- Email: [email protected]
Some halogen measurements on achondrites
EARTH AND PLANETARY SCIENCE LETTERS 6 (1969) 316-320. NORTH-HOLLAND PUBLISHING COMP.. AMSTERDAM
SOME HALOGEN
MEASUREMENTS
ON ACHONDRITES
*
G.W.REED and S.JOVANOVIC Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
Received 20 May 1969
Data are presented on halogen concentrations in various classes of achondritic meteorites. The importance of the lability of the halogens to the interpretation of rare gas data is pointed out.
1. INTRODUCTION Few data have been reported on the halogen contents of achondrites. These objects have added significance today since rock of the composition of basaltic achondrites is a candidate for lunar surface material [I] . Achondritic minor and trace element composition, the halogens in the work presented here, may provide some indications as to what to expect on the moon. The lunar surface has had a long exposure to solar and galactic particle irradiation. Rare gases are products of such an irradiation of the halogens; detailed study of these gases will require a knowledge of the halogen concentrations. Iodine concentrations are necessary for extinct 1291-129Xe formation interval estimates. The halogens are active chemical agents; they and many of their compounds are volatile; they span a wide range in chemical properties such as electronegativities, binding energies and oxidation states and may therefore provide clues to lunar chemical processes. In the course of a study of the feasibility of determining F, Cl, Br, and I simultaneously, some values for the concentration of these elements in achondrites have been obtained. We have surveyed most types of achondrites for their F content and in a few cases have estimated the Cl and Br contents. Te and U * Work performed under the auspices of the U.S. Atomic Energy Commission and National Aeronautics and Space Administration.
values were obtained to detect I.
as by-products
of the attempts
2. EXPERIMENTAL Consecutive photon and neutron irradiations were carried out to produce 1.8 hr l*F and 37.5 min 38C1, 35.3 hr 82Br, and 25 min 12*1, respectively, via (r,n) and (n,?) reactions. The procedures used in each type irradiation were modifications of those already reported [2,3]. A number of photon irradiations was conducted in which Cl, Br and I as well as F were separated. No radioactivity attributable to 38C1, *OBr, or 82Br and 12*1 was observed, verifying that (r,n) (-r,an), etc. reactions would not contribute significantly to the (n-y) produced radioactivity at the intensity (30 -40 pa average beam current) and energy (16- 17 MeV) of the Argonne National Laboratory linac photon beam. In the case of Cl, however, 0.141 and 0.511 MeV photopeaks characteristic of 34C1 were observed. The production of 32.4 min 34C1 was monitored with Saran, polyvinyl chloride, foils. Since the radioactivity was usually too low to be adequately characterized, concentrations based on 34C1 are not reported here. Exploratory experiments were carried out to assess the effect of contributing reactions on 34C1 production. The two most likely reactions are 39K(y,an)34C1 and the secondary reaction 34S(p,n)34C1. The former is energetically prohibited for 16 - 17 MeV photons.
SOME HALOGEN MEASUREMENTS ON ACHONDRITES
317
Table 1 Fluorine in achondrites. Irradiation number Enstatite 3 4
10 5 8 Hypersthene 9 10
Sample
IFI leach @pm)
Rishopville Cumberland Falls Cumberland Falls Norton County Norton County
f 1.5 < 7.8 (b) -0 ND
Tatahouine Johnstown
< 8.9
[Fl sample @pm)
Literature
6.8 + 1.3 (a) GO.34 7.7 f 0.9 11.0 f 2.6 [ 22.3 ‘7.41 (c)
-0
10.7 If:4.5 (1)
12.2 + 2.1 3.5 + 0.4
Howardite
11 13
Frankfurt Frankfurt
G2.6 +0.9
[ 174 +58] 57.1 + 1.7
(c)
Eucrite
11 13 5 I I 9 Terrestrial samples 6 8 6
Moore County Moore County Shergotty S tannern Pasamonte Nuevo Laredo
W-l W-l G-l
ND < 6.1 < 2.9 < 15.7 < 10.3
[266 -+ 91.5 + 0.6 50.1 + 19.9 + 30.4 + 50.6 +
16.1 f 3.5 ND 31.4 I! 11.7
881 (c)
60 f 10 ($1)
5.0 1.7 3.5 3.0
263 + 28 ]994+329] 800 f 65
(c)
426 (I), 552 (1) 208 (2), 31.5 (3) 1100 (1), 705 (2), 723 (3)
ND = not determined. sample not leached. (a) (b) photopeak observed but decay not followed. original concentration ‘corrected for contribution from neutron irradiation (see text). (c) (1) Reed (1964), ref. [2]. (2) Huang and Johns, Geochim. Cosmochim. Acta 31 (1967) 597. (3) RCarpenter, Thesis, University of California, La Jolla (1968).
Reagent grade K2CO3 and Na2S04 salts were irradiated. In spite of the confirmed low Cl concentration, unexpected and as yet unexplained amounts of 34C1 were produced in each. A 30 cm3 lithium drifted germanium detector was employed to obtain many of the results in the expectation that the high resolution and low background under a photopeak might permit a reduction in the time necessary for radiochemistry. At the ppm level this was feasible. Below about 0.1 ppm P,-y coincidence counting was necessary. Greater sensitivity will be achieved when the new high current linac is in
operation at ANL. A correction factor was applied to the counting data from the polyvinyl fluoride, PVF, discs used to monitor the photon intensity. The discs were - 2 mg/cm2 and of S mm diameter whereas the CaF2 samples counted were thicker and 18 mm in diameter. The correction was 2.98 for samples of 25 -60 mg/cm2 and 2.36 for heavier samples and was due to the slowing down or stopping of the 0.65 MeV /3+ within the sample, causing the annihilation to occur closer to the detector than in the case of the thin monitor.
G.W.REED and SJOVANOVIC
318
Cl, Br, Te, and U Sample
C1leach (ppm)
Clsample (ppm)
Literature
Brleach (ppm)
Brsample (ppm)
Literature
Norton County
ND
not detectable
1.9, 5.6 (1)
ND
0.010 + 0.002
0.067 (5) 0.077 (6)
Frankfurt
13.6 + 10.0
1.3 +0.3
0.21 f 0.05
0.15
Moore County
20.5 f
4.3
5.5 f 1.3
0.48 + 0.08
0.075 zb0.017
15.7 It 2.7
5.8 f 0.7
0.46 f 0.05
0.061 ?r 0.009
ND
0.15
W-l
ND
16.3 f 1.3
25.6 (2) 187-191 (3)
rto.04
f0.03
0.039 * (6)
0.40 (2)
198-219 (4) ND = not determined. * value for the eucrite Pasamonte. (1) Von Gunten et al., Geochim. Cosmochim. Acta 29 (1965) 475. (2) Reed and Allen (1966), ref [3]. (3) Huang and Johns, Geochim. Cosmochim. Acta 31 (1967) 597. (4) Johansen and Stennes, Geochim. Cosmochim. Acta 31 (1967) 1107.
3. RESULTS AND DISCUSSION The results obtained in this work are listed in tables 1 and 2 along with previously reported data. In halogen determinations we have adopted the practice of leaching the samples before fusion with a hot aqueous solution containing the various carriers. In the tables the concentrations in the leach solution, where measured, and the concentrations in the residues are listed. The errors quoted are based principally on counting statistics; weighing and pipetting errors were, in general, small. Because of the number of samples with short half-lives, decay measurements were not always possible. Spectroscopy alone is not always reliable for identification and we have, therefore, designated with an equal or less than sign those measurements in which decay was not followed. A higher F content was observed in the photon followed by neutron irradiations than in the photon only experiments. A neutron irradiation established that F was being produced in the meteorite but not in the PVF foils. This production probably arises from the following reactions: (1) 6Li(n,cr)T and (2) T(leO,n)laF [4]. A comparison of the 18F activity observed in neutron only and photon only irradiations yielded a cor-
rection for the amount of F produced in the neutron irradiation. This factor (- 0.33) was applied to the F concentrations measured in irradiations 8 and 11. This is a large extrapolation, especially in the rung, since it assumes the same Li/O and Li/F ratios in sampIes of different origin and mineralogy as well as similar matrix effects on the tritium induced reaction. The lithium content of W-l is 12 ppm [5] , and of meteorites about 0.2- 1 ppm [6,7]. The amount of Li related F activity in W-l was, as expected, larger than in Moore County or Norton County. The differences that continue to appear in the USGS standards will not be discussed here. The G-l and W-l samples were different aliquots from those we previously measured. A review of the literature reveals that trace element concentrations in samples of the same meteorite measured in different laboratories may agree, while concentrations in samples of another meteorite measured during the same experiments will disagree. A sampling problem seems to be a reasonable explanation. The agreement or disagreement with reported results can be seen in the tables. The U concentrations are consistent with those of Patterson et al. [8] and Morgan and Lovering [9] ; they are at variance with
SOME HALOGEN MEASUREMENTS ON ACHONDRITES
319
ble 2 in achondrites. Teleach (ppm)
Tesample (ppm)
Uleach (ppb)
ND
0.025 + 0.007
ND
ND
0.023 f 0.014
ND
0.030 +_0.007
0.31 + 0.05 ND
Literature
Usample (ppb) 9.7 f 1.9
ND
21.6 +6.1
ND
13.5 + 3.8
0.015 ?I 0.003
not detectable
15.2 + 2.1
0.48
ND
0.16, 0.14 (7)
+ 0.05
1037 + 105
Literature _____ LO(8)
19.6 (9) so.39 (7)
500-900 (10)
(5) Wyttenbach et al. (1965), ref. [ 111. (6) Liberman and Ehman, J. Geophys. Res. 72 (1967) 6279. (7) Clark et al. (1967), ref. [lo]. (8) Patterson et al. (1953), ref. [ 81. (9) Morgan and Lovering (1964), ref. [ 91. (10) Cherry, Geochim. Cosmochim. Acta 27 (1963) 183.
the higher values of Clark et al. [lo] . No evidence for U leachability was observed in the Moore County sample measured in these experiments nor in the several chondrites reported earlier [2] . The factor - 10 lower Te value observed in the residue of Moore County after leaching is striking. Since Te is not a likely contaminant it appears that Te is in a very labile site. This trend has been noted before for Te and the halogens in chondrites [3] . This may also explain the difference between our Norton County bromine concentration and that of Wyttenbach et al. ]lLl. The importance of the lability of the halogens to the interpretations of rare gas data should be emphasized. Hohenberg [ 121 measured I in meteorites via neutron produced 12*Xe using mass spectrometry. His results were lower by an order of magnitude or more than those obtained by other methods. He points out that neutron produced 128Xe is not retained at sites where most of the iodine resides. This introduces large uncertainties in the I-Xe formation interval based on total I and 129Xe [ 131. The fact that the halogens are so readily leached suggests that they may be, in part, not only in soluble phases but also at surfaces where recoils from radio-
active decay or (n-r) etc. reactions could cause rare gas loss. The small amount of data permits a few tentative generalizations: (1) Cl and Br contents fall in the ranges observed in chondrites but F tends to be lower; (2) the enstatite and hypersthene achondrites have F contents of the order of 10 ppm whereas (3) the calcium-rich howardite and eucrites have F contents of about 40 - 100 ppm; finally, (4) insofar as data permits, the abundance trend is F > Cl > Br.
ACKNOWLEDGEMENTS We are grateful to Miss Irene Fox for performing several critical chemical analyses and to L.Fuchs for critically reading this manuscript. Those who have kindly provided samples will be acknowledged in a report in preparation.
REFERENCES [l] A.L.Turkevich, E.J.Franzgrote
and J.H.Patterson, Chemical analysis of the moon at the Surveyor V landing site, Science 158 (1967) 635.
320
G.W.REED and SJOVANOVIC
[ 21 G.W.Reed, Fluorine in stone meteorites, Geochim. Cosmochim. Acta 28 (1964) 1729. [ 31 G.W.Reed and R.O.AlJen, Halogens in chondrites, Geochim. Cosmochim. Acta 30 (1966) 779. [4] H.J.Born and D.C.Aumann, Aktivierungs-analytisches Bestimmung von Lithium mit Hilfe der Reaktionskette 6Li(n,a)3H und 16O(t,n)l8F, Naturwissensch. 51 (1964) 159. [S] M.Shima and M.Honda, Isotopic abundance of meteoritic lithium, J. Geophys. Res. 68 (1963) 2849. [ 61 DKrankowsky and O.MiJler, IsotopenhSfigkeit und Koruentration des Lithium in Steinmeteoriten, Geochim. Cosmochim. Acta 28 (1964) 1625. [ 71 H.Balsiger, J.Geiss, N.GroegJer and A.Wyttenbach, Distribution and isotopic abundance of lithium in stone meteorites, Earth Planet. Sci. Letters 5 (1968) 17. [ 81 C.Patterson, H.Brown, G.Tilton and M.Inghram, Concentrations of uranium and lead and the isotopic composition of lead in meteoritic material, Phys. Rev. 92 (1953) 1234.
[ 91 J.W.Morgan and J.F.Lovering, Uranium and thorium abundances in stony meteorites, J. Geophys. Rcs. 69 (1964) 1989. [lo] R.S.Clark, M.W.Rowe, R.Ganapathy and P.K.Kuroda, Iodine, uranium and tellurium contents in meteorites, Geochim. Cosmochim. Acta 31(1967) 1605. [ 1 l] A.Wyttenbach, H.R.Von Gunten and W.Scherle, Determination of bromine content and isotopic composition in stony meteorites by neutron activation, Geochim. Cosmochim. Acta 29 (1965) 467. [ 121 C.M.Hohenberg, Extinct radioactivities in meteorites, Nininger Meteorite Competition Paper (1968), University of California, Berkeley. [ 131 C.M.Hohenberg and J.H.Reynofds, Preservation of the iodine-xenon record in meteorites, submitted to J. Geophys. Res. (1969).
SOME HALOGEN
MEASUREMENTS
ON ACHONDRITES
*
G.W.REED and S.JOVANOVIC Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
Received 20 May 1969
Data are presented on halogen concentrations in various classes of achondritic meteorites. The importance of the lability of the halogens to the interpretation of rare gas data is pointed out.
1. INTRODUCTION Few data have been reported on the halogen contents of achondrites. These objects have added significance today since rock of the composition of basaltic achondrites is a candidate for lunar surface material [I] . Achondritic minor and trace element composition, the halogens in the work presented here, may provide some indications as to what to expect on the moon. The lunar surface has had a long exposure to solar and galactic particle irradiation. Rare gases are products of such an irradiation of the halogens; detailed study of these gases will require a knowledge of the halogen concentrations. Iodine concentrations are necessary for extinct 1291-129Xe formation interval estimates. The halogens are active chemical agents; they and many of their compounds are volatile; they span a wide range in chemical properties such as electronegativities, binding energies and oxidation states and may therefore provide clues to lunar chemical processes. In the course of a study of the feasibility of determining F, Cl, Br, and I simultaneously, some values for the concentration of these elements in achondrites have been obtained. We have surveyed most types of achondrites for their F content and in a few cases have estimated the Cl and Br contents. Te and U * Work performed under the auspices of the U.S. Atomic Energy Commission and National Aeronautics and Space Administration.
values were obtained to detect I.
as by-products
of the attempts
2. EXPERIMENTAL Consecutive photon and neutron irradiations were carried out to produce 1.8 hr l*F and 37.5 min 38C1, 35.3 hr 82Br, and 25 min 12*1, respectively, via (r,n) and (n,?) reactions. The procedures used in each type irradiation were modifications of those already reported [2,3]. A number of photon irradiations was conducted in which Cl, Br and I as well as F were separated. No radioactivity attributable to 38C1, *OBr, or 82Br and 12*1 was observed, verifying that (r,n) (-r,an), etc. reactions would not contribute significantly to the (n-y) produced radioactivity at the intensity (30 -40 pa average beam current) and energy (16- 17 MeV) of the Argonne National Laboratory linac photon beam. In the case of Cl, however, 0.141 and 0.511 MeV photopeaks characteristic of 34C1 were observed. The production of 32.4 min 34C1 was monitored with Saran, polyvinyl chloride, foils. Since the radioactivity was usually too low to be adequately characterized, concentrations based on 34C1 are not reported here. Exploratory experiments were carried out to assess the effect of contributing reactions on 34C1 production. The two most likely reactions are 39K(y,an)34C1 and the secondary reaction 34S(p,n)34C1. The former is energetically prohibited for 16 - 17 MeV photons.
SOME HALOGEN MEASUREMENTS ON ACHONDRITES
317
Table 1 Fluorine in achondrites. Irradiation number Enstatite 3 4
10 5 8 Hypersthene 9 10
Sample
IFI leach @pm)
Rishopville Cumberland Falls Cumberland Falls Norton County Norton County
f 1.5 < 7.8 (b) -0 ND
Tatahouine Johnstown
< 8.9
[Fl sample @pm)
Literature
6.8 + 1.3 (a) GO.34 7.7 f 0.9 11.0 f 2.6 [ 22.3 ‘7.41 (c)
-0
10.7 If:4.5 (1)
12.2 + 2.1 3.5 + 0.4
Howardite
11 13
Frankfurt Frankfurt
G2.6 +0.9
[ 174 +58] 57.1 + 1.7
(c)
Eucrite
11 13 5 I I 9 Terrestrial samples 6 8 6
Moore County Moore County Shergotty S tannern Pasamonte Nuevo Laredo
W-l W-l G-l
ND < 6.1 < 2.9 < 15.7 < 10.3
[266 -+ 91.5 + 0.6 50.1 + 19.9 + 30.4 + 50.6 +
16.1 f 3.5 ND 31.4 I! 11.7
881 (c)
60 f 10 ($1)
5.0 1.7 3.5 3.0
263 + 28 ]994+329] 800 f 65
(c)
426 (I), 552 (1) 208 (2), 31.5 (3) 1100 (1), 705 (2), 723 (3)
ND = not determined. sample not leached. (a) (b) photopeak observed but decay not followed. original concentration ‘corrected for contribution from neutron irradiation (see text). (c) (1) Reed (1964), ref. [2]. (2) Huang and Johns, Geochim. Cosmochim. Acta 31 (1967) 597. (3) RCarpenter, Thesis, University of California, La Jolla (1968).
Reagent grade K2CO3 and Na2S04 salts were irradiated. In spite of the confirmed low Cl concentration, unexpected and as yet unexplained amounts of 34C1 were produced in each. A 30 cm3 lithium drifted germanium detector was employed to obtain many of the results in the expectation that the high resolution and low background under a photopeak might permit a reduction in the time necessary for radiochemistry. At the ppm level this was feasible. Below about 0.1 ppm P,-y coincidence counting was necessary. Greater sensitivity will be achieved when the new high current linac is in
operation at ANL. A correction factor was applied to the counting data from the polyvinyl fluoride, PVF, discs used to monitor the photon intensity. The discs were - 2 mg/cm2 and of S mm diameter whereas the CaF2 samples counted were thicker and 18 mm in diameter. The correction was 2.98 for samples of 25 -60 mg/cm2 and 2.36 for heavier samples and was due to the slowing down or stopping of the 0.65 MeV /3+ within the sample, causing the annihilation to occur closer to the detector than in the case of the thin monitor.
G.W.REED and SJOVANOVIC
318
Cl, Br, Te, and U Sample
C1leach (ppm)
Clsample (ppm)
Literature
Brleach (ppm)
Brsample (ppm)
Literature
Norton County
ND
not detectable
1.9, 5.6 (1)
ND
0.010 + 0.002
0.067 (5) 0.077 (6)
Frankfurt
13.6 + 10.0
1.3 +0.3
0.21 f 0.05
0.15
Moore County
20.5 f
4.3
5.5 f 1.3
0.48 + 0.08
0.075 zb0.017
15.7 It 2.7
5.8 f 0.7
0.46 f 0.05
0.061 ?r 0.009
ND
0.15
W-l
ND
16.3 f 1.3
25.6 (2) 187-191 (3)
rto.04
f0.03
0.039 * (6)
0.40 (2)
198-219 (4) ND = not determined. * value for the eucrite Pasamonte. (1) Von Gunten et al., Geochim. Cosmochim. Acta 29 (1965) 475. (2) Reed and Allen (1966), ref [3]. (3) Huang and Johns, Geochim. Cosmochim. Acta 31 (1967) 597. (4) Johansen and Stennes, Geochim. Cosmochim. Acta 31 (1967) 1107.
3. RESULTS AND DISCUSSION The results obtained in this work are listed in tables 1 and 2 along with previously reported data. In halogen determinations we have adopted the practice of leaching the samples before fusion with a hot aqueous solution containing the various carriers. In the tables the concentrations in the leach solution, where measured, and the concentrations in the residues are listed. The errors quoted are based principally on counting statistics; weighing and pipetting errors were, in general, small. Because of the number of samples with short half-lives, decay measurements were not always possible. Spectroscopy alone is not always reliable for identification and we have, therefore, designated with an equal or less than sign those measurements in which decay was not followed. A higher F content was observed in the photon followed by neutron irradiations than in the photon only experiments. A neutron irradiation established that F was being produced in the meteorite but not in the PVF foils. This production probably arises from the following reactions: (1) 6Li(n,cr)T and (2) T(leO,n)laF [4]. A comparison of the 18F activity observed in neutron only and photon only irradiations yielded a cor-
rection for the amount of F produced in the neutron irradiation. This factor (- 0.33) was applied to the F concentrations measured in irradiations 8 and 11. This is a large extrapolation, especially in the rung, since it assumes the same Li/O and Li/F ratios in sampIes of different origin and mineralogy as well as similar matrix effects on the tritium induced reaction. The lithium content of W-l is 12 ppm [5] , and of meteorites about 0.2- 1 ppm [6,7]. The amount of Li related F activity in W-l was, as expected, larger than in Moore County or Norton County. The differences that continue to appear in the USGS standards will not be discussed here. The G-l and W-l samples were different aliquots from those we previously measured. A review of the literature reveals that trace element concentrations in samples of the same meteorite measured in different laboratories may agree, while concentrations in samples of another meteorite measured during the same experiments will disagree. A sampling problem seems to be a reasonable explanation. The agreement or disagreement with reported results can be seen in the tables. The U concentrations are consistent with those of Patterson et al. [8] and Morgan and Lovering [9] ; they are at variance with
SOME HALOGEN MEASUREMENTS ON ACHONDRITES
319
ble 2 in achondrites. Teleach (ppm)
Tesample (ppm)
Uleach (ppb)
ND
0.025 + 0.007
ND
ND
0.023 f 0.014
ND
0.030 +_0.007
0.31 + 0.05 ND
Literature
Usample (ppb) 9.7 f 1.9
ND
21.6 +6.1
ND
13.5 + 3.8
0.015 ?I 0.003
not detectable
15.2 + 2.1
0.48
ND
0.16, 0.14 (7)
+ 0.05
1037 + 105
Literature _____ LO(8)
19.6 (9) so.39 (7)
500-900 (10)
(5) Wyttenbach et al. (1965), ref. [ 111. (6) Liberman and Ehman, J. Geophys. Res. 72 (1967) 6279. (7) Clark et al. (1967), ref. [lo]. (8) Patterson et al. (1953), ref. [ 81. (9) Morgan and Lovering (1964), ref. [ 91. (10) Cherry, Geochim. Cosmochim. Acta 27 (1963) 183.
the higher values of Clark et al. [lo] . No evidence for U leachability was observed in the Moore County sample measured in these experiments nor in the several chondrites reported earlier [2] . The factor - 10 lower Te value observed in the residue of Moore County after leaching is striking. Since Te is not a likely contaminant it appears that Te is in a very labile site. This trend has been noted before for Te and the halogens in chondrites [3] . This may also explain the difference between our Norton County bromine concentration and that of Wyttenbach et al. ]lLl. The importance of the lability of the halogens to the interpretations of rare gas data should be emphasized. Hohenberg [ 121 measured I in meteorites via neutron produced 12*Xe using mass spectrometry. His results were lower by an order of magnitude or more than those obtained by other methods. He points out that neutron produced 128Xe is not retained at sites where most of the iodine resides. This introduces large uncertainties in the I-Xe formation interval based on total I and 129Xe [ 131. The fact that the halogens are so readily leached suggests that they may be, in part, not only in soluble phases but also at surfaces where recoils from radio-
active decay or (n-r) etc. reactions could cause rare gas loss. The small amount of data permits a few tentative generalizations: (1) Cl and Br contents fall in the ranges observed in chondrites but F tends to be lower; (2) the enstatite and hypersthene achondrites have F contents of the order of 10 ppm whereas (3) the calcium-rich howardite and eucrites have F contents of about 40 - 100 ppm; finally, (4) insofar as data permits, the abundance trend is F > Cl > Br.
ACKNOWLEDGEMENTS We are grateful to Miss Irene Fox for performing several critical chemical analyses and to L.Fuchs for critically reading this manuscript. Those who have kindly provided samples will be acknowledged in a report in preparation.
REFERENCES [l] A.L.Turkevich, E.J.Franzgrote
and J.H.Patterson, Chemical analysis of the moon at the Surveyor V landing site, Science 158 (1967) 635.
320
G.W.REED and SJOVANOVIC
[ 21 G.W.Reed, Fluorine in stone meteorites, Geochim. Cosmochim. Acta 28 (1964) 1729. [ 31 G.W.Reed and R.O.AlJen, Halogens in chondrites, Geochim. Cosmochim. Acta 30 (1966) 779. [4] H.J.Born and D.C.Aumann, Aktivierungs-analytisches Bestimmung von Lithium mit Hilfe der Reaktionskette 6Li(n,a)3H und 16O(t,n)l8F, Naturwissensch. 51 (1964) 159. [S] M.Shima and M.Honda, Isotopic abundance of meteoritic lithium, J. Geophys. Res. 68 (1963) 2849. [ 61 DKrankowsky and O.MiJler, IsotopenhSfigkeit und Koruentration des Lithium in Steinmeteoriten, Geochim. Cosmochim. Acta 28 (1964) 1625. [ 71 H.Balsiger, J.Geiss, N.GroegJer and A.Wyttenbach, Distribution and isotopic abundance of lithium in stone meteorites, Earth Planet. Sci. Letters 5 (1968) 17. [ 81 C.Patterson, H.Brown, G.Tilton and M.Inghram, Concentrations of uranium and lead and the isotopic composition of lead in meteoritic material, Phys. Rev. 92 (1953) 1234.
[ 91 J.W.Morgan and J.F.Lovering, Uranium and thorium abundances in stony meteorites, J. Geophys. Rcs. 69 (1964) 1989. [lo] R.S.Clark, M.W.Rowe, R.Ganapathy and P.K.Kuroda, Iodine, uranium and tellurium contents in meteorites, Geochim. Cosmochim. Acta 31(1967) 1605. [ 1 l] A.Wyttenbach, H.R.Von Gunten and W.Scherle, Determination of bromine content and isotopic composition in stony meteorites by neutron activation, Geochim. Cosmochim. Acta 29 (1965) 467. [ 121 C.M.Hohenberg, Extinct radioactivities in meteorites, Nininger Meteorite Competition Paper (1968), University of California, Berkeley. [ 131 C.M.Hohenberg and J.H.Reynofds, Preservation of the iodine-xenon record in meteorites, submitted to J. Geophys. Res. (1969).