Determination of elemental composition of settling particles in Israel following Saharan dust storms by neutron activation analysis

Journal of Radiotmalytical and Nuclear Che,dstry, Articles, VoL 163, No. 2 (1992) 313-323

DETERMINATION OF E L E M E N T A L COMPOSITION OF S E T r L I N G PARTICLES IN ISRAEL FOLLOWING SAHARAN

DUST STORMS BY NEUTRON ACTIVATION ANALYSIS

N. LAVI,* E. GANOR,** E. NEEMAN,** S. BRENNER**

* Soreq Nuclear Research Center, Yavne (Israel) Research lnstttute for Envtromnental Health, Ministry ofHealth, Tel A viv University, Tel A vlw (Israel)

(Received February 26, 1992)

Several cases of transportation and deposition of settling particles following dust storms over Israel, occurring between 1973 and 1987, were experimentally investigated. The storm particles were collected in Jerusalem and Ramat Hasharon, north of Tel Aviv. Meteorological conditions during the storms were examined and classified according to their trajectories into two types: (a) North African and (b) Arabian Desert. The North African type is by far the most common. In the present work, the concentrations ,~f 26 elements (A1, Ba, Br, Ca, Ce, Co, C1, Cr, Eu, Fe, Hf, K, La, Mg, M_n, Na, Rb, Sb, So, Si, Ta, Th, Ti, U, V, and Yb) in settling particles were determined by instrumental neutron activation analysis. The validity of the method was checked by analyzing U.S. NBS Standard Reference Material SRM-1633a; the elemental content found agreed well with the published certified data. Since AI as well as Si were determined through the reactions 27Al(n, y)28A1 (2.24 rain) and 28Si(n, p)28Al, respectively, thermal and eaolthermal neutron activation was applied in order to determine the contribution of silicon to the total ~"A1 activity. Interpretation of the chemical analyses using Enrichment Factors reveals that settling particles are relatively enriched in Ca probably from the local terrain and in CI derived from the Mediterranean Sea,

Introduction

There are two types of typical natural aerosols prevalent in Israel: marine and desert. "Flats is due to the geographical location of the country between the Mediterranean sea and large desert areas. The marine aerosols are derived mainly from sea spray whilst the desert aerosolts are mainly composed of materials such as quartz, calcite, dolomite, feldspars, gypsum and clay minerals. 1 A third type of aerosol present in Israel is anthropogenic and is due to industrial emissions, power generation, vehicular traffic and agriculture; during the winter domestic heating also contributes. 2

Mineral aerosols are present in the atmosphere during most of the year, especially during winter and transitional periods when low barometric pressure systems tend to cross the east Mediterranean basin. 3

Desert aerosols are important because they have manifold effects: (1) Deposition and fertilization of soils, 4 (2) influence on ground water composition, e.g., leaching of

Elsevier Sequoia S. A., Lausanne Akaddmiai Kiadd, Budapest

N. LAVI et al.: DETERMINATION OF ELEMENTAL COMPOSITION

fluoride from aeolean soils to ground water, 5 and (3) effects on cloud physics and

chemistry especially from that part o f the desert aerosol w N c h passes over the

Mediterranean sea and scavenges gases, marine salts and pollution, e.g., sulfate and

nitrate 6 and also acid cloud and acid rain. 7

Meteorological conditions during the storms were exatnined and the storms classified according to their trajectories into two types: (a) North African (Saharan Desert) and (b) Arabian Desert. The North African type is by far the most common.

Table 1 Radionuclides produced by activation of elements in a nuclear reactor together with the nuclear data

Radionuclides Gamma -lines, Element Abundance, produced Half-life keV, %

by (n, 7) reaction (intensities, %)

AI 100 28A1 2.24 m 1778 (100) Ba 0.10 131Ba 11.8 d 496 (47.1)

Br 49.31 82Br 35.34 h 554 (70.6), 776 (83.4)

Ca 0.19 49Ca 8.72 m 3084 (92.1) Ce 88.5 NICe 32.5 d 145 (48.4)

Co 100 60Co 5.27 y 1173 (99.9), 1332 (100) C1 24.23 38121 37.2 m 1542 01.6) Cr 4.35 51Cr 27.7 d 320 (9.83) Eu 47.80 152Eu 13.3. y 779 (13), 1408 (20.8)

Fe 0.31 59Fe 44.6 d 1099 (56.5), 1292 (43.2) I-If 35.10 181Hf 42.4 d 346 (!4), 482 (85.5)

K 6.70 42K 12.36 h 1525 (18.3)

La 99.91 140La 40.2 h 486 (45.9), 1596 (95.4)

Mn 100 56Mn 2.58 h 847 (98.9), 1811 (27.2) Mg 11.01 27Mg 9.46 m 843 (72), 1014 (28) Rb 72.17 86Rb 18.65 d 1076 (8.8)

Sb 42.70 124Sb 60.2 d 603 (98.4), 722 (11.3)

Sc 100 46Se 83.8 d 889 (100), 1120 (I00) Ta 99.98 182Ta 115 d 1121 (35), 1221 (27.4) Th* 100 233pa 27 d 300 (6.63), 312 (38.6) Ti 5.30 51Ti 5.76 m 320 (93)

U** 99.28 239Np 2.35 d 228 (11.2), 277 (14.5) V 99.75 52V 3.75 m 1434 (100) Yb 31.80 175yb 4.19 d 282 (3.08), 396 (6.55)

*Th was determined by 232Th(n, "/)233Th (13-')---,233pa reaction. **U was determined by 238U(n, ?)239U (13-)---,239Np reaction.

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Neutron activation analysis (NAA) has in recent years become one of the most promising and attractive analytical methods for simultaneous multielemental analysis of biological as well as geological materials.

Usually, the amount of the radionuclide produced has been measured by ,/-ray spectrometry either without any chemical treatment, i.e., instrumentally, or after chemical separation.

Non-destructive reactor neutron activation of geological or biological materials is generally not feasible because of the considerable activity produced by the major components (sodium, bromine, chlorine, potassium and phosphorus) of these matrices. Only very short irradiations may be carried out, and only short-lived isotopes can be determined by this method. Table 1 gives the radionuclides produced by activation of elements in a nuclear reactor together with the nuclear data.

The aim of this work was to demonstrate the effectiveness of INAA for the determination of elemental concentration of the ambient aerosols in Israel by studying dust storm compositions. The accuracy of the method was examined by analyzing U.S. NBS Standard Reference Material SRM-1633a (fly ash).

Materials and methods

Sampling

Settling particles were collected from 5 Saharan heavy dust storms over Israel, occurring between 1973 and 1987. The samples were collected in dry polypropylene dusffall collectors modeled on the ASTM standard. 8 The collectors were situated in Jerusalem (Dept. of Geology, Hebrew University) and in Ramat Hasharon, north of Tel Aviv. During the last 20 year period in question some 200 dust storms were recorded in Israel. However, most of these storms did not deposit enough material for analysis. The samples analyzed for this work comprise almost all those which deposited enough dust for analysis and mostly occurred during the months of March to May.

Preparation of multielemental standard solution

For every element to be determined, a concentrated standard stock solution was prepared by dissolving specpure chemical compounds in de-ionized, doubly distilled water. From these concentrated stock solutions, diluted multielemental standard solutions (MES) were prepared. Two ml from the standard solution (for short irradiation times) was transferred directly by micropipette into precleaned and dried half-dram polyethylene vials used for irradiation. The final multielement standard solution contained the following elements: A1, Ca, C1, K, Mg, Mn, Na, Ti and V.

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For Si determination via reAl, a separate standard of silicon powder was used. For long irradiation times, another two multielement standard solutions were prepared containing the following eiements: (a) Br, Co, Cr, Fe, La, Se, Ba, and Ce, and (b) Eu, Hf, Rb, Sb, Ta, Th, U, and Yb.

0.2 ml of these multi-element standard solutions was transferred directly by micropipette onto a very thin aluminium foil, which was left to dry in a vacuum desiccator containing P205. Several standards were prepared for the two types of irradiation.

Preparation of deposited dust samples

For short irradiation times, dried samples of 100 mg were weighed in a half-dram polyethylene vial used for irradiation. From every unit 3-5 samples were prepared for

irradiation. All the polyethylene vials holding the standard solution as well as the dust samples were heat-sealed to prevent any losses during irradiations. Blanks of 0.5 ml de-ionized, doubly distilled water and empty vials were used in all runs. All the samples, standards and blanks were placed in heat-sealed polyethylen bags in order to

avoid contamination of the external surface of the polyethylene vials. For long irradiation times, dried samples of 200-300 mg were inserted into quartz

ampoules (precleaned with HNO3, "Suprapur" and de-ionized, doubly distilled water) which were heat-sealed. From every unit 3--4 samples were prepared. Standards (MES) and blanks were inserted in quartz ampoules together with a neutron flux monitor in order to correct for neutron flux variations. Several samples of U.S. NBS Standard Reference Material SRM-1633a (fly ash) were prepared in order to determine the accuracy of the method.

Irradiations

Two types of irradiations were performed. For determination of the short-lived radionuclides, samples, standards and blanks were irradiated for 5 minute in a thermal neutron flux of 1.1012 n . cm-:. s -1 and transferred using the pneumatic transfer facility.

After irradiation, 1 ml of the irradiated multielement standard solution was transferred by a micropipette into a clean polyethylene vial. For determination of the long-lived radionuclides, both samples and standards were irradiated for 10 hours in a thermal neutron flux of 2.1013 n �9 cm -2. s -1.

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Counting

The '/-rays of the activated samples were measured using a calibrated 100 cm 3 Ge(Li) detector. The resolution of the system was 2.5 keV for 1332 keV of 6~ For short irradiation times samples were counted for 300 seconds (for determination of AL Ca, Si, Ti and V) after a cooling time of 2 minutes. For determination of chlorine and magnesium, samples were counted for 600 seconds and for manganese, sodium and potassium for 2000 seconds, respectively.

For long irradiation times, samples were counted for 3000-10000 seconds, after a cooling time of one week. Before counting, irradiated samples were transferred into precleaned polyethylene vials and weighed again.

Determination ofAl and Si from the amount of 2SAl

Since A1 as well as Si were determined through the formation 27Al(n,-I)2SA1

(2.24 min) and 2SSi(n, p)2SA1, respectively, thermal and epithermal neutron activation was applied in order to determine the contribution of silicon to the total 28A1 activity. 9 Irradiation of the sample of the material checked, once with reactor neutrons and once with epithermal neutrons (using a Cd sheet or a powdered envelope of some boron carbide) followed by counting of 1778 keV "/-my of 28A1 will give two equations with the unknown masses of A1 and Si.

If the specific activity (measured counts under the experimental set-up per one gram of the element) for irradiation with reactor neutrons will be a R and b R for A1 and Si, respectively, and for irradiation with epithermal neutrons a E and bE, respectively, then the activities per gram of sample, C, measured for a sample containing m~ grams of A1 and msl grams of Si per one gram of sample will be as follows: for irradiation with reactor neutrons,

C R --- aRmAl + bRmsl (1)

for irradiation with epithermal neutrons,

C E = a~m~ a + bEmsi (2)

The amounts of A1 and Si in a given sample were calculated by the solution of these two equations.

The cadmium ratio of ~A1 is given by

a R + bR(Si/A1 ) Red = aE + bE(Si/A1 ) (3)

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o4

0 5 10 =-

AI: Mg ratio

8

I I 50 100

Si: AI ratio

Fig. 1. The cadmium ratio (the ratio of activities induced by activation with and without a cadmium cover) of 27Mg for (a) mixtures of aluminium and magnesium and of 28A1 for (b) mixtures of aluminium and silicon, respectively

where Si/A1 is the mass ratio of silicon and aluminium

Si/A1 = msl/m, a (4)

The change of the cadmium ratio of the 1778 keV peak of 28A1 for mixtures of A1

and Si is shown in Fig. 1.

Correction for interferences in determination of magnesium

There are two interferences for determination of Mg by the 26Mg(n, g)27Mg reaction. The first one is due to the formation of ZTMg by another reaction, 27Al(n, p)27Mg. Magnesium was determined by RNA followed by measurement of 27Mg, after taking into account the contribution of aluminum to the total 27Mg activity.

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The change of the cadmium ratio (ratio of activities induced by activation with and without a cadmium cover) of 27Mg.for mixtures of aluminium and magnesium is shown

in Fig. 1. The second interference is due to 56Mn, which has a peak with an energy close to

that of 27Mg.

The activity of the 844 keV peak in 27Mg is 3.07 times higher than that of the 1014 keV peak, but the 844 keV peak can suffer from an interference of the 847 keV

peak of 56Mn. Consequently, it is very important to verify the half-life of this peak (9.46 min for 27Mg compared with 2.58 hours for 56Mn) or to use the 1014 keV peak in spite of its larger statistical error. The change of the cadmium ratio of the 1014 keV peak of 27Mg for mixtures of A1 and Mg is shown in Fig. 1.

Results and discussion

Five cases of transportation and deposition of settling particles (dustfall) following Saharan dust storms over Israel, occurring between 1973 and 1987, were experimentally investigated.

The elemental content of dustfall samples determined by instrumental neutron activation analysis is summarized in Table 2.

In order to check the validity of the method, we analyzed the Standard Reference Material SRM-1633a (coal fly ash) from the NBS (USA). Table 3 shows the correlation between our results for this standard and literature values. It can be seen that the

correlation is fair, indicating that the proposed method is appropriate for environmental materials.

The concentrations of aluminium and silicon determined by both reactor and epithermal neutron activation as well as the cadmium ratio (the ratio of activities induced by activation with and without a cadmium cover) of 28A1 for mixtures of aluminium and silicon are summarized in Table 4. - /

Aluminium was determined by reactor neutron activation taking into account the contribution of silicon to the total 2SA1 activity. Since phosphorus can contribute to the amount of ~AI through the reaction 31P(n, ct)~A1, its contribution has to be taken into account in the determination of aluminium.

The cadmium ratio of the 1778 keV peak of 28A1 for Al, Si and P under the prevailing experimental conditions of irradiation and counting, were found to be 124;30, 1.05 and 1.04, respectively. As is seen from Table 4 the cadmium ratio of 28AI for synthetic mixtures of Si and A1 (Si/A1 mass ratio = 5) and for P and A1 (P/A1 mass ratio -- 5), was found to be 45 and 75, respectively.

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Table 2 Determination of AI, Ba, Br, Ca, Ce, Co, C1, Cr, Eu, Fe, Hf, K, La, Mg, Mn, Na, Rb,

Sb, Se, Si, Ta, Th, Ti, U, V and Yb in settling particles eolleeted from five heavy dust storms (occurring between 1973 and 1987) by INAA

Element 1973 1975 1980 1984 1987

~* 31.0• 33.3• 41.3• 43.9• 41.2• Ba 220.6• ~1.5• 517.5• 374.6• 2~.6• Br 16.2• 4.8• 8.9• 9.6• 12.9• Ca* 108.4• 131.9• 90.5• 86.7• 79.5• Ca ~.3• 38.2• 44.5• 50.6• ~.4• Co ~.4• 15.8• 12.9• 14.2• 15.7• ~* 1.0• 1.2• 2.3• 5.1• 2.5•

76.1• 84.4• ~.6• ~ .1 • 169.5• 0.9• 0.7• 0.7• 0.8• 1.0•

~* 39.3• ~.2• 31.4• 34.4• 36.7• 21.3• 11.2• 5.2• 4.6• 8.9•

K* 18.3• 9.6• 7.1• 11.1• 13.6• 32.4• ~.1• ~.8• 30.6• 40.4•

Mg* ~.9• ~.9• 16.2• 2.1• ~.1• Mn 821.6• 43.3• 545.6• 538.5• 444.5• Na* 4.9• 3.5• 4.1• 5.9• 6.2• Rb ~.4• 35.3• 37.8• 39.8• 38.8•

2.5• 1.9• 0.9• 2.1• 1.4~0.2 12.8• 9.8• 13.7• 14.8• 17.3•

~* 155.6• 179.3• 146.8• 136.6• 1~.7• 1.0• 0.6• ~.6• 0.8• 0.8• 7.7• 4.1• 4.4• 4.5• 7.1•

Ti* 4.0• 2.1• 3.9• 4.6• 1.3• U 0.4• i.4• 2.6• 2.2• 2.8• V 71.3• 68.2• 89.2• 57.3• 119.6• Yb 3.2• 2.8• 1.2~0.1 1.5• 1.8~0.1

Units: Elements marked *in rag/g, others ~g/g.

The cadmium ratio of 28A1 in dustfall samples collected in 1973 and 1975, was found

to be 45.69 and 43.75, respectively, corresponding to a Si/A1 mass ratio of 5.02 and

5.38, respectively. The concentration of phosphorus determined by inductively coupled

plasma atomic emission spectrometry (ICP) was found to be 0.3--0.4%. Therefore, its

contribution to the amount of 2SA1 is negligible.

The concentration, C, of an element of interest, E, found in settling particles (CE~)

was compared with the average concentration of the same element in the earth's crust

(CEo) and the enrichment factors (EF) were calculated by the following equation:

E F - CEa/CE~ CFea/CFe r

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N. L A V I et al.: D E T E R M I N A T I O N O F E L E M E N T A L C O M P O S I T I O N

Table 3

De te rmina t ion o f e lementa l con ten t o f N B S s tandard reference mater ial (fly ash)

S R M - 1 6 3 3 a (n = 7) by ins t rumenta l neutron act ivat ion analys is

E lement This w o r k Reference 13 Reference 14 NBS

AI* 13.8 • 0 .2 - 13.6 • 1.0 (14)

Ba 1495 • 25 1520 • 20 1280 • 142 (1500)

Ce 176 • 7 186 • 4 163 • 8.4 (180)

Co 43.7 • 2.6 37 • 3 45 • 2.4 (46)

Cr 192.4 • 6.8 - 197 • 6.6 196 • 6

Eu 3 .6 • 0 .3 2 • 2 3.9 • 0.28 (4) Fe* 9 .2 • 0 .3 9.4 • 0.1 8.9 • 0.4 9.4 • 0.1

H f 7 .4 • 0 .3 7.8 • 0.2 7.2 • 0.4 (7.6)

K* 1.92 • 0 .07 1.99 • 0.03 1.89 • 0.09 1.88 • 0.06

La 86.4 • 4.8 84 • 6 91 • 4.2 -

Mn 187.5 • 8 .2 - 183 • 10 (190)

Na* 0 .17 • 0.01 0 .178 • 0.03 0.17 • 0.01 0.17 • 0.01

Rb 131.6 • 5 163 • 2 135 • 7 131 • 2

Sb 6 .8 • 0 .5 7.7 • 0.05 6.7 • 0.4 (7)

Sc 40.8 • 1 43 • 1 41 • 2 (40)

Ta 1.95 • 0 .2 2.1 • 0.2 1.98 • 0.2 -

Ti* 0.76 • 0.04 - 0.77 • 0.05 (14)

Th 24.6 • 1.1 25 • 1 24 • 1.2 24.7 • 0.3

U 10.1 • 0 .2 10.2 • 0.1 10.4 • 1.3 10.2 • 0.1

Yb 6.9 • 0.3 - 7.2 • 0.4 -

Zn 222 • 12 256 • 12 230 • 11 220 • 10

*Elements m a r k e d in %, others ppm.

Table 4

The ratio o f act ivi t ies i nduced b y act ivat ion with and wi thout a c admium cover (the c a d m i u m ratio)

o f 28AI for mixtures o f a lumin ium and sil icon, a lumin inm and phosphorus and dusffall samples

Synthe t ic mix tures Measured masses o f AI and Si

wi th k n o w n masses , m g in dustfall samples

Sample , A1 Si P Mass ratio, Rca Sample, Si, A1, No. (P/A1, Si/AI) year m g / g mg /g

1 1 - 5 5 - 75.30 - - -

2 1 5 - - 5 45 .20 - - -

5 .02 45.69 1973 155.6 31.0

5.38 43 .75 1975 179.3 33.3

3.55 55 .97 1980 146.8 41.3

3 .12 60 .05 1984 136.9 43.9

3.06 60 .56 1987 126.7 41.4

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Table 5 Enrichment factors EF(Fe) calculated for the elements determined

in the settling particles

Geometric Element mean AEF(Fe)

concentration

RAHN et al. 12

Sahara World

AI* 37.79 0.69 0.93 1~00 t3a 303.07 1.06 - - Ba 9.69 4.98 - - Ca* 97.73 4.01 0.69 2.8 Ce 47.65 1.18 1.85 2.6 Co 16.18 0.96 0.88 3.5 CI* 2.04 23.41 - - Cr 93.41 1.39 1.02 8.1 Eu 0.81 1.00 1.73 2.7 Fe* 3~.52 1.00 1.00 2.1 I-If 8.73 4.34 1.98 2.0 K* 11.34 0.65 0.65 2.0 La 30.14 1.50 1.78 2.7 Mg* 25,07 1,79 0.78 2.4 Mn 542.09 0.85 1.07 3.9 Na* 4.80 0.25 0.14 4.4 Rb 41.02 0.68 1.03 3.4 Sb 1.66 12.39 5.80 1430 Sc 13.45 0.91 0.73 1.2 Si* 147.94 0.80 - - Ta 0.74 O.55 - - Th 5.36 1.11 - Ti* 2.87 0.97 1.39 1.39 U 1.55 1.28 - V 78.51 0.87 0.88 14 Yb 1.96 0.86 0.91 1.06

*Units in rag. g-l, others Itg" g-1. AEF(Fe) = average enrichment factor (Fe was selected as the normalizing element).

whe re CFe~ and C F % are the concen t ra t ions of i ron (which was selected as the

no rma l i z ing e l emen t ) in the se t t l ing part icles (a) and in the ea r th ' s crust, (c)

respectively. T a b l e 5 s h o w s the r ange o f the en r i chmen t factors for the e lements

analyzed. The e n r i c h m e n t f a c t o ~ were ca lcula ted us ing the average crusta l va lues g iven

by M A S O N and M O O R E . 1~

A s is seen f rom Tab le 2, the dust compos i t i on is ra ther monoton ic . B U C H E R and

L U C A S 11 ana lyzed the fal lout o f Saha r an dust in the nor thwes te rn Medi terraneaf i reg ion

322


and also found a monotonic composition. The composition of the "Saharan aerosols" analyzed by RAHN et al. 12 was very similar to that of the settling particles in Israel. The

main difference is that the settling particles in Israel are relatively enriched in Ca. The high EF of C1 is presumably due to the entrainment of sea spray. Br enrichment is presumably due to contamination from the use of leaded petrol in motor cars or from the sea.

Conclusions

The method of instrumental neutron activation analysis (INAA) using both reactor and epithermal neutron irradiation, is nondestructive, accurate, highly sensitive and may

be routinely applied on a laboratory scale. The composition of an Israel Background Reference Standard is suggested for use in

future ecological studies of settling particles in Israel.

References

1. E. GANOR, Y. MAMANE, Transport of Saharan Dust Across the Eastern Mediterranean, Atmos. Environ., 16 (1982), No. 3, 581.

2. Z. LEVIN, J. D. LINDBERG, Size Distribution, J. Geophys. Res., 84 (1979) 6941. 3. P. ALPERT, E. ZIV, J. Geophys. Res., (in press). 4. D. H. YALON, E. GANOR, East Mediterranean trajectories of dustcarrying storms from the Sahara and

Sinai, in C. MORALES (Ed.): Scope 14: Saharan dust (Mobilization, Transport, Deposition). John Wiley and Sons, Chichester, 1979, p. 187.

5. U. KAFRI, A. ARAD, L. HALICZ, E. GANOR, Southern Israel, J. Hydrol., 110 (1989) 373. 6. Y. MAMANE, E. GANOR, A. E. DONAGI, Aerosol Composition of Urban and Desert origin in the Eastern

Mediterranean, in: Individual Particle Analysis: Water, Air, and Soil Pollution, 14 (1980) 29. 7. Z. LEVIN, C. PRICE, E. GANOR, Atmosph. Environ., 24A (1990), No. 5, 1143. 8. ASTM: Standard Method for Collection and Analysis of Dustfall (Settleable Particulates), ASTM D

1739-70, in: ASTM (Ed.): Annual Book of ASTM Standards, Part 26. ASTM, Philadelphia, 1981, p. 521. 9. Z. B. ALFASSI, N. LAVI, Analyst, 109 (1984) 959.

10. B. MASON, C. B. MOORE, Principles of Geochemistry, 4th ed.;John Wiley, New York, 1982, p. 46. I1. A. BUCHNER, C. LUCAS, Aeolean intercontinental sedimentation. Saharan dust and geology. Bull.

Centres Rech. Explor.-Prod. Elf-aquitaine, 8 (1984), No. 1,151. 12. K. A. RAHN, R. D. BORYS, G. E. SHAW, L. SCHUTZ, Long range impact of desert aerosols on

atmospheric chemistry: two examples, in: C. MORALES (Ed.), Scope 14: Saharan Dust (Mobilization, Transport, Deposition). John Wiley and Sons, Chichester, 1979, p. 243.

13. E. S. GLADNEY, W. H. ZOLLER, A. G. JONES, G. E.'GORDEN, Environ. Sei. Technol., 8 (1974) 551. 14. SHAO-JIN YANG, QIN-FANG QIAN, YI-NAN YANG, BING-RU CHEN, Modern Trends in Activation

Analysis, Copenhagen, Vol. 2, 1986, p. 1105.

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Documents

Determination of elemental composition of settling particles in Israel following Saharan dust storms by neutron activation analysis