STRONTIUM-90 AND STRONTIUM-89: A REVIEW OF MEASUREMENT TECHNIQUES IN ENVIRONMENTAL MEDIA
Robert J. Budnitz Lawrence Berkeley Laboratory University of California Berkeley, CA 91*720
1. IntroiUiction 2. Sources of Enivronmental Radiostrontium 3. Measurement Considerations a. Introduction b. Counting c. •»Sr/"Sr Separation 4. Chemical Techniques a. Air b. Water c. Milk d. Other Media e. Yttrium Recovery after Ingrowth f. Interferences S- Calibration Techniques h. Quality Control 5. Summary and Conclusions 6. Acknowli'J.jnent 7. References
-NOTICE- This report was prepared as an account of worK sponsored by the United States Government. Neither the United States nor the United Slates Atomic Energy Commission, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any wananty, express or implied, or asjumes any legal liabili:y or responsibility for the accuracy, com pleteness or usefulness of any Information, apparatus, J product or process disclosed, or represents that its use I would not infringe privately owned rights. Mmh
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1. INTRODUCTION
There are only two radioactive isotopes SrflO of strontium of significance in radiological measurements in the environment: strontium-89 Avg.jS energy 196-1 k«V and strontium-90. 100 Strontium-90 is the more significant from the point of view of environmental impact. 80 Energy keV 644 This is due mostly to its long half-life % Emission 100 (28.1 years). It is a pure beta emitter with 60 Typ* of only one decay mode, leading to yttrium-90 •mission by emission of a negative beta with HUBX * 40 h S46 keV. Subsequently, the "Y daughter nucleus almost always decays be emitting a 20 6" (Emax - 2.27 MeV) with a 64 hour half-life, leading to stable zirconium-90. The beta J- energy spectra arc shown in Figure 1 and X. 010 0 20 0 30 0 40 0 50 Figure 2 (from Ref. 1). Particle energy. MeV Strontium-89 has a 52 day half-life, much shorter than that of *°Sr but still FIGURE 1. Spectrum of beta energies from decay quite long in its own right. It decays by of etrontium-90 (from Ref. 1). nearly pure 8" emission to stable yttrium-89, the maximum beta energy being 1.463 MeV.
The main radiological impact of radio- strontium in man is due to its biochemical Y 90 resemblance to calcium. When ingested, some of the strontium becomes lodged in the bones, Avg. fi energy 933-5 keV where it remains for a long time (almost permanently). Its subsequent decay produces 100 radiation dose directly at the site (the Energy keV 2270 2.27 MeV highest-energy beta of the daughter 80 ,0Y has a maximum range of only about 1.0 % Emission 100 g/cms). Because of this, the recommended Type ol »- maximum permissible concentrations (MFC) % «0 in air and water are quite small. For oc cupational exposure, the ICRP (Ref. 2) has 40 recommended the following MPC's on a 168-hour- per-week basis for soluble strontium: 20 168-hour-week 168-hour-week J 1 L X Occupational Occupational 0 40 0 80 1 20 1 60 2 00 MPC in air MPC in water Isotope CpCi/m3) (pCi/liter) Panicle energy, MeV
Strontium-90 100 1,000 FIGURE 2. Speetrum of beta energies from decay of yttrium-90 (from Ref. 1). Strontium-89 10,000 100,000 2. soimcns OF ENVIRONMENTAL RADIOSTRONTIUM
The maximum permissible body burdens The two main sources of radiostrontium (MPBB) are 2 uCi (for "Sr) and 4 pCi (for are from (i) nuclear reactors and their fuel "Sr), both for burden in the bone (Ref. 2). reprocessing plants; and (ii) from fallout For individuals of the general public, the after atmospheric nuclear bomb tests. Both MFC and MPBB levels are a factor of 10 strontium radioisotopes are among the important smaller; and for a suitable average sample fission products. of a large general population, another factor of 3 smaller still. -2-
In iu>laar rmcier*. there is a signifi Fallout is, of course, the source of cant production of both "Sr Jind "Sr. Refer radiostrontium that has gained the widest ence 3 projects (hat the total anoints of cognizance in the minds of the general public. activity produced annually will increase Indeed, strontiiavM was a household word in dramatically in the coating decades because of tit* early 19*0' s. This widespread concern in growth in the nuclear power industry. In 1970 the era of large-scale atmospheric nuclear the total strontium-90 annua! production rate boab testa led to a great deal of research %..is 4.0 megacuries/year; the projected figures into the environmental behavior of radiostron- for the years 1910, 1990. and 2000 are lit, tlum In its pathwa>s from the nuclear fireball 410, and 460 MCi/year, respectively. The to man. Fallout concentrations war* measured integral (accumulated) strontium-90 activities extensively, and at* still being measured in those three years arc projected to be 9»0, routinely (Ref. 6). The deposition was con 4600, and 9SS0MCi, respectively. This is siderable. Me quote from the Federal Radia based upon an Oak Ridge National Laboratory tion Council (Ref. 7). "C»> January I, IMS, projection whose detailed input is subject the accumulated level* of Street! lum-90 deposited to revision, but the trend is clear. The over the United States varied from about 100 strontium-89 proJuction rates will grow simi to 12S mtilicuries per square mile in the 'wet' larly, although there is no long-term build-up areas (areas of greatest annual precipitation) of strontium-89 (because of its 52-day half- to 40 to SO millicuries per square mile in the 'dry' regions." The recent French and Chinese life). nuclear tests have again deposited strontium-90 as fallout. Reactors can be designed and built so that aost of the activities in the reactor fuel do not escape into the environment. At Studies of the fate of strontium-90 frea a reactor site itself, the average release fallout have revealed that an important measure rates of fission product* arc only very Mill of its impact on nan is the ratio of strontium fractions of the tola' fuel inventories. to calcium in the total diet. "The (Sr/Ca) For example, at the Dresden Nuclear Power ratio in new bone being formed is one-fourth Station in Illinois, the ratios or released of that in the average diet because the body to produced activities in 1968 (Kef. 4) were selectively discriminates against strontium" 4 x 10-' (for strontita»-90! and 6 « lO"* (R»f. •). Typical "Sr/Ca ratios in total (for strontiiM-89). The average release diet in 196} (Ref. 8) were 10 to SO pCi/gram Ca rates in stack effluent were 700 pCi/second (1 pCt of strnniium-90 weighs about 7 • To*" (strontium-89) and J pCi/second (strontium- grams). Activities in milk were 10 so JO 90), while in liquid effluent the numbers pCi/liter; and in flour about 40 pCi/kg. were 8000 and 900 pCi/second, respectively. Strontium-89 in milk averaged 40 to SS pCi/liter in 1963.
The potential source for environmental These figures indicate the range of acti release it mainly the nuclear fuel-reproces vities requiring measurement, tn biological sing plants , where the fuel rods and food samples, fallout measurements must be arc dissolved and the radiostrontiuat is sensitive to a few pCi/liter of «tU. and released fron the cladding- However, suffi perhaps fractions of a pCi/kg of other foods cient precautions have been designed into the such as vegetables and baked foods, tn air- more recent plants to assure practically com particulate samples from reactors or fuel- plete containment in noma! operation. For reprocessing plants, average release rates in example, the ISO-day storage of fuel elements the range from a few pCi/second to perhaps a before reprocessing allows 86t of the **Sr few uCi/sec need measurement. to "ecay (but only It of tne "Sr). At the Midwe.=t rue! Recovery Plant in Morris, Finally, the standard "gross beta" measure Illinois, the design calls for no environ- ments in both drinking water and resptrable air noma! release of radioactive waste in either are designed nainty to place upper limits on solid or liquid form. A limit on emissions strontiun-90 in these media. For example, of gaseous gross beta (particulates in air) at 7.0 uCi/second has been suggested (Kef. S), the standard method for gross-beta in drinking based upon strontium-90 as the limiting water (Ref. 9) explicitly states that a limit radionuclide. From this it can be seen that of 10 nCi/llter is allowed for strontium-90, the total environmental emissions should be but if strontium-90 is known to be absent, small indeed. then from the point of view of beta activity "the water supply would usually be regarded as radiologically acceptable provided that the gross beta concentration does not exceed 1,000 pCi/liter" (Ref. 9). -3-
•CASUHJCOT COKSIQEMTIONS such as urine, bone, or soft tissue. A. Introduction We shall discuss Methods for strontium-90 B. Counting and strontium-89 deterain.ition in air, vattr, milk, mi othtr media. Hither of two types Beta counting is ultimately required in of measurement* it commonly required: In iny of the methods. The final strontium one type, a quantitative measurement of sample has to be prepared properly for counting: strontiua-90 specific activity (e.g., pCi/g) for most of the counting instruments it must it aadc, while in the second type it is Merely be a thin sample distributed reasonably uni necessary to determine an upper limit of ac formly over an area coapatible with the instru tivity to assure safety. In the second type, ment . • gross-beta aretureawnt is usually perforated at a first screening step, since it is easier Counting is done with any of a number of than elaborate strontium-isolation chemistry. instruments. Typical instruments include Only when the gross-beta Measurement exceeds internal (or external thin-window) gas pro guidelines, or when a strong suspicion of portional counters; C-M tubes; semiconductor atrontiuM contamination is present, iti speci detectors; and less frequently liquid or fic strontium analysis called for. plastic scintillation counters, which require different saaple-preparation methods. The Here we shall concern ourselves predomi problems and differences which characterize nantly with the spanxiiativt msal^nt of the various beta counting techniques have radiostrontiua specific activity in various been discussed elsewhere Media, because ttrontiua aust be determined at activity levels well below the permissible gross-beta levels in strontiua's absence, radiochemical separation techniques an in C. Strontluf90/Strontiua-89 Separation variably required. The chemical separation techniques cannot, There is an extremely wide variety of of course, separate the two strontium radio Methods for radios!rontium, but alt follow a isotopes from each other or from stable siailar outline: cheaic.il <-e«t.vM!iia:io«, strontium. Consequently the end product of followed by purification and sample preparation, the chemical separation contains all strontium followed by tomtinj. isotopes, including carrier strontium and in some cases strontium 85 added as a tracer for Chemical techniques for radiostrontiua chemical yield. have been tailored to the requirements of the various media to be measured. Since the Separation of strontium-89 from strontiua- chemical properties of yttrium play nearly 90 is performed using one of two methods. as important a role as those of strontium The first is ktta tpectremttry, which relies itself, the procedures have generally depended upon the differences in the maximum energies upon multiple-step separations of yttrium as of the beta spectra (Emax * 1.463 MeV for well as strontium free the bulk material. strontium-89; Env • 546 keV for strontium-90; Also, media containing the radiostrontiums are and Enax • 2--7 MeV for yttrium-90). This frequently contaainated with radioactive type of measurement is not well suited to cesiua-137 (also a long-lived beta emitter), the cases in which the strontium-89/strontium- iodine-131, and perhaps other radionuclides 90 ratio is either very large or very small. as well, so that the radiochemistry can be complicated. The most commonly used spectronetry technique erploys a succession of different Ilere we shall give separate treatments absorbers to count selectively the highest- to the various media: air, water, milk, and energy betas (ymium-90). If yttrium has other tacdia (principally foodstuffs and soil). been separated out chemically, the strontium- The separate treatment is necessary because 89 betas arc counted. Detection efficiencies of the differences in the chemical techniques: Mrot*«9 «<«•* i? T k }7 PC PL 24 * 2 6 PLPL 3 27 A I t PCPl Correct vOKrt* *°5r 2C PCPL "5r 21 PCPL FIGURE 3.Beta pulte height ipeotra (from Ref. ID. PCPl m pCi/liter ~~T determination of beta spectral efficiency in *^~j — *et*i Aci. \i -.— —n ISC < any of the Methods being described. i i 1 ! 90 : too /Li i 1 The beta spectroscopy technique which shows the most promise is liquid scintillation * » ^r i 1 spectroscopy, since after th; sample is dis >!*. ITI90' 1 i solved or suspended in a scintillator the 1 geometrical efficiency factor.'- are well under 5 / 1 1 /i 1 ! stood. Direct counting of a sanple with liquid 1 ' • : scintillators suffers from severe limitations /! ; ! ! ii (Ref. 10). However, Piltingsrud and Stcncel ft •» i 21 (Ref. 11) have described a technique which "< •i 2 1> 11 first separates strontium chemically as car bonate, using methods to be described lat*r in FIGURE 4. ntriun-10 vs. strontiun-90 this discussion. The SrCOj is then suspended activity aa a function of tvr.n. in liquid scintillator using a gelling agent, (from Ref. 9) and counted, typically for 2 to 12 hours, usir<> a Packard 'Tri-Carb' system and a 512- chaniisl analyzer. For a 12-hour counting period, the ninijnum detectable activ ity is about 1 pCi. A typical spectrum is Measurements of "total radiostrontiun" shown in Figure 3; the unfolding of the three usually refer to the total activity of a stron isotopic spectral shapes ("Sr, "Y, MSr) tium fraction immediately after yttrium is is done by computer. Another application of separated chemically. The time elapsed before this technique is that of Kamada et al. (Ref. counting is critical, of course, because after 12), who give detailed descriptions of the way strontium-90 and yttrium-90 reach parent/ the beta spectrum is unfolded. daughter equilibrium the "gross beta" counting rate represents exactly twice the activity of the parent strontium-90 itself. The second, and today the more common technique for strontium-89/strontium-90 separation uses the inyrouth of the daughter 4. CHEHICAL TECHNIQUES yltrium-90. Figure 4 (from Ref. 9) shows the fanner in which yttrinn-90 .ml (yttrium-90 • A goal summary of the various ty;>cs of strontium-90) activities grow in time from a chemical separation techniques has been given pure strontium-90 sample. Counting rates (cor by Rouen (lef. 13). he shall quote from his rected for efficiency) can be compared from work extensively below. In the quotation, two measurements, the first immediately after Bowen refers to sea-water measurements, but his strontium chemical reparation (within a few comments should apply to other liquids. He hours, say) and the second 3 to 6 days later. begins by discussing two attempts to extract Alternatively, chemical separation of t>e yttrium-90 directly from environmental samples, yttrium daughter can be performed after allow using thenoyltrifuoroacetone (TTA) in benzene. ing for ingrowth. Both techniques are fre He continues as follows: quently used. "With the exception of these two "(1) Selective complexation precipi ventures, all the procedures known tation, followed by fuming nitric acid to us for strontium-90 analysis in precipitations to obtain pure strontium the oceans depend on the separation nitrate [Ref. 13d, f]. of most of the strontium, together "(2) Oxalate reprecipitation, with more or less of the calcium, followed by fuming nitric separations followed by removal of all or most of (Shvedov and Ivonova, referred to in the calcium and then by decontamination [13f]). of the strontium fraction from other natural or artificial radionuclides "(3) Nitric acid precipitations by a series of ferric hydroxide and without other treatment (cf. Ref. [13c, e]; barium chromate scavenges; the cleaned many others). strontium, usually after precipita "(4) Selective elution serially, tion with ammonium carbonate for con from cation exchange columns [Ref. 13a]. venience, is then stored for enough time to al'ow yttrium-90 to come again "(d) The overall chemical yield to equilibrium with its parent, two of strontium in the separatio- procedure weeks being a convenient time; yttrium- may be determined gravimr ric*lly [Ref. 90 is separated with a minimum amount 13b], by counting tracer strontium-8S of iron, samarium or yttrium carrier, (e.g., Ref. [13c]) by flame photometry or often with some additional scavenging atomic absorption spectrophotometry, or steps, finally filtered, weighed and volunetrically [Ref. 13a]. mounted for beta counting. Counting has been done using a variety of gas- filled Geiger-Muller or proportional "(e) The final separation of daughter counters, or with solid plastic beta yttrium-90 may be made using ferric scintillator. The amount of data hydroxide [Ref. 13d, e, f) or vttrium obtained to confirm the shape of the hydroxide [Ref. 13c], or samarium hydroxide. expected 64-hr half-life decay curve In each case the choice hns been based has varied widely, in response largely on the availability - or ;ase of prepa to economic factors; although 'good ration - of radiochemically pure carrier radiochemical technique' dictates the and of the physical properties of its use of repeated milkings of yttrium- dried hydroxide as a counting medium." 90 and insistence on superimposable decay curves, this has been a nicety often omitted. A. Air In air, measurements of radiostrontium are "In such a separation scheme, the nearly always made by examining particulate number of variations available is not matter. The sampling technique is relatively large: straightforward: particulate matter is collected on a high-efficiency filter in a Hi- "(a) Strontium may be initially Vol sampler. Air sampling rates of 1000 ra'/day precipitated as carbonate or as oxalate are typical. [Ref. 13b,c] and fur the carbonate precipitation, sodium carbonate [Ref. 13d, e], sodium carbonate plus ammonium Chemical separation is required because chloride [Ref. 13f], or ammonium of the normal presence of other beta-emitting radionuclides in the particulate matter: for carbonate [Ref. 13g) may be used. example, naturally-occurring radon daughters Although other reagents have been can adhere to particulate matter and produce proposed: manganese dioxide by Shipman sizeable beta activities. The confutation of [Rcf. 13h] or coprccipitation with Methods of Air Sampling and Analysis (Ref. 14) rhodizonic acid, we know of no data recently issued by the Interscciety Committee reported to have been obtained by contains tentative methods for measuring both these or any other separation pro strontium-90 and strontium-89 in air. The cesses than those cited above. chemical separation is the same for both radio- strontium isotopes, and this method is likely "(b) The oxalate precipitate may to be adopted as a "standard Method" in the be decomposed by dry ignition [Ref. 13e] near future. or by wet combustion with nitric acid. "(c) Strontium may be separated from such calcium and magnesium as accompany it in the initial precipi tation by: -6- The filter is ashed in a muffle furnace explicit limit is given for strontium-89, but prior to the chemical procedure. We quote the maximum permissible level for it would be from Ref. 14: significantly higher: for example, the "Strontium is separated from ICRP's maximum permissible concentration for calcium, other fission products, and strontium-89 in water is a f.-ctor of 100 natural radioactive elements. Nitric higher than for strontium-90. acid separations remove the calcium and most of the other interfering In Standard Methods (Ref. 9) the method ions. Radium, lead, and barium for total radiostrontium and strontium-90 are removed with barium chromate. in water applies to either drinking water or Traces of other fission products filtered raw water. We quote from Ref. 9: are scavenged with iron hydroxide. After the strontium-90 • yttrium-90 "It is applicable to sewage and equilibrium has been attained, the industrial wastes, provided that steps yttrium-90 is precipitated as the are taken to destroy organic matter hydroxide and converted to the oxalate and eliminate other interfering ions. lor counting. Strontium chemical In this analysis, u known amount yield is determined gravimetrically of inactive strontium ions, in the as strontium carbonate, 0.5 pCi form of strontium nitrate, is added strontium-90 can be determined by as a "carrier". The carrier, alkaline this method with an error of less earths and rare earths are precipi than ilOt at the 951 confidence tated as the carbonate to concentrate level under usual conditions (counter the radiostrontium. The carrier, background of less than 1 cpm and along with the radionuclides of a 60-minute count)." strontium, is separated from other radioactive elements and inactive Another technique for air ."' ters has sample solids by precipitation as been developed at Atomic Knergy of Canada strontium nitrate from fuming nitric Limited (A.E.C.L.) (Ref. IS). The first acid solution. The strontium carrier, stages of the separation are described as together with the radionuclides of follows: strontium, is finally precipitated "The ashed air filter is fumed as strontium carbonate, which is with hydrofluoric and perchloric dried, weighed to determine recovery acids to remove silica. After extrac of carrier, and then measured for tion with nitric acid and fusion with radioactivit;-. The activity in the sodium carbonate, an anion exchange final precipitate is due to radio column is used to separate plutonium active strontium only, because all from iron and other elements. The other radioactive elements have been column effluent is retained for the removed.... estimation of barium (140), strontium "Radioactive barium ('""Ba, "La) (89, 90) and cesium (137)." interferes in the determination of radioactive strontiun inasmuch as it An alternative separation method, also precipitates along with the radio- described in the A.K.C.L. Manual (Rer. IS), acti •• strontium. This interference is applicable when the ashed air filters con is eliminated by adding inactive tain little acid-insoluble.material. In barium nitrate carrier and separating this method, "plutonium is separated from this from the strontium by precipitating barium, strontium, and cesium by hexone ex barium chromate in acetate buffer traction from a saturated ammonium nitrate solution. Radium isotopes are also solution" (Ref. IS). Hexone is methyl iso- eliminated by this treatment.... butyl ketone. This method is shorter and easier than either of the others mentioned, "IVio alternate procedures are making it attractive where the conditions for given for the separation of "Y. In the first method, ,0Y is separated by its use .ire applicable. Use of either A.t.C.L. : separation method must be followed by another extraction .nto tributyl phosphate from stage to isolate radiostrontium from barium concentrated nitric acid solution. It and cesium. is back-extracted into dilute nitric acid and eva|wrated to dryness for beta counting. The second method con B. Water sists of adding yttrium carrier, separa ^Vo types of water are of most concern: ting by precipitation as yttrium hydrox Drinking water and waste water. We have already ide, and finally precipitating yttrium referred above to the U.S. ;\iblic Health Service oxalate for counting." Drinking Water Standards (Ref. 16). The limit for strontium-90 is 10 pCi/liter, when other A similar technique, not identical in .11 sources of intake are not considered. No respects but following the same general lines, is described in the A.E.C.L. Manual (Ref. IS). -7 C. Milk Another method in the U.S.P.M.S. manual (Ref. 21) removes milk proteins by precipitation Milk is one of the most important path with trichloroacetic acid (TCA); precipitates ways to man for environmental strontium. The the alkaline earths as oxalates, subsequently U.S.P.M.S. Pasteurized Milk Network has devel converted to nitrates; and separates strontium oped a standard analytical procedure (Ref. 18- from calcium by solubility. When working in 22) which will be discussed here as typical of humid climates, care is required since the sam several other methods. The metliod removes ple is counted as strontium nitrate on a stain strontitM (and other alkaline and alkaline earth less steel planchet, which can corrode the ions) by passing a liter of milk through a counting chamber if nitric acid is formed at cation exchange resin, followed by removal of high humidities. The Handbook of the Environ yttrium in an anion exchange resin. mental Protection Agency's National Environ mental Research Center (Las Vegas) (Ref. 24) He quote from Ref. 20: describes a method very similar to this last (TCA) technique. "The procedure consists of storing the milk samples with for D. Other Media maldehyde preservative for the in growth of the yttrum-90 daughter Chemical separation techniques have been of stronti'vn-90, adding yttrium developed for a wide variety of media besides carrier, and then passing the milk air, water, and milk. The techniques are as consecutively through cation and varied as the problems, since media such as anion exchange resin columns. food or biological samples can have any of a - The alkaline earth ions in milk large number of (radioactive or stable) impuri are replaced by sodium ions in the ties. Here we shall only mention briefly a cation exchange column, after which few methods. the yttrium is retained as an anionic complex - probably of citrate - in In most biological samples, the first the anion exchange column. The efflu procedure is to convert the sample to ash ent milk is discarded and the yttrium in a muffle furnace (500° to SOOT). This complex on the anion exchange resin eliminates the large organic substrate, which is destroyed with hydrochloric acid. might originally contain strontium or yttrium The yttrium, eluted with the acid, in complexed form. Ashing is also performed is precipitated as the oxalate, and on milk and bone samples. For some samples, the radio-yttrium is measured with which are volatile at dry-ashing temperatures, a low-background beta counter.... it is preferable to perform uet ashing with nitric acid, followed by an equal-volume mix Initially, the maximum yttriuo ture of perchloric and nitric acids (Ref. 25). yield was 65t and average yields The U.S.P.H.S. manual (Ref. 21) contains good were SSI. Yttrium retention on the outlines of the procedures for both dry and resin was improved from SO to 90t wet ashing. by adding sodium citrate to the milk. The per cent eluted in 35 ml of Fusion is used for those samples (e.g., hydrochloric acid was increased soil, silt) which are not easily dissolved by from SI to 96* by decreasing the acid digestion because of their high silica amount of anion exchange resin and content. The fusion procedure in the U.S.P.H.S. by thoroughly stirring the resin manual is typical: the sample, with carrier during elution. Other losses plus 5 g of NaOH pellets per gram of sample, were minimited by small procedural is fused over a Meeker burner for 20-30 minutes. chanfes, so that the overall aver Then 0.S g of anhydrous MajCO, per sample gram age yield was increased to 86t." is slowly stirred in and heated again. The malt is cooled, taken up in water, centrifuged, The U.S. Public Health Service manual heated again after 3N Na?CO, is added and cen (Ref. 21) describes other methods for milk trifuged again. The precipitate is dissolved analysis. Their "reference method", used in 6N fCl, ready for analysis (Ref. 21). mainly for quality control, is not applicable for routine analysis. The method uses stron Once ashing or fusion has provided a tium- 65 as a tracer; strontium is separated dissolved sample, the radiochemical methods by successive carbonate precipitation and are s^uite similar to tho:;e already described. hW> washing, and the yttriun-90 ingrowth There are some differences, but we refer the occurs in solution. The special feature is reader to the appropriate references for details. separation of ingrown yttrium from contamina ting lanthanun-140 us inn tributyl phosphate. . The U.S.P.H.S. manual (Ref. 21) contains A similar method is described in the Procedures radiostrontiun techniques for urine, bone, Manual of the USAEC Health and Safety Laboratory bone ash, tobacco, vegetation, soil, and silt. (Ref. 32). -8- The A.E.C.L. manual (Ref. 15) has techniques strontium-89 is counted as yttriuin-90, while for animal and fish flesh, cereals, eggs, fats, the strontium-90 yields are typically 851 and and various vegetation as well as bone. The the yttriim yield in the solvent extraction is HASL Procedures Manual (Ref. 22) contains greater than 95%. methods for vegetation, tissue, soil, and urine. The British A.F..R.F.. has published radiostron- Proper analytical procedure demands tium methods in hone ash, milk ash, vegetable that calibrations be taken periodically to matter, human teeth, and soil (Ref. 2b). Porter check the 64-hour >aif-lif* of yttrium-90 et al. (Ref. 27) have developed a method using measured from the final yttriui* sample. This excess ethylenediaminetetraacetic acid (EDTA) half-life is in the range where such measure which is applicable in samples* with very ments are easy, yet they are omitted in some large calcium/strontium ratios, yet still laboratories for reasons of economics or permits strontium yield (as carbonate) to be inconvenience. This check is one of the easiest determined gravijitetrically. It has been used ways to exercise internal quality control on for a wide variety of organic media. Finally, a modest scale. Baratta and Reavey (Ref. 28) have described a method used by the U.S. Food and Drug Admin istration for food and other biological samples, F. Interferences which uses tributyl pliosphate extraction and analysis of yttrium-90. When chemical separation is performed, the main interferences in environmental samples are stable aaloiun, bariur-UO, zrd This is only a partial list of the many stable phosphates. The chemical considera radiochemical analysis techniques in the liter tions have been well discussed by Goldin, Velten ature; for more complete coverage, the reader and Frishkorn (Ref. 25), from whan we quote: is referred to the literature cited. "Calaiwi. Strontium as an alkaline earth element is chemically similar to the other members of this family. Its resemblance to calcium, barium, E. Yttrium Recovery after Ingrowth and radium is especially marked. Calciun, which is widely distributed The chemical separation of radiostrontium in nature, is one of the inert elements is often followed by ingrowth of yttriim-90, whose separation from radiostrontium yttriim separation, and counting of yttrium-90. has been most studied. Such separa This method is especially useful to determine tion is necessary if the strontiun strontium-90 in the presence of strontium-89. radiations are to be measured directly in samples of moderate or high calcium One critical parameter is the specificity content, or if the final precipitate of this yttrium-90-separation scheme for is weighed to determine the chemical strontiim-90. This specificity has been studied recovery of strontium. Occasionally by Goldin et al. (Ref. 25), whose procedure, calcium is present in such large after purifying SrOOi precipitate, is described quantities as to give unmanageable as follows: amounts of precipitate unless it is removed. "After ingrowth of yttrium, the strontium carbonate precipitate "The precipitation of strontium is dissolved with hydrochloric (and barium) nitrate in concentrated acid, neutralized to methyl orange nitric acid also separates strontium with ammonia, and buffered at pH S. from calcium. The concentration of The yttrium is extracted into 2- nitric acid is critical, as too dilute thenoyltrifluoroacetone solution. a nitric acid solution will solubiliie After the ornanic phase is washed too much strontiun, while too strong with water buffered at nil 5, the a nitric acid will precipitate cal yttri'im-90 is stripped by extrac cium with the strontium. The- most tion with IN hydrochloric acid. The hydrochloric acid extract is evapora- favorable range is from 05 to "So tcd on copper planchets, heated nitric acid. Concentrated nitric thoroughly to destroy residual acid will suffice. If the sample is organic matter, and counted, correct in aqueous solution, fuming nitric ing for decay of the yttrium-90 acid probably will be needed to take between its extraction and the care of the dilution counting time." "Barium ami Radium. The firsion product barium-NO, also a membi t of The yield of strontium-8!) is very small the alkaline earth group, is carried in this procedure: only 4 x 10"' of the along with strontium as carbonate. -9- It must lie removed whether the strontium As in any analytical procedure, much of or its daughter is to l>c cam ted, ns the success of radiostrontium assay depends there is a radioactive daughter, lan upon the care of the analyst ... an obvious thanum- 140, which will contaminate the point but one which cannot be overemphasized. yttrium. It is precipitated, with carrier bariim, as chromate from a solution H. Quality Control buffered at pi I S. Radium, which follows barium in this procedure, can he Quality control is one of the irost determined, although rather crudely, important elements of any radionuclide-analysis by alpha-counting the barium chromate rogram. Unfortunately, quality-control checks precipitate.... Rave usually revealed significant variations among laboratories analyzing for '"Sr at low "PHoiphat*$. Phosphates interfere levels. These variations are a cause for by causing precipitation of strontium concern since they demonstrate the fundamental when the solution is made basic in the difficulty in making routine, reliable, accu hydroxide scavenging step. Although rate "Sr measurements in environmental media. the phosphate content of water is usually too low to be of consequence, this We shall discuss one recent study as an interference is very troublesome in example ... others show comparable results. the analysis of biological sar.ples, In 1971, the EPA Office of Radiation Programs whose ash is largely calcium phosphate. carried out a study of analysis capabilities Phosphates are removed in the nitric in milk (Ref. 31). Thirty-five participating acid treatment already described, laboratories made triplicate dtterminations of being converted to phosphoric acid, unknown concentrations of "Sr, "Sr, "'I, which is removed with the supernote. and "'Cs at activity levels (t2t) of 3!, 42, Several treatments usually are necessary 69, and 52 pCi/liter, respectively. Unfortu to ensure complete removal." nately, nine laboratories reported results whose mean exceeded the 'control level' of G. Calibration Techniques about ilOt for *'Sr. [For "Sr, ,J1I, and "'Cs the outlying laboratories numbered 4, 6, and There are a number of problems in perform 2 respectively.] For many of the outlying ing accurate measurements using the chemical laboratories in the "Sr study, the rar ? of techniques discussed above. Among them are reported results for the triplicate analyses losses of radiostrontiun, losses of yttrium, exceeded 25t. This study seems to show that, and counting errors. while many laboratories can perform "Sr analyses well, a significant minority cannot. The use of standard radiostrontium pre parations can help to reduce counting efficiency errors. The detection efficiency oner the i. SOWWRY AMD CONCLUSIONS spectrin of strontium-90 (and it daughter yttrium-90) must be understood, and for this In this section we have attempted to give purpose low-level solid SrCOj sources have an overview of the present status of radio- been prepared by the USAEC Health and Safety strontium measurements in environmental media. Laboratory (Ref. 29) by dilution of primary sources from the National Bureau of Standards. Perhaps the key point to make first is Standard sources for strontium-90 in milk that, at the low levels which concern us here, have also been prepared (Ref. 30). the only methods for specific raiiottrontium analyst* involve analytical chmxatry followed Chemical yields can be studied using by btta counting, he have therefore emphasized strontiun- Another quality control measurement, This point has been made extremely well mentioned above, is the observation of yttrium- by Bowen, from whom we quote (Ref. 13): 90's 64-Ixxir half-life in counting of the yttrium fraction. -10- "In the extensive series of studies of strontium-90 in sea-water choice among these various possibilities has been made partly on the basis of pre judice, partly on economics, partly on the basis of which other radionuclides were to be sought on the same samples, partly on the basis of which alterna tive used fewest reagents kniwn or suspected to be significant contribu tors to the radiochemical blank and partly on the basis of safety. In most of these variations the decis ions have been legitimate ones, but we feel of even more importance have been questions which one can still only describe as those of art: in the hands even of very competent and experienced analysts, no one method, whether of trace element or of low- level radiochemical analysis, appears ever to have been uniformly superior in quality of results. For this reason, we strongly resist the suggestion that a single 'standard' method be selected and recommended," In support of his viewpoint, Bowen cites interlaboratory calibration analyses in which nearly the full spectrum of possible radio chemical procedures was represented. We quote Bowen again: "... it is clear, we believe, that in suitable hands each method was capable of delivering data of high quality; it is also clear from some of the entries ... that these well-established methods were capable in unsympathetic hands of yielding some pretty bizarre sets of numbers, indeed." Ke agree with this general viewpoint. Apparently, none of the techniques suffers from critical intrinsic flaws; yet equally apparently, the results obtained with a par ticular method seem to depend upon a specific skill of the analyst rather than upon his general competence. This situation is not satisfactory or necessary. Much can be done in the development of these or other methods to make them less dependent upon individual talents. We can summarize by stating first that sensitivity is adequate in the methods commonly used; second, that further research and devel opment in this field is most needed in simpli fying, standardizing, and automating the methods; but finally, that the market for a fully automated system (even if available) is probably insufficient to justify its development. -11- 6. ACKNOWLEDGMENT The constant support and encouragement of D.A. Mack and R.M. Graven is gratefully acknowledged, as is the generous advice and review of E.M. Baratta, P.W. Durbin, G.A. Morton, and C.W. Sill. This research was conducted in conjunction with a "Survey of Instrumentation for Environmental Monitoring" (Ref. 32), which was funded under Grant No. AG-271 from Research Applied to National Needs, National Science Foundation, and performed at the University of California, Lawrence Berkeley Laboratory in facilities provided by the United States Atomic Energy Commission. The mention of commercial products, their source or their use in connection with material reported herein is not to be con strued as either an actual or implied endorsement of such products. The opinions expressed herein do not necessarily express the opinion of the National Science Foundation, the Atomic Energy Commission, or the Uni versity of California. -12- 7. REFERENCES 1. J. Mantel, "The Beta Ray Spectrum and Averege Energy of Several Isotopes of Interest in Medicine and Biology", Int. J. Appl. Radiat. Isotopes 23, 407 (1972). 2. International Commission on Radiological Protection, ICRP Pub. 2, Pergamon Press, Oxford (19S9). 3. "Siting of Fuel Reprocessing and Waste Management Facilities", Report ORNL-4451, Oak Ridge National Laboratory, Oak Ridge, TN 37830 (July, 1971). 4. B. Kahn et al., "Radiological Surveillance Studies at a Boiling Water Nuclear Power Reactor", Report BER/EER" 70-1, EPA Radiological Engineering Laboratory, 555S Ridge Avenue, Cincinnati, OH 4S213 (1970). 5. "Applicant's Environmental Report, Midwest Fuel Recovery Plant, Morris, Illinois", Report NEDO-14504 and "Supplement 1", Report NEDO-14S04-Z, General Electric Company, Reactor Fuels and Reprocessing Department, San Jose, CA 9S12S (June, 1971). 6. U.S.A.E.C, "Fallout Program Quarterly Summary Reports", a series of quarterly reports available from U.S.A.E.C. Health and Safety Laboratory, 376 Hudson Street, NY, NY 10014. 7. FRC Report No. 4, "Estimates and Evaluation of Fallout in the United States from Nuclear Weapons Testing Conducted Through 1962", Federal Radiation Council, Washington, DC (1963). 8. FRC Report No. 6, "Revised Fallout Estimates for 1964-1965 and Verification of the 1963 Predictions", Federal Radiation Council, Washington, DC (1964). 9. Standard Methods for the Examination of Water and Wastewater, 13th Edition, American Public Health Association, 1015 - 18th St., N.W., Washington, DC 20036 (1971). 10. A.A. Moghissi, "Low Level Liquid Scintillation Counting of Alpha and Beta Emitting Nuclides", Section II, part 7 in The Current Status of Liquid Scintillation Counting, E. Bransome (ed.)« Greene 6 Stratton, NY (1970). 11. H.V. Piltingsrud and J.R. Stencel, "Determination of ,0Y, ,0Sr and "Sr in Samples by Use of Liquid Scintillation Beta Spectroscopy", Health Physics 23, 121 (1972). 12. H. Kamada, M. Mita, and M. Saiki, "Measurements of "Sr and '°Sr in Environmental Samples by a Low-Background Beta-Ray Spectrometer", p. 427 in Rapid Methods for Measuring Radio activity in the Environment, Proceedings of a Symposium in July 1971, International Atomic Energy Agency, Vienna (1971). 13. V.T. Bowen, "Analyses of Sea-Water for Strontium and Strontium-90", p. 93 in Reference Methods for Marine Radioactivity Studies, International Atomic Energy Agency, Vienna (1970). 13a. V.E. Noshkin, N.S. Mott, "Separation of Strontium from Large Amounts of Calcium, with Appli cation to Radiostrontium Analysis", Talanta 1£, 45 (1967). l>b. Y. Miyake, K. Saruhashi, Y. Katsuragi, "Strontium-90 in Western North Pacific Surface Waters", Pap. Met. Geophys., Tokyo U, 188 (1960). 13c. G.G. Rocco, W.S. Broecker, "The Vertical Distribution of Cesium-137 and Strontium-90 in the Oceans", J. Geophys. Res. 68, 4501 (1963). 13d. T.T. Sugihara, II.I. James, E.J. Troianello, V.T. Bowen, "Radiochemical Separation of Fission Products from Larj:e Volumes of Sea Water Strontium, Cesium, Cerium and Promethium", Anal. Chem. 31, 44 (1959). 13e. R. Higano, M. Shiozaki, "Radiochemical Analysis of Strontium 90 and Cesium 137 in Sea Water", Contrib. Marine Res. Lab., Hydrogr. Off. Japan 1_, 137 (1960). 13f. E.G. Azhazha, "Methods for the Determination of Strontium-90 in Sea Water", Radioactive Contamination of the Sea (V.I. Baranov, L.M. Khitrov, Eds.), Akad. Nauk USSR-Oceanographic Commission (1964); Trans. 1966 Israel Program Scient. Transl., US Dept. of Commerce, 177. 13g. D.C. Sutton, J.J. Kelly, "Strontium 90 and Cesium 137 Measurements of Large Volune Sea Water Samples," U.S.A.E.C. Health and Safety Laboratory, Fallout Program Quarterly Summary Rep. HASL-196 (1968). -13- 13h. W.H. Shipman, "Concentration of Strontium from Sea Kater by Manganese Oioxide, Determination of Sr" in Large Volumes of Sea Water", Rep. USNRDL-TR-99S (1966). 14. Methods of Air Sampling and Analysis, Intersociety Committee for a Manual of Methods for Ambient Air Sampling aiid Analysis. American Public Health Association, 1015 - 18th Street, N.W., Washington, UC 20036 (1972]. IS J.H. Guthrie and W.E. Grumitt, "Manual of Low Activity Environmental Analysis", Report AECL- 1745, Atomic Energy of Canada Limited, Chalk River, Ontario, Canada (1963). 16. "Public Health Service Drinking Water Standards, Revised 1962", P.H.S. Publication No. 9S6, U.S. Public Health Service, Washington, DC 20525. 17. Tin; U.S. IViblic Health Service's Pasteurized Milk Network reports its radionuclide measure ments periodically in Radiation Data ij Reports. Nuclides analyzed are strontium-89 and 90, iodine-131, cesium-137, and barium-140~ The most recent extensive discussion of its proce dures is in vol. 9, pp. 731 ff. (December, 1968). 18. R. Kahn, G.K. Murthy, C. I'orter, C.R. Hagee, G.J. Karches, and A.S. Goldin, "Rapid Methods for Estimating Fission Product Concentrations in Milk", Environmental Health Series, U.S. Dept. of HEW, Public Health Service, Publication PUS-999-R-2 (J963). 19. C. Porter, "Rapid Determination of Strontium-89 and Strontium-90 in Milk", p. 11 of Ref. 18. 20. C. Porter and B. Kalm, "Improved Determination of Strontium-90 in Milk by an Ion Exchange Method", Anal. Chem. 36_, 67b (1964). 21. "Radioassay Procedures for Environmental Samples", PUS Publication No. 999-RI1-27 (1967), U.S. Public Health Service, Bureau of Radiological Health, Rockville, MD 20852. 22. C. Porter, D. Cahill, R. Schneider, P. Robbins, W. Perry, and B. Kahn, "Determination of Strontium-90 in Milk by an Ion Exchange Method", Anal. Chem 33_, 1306 (1961). 23. J.H. Harlev (ed.), HASL Procedures Manual, Report HASL-300, USAEC Health and Safety Labora tory, 376 ifudson St., N'ew York, NY 10014 (1972). Earlier editions of this manual were published as Report NYO-4700. 24. F.B. Johns, "Southwestern Radiological Health Laboratory Handbook of Radiochemical Analytical Techniques", Report SKRIH.-ll (1970). Available from SWRHL, now EPA National Environmental Research Center, Las Vegas, NV 89114. 25. A.S. Goldin, R.J. Velten, and G.W. Frishkorn, "Determination of Radioactive Strontium", Anal. Chem. 31, 1490 (1959). 26. A. Parker, F.ll. Henderson, and G.S. Spicer, "Analytical Methods for the Determination of Radiostrontium in Biological Materials", Report AERE-AM 101, Atomic Energy Research Estab lishment, Harwell, U.K. (1965). 27. C. Porter, B. .Kahn, M. Carter, G. Rehnberg, and E. Pepper, "Determination of Radiostrontium in Food and Other Environmental Samples", Environ, Science and Technology 1_, 745 (1967). 28. E.J. Baratta and T.C. Reavey, "Rapid Determination of Strontium-90 in Tissue, Food, Biota, and Other Environmental Media by Tributyl Phosphate", J. Agricultural and Food Chemistry .17, 1337 (1969). 29. J.II. ilarley, "Opcrat ion of a Laboratory Intcrcomparison Program", p. 92 in "Fifth Annual Meeting of the Bio-Assav and Analytical Chemistry Group", U.S.A.E.G. Report TID-7591 (1960), U.S.A.E.C. Teclinical Info. Div., Washington, DC. 30. M. Rosensteil, P.B. Hahn, and A.S. Goldin, "Interlaboratory Study of Strontium-90 Measuronents in Milk - August 1963", Health Physics 11_, 966 (1965). 31. F. Knowles, "Interlaboratory Study of "lI, l,7Cs, e,Sr and 9°Sr Measurements in Milk, July 1971", Technical Experiment 71-MKAQ-l, EPA Analytical Quality Control Service, 109 Holton Street, Winchester, MA 01890 (1971). 32. Environmental Instrumentation Group, Lawrence Berkeley Laboratory, Survey of Instrumentation for Environmental Monitoring, Report LBL-1 (unpublished), 1973. ,2 " 64 days) by electron capture followed chemical techniques in common use. by emission of a 514-keV gamma ray. Its routine use is uncommon partly because of its own One difficulty in comparing dif'srent intrinsic radiological hazard, but it serves chemical techniques is that so much rests in a valuable function in periodic quality control. the hands (and mind) of the analyst himself. Other methods for determining chemical yield A choice among the various 'commonly used' rely on classical chemical techniques, such as techniques may depend nore on the particular gravimetric measureme.its of carrier strontium equipment and skills available than on the or of possible interfering radionuclides. differences among the techniques themselves.