RAPID QUALITATIVE TEST
Californium-252 mrty be readily detected qualitatively by observation of its continuous heterogeneous spectrum out to about 5 m.e.v. The typical spectrum (Figure 1) is quite obvious in the presence of all the fission products, particularly a t energies greater than 1 m.e.v. QUANTITATIVE DETEIMINATION O F CALIFORNIUM-252
The direct nondestructive quantitative determination o ‘ californium-252 is easily performed by calibration of the counter with a suitable standard. The following three categories demonstrate the wide applicability of the method. 1. Determination of Californium252 in Presence of IFission Products and Actinide Elements. This method should find considerable application by the analytical rac iochemist, process chemist, and engineer in transplutonium work. Sensitivity depends o n the situation (see 1)iscussion) but is at least nanogram of californium252. For the analyt cal chemist, the method allows the rapid analysis of large numbers of samples and eliminates much handling of h ghly radioactive
materials. For the processor, future applications doubtless will be found in monitoring for californium-252 in various production processes. One of the most practical applications of the technique may be found in monitoring for californium in salt deposits or man-made ores resulting from underground nuclear explosions (6). y-Scintillation spectrometry will be particularly valuable for following the fate of californium because absorption of the high energy y-rays is negligible. Thus, it may readily be detected in various salts, vessels, pipes, precipitates, solutions and resins-a technique which can be predicted to have growing uses as the chemist moves into this new area. 2. Determination of Californium252 in Actinide Group. The actinide group separation from other elements is a key step in purification schemes. After this group separation, the californium-252 may be readily determined by the method described. I n this case the sensitivity is increased considerably because of the lower bias voltage which may be used. The sensitivity (radioactivity equivalent to 0.1 background counting rate) in this instance is a t least 7 X nanogram. 3. Californium-252 as Convenient Tracer in Physical, Chemical, and Engineering Studies. One of the most valuable immediate applications
of the method is found in the use of pure californium-252 in various research studies. The simple measurement of the gross y-radioactivity using a well-type counter greatly facilitates such research by eliminating the conventional tedious preparation of solid-free plates so necessary for a-particle or fissionfragment counting. LITERATURE CITED
(1) Bowman, H. R., Mann, L. G., Phys. Rev. 9 8 , 2 7 7 ( a ) (1955). (2) Chart of the Kuclides, General
Electric Co., Schenectady, N. Y., sixth
ed. (19611. ( 3 ) Fiklds, P. R., etal., Phys. Rev. 102, 180 (19.56) \ - - - - I .
(4) Fields, P. R., Diamond, H., U . S. A.E.C. Rept. TID-17527(1962). (. 5.) Hiarrins, G. H.. “The Radiochemistrv of tK< Transcurium ElementP,” NAsXS-3031 (1960). Available from Office of Technical Services, Department of Commerce, Washington 25, D. C. (6) Hoff, R. W., Dorn, 13. W., University of California, Unclassified Rept., UCRL7347 (1963).
( 7 ) Seaborg, G. T., Physics Today 15, 19 (1962). (8) Smith, A. B., Fields, P. R., Friedman, A. M., Phys. Rev. 104, 699 (1956).
RECEIVED for review October 23, 1963. Accepted December 20, 1963. Oak Ridge Sational Laboratory is operated by Gnion Carbide Corp., Nuclear Division, for U.S. Atomic Energy Commission.
Combined Radioc hemica I-N eut ron Ac tiva ti o n An a lysis Method for the Determination of Sulfur and Phosphorus in High-Purity Paper and Beer ANTHONY G. SOULlOTlS Chemistry Department, Nuclear Research Center Democritus, Athens, Greece
b Sulfur and phosphorus were evaluated by a mathematical treatment of the specific activities, expressed as P32, of analyzed materials and of standards after a dc’uble irradiation with and without cadmium protection of the targets. After demineralization of the sample by treatment with acid and evaporation of the whole solution to dryness, lphosphorus was extracted with ether containing 5% sulfuric acid, and then precipitated as ammonium magnesium phosphate followed by a beta coilnt of P32. Numerical data were obtained for American and Greek papers and for beers of different types and origin. The sensitivity of this method reaches the value of 10-3 p.p.m. for sulfur and phosphorus determinations.
materials: phosphorus was determined in iron (8); sulfur and phosphorus were determined in high purity alumilium (1, IS); sulfur was determined in chromium and arsenic using a double irradiation technique (7) ; phosphorus was determined in biological material ( 4 ) ; sulfur and phosphorus were determined in meat (11); sulfur and phosphorus were determined in steel ( 3 ) ; and phosphorus was determined in aluminum-silicon alloys (2). As an extension of these studies, and also using neutron activation analysis, the above mentioned elements were determined in high purity paper and beer using double irradiation techniques and radiochemical separations.
N
Nuclear Reactions. On irradiating any material with neutrons, various nuclear reactions take place, those in Table I being of interest for sulfur and phosphorus determination:
analysis has been used by several investigators for the quantitative determination of sulfur and phosphorus in a variety of EUTRON ACTIVATI~N
EXPERIMENTAL
All of the reactions in Table I result in fi- radiation. Although the activation cross section of S34 was higher than that of S32, reaction (11) was used because the abundance of S3*was higher than t h a t of S34. Reaction (I) can be eliminated to a great extent by cutting off the thermal neutrons by means of 1-mm. cadmium foil. Reaction (111) interferes (6) but this interference is negligible and does not exceed 1% even though the quantity of chlorine is one third t h a t of the sulfur (3, 7). Reagents. P3* RADIOTRACER. Radiotracer techniques were used to investigate the different analytical steps of this experiment and to evaluate the chemical yields. Johnson-hlatthey spectrographically pure diammonium phosphate was irradiated and a 50 mc./ml. solution was prepared; Johnson-Matthey spectrographically pure ammonium sulfate was also used. Procedure for High Purity Paper. DEMINERALIZATION OF PAPER. The paper was heated with nitric acid in a flask equipped with reflux conVOL. 36,
NO. 4,
APRIL 1964
* 81 1
-1mrn. cadmium foil
Table
Nuclide ( I ) P32 (11) Pa2 (111) P32 (IV) S35
Reaction
I.
Initiator
P31(n,y)P32 thermal n S32(n,p)P32 fast n C135(n,~)P32 fast n thermal n S34(n,y)S36
Nuclear Reactions
Abundance,
polythene tube
Cross
O/c
section, mbarns
100 95 75.53 4.22
190 60 140 260
paper
T1/2, days
E,,*, m.e.v.
14.3 14.3 14.3 87.1
1.712 1,712 1.712 0.165
polythene tube standard
[A-l m m . cadmium foil (NH4)zHP04solution were then added. denser. I n general, 1 gram of A new adjustment of p H t o 9 was made paper requires 5 to 10 ml. of nitric and precipitation was conducted by acid, and the time required varies adding 10% MgC12.6H20solution dropfrom t o 2 hours depending on the wise until the colloidal precipitate quality of t h t paper. Concentrated HC1 with a few drops of H20zenhances MgNH4P04,was no longer formed. (If precipitation as phosphomolybdate was the dissolving action but does not disattempted an average chemical yield solve the paper. Concentrated HzS04 (10 t o 20 ml. of concd. H2S04per gram of 88% was attained, but the preof paper) with provision for the concipitate was contaminated with other tinuous removal of the sulfite vapors radionuclides.) The mixture was heated for a short time and then cooled at dissolves the paper. However this method is slow, and more complete once by immersing into the ice-water mixture. After coagulation the colloidal evaporation of thc solution is not attainable because of the concentrated precipitate was rapidly filtered with suction. The filtration apparatus was HzS04. specially designed for radioactive preMETHOD. A 0.5-gram piece of paper, cipitates and used 26 mm. in diameter 20 drops of inactive carrier (NH4)1Whatman KO. 50 filter paper. Care HPO4 solution (2 mg. of P/ml.), 0.2 was taken to precipitate homogeneously ml. of the radioactive solution of P32, on the filter paper by the following and 5 t o 10 ml. concentrated nitric acid were placed in an internally procedure. -4horizontal filtration apparatus was used, and the precipitate siliconated flask and the mixture was was continuously stirred before filtrarefluxed until it became clear. The tion. -4glass stirrer just touched the siliconation of the glassware with 2% silicon in acetone becomes necessary center of the paper and the filtration apparatus was never quite filled. The since radioactive P32 either exchanges with the nonactive P of glassware or is precipitate was washed with distilled absorbed (12). water. The chemical yield of P32as After the reaction, the clear solution ammonium magnesium phosphate was was transferred into a 50-ml. centrifuge 87y0. h second and third precipitation and filtration were carried out in tube externally isolated by means of a n identical manner; the filter paper an asbestos cord and was then placed was not changed (total chemical yield in a sand bath and brought to dryness. The color of the residue was yellow. of P32, 99%). Carbonization should not be allowed RADIOACTIVITY MEASUREMENTS. The filter paper with the precipitate was as the extraction, and especially the dried by means of hot air. The filter transfer of the ether layer, then bepaper was transferred t o a plastic countcoines difficult since a black residue forms contaminating the ether layer. ing tray (anti-coincidence) and the preISOLATION of Pa2 BY SOLID-LIQUID cipitate covered with cellotape. Counting of P32 was carried out using a Geiger EXTRACTION ( 1 4 ) . The dried residue was subjected t o a solid-liquid extraccounter connected in anti-coincidence tion carried out with a 5-ml. portion arrangement. PREPARATION OF SAMPLES TO BE of dry ether containing 50/, concentrated IRRADIATED. The following quantities H2S04. (If one attempts to extract the residue by means of dry ether without of (hTH4)$04 and (NH4)2HP04 were weighed into four polythene snap HzS04 the phosphorus yield is only closure tubes ( d = 8 mm., h = 15 mm.) 20y0.) The dried residue was stirred for a few minutes with a glass stirrer to serve as standards: (NH4)2504, 100 mg. and 150 mg.; (NH4)2HP04, 10 mg. and then centrifuged at 3000 r.p.m. and 100 mg. These were labeled s, The ether layer can be separated either by careful decantation into a beaker or s', p , and p', respectively. Finally, with a pipet. The chemical yield of P3* two 0.5-gram pieces of paper (weights denoted by x and s') were weighed. The after extraction was 88%. The above standards s and p were rolled in the paper extraction should be repeated three x and the packet was put into another times. The ether layers were combined polythene snap closure tube (s = 15 and finally ether was removed on a mm., h = 30 mm.); the same arrangesteam bath (total chemical yield of P32J ment was followed for the other twp 99%). standards, s' and p' and the paper x , ISOLATION OF P32 BY PRECIPITATION but in addition these were wrapped in (5, 9, 15, 16). After evaporation of the ether, t h e remaining solution was 1-mm. cadmium foil cylinder thereby preventing thermal neutron penetracarefully brought with 50% ",OH tion. The two above-mentioned tarto a p H value of 9 and t o a final volume gets were placed as follows: The shielded of 20 ml. T h e solution was heated t o target was placed above the unshielded 80" C., 1 ml. of 10% ammonium citrate one and was held together by cellosolution and 10 drops of inactive carrier ~
812
ANALYTICAL CHEMISTRY
polythene tube beer polythene tube polythene tube standard stopper
ogo
1 mm cadmium foll polythene tube standard polythene tube beer
C Figure 1. ards
Target samples and standA. B. C.
Paper Beer, liquid form Beer, solid form
tape; they then were put into a waterproof polythene bag. IRRADIATION CONDITION.The aboveprepared targets were put on the top of the enriched uranium fuel elements to avoid thermal neutron shielding by the cadmium foil of the shielded sample. Figure 1 shows targets separately, before having been taped into place and put into a waterproof polythene bag. The targets were irradiated for 4 hours in a neutron flux of lO%/cm.*/ seoond in the Democritus swimmingpool nuclear reactor. CONTROL OF FIXEDMETHOD BY SYNTHETIC EXPERIMENT. Weighed amounts of Johnson-Matthey spectrographically pure sulfur and phosphorus were mixed and diluted. From this solution several aliquots were taken. These aliquots contained sulfur and phosphorus in concentrations of 1 to 2 p.p.m. They were irradiated and analyzed according t o the above-mentioned procedures. The results obtained corresponded fully t o the known quantities of sulfur and phosphorus with a relative error of less than i 2 7 & ANALYTICALPROCEDURE. After irradiation the samples were quickly opened behind a lead shield. Care should be taken with the highly radioactive cadmium foil. The two pieces of paper were separated into two parts (each sample being in duplicate) which were then weighed into flasks and the steps previously employed once again followed-attack, extraction, precipitation, and counting. The four standards were dissolved in water and diluted to 50 ml. From these, 5-ml. portions were taken and the previously outlined steps of extraction, precipitation, and counting were repeated. After determining their specific activities, the
10‘
8 -
8
66 4.4
g 3 9
E
5
-
Papor
=
X’
--___
-
--a
P -
P 102
7’
’
Figure 2. Decay curve for isolated precipitate of phosphorus from paper
Procedure for Beer. PREPARATiON weights of sulfur and phosphorus per OF SAMPLES TO BE IRRADIATED. Equal gram of paper were calculated as quantities of the standards were shown later. weighed into polythene snap closure IDENTIFICATION IND CONTROLOF tubes. These were labeled as before. RADIOCHEMICAL PURITY OF P32. To Two aliquots of 12 ml. of beer were identify P32 and cor trol its radiochempipeted into two polythene snap ical purity in the isolated precipitate of closure tubes (d = 25 mm., h = 70 mm.) ammonium magnesium phosphate, coming from both the standards (NHJ2S04 each of which had along its axis another tube (d = 13 mm., h = 65 due to the nuclear reaction S32( T L , ~ ) P polythene ~~ mm.). The upper end of this latter and from the paper, the following experiments were carr led out: tube was closed and the lower one Determination of the Half-Life of fused with the base of the cylinder the Isolated Radiochlement P32. This containing beer. The small tubes containing the standards were put into the was accomplished b.y plotting a decay central tubes which then were stoppered curve on semi-log paper for the precipitate (XH4)MgPO4; it was prea t their base. Again, as before, one of these targets was wrapped up in a 1-mm. cipitated from three sources by MgC12 cadmium foil cylinder; the shielded NH40H solution. The half life was obtained from the slope of the target was put on top of the unshielded one, being held in place by cellotape, straight line calculated by the method of least squares. A value of 14.29 and both put into a waterproof polythene bag. days with a standard error of 10.116 IRRADIATION CONDITIONS.The above days was found (Figure 2) instead of prepared targets were also put on the 14.3 days reported in the literature (IO). Investigation of t ?e Isolated Radiotop of the fuel elements for the reasons mentioned. The neutron flux and exisotope by the Use of Aluminum Abposure time were the same as before. sorbers. This study sought any inANALYTICAL PROCEDURE. After the dication of the existence of p energies irradiation of the samples 5 ml. of different from P32 (1.712 m.e.v.). Thus beer were taken in duplicate and the the plot of the coun-ing rate us. thickness (mg./cm.z) of ahsorber was carried out for the precipitate (NH4)MgPOl originating from thcb paper. The linearity of the plot was good. (Figure 3). Gamma Spectrom:tric Examination of the Isolated Radioisotope. The absence of any y-emi ,ting contaminant in the isolated precipitates of Pa?coming from the analyzed sttmple would serve a s an additional indication of the radiochemical purity of the P32. Thus, 4 hours after withdrawil from the reactor the isolated precipitc.tes of P32coming from the analyzed semple were qualitatively examined by scintillation counting. The energy spectrum indicated the absence of y-emi tting radionuclide. Investigation and Zomparison of All Isolated Precipitates by Aluminum Absorbers. The behavior of all the 101 , . , isolated radioactive precipitates were studied using alumiiium absorbers of 1 I00 900 300 400 500 600 various thicknesses. The counting rate THICKNESS, mg./crn.* was plotted us. thickness for those P 3 2 Figure 4. Absorption curves for isoprecipitates which had no cadmium foil lated precipitate of phosphorus from protection. Inspection of the various standards s and p and paper x plots showed them to be very similar (Figure 4). Without 1 -mm. cadmium foil protection
+
1
’
1 -mm. cadmium foil protection
Table II.
Concentrations of Sulfur and Phosphorus in Paper
Phos-
Sulfur, p.p.m.
Paper sample American origin
phorus, p.p.m.
0 0 0
101 135 138
474 518 550
95 102 98
1 2 3
Greek origin 1 2 3
~~
Table 111.
Concentrations of Sulfur and Phosphorus in Beer
Beer sample
Sulfur,
1
22 22 135 313 293 397 21 103 247
Phosphorus,
p.p.m.
2 3 4 5 6 7 8 9
p.p.m. 5
5 162 7 195 G 325
io4
68
same analytical procedures followed both for the beer and standards. Calculations. Let R represent counting rates of P32activity (c.p.m.); W , weight in grams, and S, specific activities (c.p.m./gram). Subscripts s, p , and x refer t o sulfur, phosphorus, and the analyzed sample, respectively. The letters with (’) correspond to targets with 1-mm. thick cadmium foil protection. The following relations hold: R, R, R,
= Sa *
Sp
*
= S,
*
=
W, W, W,
R,’ R,‘ R,’
= = =
S,’ . W,’ Sp: . W p : S, ’ W ,
If X and Y are the weights of sulfur and phosphorus contained in 1 gram of irradiated material, respectively, it follows that:
S, = 8,’
=
xs,+ Y S ,
(1) (2)
XS,’+ YS,‘
By solving the above system of equations the required weights of sulfur and phosphorus in the sample are obtained: VOL. 36, NO. 4, APRIL 1964
0
813
- S,‘S, X = S,S,’ S,S,’ - S,S,’ Y = S,’S, - SS,’ S,S,’ - Suss,’
(3)
must be used to avoid P32absorption by polythene tubes (6). DISCUSSION
(4)
It is unnecessary t o perform the six radioactivity measurements required by Equations 1 and 2 simultaneously, but it is necessary to run samples s, p , and 2 as a unit as well as s’, p ‘ , and 2’ as a unit t o make Equations 1 and 2 valid. After determining the specific activities of the samples, the values were inserted into Equations 3 and 4 and the weights of sulfur and phosphorus calculated. RESULTS
By the above method both sulfur and phosphorus are simultaneously determined. The errors in phosphorus determination due to nuclear reaction from S32(n,p)P32 can be nearly eliminated; the isolated precipitate of P32 shows remarkable radiochemical purity. The results are reproducible within a relative error of less than *5 % and the sensitivity of this method reaches the value of, p.p.m. for sulfur and phosphorus, if higher neutron flux and longer irradiation periods are used.
Sulfur and phosphorus quant,itative
data were obtained for American and Greek handkerchief tissues as well as for beers of different types and origins. These have been collected in Tables I1 a n d 111. Further experimental work could take the following direction: instead of irradiating beer in liquid form its dry residue could be irradiated. Thus, one could evaporate 25 ml. of beer in a platinum basin, and after evaporation to dryness the residue could be weighed a n d then divided and inserted into polythene snap closure tubes and reweighed. This arrangement is illustrated in Figure IC. This technique
ACKNOw LEDGMENT
The author is indebted to his collaborator, N. A. Tsanos, for his assistance in obtaining numerical data for paper and beer samples and to M. G. Vassilaki for several of the radioactivity measurements. LITERATURE CITED
(1) Albert, P., Ann. Chim. (Paris) 1 , 827-96 (1956). (2) Blackburn, R.1 Peters, B. F. G.1 ANAL.CHEM.35, 10 (1963). (3) . , Bouten. P.. Hoste. J.. Anal. Chirn. Acta 27, 315 11962). (4) Bowen, H. J. M., Cawse, P. A,, Analyst 86, 509 (1961). I
,
(5) Charlot, G., Bezier, D., “Analyse Quantitative Minerale,” 3rd ed., p. 631, Masson, Paris, 1955. (6) Cook, .G. .B., “Proceedings of the
Radioactivation Analysis Symposium, Vienna, June 1959,’’ pp. 21, 28, 29, Butterworths, London, 1960. (7) Gibbons, D., Simpson, H., Rept. RICC-7( 1960), Conference on the Use of Radioisotopes, Copenhagen, Sept. 1960. (8) Herr, W., Arch. Eisenhuettenw. 9. 523 (1955). ‘ (9) Hillebrand, W., Lundell, G., Bright, H., Hoffman, J., “Applied Inorganic Analysis,” 2nd ed., p. 701, Wiley, New York, 1955. (10) Hughes, D. J., Schwartz, R. B., “Neutron Cross Sections.” 2nd ed.. U. S. Atomic Energy ‘Commission Rept. BNG325 (1958). ( 1 1 ) Koch, R. C., Roesmer, J., “Pro-
ceedings of the International Conference on Modern Trends in Activation Analysis,” p. 95, Agri. and Mechan. College of Texas, College Station, 1961. (12) Laverlochere, J., Centre d’Etudes NuclBaires, Grenoble, France, private communication, 1962. (13) Leddicotte, G. W., Emery, F., C. S. Atomic Energy Commission Rept. ORNL-2453, p. 23 (1957). (14) Morrison, G., Freiser, H., “Solvent Extraction in Analytical Chemistry,” p. 224, Wiley, New York, 1957. (15) Scott, W., “Standard Methods of Chemical Analvsis.” 5th ed.. Vol. I. p. 695, Vol. 11, p. 1901, Van gostrand; New York, 1939. (16) Treadwell, F., Hall, W., “Analytical Chemistry,” 9th ed., Vol. 11, p. 370, Wiley, Xew York, 1947. RECEIVEDfor review July 5, 1963. Accepted Xovember 29, 1963.
I
r
. .
Simultaneous Determination of Mercury and Arsenic in Biological and Organic Materials by Activation Analysis BERNT SJOSTRAND Division of Nuclear Chemistry, Royal Institute of Technology, Stockholm, Sweden
b A method has been developed to determine quantitatively nanogram amounts of mercury and arsenic in biological and organic base materials. After neutron irradiation of the sample in a nuclear reactor, followed by a chemical separation based mainly on distillation of volatile compounds of the elements, mercury and arsenic are determined by y-spectrometry. The sensitivity limits are about 5 X l o M 4 p.p.m. for mercury and to lo-‘ p.p.m. for arsenic when a sample weighing about 0.5 gram is irradiated for 2 to 3 days in a thermal neutron flux of about 1 0l2 n./sq. cm.-second. The samples produced after the chemical separation are usually of high radiochemical purity. It is therefore possible to predict a sensitivity of about 10-5 p.p.m. for mercury and 10-4 to 10-5 p.p.m. for arsenic if 8 14
a
ANALYTICAL CHEMISTRY
the neutron irradiation is performed in a higher flux, say a few times 1013 n./sq. cm.-second, and if certain improvements in the radioactivity measurement technique are introduced.
has been published (fa) for the determination of mercury in biological and organic materials by direct y-spectrometry of the sample after neutron irradiation in a sealed quartz tube. The sensitivity limit by that nondestructive method is about 0.03 pg. of mercury or 0.1 to 0.5 p.p.m. in biological material, depending on the character and weight of the sample. During the last five years the method has been successfully applied to the analysis of several hundred samples of various biological and organic materials with mercury contents ranging from 0.1 to 100 p.p.m.
A
METHOD
It soon became clear, however, that the method was not sufficiently sensitive to solve all the problems met. The far more sensitive method presented in this paper was therefore evolved. The sensitivity limit by this destructive method is about 5 X lod4 p,p.m. of mercury for a 0.5-gram sample irradiated for 2 to 3 days in a thermal neutron flux of 10’2 n./sq. cm.-second. The present procedure of determining mercury is similar to the one described previously ( l a ) , except that a chemical separation procedure including purification of the desired elements has been introduced. Thus the determination of mercury is still based on the detection of the 68-k.e.v. x-quanta and 77-k.e.v. y-quanta of 65-hour Hglg7 by y-spectrometry. ils most mercury compounds are rather volatile, it seemed natural to
