wide concentration of germanium. The lower limit of germanium content in titanium is about 0.1% for nondestructive determination. The presence of zirconium would interfere seriously in this case. The interference from secondary neutron produced by the (7,n)
0.51 m.8.v
]
I
I
0
50
I
100 Chinnel Number
, 150
Figure 1. Gamma-ray spectrum of photoactivated germanium
0
1 0.I6m.e.v.
50
1 3
Time (hours)
Figure 3. Decay of 0.51-m.e.v. photopeak of Ge-Ti mixture
0.5 I m.e.v.
Sample: Ti02+Ge02.50 mg. (Ge/Ti = 0.0498)
Spectrum taken 96 hours after irradiation
hours and 3.43 days, respectively. These peaks were assigned to Ti46, formed by Tiu (y,n)Ti46 reaction and Sc4', formed by Ti48(ylp)S~47 reaction, respectively. The high energy ?-rays observed in the spectra were ascribed to those of Sc4*, formed by Ti49(y,p)S~48 reaction. Germanium Determination in Titanium Oxides. To show the usefulness of 40.4-hour Gee9 as an approach to germanium determination, titanium oxide samples containing various amounts of germanium oxide were irradiated for 1 hour with a 20-m.e.v. bremsstrahlung. The amounts of Geeg and Sc47 formed in the samples were determined from the area under the 0.51-m.e.v. and 0.16-m.e.v. photopeaks, respectively. A typical decay curve of the 0.51-m.e.v. photopeak of Ti-Ge mixture is shown in Figure 3. For the counting of Ges9 activity] it was necesIO' I I sary to delay the determination until a 0 50 100 150 900 sufficient number of titanium45 half Channel Numbw lives had elapsed, reducing its contribuFigure 2. Gamma-ray spectra of tion to negligible levels. The measurephotoactivated titanium ment of Gee9 photopeaks other than 0.51 m.e.v. would be less sensitive and 1. Spectrum taken 10.7 hours after irradiation disadvantageous for titanium samples. II. Spectrum taken 1 16.2 hours after irradiation I
reaction is negligible in this experimental condition. This type of analysis is also advantageous when it is impractical to reproducibly position or orient samples. ACKNOWLEDGMENT
The author is particularly indebted to Y. Oka a t Tohoku University for his discussion and encouragement during this investigation. LITERATURE CITED
(1) Abe, S., J . Chem. SOC.Japan, Pure Chem. Sec. (Nivvon .. Kaaaku Zasshi) 86, 641 (1965). ( 2 ) B a d e , R., Hure, J., Leveque, P., Schuhl. C.. Comvt. Rend. 239, 422 (1954): ' (3) Beard, D. B., Nucleonics 17 (7), 90 (1959). f4) ~, Gaudin. A. M.. ANAL. CHEW 23, 1261 (1951). ( 5 ) Lukens, H. R., Jr., Otvos, J. W., Wagner, C. D., Intern. J . Appl. Radiation Isotopes 11, 30 (1961). ( 6 ) Oka, Y., Kato, T., Sasaki, &I., J . Chem. SOC. Japan, Pure Chem. Sec. (Nippon Kagaku Zasshi) 84, 558 (1963).
SHIGEKI ABE Department of Chemical Engineering Yamagata University Yonezawa-shi, Japan
VOL 38, NO. 1 1 , OCTOBER 1 9 6 6
1623
