Table I.
Radioassay of Fractions Obtained in the Recrystallization of a-DGlucose- I -f and a-~-Glucose-6-f Tt.,
Sample,
1.000
25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25
Material Original a-D-glucoseI-t Fraction 1
0,483
Fraction 2
0.220
Fraction 3
0 128
Fraction 4
0.098
Fraction 5 Original a-D-glucose-
0,041 1,000
6-t
Gram
Fraction 1
0.511
Fraction 2
0.184
Fraction 3
0.131
Fraction 4
0.081
Fraction 5 a d t o t a l counts total counts
0.044
Mg.
247 350 514 060 363 452 247 103 200 184 370 046 300 055 240 439 041 035 260 152 163 160
Probable Relative Counts Statistical Specific Radioin 500 Srariazon,o kctivity, activity, pc./Mg. Seconds YO % 0.1598 100.00 15,503 10.80 0.1581 0.80 15,398 0.1596 0.80 99.21 15,647 0.81 0.1588 14,997 0.80 0.1585 99.72 15,446 0.80 0.1585 15,500 100.16 0.80 0.1598 15,500 0.81 0.1586 15,297 99.47 0.1586 0.81 15,356 0.1576 0.81 15,248 0.80 0.1590 100,03 15,500 0.1444 100.00 10.85 13,893 0.1451 0.85 14,103 99.41 0.1434 0.85 13,800 0,1444 0.85 14,000 99.76 0.1438 0.85 14,051 0,1450 0.85 13,948 0,1423 98,83 0.85 13,681 0,1438 0.85 13,952 99.48 0,1436 0.85 13,873 0.1454 0.95 11,247 97.96 0.1418 0.85 13,700
x 100.
to the point of incipient turbidity, and a second crop of crystals was obtained. The mother liquor from this crop was concentrated and again treated with ethyl alcohol to yield additional crops of the sugar. The crystals in the tubes were drird in the same manner as the original sugar. Radioactivity measurements were made a t 1800 volts with a commercial, 2 ~ windowless, , gas-flow, proportional counter (Uodel PC-3 of Suclear Measurements Corp., Indianapolis, Ind.) fitted with a water-cooled slide and a stainless steel sample cell (36 mm. in diameter) ( 3 ) . For radioassay, accurately \veighed samples of the fractions, in small test tubes, were dissolved in weighed amounts of formamide (about 1 ml. each). Each solution was counted for five successive periods of 100 seconds; there was no progressive change during these periods; hence, only the total count, corrected for background, is recorded. The second series of determinations was made in a similar manner, after an interval of several days. The weights of the crops and their radioactivity measurements are given in Table I. The radioactivity 15 as calculated from the empirical relationship, A = amk,
lizing sugars), an isotope effect does not exist. The work does not disprove the existence of a n isotope effect in the rate of anomerization reactions, or in side reactions that may accompany crystallization processes. Either of these may account for the striking isotope effects observed by the previous authors in the recrystallization of D-mannose-I-t phenylhydrazone. EXPERIMENTAL
a-D-Glucose-14. prepared as described previously (I), !vas recrystallized four times from methanol by the addition of isopropyl alcohol. It was then dried in a vacuum oven a t 60" C. for 4 hours and a t 70" C. for 1 hour, and
finally stored in a vacuum desiccator over anhydrous calcium chloride. CPDGlucose-64, also prepared as dwcribed previously ( 2 ) , was similarly dried and stored. I n the fractional recrystallization, 1 gram of the labeled sugar (either a-D&cow-1-t or a-D-glucose-6-f) was placed in a Tveighed test tube and dissolved in 0.6 ml. of water. After a clear solution had been obtained by warming the mixture slightlr. a few drops of ethyl alcohol Tvere added. The solution was seeded with a trace of crystalline a-D-glucose, and the tube lvas stoppered and stored a t room temperature. After several hours, the mother liquor n-as separated from the crystals by a capillary pipet and transferred to a second weighed tube. Ethyl alcohol vias added to thp mother liquor Y
n-here A is the activity, in microcuries, corresponding to a, the observed counts per second, k is a calibration factor (0.112), and m is the combined weight of the solvent and solute. The specific activities in Table I are espressed in microcuries per milligram of the sugar. LITERATURE CITED
(1) Isbell, H. S., Frush, H. L., Holt, S . B., Mover. J. D.. J. Research Natl. Bur. %andards WA', 177 (1960). (2) Isbell, H. S., Frush, H. L., Moyer, J. D., Ibid., MA, 359 (1960). (3) Schwebel, A., Isbell, H. S., Moyer, J. D., Ibid., 53, 221 (1954). (4) Weygand, F., Simon, H., Keil, K. D., Chem. Ber. 92, 1635 (1959). RECEIVEDfor review August 29, 1960. Accepted Xovember 2, 1960.
Resolution of Time-Dependent Gamma Spectra with a Digital Computer and Its Use in Activation Analysis OSWALD U. ANDERS and WILLIAM H. BEAMER Radiochemistry Laboratory, The Dow Chemical Co., Midland, Mich.
b Recent developments in activation analysis are emphasizing completely instrumental methods employing V a Y spectrometry- For such analyses data handling is a problem. To make better use of the obtainable data a small electronic digital computer has been programmed tocorrect,normalize, and resolve time-dependent y-spectra from short-irradiation-time neutron-acti226
ANALYTICAL CHEMISTRY
vation samples. Its use permits obtaining maximum information from mixed y-spectra and freedom from simultaneous irradiation of elemental standards. Typical analyses using 5minute irradiations are given and the Peeling technique used described* Reference spectra have been collected and are available for 69 elements.
A
N INCREASING interest in short-ir-
radiation-time neutron-activation analysis can be noticed in .the recent literature (I, 3-7). A requirement of this type of activation analysis is rapid and efficient data taking, following either immediately after the activation or after rapid and efficient chemical group separations. In several cases much of the burden of the analysis is
left to y-ray spectrometry for both qualitative and quantitative detection of the sample constituents. Guinn and Wagner (5) report on such a completely instrumental method of activation analysis for 27 elements using the 8 X lo7 n/sq. cm./sec. flus of a Van de Graaff accelerator and y-rav spectrometry. They use the singlecount gamma spectra for qualitative identification of the constituents of a sample and compare the areas of the photopeaks above the Compton region of more energetic y-rays with the equivalent spectra obtained from simultaneously activated standards. As a further development of this general technique, this paper reports the procedure used in this laboratory. I t makes better use of the available activity and tries to get from the gamma spectra the maximum amount of information obtainable with the available counting equipment. The procedure employs the gamma spectra of the irradiated sample and the change of these spectra with time for the qualitative and quantitative identification of the elemental constituents in the sample. Since the shape of the gamma spectra depends on the length of time of neutron irradiation, a set time schedule is used. The spectrum of the unknown is compared with standard spectra of known elements obtained with the same time schedule. The counter employed for this work consists of a cylindrical KaI (Tl) scintillation crystal 3 inches long and 3 inches in diameter, mounted on a DuRlont Type 6363 multiplier phototube. The detector is mounted in a cubical lead shield with %inch wall thickness and 13-inch inside edge length. The sample is reproduc>ibly positioned near the center of the (lave by a polyd l styrene trough of -‘/Isinch thickness suspended directly above the center of the face of the crystal. This arrangement provides satisfactory counting geometry of -28% as well as an efficient low bremsstrahlenproducing 8-absorber for @-rays up to 2 m.e.v. EXPERIMENTAL PROCEDURE FOR ACTIVATION A N D DATA COLLECTION
The weighed sample packaged in a small Lusteroid tube is irradiated for exactly 5 minutes in the 2 X 108 n/sq. cm./sec. paraffin-moderated neutron flus (2) of the 2-mv. positive-ion Van de Graaff accelerator (High Voltage Engineering Corp., Burlington, Mass.). A weighed gold foil is irradiated simultaneously with the sample as flux monitor. After the irradiation. the sample without monitor foil is transferred to the 3 X 3 inch NaI(T1) scintillation counter. Spectra taking comniences exactly 1 minute after the end of the irradiation. An RIDL Model 34 200channel analyzer is uqed to collect the
spectra. The data are automatically printed out by a Friden Model A P T Add-punch after the count is completed and are simultaneously punched on paper tape in a code compatible with a Royal McBee LGP-30 electronic digital computer. Two spectra covering the energy range 0 to 1.5 m.e.v. are taken into 100 channels each for 1-minute counting time a t 1 and 2 nlinutes after the end of the irradiation. Three additional spectra covering the range 0 to 3.0 m.e.v. with 200 channels for 3-minute counting times are collected 8, 17, and 26 minutes after the irradiation. Finally the gold foil is counted for 5 minutes in the same counting position. ANALYSIS O F G A M M A SPECTRA
The punched paper tape containing the ran. spectral data is fed to the computer, which is programmed to perform the follo-iving operations: Reduction of data points to half their original number t o smooth the curves and increase statistical significance. Correction for dead time, the period during which the multichannel analyzer had been insensitive t o incoming pulses while occupied with analyzing a previous pulse. Conversion t o counts per minute. Subtraction of the background. Normalization of the spectra of 1-gram sample size and 1 X 108 n/sq. cm./sec. neutron flux. This flux was found experimentally t o induce a photopeak-count rate of 8340 counts per 5 minutes in a gold monitor foil of 15-mg. n-eight. The calibration was carried out with the aid of an absolute Au198 standard obtained from the Nuclear Chicago Corp. Calculation of the logarithm of the corrected and normalized data. The computer finally prints out the corrected and normalized data and plots them as a four-cycle semilog plot. Yisual inspection of the plotted spectra and comparison with spectra of known pure elements make possible qualitative determination of the elements present. Comparison of the areas of y-ray photopeaks with those of the standards permits the quantitative determination of the activated elements in the sample. Since there is a contribution to the gamma spectrum by the Compton plateau associated with each photopeak, a “peeling” computation is used in which the computer is programmed to resolve the unknown spectrum by repeated subtraction of standard spectra until only statistical noise remains. STANDARD SPECTRA
The reference collection of standardized y-ray spectra for the elements was compiled using the time schedule described. This collection contains the spectra of 69 elements which were obtained by activating the purest available samples of the elements, their oxides, or their carbonates. These spectra should find general usefulness
Table I. Examples of Analyses Sam- Chem. Element Present, Found, Species Wt., Mg. yo yo ple 1 MnrOc 7.56 1.04 1.02 V*O5 2.68 0.37 0.37 ... CaC03 282.3 39.1 Mn304 7.56 1.04 1.01 V2O6 2.68 0.37 0.38 CaC03 282.3 39.1 ... 1.76 1.77 2 AgPL‘03 10.8 29.5 4.81 4.90 SH4Br Na2C03 242 6 39.6 38.8 AgSO3 20.3 1.88 1.93 3 33.5 3.12 3.17 XH4Br Na2C03 434.4 40.4 39.9 8.9 0.94 0.94 4 AgT\TO3 SH4Br 15.2 1.60 1.56 Na2C03 395.7 41.9 41.9 Zn 692.1 8 7 . 1 89.7 0 39.3 4.94 4 . 7 A1 63.5 8.00 8 . 5 Ga 796.5 89.6 84.3 Zn 6 38.0 4.27 4.30 A1 Ga 53.7 6.04 6 . 4 7 MgO 158.9 35.5 36.1 57.5 12.8 1 3 . 2 BaC03 62.4 13.9 14.3 SrC03 730.8 73.5 77 NiO 8 0.75 0.74 COsOc 7.5 ”4C1 36.7 3.68 3 . 5
and will be made available by the authors upon request. EXAMPLES O F ANALYSES
Sample 1 of Table I, containing two impurities in calcium carbonate, was irradiated and the data were collected and treated as described. The fourcycle plot of the gamma spectrum of the sample (No. 1 of Figure 1) shows a rapidly decaying peak a t 1.47 m.e.v. and three slowly decaying peaks a t 0.84 and 2.1 m.e.v. Comparison with the set of standard spectra permits identification of manganese and vanadium as Rln and well as a first estimate of -1%
