Atmospheric particulates collected around East Coast Australian cities and Port Moresby, just before and after the French Atomic Test Series of 1974 in the Pacific, have been analysed by proton activation using the Melbourne University Cyclotron. A number of elements, namely S, Ca, Ti, Cr, Fe, Ni, Cu, Zn, Se and Hg, ranging in concentrations from .001 ug/m3 to up to 3.27 ug/m3 have been detected. The changes observed in the concentrations of these elements in the two sets of samples, taken just before and just after the Atomic Tests, are attributed to Synoptic rather than Nuclear Fall-Out effects

Chaudhri, M Anwar

Lee, M M

Rouse, J L

Spicer, B M

IEEE Transactions on Nuclear Science

Flinders Academic Commons

IEEE Transactions on Nuclear Science, Vol. NS-26, No. 2, April 1979CYCLOTRON ANALYSIS OF AUSTRALIAN ATMOSPHERICCONTAMINATION BEFORE AND AFTER THE 1974FRENCH NUCLEAR TESTS IN THE PACIFIC *M. Anwar Chaudhril'2, M. M. Lee2, J. L. Rouse2 and B. M. Spicer2AbstractAtmospheric particulates collected, around EastCoast Australian cities and Port Moresby, just beforeand after the French Atomic Test Series of 1974 in thePacific have been analysed by proton activation usingthe Melbourne University Cyclotron. A number of ele-ments, namely S, Ca, Ti, Cr, Fe, Ni, Cu, Zn, Se and Hg,ranging in concentrations from .001 Vg/m3 to up to3.27 Vg/m3 have been detected. The changes observedin the concentrations of these elements in the two setsof samples, taken just before and just after theAtomic Tests, are attributed to Synoptic rather thanNuclear Fall-Out effects.IntroductionIn the event of any possible fall-out from nucleartests not only would the radioactive contamination inthe atmosphere increase but also the concentrations ofvarious stable isotopes would change. Therefore, ananalysis of the elemental composition of the atmos-pheric particulates taken from an area just before andafter nuclear tests should give some indication aboutthe extent of fall-out in that particular region.France carried out an extensive series of nucleartests in the Pacific between June and September, 1974.It was widely feared that some of the nuclear fall-outwould reach Australia and New Guinea, especially theEast Coast cities.The Commonwealth Scientific and Industrial Re-search Organization (C.S.I.R.O.) has a number of con-tinuously operating high volume air samplers, collect-ing particulates in polystyrene filters, stationed invarious locations in and around Australia for atmos-pheric research. Therefore, it was decided to analysethe aerosol particulates collected by these samplersin the time period just before and after the Frenchtests in order to investigate the extent and nature ofany fall-out.Conventional analytical techniques such as gravi-metry, colorimetry, emission spectroscopy and atomicabsorption spectrophotometry can usually supply therequired sensitivity for medium atomic weight elementsbut they are quite time consuming and are destructivein that the sample must be dissolved, which is notalways convenient, especially for these historicalsamples. The wet chemical preparations can also leadto additional sources of error from the reagents used.These techniques may also suffer from incomplete re-covery of the elements from the solution. So a non-destructive method of analysis with adequate sensitiv-ity was needed in this case.1. School of Physical Sciences, The Flinders Universityof South Australia, Bedford Park 5042, SouthAustralia.2. School of Physics, University of Melbourne, Park-ville 3052, Victoria, Australia.* This work has been supported by a grant from theColgate-Palmolive Pty. Ltd.2244Chaudhri and Batral have shown that sensitivitiesof up to ppb levels are obtainable through thick targetactivation analysis using charged particles. With theMelbourne University Cyclotron, we have shown that pro-ton activation analysis is capable of being applied toa vast range of matrices for elemental determination inthe sub ppm region. Recently, Debrun and Barrandon2have also published detection limits ranging from fewtens of ppm to up to 1 ppb for a number of elementsbetween Z = 3 to Z = 82 through activation analysis by10 MeV protons. We applied thick-target proton activa-tion to analyse non-destructively the polystyrene fil-ters containing atmospheric matter, using the MelbourneUniversity Cyclotron.Experimental ProcedureThe particulate samples were collected from var-ious cities along the eastern coast of Australia aswell as in New Guinea by the C.S.I.R.O. Division ofAtmospheric Physics. These cities were Port Moresby,Townsville, Brisbane, Sydney, Melbourne and Hobart. Ineach case, approximately 5000 cubic metres of air waspumped through a 0.2 micron polystyrene filter in ahigh volume sampler for one week during June, 1974(just before the French tests - Set A). Another wasobtained in a similar way during September, 1974 (afterthe French tests - Set B). This allowed any possibledifference in the elemental/isotopic composition due tothe fall-out to be determined.Sample preparation involved cutting a 1 cm squarepiece from each filter, originally about 15 cm square,placing it in a recessed groove in the aluminium targetholder and covering it with a thin piece of aluminiumfoil. Great care had to be taken with the samples soas not to introduce any contaminants. Handling was doneusing various instruments that were thoroughly cleanedand rinsed in multiply distilled water. The aluminiumfoil was in turn held down with a brass bracket.A standard was prepared by placing a blank pieceof filter paper of known dimensions into a solutioncontaining compounds of the elements of interest dis-solved in multiply distilled water. The compounds usedwere CaCO3, TiO2,K2Cr2O7, Fe2O3, NiC12.6H20, CuSO4.SH20,ZnO, SeO2, ZrNO3,HgCl2, SrO, Sc203, As203, Sb203, PbF2and V205. The filter was then allowed to dry in freeair and irradiated under the same conditions as theother samples. A number of blank filters were alsoused to determine their elemental contributions.Each sample was irradiated with 8.5 MeV protonsfor 1 hour at a current of 1 pA. During each run, thetarget assembly was cooled with liquid nitrogen, thevolume contained in the target arm being more than ade-quate for the 1 hour. Each filter appeared intact atthe end of the irradiation period with no evidence ofscorching. After a waiting period of 1 hour, each sam-ple was counted with the Ge(Li) detector and PDP-9 com-puter system. This delay was necessary in order to re-duce the high count rates due to the induced shortlived, mainly positron, activities.0018-9499/79/0400-2244$00.75© 1979 IEEEAnalysisThe analysis of the spectra was performed with asemi-automatic program developed by us for use on aDigital PDP-9 computer in 16K configuration. The 4096channels of data are firstly smoothed by a third orderconvolution process acting on groups of 5 channels.Next, the peaks are located, their exact energies foundfrom a fitting function, and their areas calculated.A printout is obtained giving all the required para-meters.At the proton energies of interest here, the (p,n)reaction is the dominant one with usually insignificantcontributions from (p,2n) and (p,d) reactions3. Quan-titative analysis was based on the thick target theoryof Ricci and Hahn4. This states that under the sameexperimental conditions, the concentration of the ele-ments in the sample and standard are related byY C Q RY C *Q Rs s s(1)where Y is the yield of gamma rays from the activationof the element considered, C is the concentration ofthat element in any convenient unit, Q is the integra-ted charge and R is the range of the protons in thetarget. Values appropriate to the standard have thesubscript s. For the equation to be valid, the matri-ces of both the sample and standard should be similar,that is, have similar densities and average atomicweights. Moreover, the element to be determined mustof course be homogeneously distributed. Both theseconditions were met in our experiments.The composition of the polystyrene filter material hasbeen determined to be 7.5% H, 88% C, 2.5% 0 and 0.3%N.5From this, the range of the protons in the filter canbe calculated from the Bragg Additivity Rule which hasonly a small error at the energies of interest here6.For convenience, Equation 1 can be rewritten in theformY C' m As Q RYs Cs ms A Qs Rs (2)where C' is the concentration (e.g. ppm) of element Zin the particulate mass, C' is the concentration of5element Z in the standard compound, m is the mass ofthe particulate on the filter, ms is the total mass ofthe infused standard compound, A is the effective areaof the filter, that is, the area exposed to the partic-ulates and A is the area of the standard filter.5Results and DiscussionA gamma spectrum of an irradiated filter is shownin Figure 1. The nuclides which, after activation,give rise to various gamma peaks in the spectrum havebeen identified and labelled accordingly. From theareas of the gamma peaks in the spectrum, the concentra-tions of various elements can be calculated usingEquation 2.The elemental concentrations of the air samplesfrom various locations in the two sets are shown inTable 1. The elemental contributions of the blank fil-ters was more than an order of magnitude smaller than2048CHANNEL NUMBERFig. 1: Gamma spectrum of the activities induced by 8.5 MeV protons in the filter containing Brisbane airparticulates. The lower curve is the continuation of the upper curve.22450C.TABLE IResults of the analysis of atmospheric particulates. Concentrations are in pg/m3 of airb.City TSP S Ca Ti Cr Fe Ni Cu Zn Se HgPort Moresby 23.9 0.002 0.10 0.05 <0.003 0.29 <0.004 0.008 0.001 0.002 0.0634.7 0.01 0.19 0.06 0.002 0.39 0.02 0.13 0.03 0.002 0.02Townsville 51.7 0.004 0.31 0.18 0.04 1.92 0.02 0.29 0.16 0.05 <0.1541.3 0.06 0.42 0.27 0.02 2.21 0.15 0.41 0.13 0.03 <0.001Brisbane 25.7 0.07 0.73 0.41 0.12 1.46 0.09 0.41 0.25 0.18 0.3551.4 0.15 2.00 0.63 0.11 3.26 0.16 0.53 0.41 <0.12 <0.01Sydney 22.9 0.05 0.12 0.06 0.03 1.04 0.07 0.24 0.11 0.05 0.0639.7 0.06 0.47 0.33 0.05 2.80 0.10 0.40 0.22 <0.11 0.27Melbourne 50.5 0.13 1.62 1.18 0.05 3.27 0.13 0.79 0.44 0.04 0.3631.8 0.05 0.97 0.81 0.05 2.43 0.12 0.39 0.29 0.11 0.30Hobart 42.0 0.05 0.84 0.28 <0.008 0.48 0.58 0.26 0.25 0.07 0.0526.5 0.02 0.17 0.22 <0.003 0.31 0.04 0.04 0.08 0.01 0.08(a) Total Suspended Particulates (b) All errors are typically < 10%those in the samples. Nevertheless, itinto consideration when calculating thein the Table.was still takenvalues givenThe first line of each city are the results forthe first set of samples (Set A) while the second lineare the results for the second set (Set B). The totalparticulate concentrations are generally below thoseof North America and Europe which are in the range50-200 pg/m3.7'8 Despite this, levels of Ni and Crare generally similar while Cu, Fe, Ti, Se and Hg arehigher. During the three month period between thetaking of Sets A and B, the elemental concentrationsat Port Moresby, Townsville, Brisbane and Sydney, thefour cities to the North, generally increased whilstthose at Melbourne and Hobart both decreased. This,however, is not regarded as coming from the fall-outbut suggests major synoptic effects such as prevailingsoutherly winds or a series of strong low pressureregions with their centres located between Sydney andMelbourne. This would have the tendency to blow in-land dust into the four Northern cities, and ocean airover the two Southern ones. Goodman et a19, using theatomic asorption method, found an unusually high levelof Ni (0.85 pg/m3) in the atmospheric particulatescollected over Hobart at the beginning of July, 1974.This striking rise is also present in our results ofSet A (0.58 pg/m3) taken at the end of June, 1974,indicating a good agreement.To investigate possible common sources of elements,linear correlation coefficients were computed betweenall possible pairs of elements as follows:r =xyxy - xy{(X2) - (-)2}1/2 {(y2) _ (y)2}1/2where x and y represent the concentrations of any twoelements to be correlated. The most significant corr-elations are listed in Table 2.These figures were studied further by drawingclusters showing elements which are highly correlated,and their form was based on the "Domain SamplingTheory" of Tyron1o originally intended for psycho-2246logical studies. The cluster for Set A showed thatmost elements correlated well except for Ni which doesnot correlate with any element, suggesting that it isa possible pollutant. The cluster for Set B showedthat all elements correlated well except for Hg,suggesting that this is also a possible pollutant.11TABLE IILinear Correlation CoefficientsSET A SET BxZnCaCuCuCuZnSCuSSSSeFeHgHgyCaTiZnTiFeTiCuCaZnCaTiCrTiCuCrrxy0.970.960.950.950.920.920.910.900.890.890.890.870.850.820.81xCuZnCaSZnSNiSeSeNiSFeSeZnyFeCrCrCrCaCaCuZnFeFeZnZnCrTirXY0.980.970.960.950.940.930.930.920.900.900.890.880.880.87The absolute concentrations of various elementsobserved, and their variations between the two Sets,suggest that the atmospheric composition around eastcoast Australian cities was not noticeably affected bythe French Atomic Test Series of 1974, in the Pacific.However, there may well be some other elements presentwhich could not be detected in the present experiment,and whose concentrations might have been influenced bythe Tests.References1. M. A. Chaudhri and G. J. Batra. Charged particleactivation analysis with cyclotrons. Paper present-ed at the International Conference on the Uses ofCyclotrons in Chemistry, Metallurgy and Biology,Oxford, 1969.2. J. L. Debrun and J. N. Barrandon. Activation Anal-ysis with particles from a cyclotron: determinationof trace oxygen in metals by He-3 activation, multi-elemental trace analysis by proton activation.Proc. 7th Int. Conf. on Cyclotrons and their Applica-tions (Birkhaeuser, Basel, 1975). P. 507-510.3. N. B. Gove and A. W. Wapstra. Nuclear reactionQ-values. Nucl. Data Tables 11, 127-280 (1972).4. E. Ricci and R. L. Hahn. Theory and experiment inrapid, sensitive He-3 activation analysis. Anal.Chem. 37, 742-748 (1965) .5. Australian Microanalytical Service, C.S.I.R.O.Analysis Report - Ref. No. 490.6. L. C. Northcliffe and R. F. Schilling. Range andstopping-power values for heavy ions. Nucl. DataTables A7, 233-463. (1970).7. U.S. Department of Health, Education and Welfare,NAPCA Report No. AP-49, P.12 (1969).8. C.E. Junge. Air Chemistry and Radioactivity.Academic Press, New York and London, 1963, P.359.9. H.S. Goodman, B. N. Noller, G. I. Pearman andH. Bloom. The heavy metal composition of atmos-pheric particulate in Hobart, Tasmania. Clean Air10, 38 (1976).10. R. C. Tyron and D. Bailey. Multivariate BehaviouralRes., 1, 95 (1966).11. M. M. Lee. Some applications of charged particleactivation analysis. Thesis, University ofMelbourne, 1977 (unpublished).DISCUSSIONW. SCHULTE: You give an error of 10%. Isthat the error of one measurement, or is thatbecause you took a number of different samplesin the same area at different times and cal-culated the error from that?M. CHAUDHRI: This 10% is the total error,comprised of the errors (1) due to thestatistics and background subtraction,(2) due to the non-uniformity of the partic-ulate concentrations at different locationson the filter, (3) in the range-energy tablesused. To obtain the absolute concentrationof a particular element, we used a number ofsamples and also different locations on eachfilter for averaging.2247

Cyclotron Analysis of Australian Atmospheric Contamination before and after the 1974 French Nuclear Tests in the Pacific

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Cyclotron Analysis of Australian Atmospheric Contamination before and after the 1974 French Nuclear Tests in the Pacific

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