SPECIFIC Yu.

RADIOACTIVITY A. S a p o z h n i k o v

OF and

POTASSIUM A . V.

IN S E A W A T E R

Merkushov

UDC 551.464.679

The natural radioactive potassium isotope 4~ provides the basic contribuLion to the intrinsic beta- and g a m m a - r a d i o a c t i v i t y of sea water [1]. It has been found that the concentration distribution of potassium K, which is among the b a s i c sea water ions, is c o r r e l a t e d with the salinity S, although considerable deviations of the K/S ratio f r o m the mean values have been observed during v a r i o u s expeditions. The isotopic abundance of potassium in seawater is usually assumed to be constant, so t h a t t h e specific activity of potassium AK in sea water is considered to be equal to the value suggested for t e r r e s t r i a l rocks, A0=28.27 • 0.05 Bq/g [2]. Our aim was to check the validity of the assumption concerning the constancy of AK in sea water. A c curate methods have been developed for determining the radioactivity of 4~ [3] and the o v e r - a l l potassium p e r centage in sea water samples, whereby the value of AK can be estimated with an e r r o r of less than 1% with a 95% confidence coefficient. In using either method, potassium is separated f r o m sea water samples by precipitation by means of a selective reagent - sodium tetraphenyl b o r a t e (Na-TPB). F o r determining the radioactivitY of 4~ 500-ml samples were taken, and the deposit was separated and dissolved in a mixture of dimethyl f o r m a m i d e and dioxane with scintillation admixtures. We used N a - T P B , labeled with 14C, for determining the overall potassium percentage; the sample volume was equal to 5 ml. Both methods involve radioactivity m e a s u r e m e n t by means of liquid-scintillator equipment. stage 1982. parts cally

Most of the ocean water samples for determining the AK value were taken in the Pacific during the second of the first voyage of the Akademik Aleksandr Nesmeyanov s c i e n t i f i c - r e s e a r c h v e s s e l in the autumn of Table 1 provides the r e s u l t s of AK determination for these samples and also water samples f r o m other of the w o r l d ' s oceans. The r e s u l t s of A K determination in n o r m a l sea water and in extra s p e c t r o s c o p i pure solutions a r e given for comparison.

Altogether, 14 s a m p l e s w e r e taken in the Pacific Ocean. Within the limits of m e a s u r e m e n t e r r o r , the mean value of AK in these samples coincided with that of A0 [2]. However, t h e r e w e r e also considerable deviations to either side of the mean value. Negative deviations w e r e r e c o r d e d in the equatorial region, while a band of positive deviations, reaching 5.9%, was observed to the north of the equatorial region (only two m e a s u r e m e n t s w e r e p e r f o r m e d south of the equator, while a negative deviation was also found in the region near the equator); this is followed by a broad region of negative deviations, with the l a r g e s t positive deviation (10.2%) observed in the subarctic front region. The sampling of the A K m e a s u r e m e n t r e s u l t s is, of course, too small f o r reaching unambiguous conclusions. It should be mentioned that the samples analyzed w e r e taken at different depths (0, 100, 300, and 500 m), so that potassium behavior at different points may have reflected different trends. In spite of this, we note a certain dependence of AK on the geographic latitude of the locations at which the s a m p l e s w e r e taken, which r e s e m b l e s the distribution of the a t m o s p h e r i c fallout of cosmic and artificial radionuclides that have reached the upper a t m o s p h e r i c l a y e r s as a result of n u c l e a r t e s t s . Considerable negative deviations of AK f r o m the accepted values (up to -7.0%) w e r e observed in water samples f r o m t h e r m a l b r i n e in d e e p - s e a basins of the Red Sea. However, in the s u r f a c e water l a y e r s of this sea, the AK value c o r r e s p o n d s to the mean value for t e r r e s t r i a l r o c k s . The positive deviations f r o m the mean values a r e possibly connected with the incoming c o s m i c dust (minute p a r t i c l e s of m e t e o r i t e matter, formed during the ablation of m e t e o r i t e s in the atmosphere), whose isotropic potassium composition differs f r o m the t e r r e s t r i a l one. Values of AK in m e t e o r i t e s that exceeded those in t e r r e s t r i a l r o c k s by two to t h r e e o r d e r s of magnitude have been recorded [4, 5]. Values exceeding the AK mean values by 40-70% have been observed in s u b m i l l i m e t e r - s i z e magnetic spherules (probably of e x t r a t e r r e s t r i a l origin), separated f r o m d e e p - s e a sediments in the Pacific Ocean [5]. F o r the oceans, which occupy N70% of the e a r t h ' s surface, the a r r i v a l r a t e of cosmic dust may r e a c h 1.4 " l0 s t o n s / y r [6]. The mean percentage o f p o t a s s i u m i n m e t e o r i t e m a t t e r is equal to T r a n s l a t e d f r o m Atomnaya t~nergiya, Vol. 59, No. 2, pp. 145-148, August, 1985. Original a r t i c l e submitred September 27, 1984.

706

0038-531X/85/5902-0706509.50

9 1986 Plenum Publishing C o r p o r a t i o n

T A B L E 1.

Specific Activity of P o t a s s i u m in Sea Water Samples

Sample No.

Level, m

Latitude

AK, Bqlg

E. long.

AK

A.

-

Ao

1oo%

Pacific Ocean 300 t0(1 0 5OO 0 50(} 0 5(10 0 0 0 0 300 0

t

2 3 4 5 6 7 8 9 10 I1 t2 t3 t4

42~ ' 41~ ' 40~ ' 40'~03,t , 24045,5 ' 2t~ ' 18~,o0,2' t2%5,6' t(1~ ' (14~ ' 0t~ ' 0i~ ' t3~ ' (t2~ ,3'

N. 1St.

N. lat. N. 1at. N. lat. N. lat. N. lat. N. 1st. N. 10t. N. l~u N. lat. N. Lat. S. 1at. S. laL N. 1at.

159~ 7" t59~ ' t59~ ' |59~20,()' 150~ ,4' t5()~08,8' 152~ ' t55~ ' 157~ ' t59~ t60~ , t (~2~ 157014,6' 146~ '

3i,i5 26,90 28,i5 27,88 27,67 27,50 27,63 28,88 29,93 28,47 27,65 27,83 28,43 28,33

+10,2 --4,8 --0,4 --1,4 --2,t --2,7 --2,3 +2,2 -4-5,9 +0,7 --2,2 --i,6 +0,6 +0,2

13t~

28,03

I

--0,8

]

--0,2 --3,t --7,0 --5,3

Sea ofJapan t5

I

o

40o08,3 ' N. lat.

I

'

Red Sea 16 17 18 t9

1460 (30m frlom bottom) Atlantis Basin (5 m from bottom) Valdivia Basin (depth. 1660 m; 3 m from bottom)

28,22 27,40 26,28 26,77

2o 2t

Normalsea water (19.3"/4% CD KC1, extra spectroscopicauy pure

28,03 28,37

--0,8 +0,4

0.15% [7], while, a c c o r d i n g to e s t i m a t e s f o r t h e t e r r i g e n o u s s u s p e n s i o n , 1-10% of m a t t e r a v a i l a b l e in the f o r m of a s u s p e n s i o n is d i s s o l v e d in s e a w a t e r [8], i . e . , t o g e t h e r with e x t r a t e r r e s t r i a l m a t t e r , 2.2 9 104 to 2.2" 105 t o n s of d i s s o l v e d p o t a s s i u m e n t e r s t h e o c e a n w a t e r a n n u a l l y , w h i l e t h e q u a n t i t y e n t e r i n g s e a w a t e r with r i v e r e f f l u e n c e a m o u n t s to 5 . 2 5 . 1 0 T t o n s [9]. An i m p o r t a n t c o n c l u s i o n has b e e n r e a c h e d in [6] on t h e b a s i s of a g e n e r a l i z a t i o n of the data p r o v i d e d by m a n y r e s e a r c h e r s : T h e s i z e d i s t r i b u t i o n of c o s m i c dust p a r t i c l e s is s u c h that t h e m e a n r a t e of a r r i v a l of p a r t i c l e s on e a r t h i n c r e a s e s r a p i d l y a s t h e i r m a s s d e c r e a s e s , up to the l i m i t i n g v a l u e of ~10-12g ( p a r t i c l e s with a m a s s of ~ 10 -14 g a r e c a r r i e d a w a y by s o l a r light p r e s s u r e b e y o n d the c o n f i n e s of the s o l a r s y s t e m ) . A s t h e y f a l l into t h e o c e a n , t h e s e f i n e p a r t i c l e s d i s s o l v e r e a d i l y i n s e a w a t e r . It is difficult to d e t e r m i n e t h e d i s p e r s i o n c o m p o s i t i o n of t h e u n d i s s o l v e d p a r t of e x t r a t e r r e s t r i a l m a t t e r e n t e r i n g the o c e a n . T h i s w a s p r o b a b l y t h e r e a s o n why d a t a on the s i z e d i s t r i b u t i o n of s p h e r i c a l p a r t i c l e s i n t h e peat at the l o c a t i o n of i m p a c t of t h e T u n g u s k a m e t e o r i t e w e r e u s e d in [10] f o r e s t i m a t i n g t h e c o n t r i b u t i o n of e x t r a t e r r e s t r i a l m a t t e r in the d i s p e r s i o n c o m p o s i tion of o c e a n i c s e d i m e n t s . It i s known thuS m e t e o r i t e s a r e l i n k e d with t h e c o n c e p t of c o s m i c o r r a d i a t i o n age, i . e . , t h e t i m e e l a p s e d f r o m t h e d i s i n t e g r a t i o n of t h e p a r e n t body and i r r a d i a t i o n of a c e r t a i n f r a g m e n t b y c o s m i c r a d i a t i o n [11]. I n c o n t r a s t to s m a l l p a r t i c l e s , l a r g e m e t e o r i t e s h a v e a l o w e r m e a n s p e c i f i c a c t i v i t y ( b e c a u s e t h e r a d i a t i o n is a t t e n u a t e d by the m e t e o r i t e m a s s ) . M o r e o v e r , it is p r e c i s e l y t h e s u r f a c e l a y e r s of m e t e o r i t e s , w h i c h a r e h i g h l y e x p o s e d to t h e a c t i o n of c o s m i c r a d i a t i o n , that a r e a t o m i z e d a s they e n t e r the a t m o s p h e r e d u r i n g t h e a b l a t i o n p r o c e s s . A s they p a s s t h r o u g h t h e a t m o s p h e r e , m e t e o r i t e s l o s e about o n e - h a l f to t w o : t h i r d s of t h e i r m a s s [12]. C o n s e q u e n t l y , it is p o s s i b l e that e v e n l a r g e r AK v a l u e s m a y b e in the f i n e - d i s p e r s i o n s u s p e n s i o n of c o s m i c o r i g i n , w h i c h is t h e m a i n s o u r c e of d i s s o l v e d f o r m s of e x t r a t e r r e s t r i a l m a t t e r in s e a w a t e r , t h a n i n r e l a t i v e l y large meteorites. T h e n o n u n i f o r m i t y of the AK d i s t r i b u t i o n in s e a w a t e r m a y b e c o n n e c t e d with the t e m p o r a l and s p a t i a l n o n u n i f o r m i t y of a r r i v a l of e x t r a t e r r e s t r i a l m a t t e r . A c t u a l l y , an i n c r e a s e in the a r r i v a l r a t e of c o s m i c d u s t by two to t h r e e o r d e r s of m a g n i t u d e in c o m p a r i s o n with t h e m e a n r a t e i s o b s e r v e d at t h e t i m e of o c c u r r e n c e of t h e known i n t e n s i v e m e t e o r i t e s h o w e r s r e a c h i n g the e a r t h ' s s u r f a c e [13]. T h e s p a t i a l n o n u n i f o r m i t y of a r r i v a l of e x t r a t e r r e s t r i a l m a t t e r on t h e e a r t h ' s s u r f a c e f r o m the u p p e r a t m o s p h e r i c l a y e r s r e s e m b l e s in m a n y ways t h e c h a r a c t e r of the f a l l o u t of r a d i o n u c l i d e s of c o s m i c o r i g i n [12] and of a r t i f i c i a l r a d i o n u c l i d e s that have e n t e r e d t h e s t r a t o s p h e r e a s a r e s u l t of n u c l e a r t e s t s [14]. T h e r o l e of e x t r a t e r r e s t r i a l m a t t e r in o c e a n i c s e d i m e n t f o r m a t i o n is s o m e t i m e s c o n s i d e r e d to be i n : s i g n i f i c a n t [10]. H o w e v e r , it i s difficult to e x p l a i n the c o n s i d e r a b l e i n c r e a s e in A K in o c e a n w a t e r s b y o t h e r c a u s e s . A n a l y s i s of o t h e r p r o c e s s e s p o s s i b l y i n f l u e n c i n g A K in s e a w a t e r ( s o r p t i o n on a r g i l l a c e o u s s u s p e n s i o n s b i o l o g i c a l a c t i v i t y , f o r m a t i o n and m e l t i n g of ice, p r o c e s s e s in the s u r f a c e m i c r o l a y e r , etc.) i n d i c a t e s that t h e i r 707

total contribution can alter the value of AK by not m o r e than 1-2~c. At the same time, it has been found that the isotopic lead abundance in d e e p - s e a sediments is close to the percentage of isotropic lead in m e t e o r i t e s [15], while siderophile elements, such as nickel and cobalt, of which there is a much higher percentage in m e t e o r i t e s than in the e a r t h ' s crust, enter the ocean also from the a t m o s p h e r e and not only with the r i v e r effluence. T h e i r entry into the a t m o s p h e r e is probably connected to a considerable extent with e x t r a t e r r e s t r i a l matter. The specificities of the state of iron in d e e p - s e a sediments are possibly also connected with the effect of both e x t r a t e r r e s t r i a l and volcanic m a t t e r [16]. I r r e g u l a r i t i e s in AK values could probably also occur as a result of volcanic activity, the contribution of which to sediment formations in oceans r e a c h e s 2-3 billion tons annually [9]. Volcanic m a t t e r can also be enriched by siderophile elements [17, 18]; however, it is not subject to the effect of c o s m i c radiation below the surface of the earth. Volcanic m a t t e r enters sea water as a result of the activity of land volcanoes and, to a g r e a t e r extent, due to undersea eruptions [18]o The water f r o m t h e r m a l b r i n e s in the Red Sea, which is c h a r a c t e r i z e d by low AK values, probably a r r i v e s f r o m a fairly great depth in the earth, w h e r e the potassium lodged t h e r e since the t i m e s of l a y e r differentiation within the e a r t h ' s crust was not subject to the action of c o s m i c radiation or exchange with the potassium a r r i v i n g with ground water f r o m the s u r f a c e l a y e r s of the e a r t h ' s crust. Dust of cosmic or volcanic origin can be retained over a long period of time by the s u r f a c e m i c r o l a y e r of sea water [19], where its composition can undergo considerable changes due to the action of s u r f a c e - a c t i v e m a t t e r and biological activity, With the subsequent slow s u b m e r g e n c e of m i c r o s c o p i c particles, which may r e m a i n in the w a t e r over periods of hundreds or thousands of y e a r s [20], f u r t h e r leaching of compounds with an anomalous isotopic potassium composition takes place, which leads to changes in the A K value in water. As a result of s i m i l a r p r o c e s s e s , the number of particles of c o s m i c origin (including magnetic spherules) in oceanic sediments is much s m a l l e r than in the ice of A n t a r c t i c a [21]. Thus, AK can be used as an indicator of elevated concentrations in l a r g e bodies of water of both e x t r a t e r r e s t r i a l (positive deviation of AK f r o m the mean value) and volcanic m a t t e r (negative deviation). The authors a r e grateful to N. I. Popov for providing the water samples f r o m the Red Sea and the Sea of Japan. LITERATURE 1. 2. 3.

4.

5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

708

CITED

N . I . Popov, K, N. Fedorov, and V. M. Orlov, Sea Water (Reference Manual) [in Russian], Nauka, Moscow (1979). R. Beckinsale and N. Gale, "A r e a p p r a i s a l of the decay constants and branching ratio of 4~ Earth Planet~ Sei. Left., 6_ 289-294 (1969). A . V . Merkushov and Yu. A. Sapozhnikov, "Scintillation-liquid determination of potassium in sea water," Vestn. Mosk. Gos. Univ., Ser. Khim., 5 (1983); deposited at the All-Union Institute of Scientific and T e c h nical Information (VINITI) on April 7, 1983, No. 1868-83. H. Voshage and H. Hinterberger, " M a s s e n s p e k t r o m e t r i s c h e Isotropenh~iufigkeitsmessungen an Kalium aus E i s e n m e t e o r i t e n und das P r o b l e m der Bestimmung der 41K-Strahlungsalter," Z. Naturforsch., 16 a, 1042-1053 (1961). T. Shimamura, O. Arai, and K. Kobayashi, "Isotopic r a t i o s of potassium in magnetic spherules f r o m d e e p - s e a sediments," E a r t h Planet. Sci. Lett., 36.__,317-321 (1977). ]~. V. Sobotovich, Isotopic Space ChemistrY [in Russian], Atomizdat, Moscow (1979). G . V . Voitkevich, Ao E. Miroshnikov, A. S. Povarennikh, and V. G. P r o k h o r o v , B r i e f Manual of Geoc h e m i s t r y [in Russian], Nedra, Moscow (1977). Oceanography, Marine Chemistry, Chemistry of Ocean Water [in Russian], Vol. 1, Nauka, Moscow (1979). A . P . Vinogradov, Introduction to Marine G e o c h e m i s t r y [in Russian], Nauka, Moscow (1967). A . P . Lisitsyn andYu. A. Bogdanov, " G r a n u l o m e t r i c composition of suspensions f r o m the Pacific Ocean," Oceanographic R e s e a r c h [in Russian], Vol. 18, Nauka, Moscow (1968), pp. 53-74. J. Wood, Meteorites and the Origin of the Solar System [Russian translation], Mir, Moscow (1971). V. Yu. Luyanas, A t m o s p h e r i c Radionuclides of Cosmic Origin [in Russian], Mosklas, Vilnius (1979). G . M . Ivanova, Yu. A, L'vov, N. V. Vasil'ev, and I~ V. Antonov, Fallout of C o s m i c Matter on the E a r t h ' s Surface [in Russian], Izd. T o m s k . Univ. (1975). I . L . Karol', Radioactive Isotopes and Global T r a n s p o r t in the A t m o s p h e r e [in Russian], Gidrometeoizdat, Leningrad (1972)o S . P . Golenetskit, "The nature of global a t m o s p h e r i c a e r o s o l s , ~ Astron. Vestn., 15__,No. 4, 226-233 (1981).

16. 17. 18~ 19. 20. 21.

Y~ Minai, T. Tominaga, T. Furuta and K. Kobayashi, "A M~Sssbauer study of deep sea sediments," Radiochem. Radioanal. Left., 4_.88,Nos. 3-4, 165-173 (1981). W. Zotler, " I r i d i u m e n r i c h m e n t in a i r b o r n e particles f r o m Kitauea volcano, January, 1983," Science, 222, No. 4628, 1118-1121 (1983). K . K . Zelenov and V. I. Ivanenkov, "Effect of c o n t e m p r o a r y undersea v o l c a n i s m on the c h e m i s t r y of ocean water," Izv. Vyssh. Uchebn. Zaved., Ser. Geolrazvedka, 2._55,No. 11, 3-26 (1982). K. Hunter, " P r o c e s s e s affecting particulate t r a c e metals in the sea s u r f a c e m i c r o l a y e r , " Marine Chem., 9_, 49-70 (1980). A . S . Monin, History of the Earth [in Russian], Nauka, Leningrad (1977). ]~. V. Sobotovich, G. N. Bondarenko, and T. I. Koromyslichenko, Cosmic Matter in Ocean Sediments and Glacier Covers [in Russian], Naukova Dumka, Kiev (1978).

COMPARISON TO T H E OF

OF

LOWER

DETECTORS LIMIT

GAMMA-EMITTING B. Y a .

Shcherbakov

OF

WITH

RESPECT

DETERMINING

THE

ACTIVITY

NUCLIDES and

V.

I.

Myshlyavkin

UDC 628.3 : 539.166 : 543 ~

Since the number of t a s k s in environmental monitoring is increasing, an experimental comparison of the capabilities of v a r i o u s d e t e c t o r s with r e s p e c t to the lower limit of activity determinations on g a m m a - e m i t t i n g nuclides is of interest. M e a s u r e m e n t s w e r e made with a g a m m a s p e c t r o m e t e r provided with an 800-channel a n a l y z e r arid det e c t o r s of v a r i o u s types and dimensions: a DGDK-32A g e r m a n i u m d e t e c t o r and NaI (T1) scintillation d e t e c t o r s withthe dimensions 63 x 63, 150 x 100, and 150 x 140 m m with a well. A 1 0 - c m - t h i c k passive lead shield of d e t e c t o r s was employed. The c o m p a r i s o n was based on 137Cs (energy of the g a m m a radiation 661.7 keV) in liquid 25-, 50-, 75-, and 100-ml s a m p l e s filled into 100-ml polyethylene bottles (see Fig. 1). The liquid s a m ples w e r e p r e p a r e d f r o m a radioactive 13~Cs standard solution of class 1 with a specific m a s s activity q (Bq/g) indicated in the specification data with an e r r o r of 3% on the 0.95 confidence level. A certain amount of the radioactive standard solution was filled into the polyethylene bottle which had been previously weighed on an analytic balance with a p r e c i s i o n of 0o0001 g; t h e r e a f t e r the bottle was weighed again and the m a s s m (g) of the s a m p l e taken was determined. The activity Q (Bq) of the quantity of the radioactive standard solution filled into the bottle was determined with the equation O = qm.

(i)

The e r r o r of Q did not exceed 4%. After that, a diluting agent r e c o m m e n d e d in the specification data was poured into the bottle to obtain a volume V=25 ml, the solution was mixed, the bottle was h e r m e t i c a l l y sealed with a lid, and then the bottle was placed on the d e t e c t o r a s indicated in Fig. l a . After that, the a v e r a g e pulse f r e quency ~ (sec -I) in the peak of total absorption of the 661.7-keV g a m m a quanta was determined (with the b a c k ground subtracted) and the detector efficiency was calculated with the formula e = n/pp,

(2)

where the g a m m a quanta yield p = 0.853 was a s s u m e d [1], Then the volume of the solution in the bottle was s u c cessively i n c r e a s e d to 50, 75, and 100 ml, the m e a s u r e m e n t s w e r e repeated, and the detector efficiency was determined in each case. The r e s u l t s obtained a r e compiled in Fig. 2. The lower limit of the determination of the 137Cs bulk activity was estimated under the assumption that no e r r o r s w e r e introduced f r o m the " h a r d e r " radiation of other nuclides because in the case of a complicated composition of the initial sample, the nuclide of interest can be isolated in pure f o r m by chemical methods. Thus, only the natural background generated by the c o s m i c radiation, the building m a t e r i a l s , and the s u r r o u n d ing objects was taken into account. The a v e r a g e pulse frequency of the background pulses and the m e a n - s q u a r e e r r o r s obtained with passive lead shields of various thicknesses on the detectors a r e listed in Table 1. T r a n s l a t e d f r o m Atomnaya ]~nergiya, Vol. 59, No. 2, pp. 148-150, August, 1985. Original a r t i c l e s u b ' mitred D e c e m b e r 13, 1984.

0038-531X/85/5902-0709509.50

9 1986 Plenum Publishing C o r p o r a t i o n

709