O R I G I N OF Ne 21 ISOTOPES I N RADIOACTIVE MINERALS

Yu. A. Shukolyukov, V. B. Sharif-Zade, G. Sh. Ashkinadze, and E. K. Gerling

UDC 546.292:553.495

Neon emitted from minerals containing uranium and from natural gases containing helium is rich in Ne 2i and Ne 22 isotopes [1-4]. Nuclear reactions with c~-particles, neutrons [1-7], and cosmic muons [I, 8] were suggested in order to explain this enrichment:

~+ OlS(a, n)Neat tt ---+ V Na2a(7, 2n)Na21 ~ Ne2t

015(c% p)F 2I --*-. Ne21 Naea(7, np)Ne 21 ~+

MgZ4(a, ~)Ne ~1 Na2a(1, , n)Na 2~- .-+ Ne~2

F~(a, n)Na ~- ~ Ne2Z Na2Z(?, p)Ne 2z. F~9(a, p)Ne ~2

Up to now, h o w e v e r , the ca lcu la t ions have been qual i ta t ive , s ince it was no t poss ib le to account fo r the lo s s of neon in the m i n e r a l s du r ing a geo log ic pe r iod , and t h e r e f o r e it was imposs ib l e to c o r r e c t l y e s t i m a t e the amount of Ne 2i gene ra t ed in m i n e r a l s .

This work conta ins data which enable us to e l imina te the mlce r ta in t i e s connected with the lo s s of neon in m i n e r a l s .

The e l emen t He 4 is f o r m e d in m i n e r a l s dur ing the c~-decay of the e l emen t s of the u r a n i u m fami ly . In addit ion, k ryp ton and xenon i so topes a r e p roduced in the spontaneous b reakup of U 238 and in the b r eaku p of U 235 induced by t h e r m a l n e u t r o n s . The known isotope compos i t ion of xenon and k ryp ton in the spontaneous b reakup of U 238 [9] and in the neu t ron induced b reakup of U 235 [10] enables us to e s t i m a t e the f r ac t ion of

T A B L E t . Radiogenic Neon Isotopes in Radioac t ive Minera l s

Sample

Isotope co mP~osi-

N ~D

Radiogenic neon .10 -9 CITI3/

. . . . !corrected , I measured k~2~ ~oo ] o g"

0 ) ~ 0

z z z z a o ~

Uraninite g-4(East- 23( 18,8 0,5 em part USSR)

Uraninite g-3 (East- 23( 69,0 0,5 em part USSR)

Hatchettotite (Ilmer 29'1 2,31 0,3 mountains, Ural)

Betafite (Ilmen 29,! 9,396,6 ] mountains, Ural)

Samarskite (Ilmen [ 330] 5,4~[t,9, mountains, UraI)

Monazite (Kol'skii 19500,t4( 2,5

i I I

0,06290,30,3969,300,0ii

0,95689,400,54t 9,75 10,t 10,019 0,160 89,0,1,27

<3t 81,2 li~176 [0,078 0,50 81 6 '0,772 t7,7 ] <50 82:t ]0,6t417,4 I0,093

0,253'25 90:~ )r t~,,864]0,361

~,62 t0,22~ 050 2,00 t2,50t0,48

99,5090,503,268 9,23I }

0,3( 9,7510,030

0,51 0,92 0,050

0,8t t,i4[0,16

0,42 3,6010,t2

0,88 ?,880,45 i

0,5~ 3,700,50

I

38--+7

i08!3

9,6_+2

15__+2

21___5

316-•

30 t27C 100012504-100

2354-t70 2t3C 4700[920+350

__ 454-t5 I

4t6+t30[ 57 2500]

3204-t00 t t25 2700 2504-100 i

180• 47 400t1304-50 I

220+12( 732 440 2004-80

I

/

T r a n s l a t e d f r o m A t o m n a y a E n e r g i y a , Vol. 31, No. 5, pp. 530-531, N o v e m b e r , 1971. Or ig ina l a r t i - cle submi t ted J a n u a r y 2, 1971.

�9 1972 Consultants Bureau, a division of Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. All rights reserved. This article cannot be reproduced for any purpose whatsoever without permission of the publisher. ,4 copy of this article is available from the publisher for $15.00.

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spontaneous breakup products of a given total amount of xenon and krypton (decay products of spontaneous breakup of the U 238 only) and of radiogenic He 4, and having es t imated the age t of the mine ra l s by an inde- pendent u r a n i u m - t h o r i u m - l e a d method [11,12] we can calculate p re se rva t ion coefficients CHe, CKr, and CXe of these radiogenic gases . ResuI ts of a study of s e v e r a l tens of rad ioac t ive mine ra l s [9] indicate that the values of p r e se rva t i on coeff icients of he l ium, krypton , and xenon depend on the a tomic weight of the gas . T h e r e f o r e , we can use interpolat ion to es t imate the p r e se rva t i on Coefficient for neon in each mine ra l .

Pa ra l l e l de terminat ions of neon (see Table 1) were ca r r i ed out for each mine ra l sample (except No. 3). This gave a somewhat di f ferent isotope composit ion, not so much because of the m e a s u r e m e n t e r r o r (• but because the a tmospher i c neon with an i so tope composi t ion sl ightly different f rom that of the samples (see Table 1) unavoidably contaminated the equipment.

Since in an isotope mix tu re the re la t ive amount of Ne 2~ exceeds that of Ne 22 (and Ne 21) by at l eas t a fac tor of 5, all of Ne 2~ was a s sumed to be a tmospher i c , and the value of excess radiogenic Ne~J and N ~z~r was computed according to the equation:

/ Ne ~ ~ N e ~ _ . N e 2 1 _ _ N e r o ~ - - l , P -- meas - meas \Ne 'z~ latin

_ , _. ,' l ~ 2 i ~ . ( 1 )

Ne~ ~- N~ea s NeZ1~ea s (Ne20)atrn

The amounts of radiogenic neon determined this way were corrected for the loss of gases by the minerals. In order to do this the coefficients of loss of neon were determined by interpolation.

The knowledge of ~-radiation dose for each mineral (the content of ~-sources and the irradiation time were known) enabled us to calculate the probable amount of Ne 21, provided that it was formed during the

reaction O 18 (~, n) according to the equation [6]:

N e e ~ N~176 ~ , (2) calc ~ N~SI

i

where Nc~ is the in tegra ted amount of a - p a r t i c l e s in the unit volume of the minera l ; q0 is the yield of the react ion of oxygen (thick target ) under the action of a - p a r t i c l e s of u r a n i u m - thor ium balanced fami l ies (this quantity is weighed to account fo r the ra t io Th/U) ; N o is the concentrat ion of oxygen nuclei; S i is the re la t ive re ta rda t ion power of chemical e iements p resen t in the minera l ; S O is the s ame for oxygen. Taking into_ account the low accu racy of Necalc2I because of the poss ib le influence of the undetermined amount of bery l l ium which has a l a rge yield in the (a , n) reac t ion , and because of the lack of val idi ty of the a s s u m p - tion about the homogeneous distr ibution of emi t t e r s and a b s o r b e r s of a - p a r t i c l e s in the m i n e r a l s , we can r e g a r d these data as a p r e l i m i n a r y exper imenta l conf i rmat ion of the hypothesis on the fo rmat ion of Ne ~ in mine ra l s in the react ion O 18 (~, n) Ne zl.

The origin of Ne 22 is not c lear yet , s ince the amount of Ne 22 is too l a rge to be explained by the f luo- r ine centained in mine ra l s leading to reac t ions Fe ~9 (~, n) and F Is (a, p).

LITERATURE CITED

I. G. Wetherill, Phys. Rev., 96, 679 (1954). 2. D. Bogard et a l . , J . Creophys. R e s . , 70, 703 (1965). 3. D. E m e r s o n et a l . , Geochim. Acta, 30, 847 (1966). 4. D. E m e r s o n et a l . , Internat . J . of Mas----s Spect r . and Ion P h y s . , 1, No. ! , 150 (1968). 5. L . K . Kishkarov and V. V. Cherdyntsev, Geokhimiya, No. 7, 632- (1968). 6. G . V . Gorshkov et a l . , Natural Neutron Background of the Atmosphe re and of the E a r t h ' s Crus t [in

Russian] , Atomizdat , Moscow (1966). 7. J . Takagi et a l . , J . Geophys. R e s . , 72, 2267 (1967). 8. J . Takagi , Nature , 227, No. 5256, 362 (1970). 9. Yu. A. Shukolyukov, Breakup of Uranium Nuclei in Nature [in Russian] , Atomizdat , Moscow (1970).

10. Yu. A. Zysin, A. A. Lbov, and L. N. Sel 'chenkov, Yields of Breakup Products and The i r Mass Distr ibution [in Russian] , Atomizdat , Moscow (1957).

11. I . E . Star ik , Nuclear Geochronology [in Russian] , Izd-vo AN SSSR, M o s c o w - L e n i n g r a d (1961). 12. E . V . Sobotovich, Isotopes of Lead in Geochemis t ry and Cosmochemis t ry [in Russian] , Atomizdat ,

Moscow (1970).

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