Table IV. Summary of Precision Tests with a Group of 10 ’/32-ln. Balls
Av. time, see.
Rel. std. dev.,
13.5559 13.5445 13.5543 13.5392 13.5187
0 164
Pooled std. dev. Rel. std. dev. of av.
5%
0 i35
0 121 0 097 0 139 0.133 0.111
times in the same oil under identical circumstances. The relative standard deviations obtained in each of the five series were pooled to give a pooled value of 0.133y0, The relative standard deviation of the averages was O . l l l ~ o . The data are summarized in Table IV. T o illustrate the application of the instrument over a range of viscosities and temperatures we showv,in Table V, the results of determinations made to obtain a calibration constant, k, for l:le-inch balls in the c.alculation of the wall effects as discussed above. The oil densities, d r , were determined in pycnometers, and the kinematic viscosities, Y , were determined in capillary viscometers according to AIST,llmethod D-445. Reverse flow capillary viscometers, which are less precise, had to be used for the last five oils and these data were not used in the calibration. Absolute viscosities were calculated from 7 = vdi. The k-value was calculated for each oil from k = 7 / ( d a -
Table V.
Temp.,
Calibration Data for ‘/l,Jnch
capillary CP.
Balls
A?, Fall time, c see. Liquid O F . /c Oil blend 77 421.2 422.1 - 0 21 10.220 Bright stock 100 541.1 540 2 0.17 13.095 Polybutene-1 210 546.4 552.7 -0.97 13 327 Oil-PBc blend 1 100 680.0 680.9 - 0 13 16.501 Oil-PB blend 2 100 984 985 -0.10 23.869 Bright stock 77 1438 1438 0.00 34 887 Oil-PB blend 3 100 1546 1544 0.13 37.400 Oil-PB blend 1 77 1846 1847 - 0 05 44.818 Oil-PB blend 2 77 2697 2670 1.00 65 703 Oil-PB blend 4 100 3789 3774 0.40 91.357 Oil-PB blend 3 77 4405 4414 -0.20 107 . 0 21 Polybutene 2 100 6641 * 6801 -2.41 164,571 Oil-PB blend 4 77 ll,094b 11,140 -0.41 269,94 Polybutene 2 77 20,534b 20,512 0.11 496,87 Polybutene 1 100 24,260* 24,295 -0.14 588 74 Polybutene 1 77 73,445b 74,711 -1.72 1812.2 a Calcd. from 7 = k ( d , - d,)t, where k = 6.0959. 6 Detd. in reverse flow capillary viscometers; data not used in calibration. c Polybutene. 1)
d i ) t , and the 12-values were averaged to obtain the calibration constant. The calibration constant includes the wall correction factor, K l . The “falling ball viscosity” was then calculated for each oil from the fall time and the calibration constant. The variations between the viscosities so determined and those obtained by means of capillary viscometers are shown in terms of per cent difference. In the last column the fall time is shown, and this can be compared with the minimum of 200 seconds required for capillary viscometry. In viev; of the wide range of viscosities studied, the agreement is considered satisfactory.
7
falling ballje CP.
LITERATURE CITED
( 1 ) FaxCn, H., Arkiv Mat. Astron. Fysik 17, 1 (1922). ( 2 ) Faxkn, 0. H., Ing. Vetenskaps Akad. Handl.. No. 187 11946). ( 3 ) Haberman, W: L., Sayre, R. XI.,
Rept. 1143, Hydromechanics Lab., Dept. of Navy, October 1958. ( 4 ) Ladenburg, I{., Ann. Phystk, 4th Series 2 3 , 447 (1907). (5) Lim, W. K., Johnson, H. W., Jr., Wilhelmsen, P. C., Stross, F. H., ANAL.CHEM.36, 2482 (1964).
E. E. SEIBERT JR. H. W. JOHXSON, F. H. STROSS Shell Development Co. Emeryville, Calif.
Liquid Alpha-Gamma Counter for Simultaneous Determination of Plutonium a n d Americium SIR: Alpha counting is the most rapid method for analyzing plutonium in low concentrations. Americium may be determined by either alpha or gamma counting. A technique for directly counting alpha emissions from plutonium-containing solutions has previously been proposed by Byrne and Rost (1).
Plutonium solutions usually contain minute quantities of americium-241. The americium has a specific activity of about 50 times that of the plutonium; therefore, it will interfere with the radioassay of plutonium. Fortunately, the americium has an abundant 60k.e.v. gamma emission, while the plutonium has a very low gamma activity. This difference in gamma activity perinits the determination of both the plutonium and americium
in a solution by simultaneously counting the alpha and gamma emissions using two independent counting systems. For the purpose of brevity, the liquid alpha-gamma counter will be referred to as the LAG counter through this paper. EXPERIMENTAL
The LAG counter consists of two vertical opposed scintillation detectors and related electronic compohents. The upper detector assembly contains the alpha detector and lower assembly contains the gamma detector. The alpha and gamma sections of the L.IG counter each contain all the electronic components for independent operation. Each section also contains a ratemeter for the iinmedinte estimation of the count rate of the sample. For reasons of safety, the alpha de-
tector, which is moveable to allow introduction of the sample, and the sample holder are enclosed. The alpha detector is raised and lowered by compressed air which is activated by opening and closing the door of the enclosure. Figure 1 illustrates the physical relationship of the detectors and the sample. When the sample is counted, the alpha detector assembly is lowered to form a light-tight unit. The alpha detector phototube is protected from ewessive light by a switch-operated relay which turns off the high voltage to the phototube as the alpha detector assembly begins to rise. The voltage is turned on again when the assembly is closed. The alpha detector is a silver activated zinc sulfide phosphor which is secured to a lucite light pipe. The gamma detector is a commercial sodium iodide crystal, 2 mm. thick and 1 3 i 4 VOL. 37, NO. 4, APRIL 1965
615
inches in diameter. The gamma detector is enclosed in l/z-inch lead and 1/2-inch stainless steel to reduce the background. The sample container is a commercial pipe cap made from polyethylene. These caps are inexpensive and remarkably consistent in dimensions. This is important since the liquid-todetector distance is critical with respect to the alpha count rate. Plutonium and americium standards are prepared in the usual manner from appropriate weights of plutonium metal and americium oxide, dissolved, and diluted to predetermined volumes. The standards are prepared to cover the range 1 x 10-3 to 2.0 grams per liter of P u and 1 x 10-4 to 1 x gram per liter of Am. Duplicate aliquots of the plutonium and americium standards are cut into pipe caps and counted for one minute. Three calibration lines are thus obtained for use in a sample calculation. These are: plutonium concentration us. alpha counts per minute; americium concentration us. gamma counts per minute: and americium alpha counts per minute us. americium gamma counts per minute. The ratio of alpha counts per minute to gamma counts per minute from the americium standards is used to correct the plutonium sample results for any americium present.
ZnS(Ag) PHOSPHOR LEAD T T
PHOTOMULTIPLIER
Figure 1 . Alpha and gamma detector assemblies
was compared to the precision of the counter obtained by ten repetitive counts of a single sample aliquot. T h e results are summarized in Table I. T h e standard deviation of the counter is well within the statistical expectations. The per cent relative standard deviation increased about 1% when the sample was aliquoted and counted ten times. Stability. T h e stability of the LAG counter was checked over a period of 30 days by repeated analysis of seven plutonium and six americium solu-
RESULTS AND DISCUSSION
Precision. T h e precision obtained b y three people aliquoting the same samples and operating t h e counter
Precision of LAG Counter and Reproducibility of Aliquoting
Table I.
Pu
Operator A A B C A A B
gram/l. 1.06 X 1.06 X 1.06 X 1.06 X 1.626 1.626 1,626
* yo RSD
=
No. of cuts
No. of
counts
Av. count
Std. dev.a f counts
1 10 10 10 1 10 10
10 10 10 10 10 10 10
2323 2350 2301 2349 327978 338308 327958
34 59 50 69 929 4527 4466
Rel. std. dev.b j=%
1.40 2.50 2.20 2.90 0.28 1.34 1.36
Std. dev. X 100 mean z
-
Table II. Accuracy of LAG Counter
Pu std., 1 6 2 3 4 4 0 1 a
gram/l. 4404 X 1446 X 1820 x l o - * 7087 X 1830 x 4177 X 31363 5712
Obsd. Pu, gram/l.a 1 7 2 3 4 4 0 1
736 x 028 x 227 x 828 x 370 X 544 x 3154 5768
Average of ten analyses.
616
ANALYTICAL CHEMISTRY
10-3 10-3 10-2 10-2
Error, yo +20 +14 +2 +3 +4 +2 +0 +0
52 36 07 23 47 87 57 36
Difference, grarn/l.
+o +o
+O +0 +O +0 +O
t0
296 x 882 x 045 X 120 x 187 X 127 X 00178 00550
10-3 10-3 10-2 10-2
10-2
tions. The relative standard deviation of the plutonium varied from =k9.6YOfor the 7 X grams per liter of solution to +1.5% for the 1.6 grams per liter solution and the americium resultb varied from i.5% for the 9.9 x 10-5 grams per liter of solution to *l.9yo for the 1.8 x 10-2 grams per liter of solution. This shows that the stability of the counter remains reasonably constant over extended periods of time. Accuracy. The accuracy of the LAG counter, Table 11, was determined by analysis of solutions prepared by the Rocky Flats Plutonium Standards Laboratory ( 2 ) . Above 10-3 gram per liter of plutonium, the error is less than 5% and above 0.3 gram per liter the error is about 0.5%. I n the lorn concentration range, the error increases to 20%. This large increase in error is due t o a change in slope of the standardization curve below 1 x 10+ gram per liter of plutonium. The slope obtained above 1 X 10-2 gram per liter of plutonium was used in all the calculations to simplify the computations and the error introduced in the low range was accepted. The positive bias indicates the counter was slightly out of calibration. Speed of Analysis. The normal radioassay procedure for sample analysis requires 8 steps and a number of relatively precise and time-consuming manual manipulations. With the LAG counter, only 3 operations are usually necessary: cut two 1-ml. aliquots, count each aliquot for one minute, and calculate the results. to Because any sample from 1 X 3 grams per liter of plutonium can be counted without dilution and the optimum counting time is one minute, two technicians can cut, count, and compute 40 aliquots per hour compared to 10 aliquots per hour by the usual radioassay techniques. Critical Conditions. As in a n y analytical operation, there are certain conditions which will produce erroneous results if not corrected or avoided. Three of the situations investigated will be described. Increasing the counting time to improve the statistics on low count rate samples lowers the alpha count rate with each increment of time, due to water vapor over the liquid sample condensing on the phosphor and acting as an alpha absorber. There is no stabilization of the alpha count rate even after 30 minutes. If a sample is aliquoted into a pipe cap and allowed to stand for a period of time before counting, the alpha count rate increases as the liquid evaporates and increases the concentration of the sample. Organic solvents of low vapor pressure can be assayed as long as standard
curves are prepared using the solvent in question to compensate for the density differences between aqueous and organic solutions. Volatile organic solvents decompose the alpha phosphor mounting material making frequent recalibrations necessary. It is, therefore, recommended that samples of volatile organic solvents should not be assayed in this instrument,
ACKNOWLEDGMENT
The authors express their appreciation to C. T. Illsley for his suggestions and assistance on technical problems concerning the counter’s operation. LITERATURE CITED
(1) Byrne, J. T., Rost, G. A., ANAL. CHEM.33, 758 (1961).
( 2 ) Doher, L. W., Chemistry Standards
Laboratory, The Dow Chemical Co., Rocky Flats Division, unpublished procedure manual, 1964. C. R. FORREY K. I. HAWKINS’ The Dow Chemical Co. Rocky Flats Division P. 0. Box 888 Golden, Colo. Present address, Children’s Hospital, E. 19th Ave. and Downing, Denver, Colo.
Dispersion of Samples in Solid Antimony Trichloride as a Method for Infrared Analysis Herman Szymanski, Kenneth Broda, Joan May, William Collins, and Dennis Bakalik, Department of Chemistry, Canisius College, Buffalo, N. Y.
A
NEW SAMPLING technique for infrared spectrometry is described. The technique consibts of utilizing solid antimony trichloride as the matrix in which sample is dispersed or dissolved. The halide melts near 80’ C. and samples for infrared analysis can be prepared by melting the halide in a beaker on a hot plate, adding the sample, pouring the hot liquid onto a salt plate which is heated to a temperature near that of the solution, and allowing the solution to solidify on the plate. d clear film is usually obtained which can be used for the infrared analysis. I n some cases the salt plate may be further heated under vacuum and the halide sublimed off leaving the sample in the form of a cast film. We have found a sufficient number of examples where conventional infrared sampling techniques are not so satisfactory or so simple as the halide one and it is for these samples we recommend this new technique. These samples include materials for which inert solvents are not available and mulling or pelleting techniques are not satisfactory. The halide can also be used as a solvent to study dissociated materials because in many cases associated compounds will dissociate in it. It can also be used as a solvent for casting films onto salt plates for infrared analysis. I t has been recognized for some time that a large number of organic and inorganic compounds will dissolve in antimony and arsenic trihalides (f-14). Inorganics such as FeCI3, AlC13, SeC14, TeC14, KC1, RbC1. CsC1, T1C1. HgC12, KF, KBr, KI. and many others are soluble in the molten halide.
Table 1. Compounds Which Interact with Antimony Trichloride Compounds dissolved without extensive interaction Benzene Manganese sulfateb Acetone Ferrous sulfateb Naphthalene Copper sulfateb Tetraanisylethylene Calcium sulfateb Succinic acida Lithium sulfateb Anisic acida Sulfuric acidb Phenylacetic acida Ammonium sulfateb p-Xitrobenzoic acid0 Arsenic trichloride Glycolic acida Lanthanum trichlorideb Phenol Zinc chloride* Resorcinol Potassium hydroxide Naphthol Boric acidb Propylene glycol Tetrakisparamethoxyphenylethylene Compounds which react extensively Albumin with antimony trichloride 3-Indoleacetic acid 2,4-Dihvdroxyacetophenone Trimethylamine Benzophenone Triethylamine 4,41-Dimethoxybenzophenone Dime thylaniline Trimethylamine hydrochloride o- Aminop henol Dioxane (3) Benzoic anhydride Cholesterol Testosterone 3,4-Toluenediamine Polymeric systems o-Phenylenediamine Phenol-formaldehyde Urea Polyesters Organo phosphorus acids (all types) Polyamides Trimethyl phosphine oxide Polyimides 2,4,4,4-Tetraniet hyl- 1,3-cyclohut anediil Polycaprolactum Polyethylene terephthalate Polymeric systems Polyhexamethylene adapamide Polyphenylene oxide Urea-formaldehyde Polycarbonates Tetrafluorethylene Polyacrylonitrile Polyvinylchloride Polystyrene Nitrocellulose Polymethylmethacrylate Cellulose Polyvinylfluoride Polyethylene Biochemical compounds Polypropylene Uracil (9) 5-Chlorouracil (9) Copper nitrate Thymine (9) Purines ( 8 ) a Spectra represents the dissociated Pyrimidines ( 8 ) compound so dimer bands are not present. Amino acids ( 7 ) * N o PhIR spectra determined here
VOL. 37, NO. 4, APRIL 1965
617
