Ligand. For maximum color development and perchlorate interference it is necessary to add at least 5.00 ml of the 7.0000-grams/liter a-furildioxime. Above 5.00 mi no further perchlorate effect is observed. Acidity. The hydrochloric acid concentration has a marked effect on the formation of the color and on the perchlorate interference (Figure 2). A volume of 4.70 ml of 1 :1 hydrochloric acid provided maximum perchlorate interference. Methanol. Figure 3 indicates that methanol has a large effect on both color development and the perchlorate interference. A volume of 17.00 ml provided maximum perchlorate interference. Potassium Perrhenate. Figure 4 shows the effect of potassium perrhenate concentration. A volume of 4.40 ml of the 0.1080-gram/liter potassium perrhenate solution provided a reasonable blank and excellent perchlorate interference. For convenience the potassium perrhenate solution was diluted and 5.00 ml of 0.0950-gram/liter solution was used in the recommended procedure.
Order of Addition of Reagents. Care must be taken that the Sn(I1) is added before the ligand. The hydrochloric acid, potassium perrhenate, sample, and methanol may be added in any order. Time. The perchlorate analysis is not affected significantly by the time of color development. Thirty minutes was chosen for use because this allows up to 12 samples to be run simultaneously. Diverse Ions. Table I shows the effect of various diverse ions. Thiosulfate ion formed a precipitate under the experiand V(V) greatly diminmental conditions. Cu(II), U0z2+, ished the perchlorate interference. Nitrite ion was a complete interference and this suggests that it might be determined in a similar manner. The chlorate ion behaves in a manner similar to the perchlorate ion, but it can be effectively removed by heating with hydrochloric acid. This phenomenon is being further investigated. RECEIVED for review November 8,1967. Accepted December 11,1967.
Separation of Zirconium-95 from Niobium-95, and the Separation of Zirconium-95 and Niobium-95 from Several Other Nuclides Richard H. Marsh Scientific Research Staff, Ford Motor Co., Dearborn, Mich. Richard B. Hahn Wayne State University, Detroit, Mich. ZIRCONIUM-95 is a readily available fission product which is used in tracer studies. Its radioactive daughter, niobium-95, is also useful. Zirconium-95 decays by beta-gamma emission with a half life of 65 days to niobium-95 which is also radioactive; niobium-95 decays by beta-gamma emission with a half life of 35 days to form stable molybdenum-95. The main gamma energies of zirconium-95 are 0.760 mev (43 %) and 0.726 mev (55%). The gamma energy of niobium-95 is 0.768 mev (99 %) ( I ) . For most applications it is desirable to separate one from the other and from other nuclides. However, it is difficult to test the separation of zirconium-95 and niobium-95 by conventional gamma-ray spectroscopy. Thallium-doped sodium iodide scintillators yield only a single peak for the three gamma-rays. Other isotopes of both elements are available, but are expensive. By using lithium-drifted germanium detectors, all three gamma-rays may be resolved. Zirconium can be separated from other fission products by precipitation as barium fluozirconate (2). Niobium can be removed by solvent extraction from hydrofluoric acid solutions (2). Anion exchange from hydrofluoric acid solutions also offers quantitative separation (2). Most procedures used for the separation of zirconium and niobium suffer (1) K. Way, et al., “Nuclear Data Sheets,” National Research Council, NRC 60-5-119(1964). (2) E.P.Steinberg, “Radiochemistry of Zirconium and Hafnium,” National Academy of Sciences, Nuclear Science Series; Office of Technical Services, Department of Commerce, Washington, D. C., 1960.
from the necessity of using strong hydrofluoric acid solutions The method described in this paper yields good separations and does not employ hydrofluoric acid. Niobium can be precipitated as a phosphate (3), and a recent study ( 4 ) demonstrated that, using phosphate ions as a precipitant, zirconium and niobium could be separated from each other. The information presented here is an extension of that study. EXPERIMENTAL
The equipment and reagents used are common to the laboratory with the exception of a cooled, lithium-drifted, germanium solid-state detector having a resolution of 5 to 6 kev, FWHM, made by William Pierson, Ford Motor Co. With resolution of this order, it is now possible to perform experiments using zirconium-95 and niobium-95 as tracers. The degree of separation for the various isotopes was determined by taking spectra both before and after separation, and comparing peak heights to the 0.726-mev y from zirconium-95 or the 0.768-mev y from niobium-95. Peak heights were determined by subtracting the background continuum, if any, from the value of the peak height read from the log plot. Decontamination factors were calculated as follows : (3) R. B. Hahn,J. Am. Chem. SOC.,73,5091-3 (1951). (4) R. H. Marsh, “Separation and Determination of Tantalum as
Tantalum Phosphate,” Ph.D. dissertation, Wayne State University, 1967. VOL. 40, NO. 3, MARCH 1968
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acid, 50 ml of nitric acid is added and the solution is boiled until the hydrogen peroxide is destroyed and the precipitate of niobium phosphate coagulates. This precipitate is easily filtered on No. 31 paper, and washed with a mixture of 10%
Table I. Decontamination Factors Decontamination Factor Element Elements from Zr Nb
47 78 854 625 2.6 955 loo0 18+ 82
Sr
Fe Te Ce-Pr Ru-Rh co
I44pr
Elements from Nb Zr
89
40 Sr
Fe Te CePr
17CP 263 28.2 771 700 13* 58
Ru-Rh co a Results of method when only Zr and Nb are present. b Color of solutions and ppts indicate much better separations.
D.F.
=
height of x before height of Zr (or Nb) after X height of Zr (or Nb) before height of x after The carrier solutions used contain 10 mg of metal per ml of solution and are made with the following materials: ZrO(N03)z.5Hz0in 1M oxalic acid, K8NbsOle.16H20in 1M oxalic acid, Sr(NO&, tellurium metal in 1 :1 hydrochloric acid, Ce(N03)3.6Hz0, RuC13, C O ( N O ~ ) ~ ' ~ H and ~ OFeC13. , 6 H z 0 in 0.1M hydrochloric acid. Method of Separation. To the solution containing the radioactive material, 10 mg each of zirconium, niobium, strontium, tellurium, cerium, and ruthenium carriers are added. (Cobalt and iron are added when those radionuclides are present.) The solution is brought to 100 ml with 2.5M hydrochloric acid. Then 0.5 gram of sodium bromate is added to destroy oxalate, 10 ml of 30% hydrogen peroxide is added, and the solution is heated to 50' to 60" C. One gram of ammonium phosphate (dibasic) is added, and the solution is digested before centrifugation. The amount of time of digestion depends on the results desired. If zirconium almost entirely free of niobium is desired, the solution should be filtered immediately after precipitation. This, however, will cause a small part of the zirconium to be left with the niobium. For a good separation of each element, the digestion time should be 2 hours. Hydrogen peroxide must be added periodically to replace that which is destroyed in boiling. After centrifugation, the precipitate of zirconyl phosphate is washed with a mixture of 10% ammonium nitrate and 5 % hydrogen peroxide, and ignited at 1100" C. To the remaining solution containing soluble peroxyniobic
F 40
0
80
120
160
200 240
280
320
360 4 0 0
l27m Te I
t
"Fe
I
I
b
Figure 1. Spectra from which peak heights were estimated I. Mixture: 86Zr, Wb, lr4Ce, l*(Pr, laeRu, IobRh, WO, before separation II. Niobium phosphate precipitate III. Zirconium phosphate precipitate 3 hours after precipitation IV. Mixture: g6Zr,06Nb, e5Sr, lz7mTe,s°Fe, before separation V. Niobium phosphate precipitate VI. Zirconium phosphate precipitate 2 hours after precipitation
642
ANALYTICAL CHEMISTRY
l
0
40
80
,
,
120
,
,
,
1
~
l
,
160 200 240 280 CHANNEL NUMBER
l
l
l
c l
320 360
~
'
400
l
ammonium nitrate in 1 :1 acetone water. After washing, the precipitate can be ignited at 1100" C or redissolved for further treatment. RESULTS AND DISCUSSION
The results of the study are presented as decontamination factors calculated from peak height ratios in Table I. The spectra from which the peak heights were estimated are presented in Figure 1. It is concluded that the method provides
excellent separation of zirconium and niobium from each other and from many other elements which would be found in fission product mixtures. Although it has not been demonstrated, it is thought that ignited niobium phosphate, when precipitated from an excess of phosphate, would make a good weighing form for the determination of recovery (4). RECEIVED for review September 11, 1967. Accepted December 12, 1967.
Cartridge-TypeVacuum Lock for a Thermal-Ionization Mass Spectrometer Rapid Determination of Relative Isotopic Ratios of Potassium Olin H . Howard, Aubrey Langdon, and Clint Sulfridge Oak Ridge Gaseous Diffusion Plant, Union Carbide Corp., Nuclear Division, Oak Ridge, Tenn. AN EXPERIMENTAL PROCESS for the separation of potassium isotopes ( I ) requires frequent determinations of the relative ratios of 4IK to 39K among the various stages of the process. Relative isotopic ratios, defined as follows, are determined by thermal-ionization mass spectrometry:
where R = relative isotopic ratio, ra = a1K/39K (Sample a), and rb = 41K/39K(Sample 6). Many of the works which have been published on the determination of potassium isotope abundances (2-6) have concerned the accurate measurement of the isotopic composition of natural potassium. The purpose of the work reported here is to determine rapidly the relative isotopic ratios of potassium altered in an experimental system. INSTRUMENTATION
A double-filament thermal-ionization source and a cartridge-type vacuum lock (Figure 1) were developed for a 60" magnetic, 6-inch radius mass spectrometer. Potassium iodide is vaporized from a sample filament. Potassium ions are generated when the vapor contacts a hotter, ionizing filament. The ions are accelerated by 3000 volts through a 0.020-inch beam-defining slit and through the magnetic analyzer. The 41K+ and 3QK+ion currents are detected simultaneously on separate collectors, amplified, and fed to a ratio recorder (7) whose output is proportional to the 41K/39K ratio. (The small amount of 40K is detected and measured with the 39K.) The input resistors to the high-current (mass (1) R. M. McGill, R . W. Browell, J. W. Grisard, S. Blumkin, E. VonHalle, and D. B. Janney, U . S. At. Energy Comm. Rept. K-1650 (1965). (2) A. Keith Brewer,J. Am. Chem. Soc., 59,869 (1937). (3) B. R. F. Kendall, Nurure, 186,225 (1960). (4) A. 0. Nier, Phys. Rec., 77, 789 (1950). (5) Carl Reutersward, Arkic. Fysik., 11, 1 (1956). (6) J. R . White and A. E. Cameron, Phys. Rer;., 74, 991 (1948). (7) W. G . Hart and A. Langdon, U . S. At. Energy Comm. Rept. K-1292 (1959).
39) and low-current (mass 41) direct-current amplifiers are 3 x 10'0 ohms. The vacuum in the source chamber is obtained with an 80liter-per-second ion pump and a liquid nitrogen cold finger. The source pressure during an analysis is usually between 5 x 10-6 and 5 X lo-' torr. The analyzer is pumped with an 8-liter-per-second ion pump to pressures less than 10-7 torr during an analysis. Ion Source. The double-filament ion source, a variation of the triple-filament source (8),includes a rhenium ionizing filament (0.001 inch thick X 0.030 inch wide X 0.5 inch long) and a platinum sample filament (0.004 inch thick X 0.030 inch wide x 0.5 inch long). The ionizing filament is mounted on the first plate of the ion lens assembly. The sample filament is mounted on a cylindrical cartridge (OS-inch diameter x 3.5 inches long) which is inserted into the source chamber through a vacuum lock. Two filaments are used instead of one for several reasons: the 10-volt input signal required by the ratio recorder can be more efficiently maintained with a multiple-filament than with a single-filament source; the ion current from a multiplefilament source is more constant than that from a singlefilament source; and the analytical precision is probably better when the ionizing filament remains undisturbed in the source during sample changes, thereby retaining constant ionization-region geometry from sample to sample. The magnitude of the ion current is strongly dependent upon the positions of the filaments. The ionizing filament must be near and in line with the source entrance slit. The sample filament must be near the ionizing filament, and in front of it relative to the direction of ion flow, as shown in Figure 2. The ionizing filament is approximately 0.125 inch from the source entrance slit. The sample filament is positioned during each analysis, by appropriate rotation of the cartridge, for maximum ion current. To minimize warping or sagging of the ionizing filament with use, it is welded to its terminals under tension. The terminals are first spread wider than the length of the filament and then sprung together sufficiently as the filament is welded to them. (8) Mark G. Inghram and William A. Chupka, Rec;. Sci. Insrr., 24, 518 (1953). VOL. 40, NO. 3, MARCH 1968
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