A Rapid Method for the Direct Determination of Elemental Oxygen by Activation with Fast Neutrons DEAN J. VEAL and C. F. COOK Phillips Petroleum Co., Bartlesville, Okla.
b An analytical method is described for the analysis of oxygen in samples which contain no fluorine or boron, b y means of activation with fast neutrons. The nondestructiveness and the fivefold increase in speed over the conventional Unterzaucher method are shown. With neutron source strengths readily available from CockcroftWaIton accelerators ( 1 O9 neutrons per second), a sensitivity of 0.032% oxygen is obtainable. At an oxygen level of 1%, the accuracy of the method is rt 17%.
A
T PRESEPI'T no
generally satisfactory method for the direct determination of oxygen exists. The direct analysis of oxygen by the isotope dilution technique of Grosse and Kirshenbaum (9, IO), despite its inherent simplicity, has not come into general use nor has the very tedious fluorination method of Sheft and Katz (17). The ter Meulen oxygen determination described by Smith (18) and others is direct, but sulfur and nitrogm interfere. There are many methods for the indirect analysis of oxygen in organic compounds which have been evaluated by Elving and Ligett (7). Their conclusion was that, for organic compounds, the most generally applicable of the indirect methods is the reduction of oxygen with carbon and measurement of the oxidation products gravimetrically, volumetrically, or titrimetrically. This principle is the foundation of the Schutze-UnterzBucher procedure (16) for organic compounds which has been modified and improved by Jones (12) and Oita and Conway (16).
The Schutze-Unterzaucher procedure
is widely used and gives satisfactory results with most organic compounds, but it is destructive of the sample, requires about one-half hour per determination, and does not give correct answers for the oxygen in certain mixtures, such as lube oils containing metal salts of organic acids, carbon blacks, high ash asphalts, coal, shale, and finally, metal salts and oxides which are of special interest to the petroleum industry. These shortcomings prompted the search for a more satisfactory method for the direct determination of oxygen. In 1949,
178
ANALYTICAL CHEMISTRY
Boyd (6) summarized the great advantages of elemental analysis by the method of activation or the production of artificial radioactivity. Mcinke (14) has reported that for most elements very high analytical sensitivities are attainable by activation with thermal neutrons. However, this latter method has very low sensitivity for oxygen. Accordingly, it was decided to investigate the possibilities of activation analysis with fast neutrons inasmuch as Coleman and Perkin (6) had used fast neutrons to analyze beryllium for oxygen. Preliminary results of this investigation have been reported ( 2 ) . The availability of particle accelerators capable of producing high energy neutrons has made the field of analysis by fast neutron activation increasingly attractive. The activities produced by the action of fast neutrons on the more abundant isotopes of elements are generally of shorter half life (less than 10 minutes) than the corresponding activities produced by thermal neutrons. Thus, generally faster methods of analysis are made possible. I n addition, the probability of producing artificial radioactivity from the lighter, more abundant elements of the earth's crust is greater with fast neutrons than with thermal neutrons. Finally, fast neutrons may be readily slowed to thermal velocities whenever the use of slow neutrons offers analytical advantages. METHOD DEVELOPMENT
Fast neutrons having energies to 14 m.e.v. can be produced with commercially available and relatively low voltage positive ion accelerators by the following reactions:
+ H2 = He3 + n* + 3.265 m.e.v. H2 + Beg = BO ' + n1 + 4.36 m.e.v. H2 + = He4 + n 1 + 17.6 m.e.v. H2
H3
(1) (2) (3)
Depending upon their energy, the neutrons so produced can participate in (n,p), (%,a), and (n,2n)nuclear reactions according to data in Table I for analytically important light elements. Table I shows that oxygen bombarded with 14 m.e.v. neutrons cannot undergo the (n,Zn) reaction and yields only the stable isotope C13 from (%,a)reactions. Therefore, radioisotope production will
occur primarily by the (n,p) nuclear transformation according to the reaction
+
0l6 n
+
We
+p
- 9.62 m.e.v. (4)
The radioactive product XI6 decays with a half life of 7.4 seconds by emission of beta particles and gamma rays having energies greater than 5 m.e.v. Measuremcnt of the radioactivity constitutes the hasis for the rapid method which has been developed for oxygen determination. A great number of other isotopes can be produced by 14 m.e.v. neutrons which would interfere in a general method for oxygen, but by using detectors that respond only to energies greater than 5 m.e.v., most of the radioactivity which is produced by interfering reactions is eliminated. Thus, only boron, fluorine, and carbon would interfere in the determination of oxygen. Because of the rapid decay of radioisotopes produced from carbon, a delay of only 0.2 second following actiration is sufficient to eliminate interference from carbon. A general method is therefore provided for the determination of oxygen in the absence of fluorine and boron. APPARATUS
Neutron source strengths of up to 1010 neutrons per second were obtained by deuteron bombardment of a tritiumzirconium (Equation 3) target. The standard 1-inch targets described by Massey (13) and h r o l ( 3 ) were obtained from Oak Ridge National Laboratories and sectioned into pieces approximately 5 X 5 mm. These sections were indiumsoldered (n1.p. 165' C.) to the copperclad aluminum target plate described by Bronner et al. (4). The deuteron beam was produced by a Cockcroft-Walton positive ion accelerator manufactured by Applied Radiation Corporation, Walnut Creek, Calif. This instrument has been described by Bronner et al. (4). The samples for analysis were contained in Marlex polyethylene plastic rabbits, Figure 1. The rabbits are introduced and reproducibly held before the target by an air pressure system shown in Figures 2 and 3. At the end of the bombardment time, the air flow is reversed by means of the reverse flow valve, and the rabbit with the sample is transferred from the target area t o the counting apparatus.
:: z a 2
"
z z N
N
VOL. 34, NO. 2, FEBRUARY 1962
179
The sample receiver, Figure 4, was mounted within a shielded well-type scintillation crystal for counting the radiation from the sample. Figure 2 includes a block diagram of the apparatus as used for counting. The scintillation crystal was 13/ inch diameter sodium iodide activated with thallium and was in optical contact with a multiplier phototube. Pulses from the multiplier phototube mere fed to a preamplifier and linear amplifier and then t o a single-channel pulse height analyzer, the output from which n a s fed to two scalers. These scalers are connected so that for a pre-determined time only the first scaler would count. Upon completion of this time interval, the first scaler would be automatically shut off, and simultaneously the second scaler would be turned on to count the background for the identical period of time. The neutron source strength v a s monitored by two methods: a standard long counter of the Hansen-hIcKibbin type was used to monitor the total neutrons, and a proportional counter was used to count the associated alpha particles from the nuclear reaction which produced the neutrons. Since there is a one to one correspondence of neutrons and alpha particles, these tm o measurements should stand in a constant ratio. In addition, the alpha counts n ere fcd to a recording rate meter to monitor variation in source strength. REAGENTS
Sational Bureau of Standards Samples 140 (benzoic acid) and 142 (anisic acid) were used as standards without further treatment other than forming them into pellets 3, 16 inch diam. X 3//16 inch long. Other Sational Bureau of Standards samples were used to determine the interference by other elements in the analysis of oxygen. These samples were also used without further
-
71 0 6-3/8
COUNTER
submit a standard sample of benzoic acid to the same procedure as described, then: /A1
.S A M P L E
,3 / 1 6 ” D I A X 3/16/’
Figure 1. Marlex holder “rabbit”
CAVITY
sample
treatment other than pressing into pellets. PROCEDURE
The entire sample cavity of a previously tared rabbit is filled with the sample to be analyzed, and the sample n eight is determined by difference. With an air pressure of 40 p.s.i.g., the rabbit is sent into the target area. Proper positioning of the rabbit is indicated by the extinction of a signal light. After bombarding the sample for 72 seconds, the sample is returned to the sample receiver and automatically counted for 72 seconds. The background, determined by a n additional automatic 72-second count, is subtracted from the first count to obtain the net counts from the rabbit plus sample. Using the source strength observed during the bombardment of the sample, the net counts are normalized to 109 neutrons per second. It is necessary to subtract the counts obtained by the same procedure given above with a n empty rabbit to obtain the corrected net counts from the sample. To determine the amount of oxygen in the sample, it is necessary to
where: d = net act’ivity = total counts first 72 seconds - background counts second 72 seconds h’ = weight of oxygen in standard in grams IV = n-eight of sample in grams S = source strength in neutron per second divided by 109. Subscripts bombardment of sample z> bombardment of empty sample rabbit 3, bombardment of standard 4, bombardment of empty standard rabbit Saturally, the same standard benzoic acid can be used repeatedly, and when there is no change made in the bombarding or counting geometries, the above formula (Equation 5) may he simplified by substituting in it the “sensitivit’y” defined as: L=A 3
-
A
= sensitivit>- in grams
fh
of
oxygen per count at 109 neutron? per second.
(The oxygen of the air contained in the sample cavity of an empty rabbit of the size shown in Figure 1 and which is displaced by the sample, amounts to approximately 23 p ~ .Since this amount of oxygen is the limit of accuracy of the method, it is necessary to correct for it in the case of samples containing less than 0.1% oxygen. This is most simply done by adding 23 pg. to the weight of oxygen found before deterniining the percentage oxygen in the sample. The reason for this addition becomes apparent when it is realized t,hat when
1
S O F T SOLDER 1/ZY RETURN BEND
I/‘
SILVER
1 /EPOXY
* f
ALUMINUM BLOCK /WITH AIR H O L E S THREADED R I N G SILVER SOLDERED TO B E N D
f
SOLDER,^
1
1/2’ F E M A L E COUPLINGT U R N OFF SOME OF H E X M E T A L CONTACT J’
4
\ 1/2” i E M A L E COUPLING
‘\POLYPROPYLENE INSERT INSULATER
SCl NTlLLATION SPRING CONTAC SECTION A-A
Figure 2. Sample transfer system
180
ANALYTICAL CHEMISTRY
Figure 3.
S E C T I O N 6-6
Switch and return bend
/
._ 1
112” PARKER 8DBTX ELBOW
-
S I L V E R SOLDER ,FITTINGS ~ - I Q / ~ / ~ ETH O GE R MAX
5-40 F L A T HD
SEC C-C
I
’
\
IV2”PARKER
Figure 5. Energy level diagram of NIB-
016(7)
Figure 4.
Sample receiver
a correction is subtracted for the activity of the empty rabbit, the correction is in error by the amount of oxygen contained in the sample cavity which is displaced by the sample.) I n routine analyses when accuracy must be sacrified for speed, the oxygen content of the Marlex rabbits is generally small enough so that individual corrections for this need not be made. Equation 5 reduces to:
2
K 100 Wt. “/c oxygen = ___ Aa
!iG
w
(6)
NUCLEAR PARAMETERS
Decay Scheme. As previously mentioned, 5 1 6 is the major radioactive isotopic product of 14 m.e.v. neutrons on oxygen. The abundances of 01’and 01* are so low that they can be ignored. The pertinent details of the decay of “6, (shorrn in the energy level diagram in Figure 5 taken from AjzenbergSelove and Lauritsen (I) are: 26% 10.40 m.e.v. beta particles; 68% 4.26 m.e.v. beta particles in coincidence with 6.14 1n.e.v. gamma rays; and 5% 3.28 m.e.v. beta particles in coincidence with 7.12 m.e.v. gamma rays. “6 Identification. The decay products of K16 were detected using a 13/4-inch sodium iodide crystal as indicated above. Because of the complex
nature of the decay of “I6, it was necessary to consider carefully the amount of material present in the rabbit, the aluminum catcher, and the crystal mounting. The beta particles and gamma rays emitted by the sample must pass through the rabbit walls, the aluminum catcher walls, and the aluminum crystal mount. The total thickness involved for these three items represents an effective absorber for beta particles to such an extent that there is a built-in lon. energy cutoff of 1.43 n1.e.v. for beta particles. Only beta particles with energies greater than 1.43 m.e.v., n-ill penetrate into the crystal counting volume. Once in the counting volume, they n-ill be detected with 100% efficiency. The crystal thickness of l/z inch corresponds to an absorption of beta rays of 8.85 m.e.v. maximum energy. Thus, beta particles in the energy range from 1.43 to 10.28 m.e.v. are detected by the sodium iodide crystal and the sample transfer system shown in Figure 2. This same system is approximately 20y0 efficient for the detection of the 6 m.e.v. gamma rays from the decay of XI6. The identity of K16 produced by activation of the oxygen in benzoic acid was established first, by following the decay of the total activity detected by the sodium iodide crystal. The half life found as indicated in Figure 6 was 7.5 seconds, in satisfactory agreement with the published value of 7.37 seconds (1).
This was accomplished by feeding the output pulses from the sodium iodide crystal to an RCL 256 channel analyzer n hich !vas modified for use so that the channels were scanned on a time basis. At a rate of one second per channel, it \vas possible to follow the decay without interruption for over 4 minutm. Secondly, the energy spectrum resulting from the bombardment of the same sample of benzoic acid as above mas plotted in Figure 7 . The peak a t 6.17 m.r.v. is in satisfactory agreement with the published value of 6.14 m.e.17. for the principal gamma ray from IT6. For the present nork, only the decay energy in the interval 5 to 10 m e.v. Tvas used for counting purposes. The total net counts in this interval in Figure 7 is 15,439, which is only 30% of the total counts in the interval 0.5 to 10 m.e.v., so that the major portion of the total energy detected from the decay of NIB is discarded by biasing in this range. However, the upper level permits discrimination against cosmic rays, while the loner level permits counting all of the beta rays above 5 m,e.v. from N16 together with about 2070 of the 6.14 m.e.v. gamma rays. At the same time, the loner level discriminates against the decay products from all other elements except fluorine and boron. This energy discrimination is accomplished by use of the single channel pulse height analyzer with the base line a t 5 m.e.v. and with the window open to 5 m.e.v. Operating the multiplier phototube a t very low voltages (500 to 600 volts) and the amplifier a t minimum gain results in an excellent signal to noise ratio and sensitivity of detection. I n the case when samples are known to contain only carbon, hydrogen, and oxygen, a threefold gain in sensitivity may be obtained by decreasing the bias threshold of the VOL. 34, NO. 2, FEBRUARY 1962
181
Figure 8. Such variations as are indicated produce an uncertainty of *7% in the neutron flux on the sample during irradiation. Sample bombardments with variations in source strength of greater than *lo% as recorded by the rate meter are not considered satisfactory and are repeated. The design of the Marlex rabbits and the sample receiver (Figure 4) readily permits repeated determinations on the same sample.
a
RESULTS AND DISCUSSION
The results of a series of standardizations are given in Table 11. The source strengths cover a twofold range which is representative of the variation normally encountered in an 8-hour period. The second 72-second period of counting normally represents only background because a t that time only 0.001 of the original activity remains; however, with the source strength indicated, samples containing over 5% oxygen have barely measurable activity during the second 72-second counting period. This activity is negligible in terms of oxygen but must be considered in estimating the background. Accordingly, the background counts in the l a d column were oxygen obtained by correcting the counts in the third column of Table I1 for residual oxygen activity. The aver-
' A
A I
Ib
IO
Figure 6.
Benzoic acid decay curve
pulse height analyzer so that all pulses in the interval 0.4 to 10 m e.v. are counted. Transfer System Reproducibility. I n the case of a n element with a half life of only 7.4 seconds such as NI6, it is essential that sample transfer be accomplished quickly and reproducibly. When the rabbit leaves the target, a switch is automatically actuated to start the counter. The design of the rabbit and its associated transfer system is such that a t 40 p.s.i. the transfer time is 0.53 i. 0.01 second. The variation of 0.01 second in transfer time has a negligible effect on the measurement of total activity from the oxygen sample. There is a variation in sample transfer time with air pressure, but a simple pressure regulating valve is used to maintain the desired pressure. The 0.53-second delay in starting the count permits any BIZ formed in the reaction C12 (n,p)BI2 to decay and results in a loss of total counts of less than 5%. Since this delay occurs with both sample and standard, there is no error from this source. Neutron Source Constancy. Neasurements have been made to determine the constancy of the neutron source strength during bombardment of samples. T h e source strengths were measured a t I-second intervals by feeding the alpha counter amplifier output pulses t o a n RCL 256 channel analyzer set t o accumulate counts at the rate of 1 second per channel. A typical acceptable plot is shown in 182
,
20 30 40 50 60 i0 80 90 IO0 110 I20 I30 I i O TIME-SECONDS
ANALYTICAL CHEMISTRY
1,250
0
BOMBARDMENT TIME=I MINUTE
0
SOURCE STRENGTH = IOto n/SECONt COUNTING TIME=72 SECONDS PHOTOMULTIPLIER VOLTAGE=500 AMPLIFIER GAIN=8 X 7/8
300
1,000
OQ
8
0
B
J
0 0
W
p a r
750
Q
V
0
a LL W
I n I-
3 0
500
V
, 250
0 '
20
40
60
80
100
120
EO
160
7
O'
Table II.
Calibration
for Oxygen
Standard = Benzoic -4cid NBS 39f 87.1 mg. = 22.82 mg. of Oxygen
(50 O1
Total Counts Source Strength, n/sec. 20
X log
1
O L 0.3
0.4
,
I
,
0.5 0.6 0.7 TIME-SECONDS
I 1
08
0.9
Figure 8. Transit time of rabbit from target to counter
age background counts can then be used to estimate the limit of sensitivity of the method. Assuming a 0.1-gram sample, a source strength of lo9neutrons per second, and that activity of two times background is significant, the limit of detectability is 0.032y0 oxygen. At a source strength of 1Olo neutrons per second which can be achieved with a fresh target for periods of 30 minutes to 1 hour, the limit of detection is 0.0032% oxygen. A series of analyses of pure compounds for oxygen is reported in Table 111 to illustrate the wide variety of substances which can be analyzed by this method. The list includes solids, liquids, organic, and inorganic materials containing from 0 to 90% oxygen. This table also illustrates the evtent to which interference from chlorine, nitrogen, silicon, and sulfur has been eliminated. Table 1V reports a series of analyses which were made on routine samples containing only carbon, hydrogen, and oxygen to compare the results obtained by activation analysis with those obtained by classical carbon and hydrogen analyses in which the oxygen was determined by difference. These data show that the oxygen results by activation are comparable with, and in every case within the range of variation found for, the results on the same samples when using the classical method. A comparison of oxygen analyses by activation and by the Unterziiucher procedure is reported in Table V. Two oil samples were chosen that were representative of the type frequently encountered in routine analyses, in that they contained appreciable quantities of nitrogen, sulfur, and aromatic compounds. Duplicate determinations were made on each sample as received and then, after chromatographic separation, on the paraffinic and aromatic portions, Excellent agreement is shown between the two methods in the analysis of the original samples.
0.92 0.98 1.52 1.59 1.57 1.62 1.65 1.61 1.56 1.48
Net
Normalized to unit source strength
2865 3083 4461 4014 4186 4890 5016 4607 4644 4284
3114 3146 2935 2525 2666 3019 3040 2861 2977 2895
First Second 72
72
2871 3089 4471 4025 4196 4901 5026 4612 4652 4292
6 6 10 11 10 11 10 5 8 8
seconde seconds
3065 3097 2886 2476 2617 2970 2991 2812 2928 2846
7.47 7.39 7.93 9.24 8.75 7.71 7.65 8.14 7.82 8.04
3 3 6 7 6 6 5 0 3 4
ilverage 2869
8.01
4
49 49 49 49 49 49 49 49 49 49
Standard deviation Relative standard deviation
Table 111.
Sensitivity, Grams On/Count Backa t 109 ground Counts n/sec.
?;et Total Counts Corrected Empty Net Total Rabbit Counts
195 6.8%
Analyses of Pure Compounds for Oxygen by Activation with Fast Neutrons
Relative 2 of Stand- StandCalcd. Found Deter- ard ard Purity, Oxygen, Oxygen, mina- Devia- DeviaSumber yo 7% % tions tion tion, % ' Xum-
Compound
...
Distilled water Potassium acid phthalate 2-Chlorobenzoic acid Acetanilide Silicon carbide Sulfur (resublimed)
185A 144 141 112
Relative standard deviation
=
Table IV.
..
*
100 100 100 99.90 96.85 100
Formula
700,
Hydroxylated Polybutadiene
2.40 1.70 1.17 0.92 0.11 0.046
2.7 5.4 5.7 7.9 19 75
X
Routine Analyses for Oxygen, Comparative Results
%
%
80.3 80.4 79.7
14.3 14.8 14.2
84.4 84.7
12.1 12.0
4.14
Hydroxylated Polybutadiene
5 6 8 5 4 3
1oou
5.91
Cholesterol Formula % 02
91.36 31.11 19.44 11.86 0.59 0.058
u
7
Microcombustion Hydrogen, Carbon, n-Octadecanol
88.89 31.34 20.44 11.83 0.58 0 0
ber
89.69 89.63
89.66 89.86
10.1 10.1
10.23 10.31
Oxygen by Difference, %
Oxygen by Activation, %
5.4 4.8 6.1 Average 5 . 4
5.42 5.29 5.37 5.36
3.5 3.3 Average 3 . 4
3.70 3.61 3.55 3.54 3.60
0.21 0.27 Average 0 . 2 4
0.21 0.14 0.16 0.21 0.18
0.11 0.00 Average 0.055
0.082 0.060 0.075 0.079 0.074
VOL. 34, NO. 2, FEBRUARY 1962
183
s0 2100
I
I
Y 2000
AV G
“
0
20
IO
30
40
50
Table V. Comparative Analyses of Standard Samples of Petroleum for Oxygen by the Unterzaucher Method
Weight - Per Cent Oxygen Enter- Activazaucher tion
60
TIME-SECONDS
Figure
9. Variation in source strength
INTERFERENCES
In the subject method, the only elements which interfere are fluorine and boron. As shown in Table I, the following reactions can occur with 14 m.e.v. neutrons.
*Lis+ - l e 0
rBell
-
half life of Be11 is 13.57 seconds and the beta particles have maximum energy of 11.48 m.e.v., this interference cannot be eliminated. Although the crosssection has not been measured, it does appear that it is significantly less than the reaction of Equation 8. If neutron soure? strengths are below 1O1O neutrons per second, and the cross section is small. boron interference could be eliminated for most samples. Fortunately, most petroleum samples submitted for analysis do not contain appreciable quantities of fluorine or horon.
+ nHe4 + 2He4 + 16.000
-leo
CONCLUSIONS
m.e.v.
+ sB11 + 11.48 m.e.v.
In the reaction given by Equation 8, the product nucleus, XI6,is identical to that formed from oxygen (Equation 4), so there is no way to discriminate between these two reactions by product nucleus examination. The presence of a tenth as much fluorine as oxygen would cause 100% error in the oxygen rcsults. In the second case, (Equation 8), the Li* formed has a half life of 0.9 second, so that when boron is present. this interference from it can be eliminated by delaying the start of the counting time for 10 spconds. This, however, results in a decrease of about 579’,, in the sensitivity of the method for oxygen. The companion reaction for boron prescmts a more difficult cas?. Since the
The subject method ha. btcn established as a routine method for the direct determination of oxygen in all classes of material which do not contain fluorine or boron. Thirty determinations are normally made in an 8-hour shift which represents a fivcfold increase in speed over the conventional Unterzaucher analyqis. K i t h a source strength of 109 neutrons per second. the sensitivity is 0.032% oxygen. At an ovygen level of 1%) the accuracy of the method is estimated as =t17% by interpolation of the relative standard deviation in Table
111. LITERATURE CITED
(1) rAjzenberg-Selo h d e a r Ph (2) Anders-0: 38 ( l r (3) Arrl AERE-I/K 1136
(4) Bronner, W.
Poso-coalinga gas oil Poso-coalinga bulk distillate Saturates-gas oil
0.30
0.28
0.32
0.24
(55.75%)
0 02
0 10
(44.02%)
0 04
0 05
1 05
0 71
0 79
0 72
Saturates-bulk distillate Aromatics-gas oil ( 43.47 %) Aromatics-bulk distillate (54.71y0)
Eukel, W. FJ-., Gordon, H. S.,Marker, R. C., Voelker, F., Fink, R. K.,.Tu-
cleonzcs 17 ( l ) ,94 (1959). ( 5 ) Boyd, G. E., ANAL. CHEX 21, 335 (1949). (6) Coleman, R. F., Perkin, J. L., Analyst 8 5 . 1.54(1960). (7)-Elving, P. G., Ligett, W. B., C‘hem. Revs. 3 4 , 129 (1914). (8) Endt, P. M., Braams, C. >I., Revs. Modern Phys. 29, 683 (1957). (9) Grosse. .4.V..Hindin. S.G.. Kirshenbaum, D.,’ ASAL. ’CHEII: 2 1 , 386 I
- - - \ - - - - I
.,
A & .
fl949’I --, \ - -
(10) Grosse, A. V., Kirshenbaum, -1.D., I b i d . , 24, 584 (1952). (11) Howerton, R. J., “Tabulated Neutron Cross Sections,” UCRL 5226, May 1958. (12) Jones, I\-.H., ANAL.CHEM.25, 1449 (1953). (13) XIassey, B. J., ORNL-223i (1957). (14) Meinke, W, IT7., Science 121, 177 (1955). (15) Oita, I. J., Conway, H. S., ANAL. CHEM.26,600 (1954). (16) Schutze, M., 2. anal. Chenz. 118, 241 (1939). (17) Sheft, I., Katz, J. J., ASAL. CHEM. 29,1322 (1957). (18) Smith, R. N., Duffield, J., Pierotti, R. A., Mooi, J., Ibid., 28, 1161 (1956). (19) Sullivan, W. H., “Trilinear Chart of Nuclides,” ORNL,January 1957. \ - - - - ,
RECEIVEDfor review June 12, 1961. Accepted December 4, 1961. 6th Tetrasectional Meeting of the ACS at Ponca City, Okla., March 1960.
Editor’s Note: The above paper by Veal and Cook describes an activation analysis method which was developed in the Phillips Petroleum Company’s radiation laboratory, using research-type accelerator facilities. The following comparable method, developed independently by Steele and Meinke at the University of Michigan, demonstrates the suitability of a relatively low-cost accelerator for this method of analysis.
184
ANALYTICAL CHEMISTRY
