Scholars' Mine
Masters Theses Student Theses and Dissertations
1971
Mass fraction and the isotopic anomalies of xenon and krypton in ordinary chondrites
Edward W. Hennecke
Follow this and additional works at: https://scholarsmine.mst.edu/masters_theses
Part of the Chemistry Commons Department:
Recommended Citation Hennecke, Edward W., "Mass fraction and the isotopic anomalies of xenon and krypton in ordinary chondrites" (1971). Masters Theses. 5453. https://scholarsmine.mst.edu/masters_theses/5453
This thesis is brought to you by Scholars' Mine, a service of the Missouri S&T Library and Learning Resources. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. MASS FRACTIONATION AND THE ISOTOPIC ANOMALIES
OF XENON AND KRYPTON IN ORDINARY CHONDRITES
BY
EDWARD WILLIAM HENNECKE, 1945-
A THESIS
Presented to the Faculty of the Graduate School of the
UNIVERSITY OF MISSOURI-ROLLA
In Partial Fulfillment of the Requirements for the Degree
MASTER OF SCIENCE IN CHEMISTRY
1971
T2572 51 pages by Approved ~ (!.{
1.94250 ii
ABSTRACT
The abundance and isotopic composition of all noble gases are reported in the Wellman chondrite, and the abundance and isotopic composition of xenon and krypton are reported in the gases released by stepwise heating of the Tell and Scurry chondrites. Major changes in the isotopic composition of xenon result from the presence of radio genic Xel29 and from isotopic mass fractionation. The isotopic com position of trapped krypton in the different temperature fractions of the
Tell and Scurry chondrites also shows the effect of isotopic fractiona tion, and there is a covariance in the isotopic composition of xenon with krypton in the manner expected from mass dependent fractiona tion. The results from this study indicate that simple isotopic frac tionation is responsible for many isotopic anomalies which have previously been attributed to nuclear reactions. iii
ACKNOWLEDGMENTS
I am thankful to Dr. 0. K. Manuel for his guidance and support.
I am likewise sincerely appreciative to Dr. William H. Webb for his
patience and support. My thanks go to Mr. B. Srinivasan for assist ance in helping me learn the operating procedure for the mass spec trometer. I am grateful to Mr. John V. Albrecht who did the data
reduction. I would also like to thank Mr. David E. Sinclair and
Mr. Victor J. Becker for assisting me in the laboratory and chart reading. iv
TABLE OF CONTENTS
Page
ABSTRACT 11
ACKNOWLEDGMENTS . . • ...... • ...... • . . • ...... 111
LIS T 0 F FIGURES . . • . • . • ...... • ...... • . . • • ...... • . v
LIST OF TABLES ...... • ...... Vl
I. INTRODUCTION . • ...... • ...... 1
II. LITERATURE REVIEW ...... 4
III. EXPERIMENTAL PROCEDURES ...... ~
IV. RESULTS AND DISCUSSION ...... 15
A. NOBLE GASES IN WELLMAN . . • ...... lS
B. KRYPTON AND XENON IN TELL AND SCURRY ...... 19
V. CONCLUSIONS ...... • ...... 22
BIBLIOGRAPHY...... • ...... 40
VITA ...... • ...... 45 v
LIST OF FIGURES
Page
1. Abundance pattern of noble gases in the Wellman Chondrite relative to the cosmic abundances of these gases ...... 24
2. Abundance pattern of krypton isotopes in the Wellman chondrite and in average carbonaceous chondrites rela- tive to solar krypton in lunar breccia # 10021 ...... 26
3. Abundance pattern of xenon isotopes in the Wellman chon drite and in average carbonaceous chondrites relative to solar xenon released at 800°C from lunar fines # 10084 28
4. Abundance pattern of krypton isotopes in the different tem perature fractions of the Tell chondrite relative to solar krypton ...... 30
5. Abundance pattern of xenon isotopes in the different tem perature fractions of the Tell chondrite relative to solar xenon ...... 32
6. Abundance pattern of krypton isotopes observed by stepwise heating of the Scurry chondrite normalized to solar krypton ...... 34
7. Abundance pattern of xenon isotopes observed by stepwise heating of the Scurry chondrite norn1alized to solar xenon • . . • ...... 36 Vl
LIST OF TABLES
Page
I. Concentration and isotopic composition of noble gases in the Wellman chondr ite ...... • . . . • ...... 3 7
II. Concentration and isotopic composition of krypton and xenon in the Tell chondrite . . . • . • • . . . . . • • • ...... • . 38
III. Concentration and isotopic composition of krypton and xenon in the Scurry chondrite . • ...... • . • ...... • • ...... 39 1
I. INTRODUCTION
This investigation of the abundance and isotopic composition of the noble gases, helium, neon, argon, krypton and xenon, in ordinary chondrites was undertaken to obtain additional data with which to ex amine the different models proposed to explain isotopic anomalies of these gases 1n nature.
It has been known for several years (Suess, 1949; Brown, 1949) that the abundance of noble gases in the earth's atmosphere relative to their cosmic abundance shows a preferential depletion of the light weight noble gases. Suess (1949) noted that the mass fractionation pattern seen across the abundances of the noble gases might be accom panied by fractionation across the isotopes of the individual gases.
Early studies of noble gases in meteorites also showed a prefer ential depletion of the light-weight noble gases. These studies reveal ed isotopic anomalies of all five noble gases due to nuclear reactions and to radioactive decay. For exan1ple, spallation reactions induced by cosmic rays have produced isotopic anomalies of all five noble gases. Radiogenic He4 and Ar40 have been generated by the decay of uranium, thorium and potassium, and excess Xel29 and Xel31-136 occur in meteorites due to the decay of now-extinct Il29 and Pu244, respectively. These processes arc well-documented, and it is gen erally accepted that natural radioactive decay or induced nuclear reactions have altered the isotopic composition of all noble gases in 2
·meteorites. However, in addition to the effects oi well-docun1ented nuclear reactions, there are also isotopic anomalies of all five noble gases in meteorites, and there is now a divergence of opinion on the role of nuclear reactions and isotopic mass fractionation in generating these anomalies.
Manuel (1967) noted a variation in the isotopic composition of neon in the Fayetteville meteorite which could not be produced by known spallation reactions. He suggested that these variations were the result of isotopic fractionation. Pepin (1968) suggested that anum ber of different con1ponents of trapped neon exist in meteorites and argued that there is no sign that diffusive fractionation is responsible for any of the isotopic variations. Anders et al. (1970) noted a vari- ation in the isotopic composition of helium and neon in carbonaceous chondrites and concluded that these isotopic variations could result from nuclear reactions. But Srinivasan and Manuel (1970) have shown that the He3/He4, Ne20fNe22 and Ar36JAr38 ratios in these carbon- aceous chondrites covary in the manner expected from isotopic frac tionation. Kuroda and Manuel (1970) suggested that an enrichment of the heavy isotopes of xenon in carbonaceous and gas-rich meteorites is due to isotopic fractionation, but Anders and Heymann (1969) attribute
this enrichment of heavy xenon isotopes to the fission decay of a vola
tile, superheavy element (Z = ll2 to ll9). Pepin et al. (1970) reported
a new type oJ cosmogenic krypton in the lunar surface. Manuel (1970)
suggested that this was not cosmogenic krypton, but an enrichment of the light isotopes due to simple isotopic mass fractionation. Thus the controversy over the role of mass fractionation versus the role of nuclear reactions and radioactive decay includes anomalies observed in all five noble gases.
This study was initiated to obtain reliable data with which to ex amine the merits of these two views of isotopic anomalies of noble gases in meteorites. Evidence for the origin of the isotopic anomalies of xenon and krypton was the primary concern of this investigation, since recent analysis of noble gases in lunar material reveals unam biguous evidence for isotopic fractionation in the three light-weight noble gases (Hohenberg et al., 1970}. Furthermore, one of the earlier proponents for the generation of isotopic anomalies of helium, neon and argon by nuclear reactions {Black, 1969} has recently admitted that additional data showing the covariance of the isotopies of these three gases in meteorites place severe constraints on the irradiation model
{Black, 1971). II. LITERATURE REVIEW
Many clues of early geologic events have been recorded in the stable noble gases, helium, neon, argon, krypton and xenon. The chemical inertness and volatile nature, even at relatively low tem peratures, resulted in almost complete loss of these elements from more condensable material when solid planetary matter formed in our solar system. Due to this early depletion of noble gases from more condensable matter, many isotopic anomalies of these elements have been generated in solid planetary n1aterial subsequent to this separa tion by induced nuclear reactions and by natural radioactive decay of more abundant elements.
The early studies of terrestrial noble gases emphasized the role of natural radioactive decay in producing noble gas isotopes. The
U-He and Th-He dating methods were developed over 60 years ago by
Strutt (1908a, l908b, 1909), and Weizsacker (1937) suggested the K-Ar dating method about 11 years prior to experimental verification {Suess,
1948) for the decay of K40 to Ar40.
Studies of noble gases in meteorites were originally confined to age determinations of iron meteorites by the U -He method (Arrol et al., 1942). The ages estimated from these early studies were later found to be in error due to the production of helium isotopes within iron meteorites by nuclear reaction induced by cosmic rays (Paneth et al., 1952). Gerling and Pavlova {1951) discovered radiogenic Ar40 in 5
stone meteorites and first estimated their K-Ar age. Stonner and
Zahringer (1958) attempted to date iron meteorites by the K-Ar method, but here, too, interference from cosmic-ray induced reactions caused errors in the original K-Ar ages estimated for iron meteorites
(Anders, 1962).
Other investigations have shown that bombardment by cosmic rays produces isotopic anomalies of neon (Reasbeck and Mayne, 1955), krypton (Clarke and Thode, 1961) and xenon (Rowe, et al., 1965) by spallation reactions, that the cosmic rays produce secondary neutrons which are captured to produce excess He3, Ar36, Ar38, Kr80, Kr82,
Kr83, Xel28, Xel29, and Xel31 (Clarke and Thode, 1961; Fireman and
Schwarzer, 1957; Goel, 1962; Marti et al., 1966; Alexander et al., 1968) and that when the meteorites formed they contained two now-extinct nuclides (Reynolds, 1960a; Kuroda, 1960) which decayed to produce excess Xel29 from 1129 (tl/2 = 17 x 106 yrs.) and excess Xel31-136 from
Pu244 (tl/2 = 82 x 106 yrs. ).
Although the generation of isotopic anomalies of all the stable noble gases by nuclear processes is well docurnented, there is also evidence for the production of isotopic anomalies of noble gases by simple isotopic mass fractionation at the t1me of the separation of these from more condensable elements. Prior to the detection of iso- topes with a mass spectrometer, Aston (1913) diffused neon through clay pipes and noted that the existence of neon atoms of different mass 6
could account for changes he observed in the density of neon. Suess
(1949) and Brown (1949) independently noted that a comparison of the earth's inventory of noble gases with the solar abundances of these ele ments showed preferential loss from terrestrial material of the gases lighter than krypton. Subsequent work on noble gases in terrestrial sediments (Canalas et al., 1968) found high concentrations of xenon which, when added to the atmospheric inventory of noble gases, show that the earth's fractionation of noble gases extends to the heaviest noble gas, xenon.
The trapped noble gases 1n stone meteorites display a similar fractionation pattern (Reynolds, 1960b; Manuel and Rowe, 1964), with the xenon preferentially retained over the neon by a factor ""'104 -105.
Signer and Suess (1963) discussed the role of mass fractionation in generating isotopic anomalies of neon and argon in planetary mate rial. They noted a covariance of Ar36 I Ar38, Ne20 /Ne22 and
Ne20j Ar36 ratios in atmospheric and meteoritic gases. Manuel (1967) reported variations in the trapped Ne20fNe22 and Ne2lfNe22 ratios in the different temperature fractions of the Fayetteville meteorite and suggested that these variations result from isotopic mass fractionation.
However Pepin and coworkers (Pepin, 1967; Pepin, 1968; Black, 1969;
Black and Pepin, 1969) reported that there is no sign that diffusive
fractionation is responsible for any of the isotopic variations of mete
oritic neon. Recent results from analyses on the isotopic composition
of trapped meteoritic helium, neon and argon at the University of 7
Minnesota, the University of Chicago and Rice University have been attributed to nuclear reactions (Black and Pepin, 1969; Black, 1969;
Black, 1970; Anders et al., 1970; Mazor et al., 1970), but other au thors (Kuroda and Manuel, 1970; Manuel, 1970; Srinivasan and Manuel,
1970) have maintained that the observed variations result from simple isotopic fractionation.
For the heavy noble gases a similar divergence of opinion has developed. Srinivasan et al. (1969) first suggested that the spontane ous fission of superheavy elements may be responsible for the enrich ment of heavy xenon isotopes in carbonaceous chondrites. Anders and
Heymann (1969) have arrived at a similar conclusion by comparing the excess heavy xenon isotopes with the content of volatile elements in carbonaceous chondrites, and Eberhardt et al. (1970) have interpreted the isotopic composition of solar-type xenon as evidence for large amounts of fissiogenic xenon in carbonaceous chondrites. However,
Kuroda and Manuel (1970) recently pointed out that the enrichment of heavy xenon isotopes in carbonaceous and gas-rich meteorites is paralleled by an enrichment of heavy neon isotopes. These authors concluded that the enrichment of the heavier isotopes of both gases re sult from isotopic mass fractionation. Additional evidence for the pro duction of isotopic anomalies of meteoritic xenon and krypton by frac tionation have been reported from noble gas analyses of the Leoville
(Manuel et al., 1970) and Potter (Manuel et al., 1971) chondrites. 8
III. EXPERIMENTAL PROCEDURES
A detailed description of the mass spectrometer was given by
Reynolds (1956) and the general operational procedures used in this laboratory were given by Canalas (1967). The specific procedure for
sample, air spike and blank analyses used in this study will be outlined below. Identical procedures were carefully followed in sample, air
spike and blank analyses. This reduced the possibility of error due to
variations in the procedure used for gas analysis.
The sample system consisted of a combined extraction and pre liminary cleaning system and a secondary cleaning and gas extraction
system. These two systems were separated by a metal bellows valve.
The secondary cleaning and gas extraction system was also connected
separately through metal bellows valves to vacuum pumps and to the mass spectrometer.
The extraction and preliminary cleaning system consisted of a
titanium furnace, a copper-copper oxide furnace, a quartz extraction
bottle, air spikes, and a cold trap. The titanium furnace and copper
copper oxide furnace acted as getters to remove the more reactive
gases in the preliminary cleaning system. The cold trap was employ
ed to prevent any residual material with a relatively low vapor pres
sure from entering the secondary clean-up system.
The components of the secondary cleaning and separation sys
tem were a charcoal finger, a titanium furnace, a cold trap and an 9
ion gauge. The charcoal finger was used as an adsorption surface for
separation of the noble gases prior to analysis in the mass s pectro
meter. The ion gauge was used to detect leaks and to check the pres
sure of both cleaning systems before each analysis. The titanium furnace of the secondary system was used for a final clean-up prior to
gas analysis in the spectrometer. The cold trap of the secondary cleaning system was used to prevent any residual contaminats with low
vapor pressure from entering the mass spectrometer.
The samples were mounted on a slide wire assembly attached to the molybdenum crucible within the water -jacketed, quartz extraction bottle. A 10 kilowatt Lepel radio-frequency induction heater was em ployed to heat the crucible, and an optical pyrometer was used to estimate the temperature of the crucible.
Prior to sample analysis the titanium furnace and copper -copper oxide furnace were degassed at elevated temperatures. Then the molybdenum crucible was degassed at 1800°C for two hours and then cooled. The valve separating the preliminary system from the secon dary system was then closed and the titanium and copper-copper oxide furnaces were brought to equilibrium temperatures of 850°C and
ssooc, respectively. After these steps had been completed, a magnet
was used to pull the pen holding the sample on the slide wire assem
bly. This released the sample which fell into the previously degassed
crucible. The crucible was heated to the desired temperature by the 10
radiofrequency generator and that temperature was maintained for 3 0 minutes. Then the induction heater was turned off, and the titanium and copper-copper oxide furnaces were cooled with compressed air for 30 minutes.
After the furnaces were cooled, solid COz was placed on the cold trap of the preliminary system. The valve connecting the secondary cleaning system to the vacuum pumps was closed, and liquid nitrogen was placed on the charcoal finger. After five minutes, the valve sepa rating the preliminary from the secondary system was opened and the gases were pumped from the preliminary to the secondary cleaning system for 15 minutes by the liquid nitrogen cooled charcoal. The two cleaning systems were then isolated and the secondary titanium fur nace was heated to 850°C. The liquid nitrogen was removed from the charcoal and replaced with a heater (T == 200°C) to drive the gases off the charcoal. After 15 minutes of scrubbing on the hot titanium, this furnace was cooled for 30 minutes with compressed air.
After the titanium furnace had been cooled, the charcoal finger was cooled with liquid nitrogen, The gases were allowed to equilibrate on the charcoal for 30 minutes at the liquid nitrogen temperature. At this time solid COz was placed on the cold trap of the secondary clean ing system. After ten minutes the valve leading to the mass spectro meter was opened for two minutes to allow helium and neon to enter the mass spectrometer. While helium and neon were analyzed, solid 11
C02 was placed on the charcoal finger to release the argon. Due to the large amount of radiogenic Ar40, the argon was analyzed in two frac tions. The first fraction, consisting of about one-tenth of the total argon, was used to measure the ratios of the argon isotopes and the second fraction was used to determine the total amount of argon re leased from the sample. While the second fraction of argon was being analyzed the remaining argon was pumped from the secondary clean up system to prevent interference with subsequent krypton analysis.
Then a bath, maintained at a constant temperature by the equilibrium between solid and liquid mercury, was placed on the charcoal finger to release the krypton. After 30 minutes the valve to the mass spectro meter was opened for three minutes allowing the krypton to enter the spectrometer for analysis. After the valve was closed, a heater was placed on the charcoal finger to release the xenon. After analysis of the krypton was completed the valve was again opened for three min utes and xenon was admitted to the mass spectrometer for analysis.
For all of these analyses the noble gases previously in the spectro meter were pumped from the tube prior to admitting the next noble
gas.
The procedure outlined above was employed for the Wellman
chondrite, for its hot blanks and for those air spikes which were run in
conjunction with this sample. The only exception to this procedure was
for the air spikes, where the molybdenum crucible was not heated. 12
In the case of Scurry and Tell meteorites the above procedure
was slightly altered. The operational procedure in the preliminary
clean-up system was not changed. Since only krypton and xenon were
to be analyzed in these two samples, these gases were pumped from
the preliminary system onto charcoal at the sublimination temperature
of solid COz. Then the secondary system was isolated from the pre liminary system and the He, Ne and Ar were pumped from the secon dary system prior to the final scrubbing on hot titanium. After the valve to the pumps was closed, the titanium furnace was heated to
850°C, a heater was placed on the charcoal driving off krypton and xenon, and the gases were scrubbed a second time for 15 minutes.
The furnace was cooled for 30 minutes with compressed air and then the mercury bath (-39°C) was placed on the charcoal separating kryp ton from xenon. The krypton and xenon were then analyzed separately in the manner described earlier.
The mass spectrometer was calibrated before and after each sample by analyzing small volumes of air (z 0.1 cc STP). The air spikes were used to determine the isotopic n1ass discrimination and the sensitivity of the mass spectrometer for each noble gas. The mass discrimination across the isotopes of each gas was calculated by comparing the observed peak ratios with the isotopic compos it ion of atmospheric neon (Eberhardt et al., 1965), argon (Nier, l950a), krypton (Nief, 1960) and xenon (Nier, 1950b). The sensitivity of the 13
spectrometer was obtained by comparing the peak height (ie., the spectrometer signal) with the volume of the air spike and the concen trations of noble gases in the atmosphere {Verniani, 1966).
Blank analyses were run before and after each sample. The spectrometer signal from the blank was always less than O.lo/o of the sample signal except at mass 78. No values for Kr 78 are reported in this study. The errors reported in the isotopic ratios are one standard deviation (cr) from the least squares line through the observed ratios as a function of residence time in the mass spectrometer. From varia tions in the mass discrimination observed in the air spikes, it is esti mated that the correction for mass discrimination introduced a maxi mum error of about ± 0. 5o/o, however, the concentration reported for gas has a n1uch larger error of about ± ZOo/o, due to variations in the signal per unit volume of a given gas,
Three meteorites were used for this investigation. The gases were extracted fron1 the Wellman chondrite by a single melt experi ment at 1800°C. Stepwise heating experiments were perforn1ed on the
Scurry and Tell chondrites. The extraction temperatures were 600°C,
900°C and at 1800°C, successively.
Relatively large meteorite samples, weighing about 10 grams each, were used in this study. These were purchased frorn the An1cr ican Meteorite Laboratory (AML). The nan1c and type of each mete orite, the sa rnple weight and the AML catalogue number of the 14
specimen from which the samples were taken are as follows: The w-ellman, Texas olivine bronzite chondrite, 10.888 grams from speci men# Hl2. 56; the Tell, Texas olivine hyperthene chondrite, 8. 474 grams, from specimen# H24. 67 and the Scurry, Texas olivine bronz ite chondrite, 7. 909 grams from specimen # H65. 25. 15
IV. RESULTS AND DISCUSSION
A. NOBLE GASES IN WELLMAN
The abundances and isotopic composition of the noble gases in
Wellman are shown in Table I together with the isotopic composition of trapped noble gases in carbonaceous chondrites and the solar-type
noble gases observed in gas-rich meteorites and in the moon. The iso topic composition of trapped He, Ne and Ar in carbonaceous chondrites are the range of values reported in a comprehensive study (Anders et al., 1970; Mazor et al., 1970) and the trapped Kr and Xe are the aver age values (Eugster et al., 1967; Marti, 1967) observed in carbonace ous chondrites. The isotopic composition of solar-type He, Ne and
Ar are from the Fayetteville gas-rich meteorite (Manuel, 1967). The
Kr is from lunar breccia# 10021 (Funkhouser et al., 1971), and the solar Xe is that released from lunar fines at 800°C (Marti et al.,
1970). The solar abundance of each rare gas is from the abundance tables of Suess and Urey (1956).
The isotopic composition of xenon and krypton in Wellman is in termediate between the isotopic composition of these gases in carbon
aceous chondrites and in the moon. Except for the obvious excess of
xel29. we interpret these two gases to represent the isotopic composi
tion trapped in Wellman. The isotopic composition of the trapped com
ponent of the three light-weight noble gases in Wellman is masked by a
cosmogenic component. For helium and argon it is not possible to 16
unambiguously separate the trapped and the cosmogenic components.
However, these two components of neon can be separated by the method of Manuel (1967). The concentration of trapped neon and its isotopic composition as calculated by this method are shown in Table I. Since
Manuel (1970) and Srinivasan and Manuel (1970) have shown that the
He3 /He4, Ne20 /Ne22 and Ar36 / Ar38 ratios in carbonaceous chondrites covary in the manner expected from a common mass dependent frac tionation process, we have shown in Table I the isotopic composition of trapped He and Ar obtained by assuming that the trapped He, Ne and Ar in Wellman have undergone a common fractionation process.
To compare the abundance of trapped noble gases in Wellman with the cosmic abundance of noble gases, we employ the equation of
Canalas et al. (1968).
where xm is any trapped noble gas isotope with mass number m. By using the abundances of trapped gases in Wellman from Table I and the cosmic abundances from Suess and Urey (1956), the fractionation pat tern is obtained for trapped noble gases in Wellman as shown in Fig. 1.
Although the fractionation across the isotopes of a given noble gas can not be quantitatively related to the separation of one gas from another since the latter may not depend on atomic mass alone (Signer and
Suess, 1963), we note that the abundances of noble gases fit a smooth 17
fractionation pattern and that this correlates with the difference be- tween the isotopic composition of solar gases and the isotopic composi- tion calculated for the trapped He, Ne and Ar in Wellman.
The fractionation pattern across the isotopes of trapped Kr and
Xe in Wellman are shown in Fig. 2 and Fig. 3. The isotopic composi- tion of Kr and Xe from average carbonaceous chondrites (Eugster et al., 1967; Marti, 1967) is shown for comparison. For these two plots,
Eq. 1 was modified to show the fractionation across trapped Kr and Xe by normalizing the mass spectrum to the heaviest isotope.
and
=
In these equations the krypton from lunar breccia # 10021 (Funkhouser et al., 1967) and the xenon released at 800°C from lunar fines # 10084
(Marti et al., 1967) were used to represent solar gases. It has been noted earlier (Manuel et al., 1971) that the possibility of gas loss and isotopic fractionation effects of the solar-type gases implanted on the lunar surface may correlate with long exposure ages and with a deple- tion of the light-weight gases (He, Ne and Ar) relative to the heavier gases (Kr and Xe). These two analyses of lunar material were chosen to minimize these effects. 18
From Fig. 2 and Fig. 3 it can be seen that the preferential deple
tion of the lighter weight noble gases from Wellman, as shown in Fig. 1,
has caused a selective depletion of the light isotopes of the two heavy
noble gases, krypton and xenon. Futhermore, there is a correlation between the fractionation observed across the isotopes of these two noble gases: For both Kr and Xe, the selective loss of the light iso topes is greater in average carbonaceous chondrites (A VCC) (Eugster et al., 1967; Marti, 1967) than in Wellman. The results of this study on the isotopic composition of trapped xenon and krypton in Wellman therefore show evidence of a common fractionation process as has been reported earlier from a stepwise heating experiment on the
Leoville carbonaceous chondrite (Manuel et al., 1970).
The fine structure features of the fractionation curve shown in
Fig. 3 are intriguing. Kuroda (1971) has considered this problem in de tail and concluded that nuclear reactions which have occurred in the sun over geologic time may be responsible for some of these effects.
Relative to solar xenon the minimum at Xel26 and the excess at Xel24 over that expected from fractionation could arise from a deficiency of
Xel24 and an excess of Xel26 in the xenon currently implanted on the lunar surface from the solar wind. It is not unlikely that the abun dance of these two xenon isotopes have been altered by nuclear reac tions in the sun. Xel24 has the largest thermal neutron-capture cross
section of any stable xenon isotope and the production of Xel26 from 19
from rlZ7 via the (y, n) reaction is ::::: 0. 5 barns for high energy photons
(Nascimento et al., 1961).
B. KRYPTON AND XENON IN TELL AND SCURRY
The abundance and isotopic composition of xenon and krypton from the stepwise heating of Tell and Scurry are shown in Table II and
Table Ill, respectively.
In Tell the atomic weight of both xenon and krypton is lightest in the gases released at the highest extraction temperature. Although there is evidence for smq.ll excesses of Kr80, Xel24 and Xel26 from spallation in the melt fraction of Tell, isotopic fractionation plus the in situ decay of rl29 seem to be the two dominant effects in generating variations in the isotopic composition of Kr and Xe. This is shown in
Fig. 4 and Fig. 5 where the Kr and Xe isotope ratios from the step wise heating of Tell are shown in the manner employed for Wellman.
The isotopic composition of Kr and Xe released by stepwise heat ing of Scurry shows the same general trend as the gases in Tell. This is shown in Fig. 6 and Fig. 7 where again we observe a covariance in the fractionation across the isotopes of Kr and Xe. In both Tell and
Scurry there is a small excess of Kr80 which we attribute to spalla tion reactions (Marti et al., 1966) induced by cosmic rays. The less pronounced minimum at Xel26 in Tell and Scurry (Fig. 5 and Fig. 7) than in Wellman and AVCC (Fig. 3) is also suggestive of a small 20
component of spallation-produced Xel26 (Marti et al., 1966) in the xenon of Tell and Scurry.
Since the xenon and krypton released in different temperature fractions of the Scurry and Tell chondrites show variations due to mass fractionation, it seems likely that mass fractionation has also played a role in generating some of the isotopic variations of noble gases re ported in the different temperature fractions of carbonaceous and gas rich chondrites (Manuel, 1967; Black and Pepin, 1967; Black, 1969;
Manuel et al., 1971; Rowe, 1968). Evidence for this process is com pelling in view of (a) the covariance of the isotopic composition of xenon with krypton in the ordinary chondrites studied here and in carbonace ous chondrites (Manuel et al., 1970), (b) the covariance of trapped xenon with trapped neon in the different temperature fractions of car bonaceous and gas-rich meteorites (Kuroda and Manuel, 1970), {c) the covariance of He3 /He4, Ne20 /Ne22 and A1·36 I Ar38 for the total trapped gas in carbonaceous chondrites (Srinivasan and Manuel, 1970) and
(d) the general agreement of the isotopic fractionation pattern observed across each noble gas with the fractionation pattern observed across the abundances of all the trapped noble gases.
Thus, there is cogent evidence of a mass dependent fractionating
process which altered both the abundance pattern of noble gases and their isotopic composition in plan(•tary n1aterial. It should be empha
sized that the isotopic fractionation of noble gases has been known for 21
years. In 1913 Aston (1913) obtained evidence for isotopes by altering the density of neon by diffusion through clay pipes. It appears that solid planetary material has behaved as the clay stems in selectively retaining the heavier isotopes of the noble gases. 22
V. CONCLUSIONS
1) The abundance pattern shown in Fig. 1 for the Wellman chon- drite is cogent evidence that mass fractionation has altered the abun- dances of all trapped noble gases (helium, neon, argon, krypton and xenon) in this meteorite.
2) A comparison of the isotopic composition of each trapped noble gas in the Wellman chondrite with the isotopic composition of solar noble gases (see Table I) shows that mass fractionation has also altered the isotopic composition of each noble gas.
3) The excess Xel29 in all three meteorites is due to the in situ decay of the now-extinct radioactive Il29.
4) There is a variation in the degree of fractionation across the isotopes of krypton and xenon in the different temperature fractions of the Tell and Scurry chondrites. The isotopic compositions of these two gases covary due to a common fractionating process which has altered both xenon and krypton.
5) In addition to the effects of mass fractionation the xenon in chondrites shows a selective depletion of Xel26 relative to solar xenon.
It is suggested that this is due to excess Xel26 which has been produced in the sun via the ('Y, n) reaction on Il2 7. 2..3
Figure l
Abundance pattern of noble gases in the Wellman chondrite relative to
the cosmic abundances of these gases. 0
-2 E u..
(!) L Ytf:LLMAN 0 -4 ...J Q COSMIC
-6 He Ne Ar Kr Xe
20 40 60 80 100 120
MASS NUMBER
Figure 1
N ~ 25
Figure 2
Abundance pattern of krypton isotopes in the Wellman chondrite and in
average carbonaceous chondrites relative to solar krypton in lunar brec-
cia # 10021. 1.04
1.00
0.96 E~ lL.
0.92 I / 0 SOLAR KRYPTON 6 WELLMAN 0.88r u 0 AVCC KRYPTON
80 82 83 84 86
MASS NUMBER
Figure 2 N 0' 27
Figure 3
Abundance pattern of xenon isotopes in the Wellman chondrite and in
average carbonaceous chondrites relative to solar xenon released at
800°C from lunar fines # 10084. 1.20
I. 10
1.00
E~ u.. 0.90
0 SOLAR XENON 0.80 6_ WELLMAN D AVCC XENON
124 126 128 129 130 131 132 134 136
MASS NUMBER
Figure 3 N 00 29
Figure 4
Abundance pattern of krypton isotopes in the different temperature frac
tions of the Tell chondrite relative to solar krypton. 1.04
1.00
0.96
E~ lL
0.92r ~ / 6 soo•c TELL e soo· c TELL 0.88J- A/' 0 MELT TELL 0 SOLAR KRYPTON
80 82 83 84 86
MASS NUMBER
Figure 4 1./.l 0 31
Figure 5
Abundance pattern of xenon isotopes in the different temperature frac
tions of the Tell chondritc relative to solar xenon. I. 10
1.00
0.90
E ~ 0.80 6_ 600 • C TELL "'- • 900• C TELL 0.70 D MELT TELL 0 SOLAR XENON
0.6
124 126 128 129 130 131 132 134 136
MASS NUMBER
Figure 5 N'""' 33
Figure 6
Abundance pattern of krypton isotopes observed by stepwise heating of
the Scurry chondrite normalized to solar krypton. 1.04
1.00
e~ LL I /- • 6 soo• C SCURRY 0.94f- /~ goo• C SCURRY 0• MELT SCURRY 0.88~ 0 SOLAR KRYPTON
80 82 83 84 86
MASS NUMBER
Figure 6 .::.VJ 35
Figure 7
Abundance pattern of xenon isotopes observed by stepwise heating of the
Scurry chondrite normalized to solar xenon. 1.10
1.00
0.90
E~ 0.80 ~ I / // 6. 6oo• c SCURRY e goo• c SCURRY o. 1or- ~~ M'/ D MELT SCURRY Q SOLAR XENON I 0.60
124 126 128 129 130 131 132 134 136
MASS NUMBER VJ Figure 7 0'- Table I
Concentration and Isotopic Composition of Noble Gases in the Wellman Chondrite
Noble Wellman Trapped Gas in Car- Solar Gases observed trapped bonaceous Chondrites Gas
He31He4 o. 0253 ± 0. 0004 0, 88 X 10-4 (1. 25-4. 20) x 10-4 < 3.1 x 10-4 He4 6. 04 x l0-7 cc STPigm 5. 25 x l0-7 cc STPI gm 3. 08 x 106 per 106 atoms Si
Ne20 /Ne22 l. 4 15 ± 0. 003 7.3 7. 77-13.10 > 12. 6 Ne21JNe22 o. 876 ± 0. 003 0.025 0.025-0.036 > 0. 033 Ne22 5. 39 X 10-8 cc STPI gm 4. 35 x 10-9 cc STP/ gm 8. 36 x 105 per 106 atoms Si
Ar381 Ar36 o. 450 ± 0. 001 0.23 0.172-0. 200 < 0.177 Ar40 I Ar36 3143 .± 26 Ar36 3. 96 x 10-9 cc STPigm 3. 27 x l0-9 cc STP/ gm l. 26 x 105 per 106 atoms Si
Kr80JKr84 0. 0423 ± 0. 002 < 0.0423 0.0392 0.0427 Kr821Kr84 0. 2048 ± o. 0007 0. 2048 0. 20 12 0.2065 Kr831Kr84 0. 2045 ± o. 0006 0.2045 o. 20 16 0.2055 Kr861Kr84 0. 3058 ± o. 0007 0.3058 0.3097 0.297 Kr84 l. 41 X 10-10 cc STP/ gm 1.41 x 10-lO cc STP/gm 2. 93 x 101 per 106 atoms Si
Xe124 I xel3 o 0. 0296 ± 0. 0002 0.0296 CJ. 0283 0. 0299 Xe126 I Xel3 0 0. 0268 ± o. 0002 0.0268 0.0253 0.0288 xel28 I xel3 0 0. 508 ± 0. 003 0.508 0.506 0. 512 xe1291xel30 8.18±0.05 (6.37) (6. 35) 6.38 xel31;xe13° 4. 97 ± 0. 03 4.97 5.07 5.00 xel32fxel30 6. 09 ± 0. 03 6. 09 6. 21 6. 05 xe134;xel30 2.36 ± 0.01 2.36 2.37 2.23 xel36;xel30 l. 95 ± 0. 01 l. 95 l. 99 l. 81 xel30 1.17 x 10-ll cc STPI gm 1.17 x 10-ll cc STPI gm l. 62 x 10-1 per 106 atoms Si
VJ -..j Table II
Concentration and Isotopic Composition of Krypton and Xenon in the Tell Chondrite
Extraction Temperature Solar Gas Noble Gas 600° 900° Melt
Kr801Kr84 o. 0384 ± o. 0004 o. 0400 ± 0. 0009 o. 0452 ± o. 0006 o. 0427
Kr821Kr84 o. 1 99 ± o. 001 o. 202 ± o. 002 o. 204 ± o. 001 0.2065
Kr83 1Kr84 o. 199 ± o. 001 o. 200 ± o. 002 o. 205 ± o. 001 0.2055
Kr861Kr84 0. 306 ± o. 001 o. 306 ± o. 002 o. 307 ± o. 001 0.297
Kr84 x lQ-10 cc STPigm 0.80 0.35 0.33
xe124 I xel3 o o. 0242 ± o. 0004 o. 0229 ± o. 0006 o. 0292 ± o. 0003 0.0299
Xe126 1Xel30 o. 0227 ± o. 0004 0. 0236 ± o. 0005 o. 0275 ± o. 0004 0.0288
xe128 1xel3 0 0.477±0.004 0.473 ± o. 006 o. 509 ± o. 005 o. 512
Xe129 1Xel30 6. 50± o. 06 6. 62 ± o. 04 7. 68 ± 0. 07 6.38
xe1311xel30 5.19±0.04 5.21±0.04 5. 03 ± 0. 03 5.00
xel32;xel30 6. 57 ± o. 05 6. 62 ± o. 03 6.16 ± 0. 03 6.05
xel34 I xel3 o 2. 53 ± o. 01 2.57 ± 0.01 2. 38 ± o. 02 2.23
xel36 I xel3° 2. 16 ± o. 01 2.19 ± o. 02 2. 00 ± o. 02 l. 81
Xel30 x 10-12 cc STPigm 5.3 1.2 7.8
I.JV 00 Table III
Concentration and Isotopic Composition of Krypton and Xenon in the Scurry Chondrites
Extraction Temperature Noble Gas Solar Gas 600° 900° Melt
Kr801Kr84 0. 0396 ± o. 0005 0. 0397 ± o. 0003 o. 0420 ± o. 0003 0,0427
Kr82/Kr84 o. 20 l ± o. 001 0.198 ± o. 001 0. 204 ± o. 001 0.2065
Kr83 1Kr84 o. zoo ± 0. 002 0.198 ± 0. 001 o. 204 ± o. 001 0.2055
Kr861Kr84 o. 306 ± o. 001 0. 306 ± o. 001 o. 306 ± 0. 001 0.297
Kr84 x 10-lO sec STP I gm 0.48 o. 79 Zd! xel241xe130 0. 0256 ± o. 0005 o. 0244 ± 0. 0002 o. 0251 ± 0. 0002 o. 0299 xel26 1 xeBO o. 0226 ± o. 0005 o. 0234 ± 0. 0004 o. 0242 ± 0. 0003 0.0288 xel281xel30 o. 4 79 ± o. 003 o. 488 ± 0. 003 0. 493 ± 0. 004 0. 512
Xe129 1Xel30 6. 58 ± 0. 04 6. 69 ± 0. 03 6. 69 ± 0. 03 6.38 xe1311 xeB O 5.17 ± 0. 04 5.19±0.03 5. 11 ± o. 02 5.00
Xel3 2 I xeB 0 6. 53 ± o. 05 6. 59 ± 0. 05 6. 40 ± o. 02 6.05 xe134 I Xel3 0 2. 51 ± 0. 01 2. 55 ± 0. 02 2. 46 ± o. 01 2.23 xe136;xel30 2.14 ± 0.01 2. 14 ± o. 01 2.07 ± 0.01 1. 81
Xel30 x 10-12 cc STP/ gm 2.4 3.6 7.6
VJ "-'! 40
BIBLIOGRAPHY
Alexander, E. C. Jr., J. H. Bennett and 0. K. Manuel (1968) On noble gas anomalies in Great Namaqualand troilite. Z. Natur forsch. 23a, 1266-1271.
Anders, E. (1962) Meteorite ages. Rev. Mod. Phys. 34, 287-325.
Anders, E. and D. Heymann (1969) Elements 112 to 119: Were they present in meteorites? Science 164, 821-823.
Anders, E., D. Heymann and E. Mazor (1970) Isotopic composition of primordial helium in carbonaceous chondrites. Geochim. Cos mochim. Acta 34, 127-131.
Arrol, W. J., R. B. Jacobi and F. A. Paneth (1942) Meteorites and the age of the solar system. Nature 149, 235-238.
Aston, F. W. (1913) Results of a diffusion experiment. In: Isotopes, Chap. 4, pp. 39-41, Edward Arnold and Co., London.
Black, D. C. (1969) Isotopic variations in trapped meteoritic argon. Meteoritics 4, 260.
Black, D. C. and R. 0. Pepin (1969) Trapped neon in meteorites -II. Earth Planet. Sci. Letters 6, 395-405.
Black, D. C. (1970) Trapped heliun1-neon isotoiJiC correlations in gas rich rneteorites and carbonaceous chondrites. Geochin1. Cos mochim. Acta 34, 132-140.
Brown, H. (1949) Rare gases and the formation of the earth's atn1os phere. In: The Atmosphere of the Earth and Planets, editor G. P. Kupier, Chap. 4, pp. 258-266, University of Chicago Press, Chicago.
Canalas, R. A. (1967) Noble gases in the earth and its atmosphere. Masters Thesis, University of Missouri at Rolla.
Canalas, R. A., E. C. Alexander, Jr. and 0. K. Manuel (1968) Ter restrial abundance of noble gases. J. Gl·ophys. Res. 73, 3 3 3]- _) _$.34.
Clarke, W. B. and H. G. Thode (1961) Xenon in the Bruderheirn lnete o rite. J • G eo ph y s . Res . 6 6, 3 57 8- 3 57 9. 41
Eberhardt, P .• 0. Eugster and K. Marti (1965) A redetermination of the isotopic composition of atmospheric neon. Z. Naturforsch. 20a, 623-624.
Eberhardt, P .• J. Geiss, H. Grof, N. Grogler, U. Krahenbuhl, H. Schwaller, J. Schwarzmuller and A. Stettler (1970) Trapped solar wind noble gases, exposure age and K/ A r-age in Apollo 11 lunar fine material. Geochim. Cosmochim. Acta 34, Suppl. l, 1037-1070.
Eugster, 0., P. Eberhardt and J. Geiss (1967) Krypton and xenon isotopic composition in three carbonaceous chondrites. Earth Planet. Sci. Letters 3, 249-25 7.
Fireman, E. L. and D. Schwarzer (195 7) Measurements of Li 6, He3 and He3 in meteorites and its relation to cosmic radiation. Geo chim. Cosmochim. Acta 11, 252-262.
Funkhouser, J. G., 0. A. Schaeffer, D. D. Bogard and J. Zahringer (1971) Noble gases in lunar material 1. Solar wind implanted gases in Mare Tranquillitatis and Ocean Proce11arum. Preprint, NASA Manned Spacecraft Center, Houston, Texas.
Gerling, E. and T. Pav lova (1951) Determination of the geological age of two stony meteorites by the argon method. Dokl. Akad. Nauk. S.S.S.R. 77, 85-86.
Goel, P. S. (1962) Cosmogenic Cl36 in iron meteorites, Carnegie Inst. Tech. Frog. Report.
Kuroda, P. K. (1960) Nuclear fission m the early history of the earth. Nature 187, 36-38.
Kuroda, P. K. and 0. K. Manuel (1970) Mass fractionation and iso tope anomalies in neon and xenon. Nature 227, 1113-1116.
Kuroda, P. K. (1971) Temperature of the sun in the early history of the solar system. Nature 230, in press.
Manuel, 0. K. and M. W. Rowe (1964) Noble gases 1n the Bruderheiin chondrite. Geochim. Cosmochim. Acta 28. 1999-2003.
Manuel, 0. K. (1967) Noble gases in the Fayetteville meteorite. Geo chim. Cosrnochim. Acta 31, 2413-2431.
Manut.d, 0. K. (1970) Isotopic anomalies of noble gases from frac tionation. Meteoritics 5, 207-208. 42
Manuel, 0. K., R. J. Wright, D. K. Miller and P. K. Kuroda (1970) Heavy noble gases in Leoville: The case for mass fractionated xenon in carbonaceous chondrites. J. Geophys. Res. 22_, 5693-5 700.
Manuel, 0. K., D. K. Miller, R. J. Wright and P. K. Kuroda (1971) Solar type krypton. Pre print, University of Arkansas, Fayetteville.
Marti, K., P. Eberhardt and J. Geiss (1966) Spallation, fission and neutron capture anomalies in meteoritic krypton and xenon. z. Naturforsch. 21a, 398-413.
Marti, K. (1967) Isotopic composition of trapped krypton and xenon in chondrites. Earth Planet. Sci. Letters 3, 243-248.
Marti, K., G. W. Laugmair and H. C. Urey (1970) Solar wind gases, cosmic-ray spallation products, and the irradiation history. Science 167, 548-550.
Mazor, E., D. Heymann and E. Anders (1970) Noble gases in carbon aceous chondrites. Geochim. Co::;mochim. -----Acta 34, 781-824. Nascimento, I. C., G. Moscati and J. Goldenberg (1961) Systematics of (l', Zn) reactions. Nuclear Physics 22, 484-491.
Nief, G. (1960) (as reported in isotopic abundance ratios given for re ference samples stocked by the National Bureau of Standards). NBS Tech. -----Note 51, editor F. Mohler. Nier, A. 0. (1950a) A redetermination of the relative abundances of the isotopes of carbon, nitrogen, oxygen, argon and potassium. Phys. Res. 7.]_, 789-793.
Nier, A. 0. (1950b) A redetermination of the relative abundances of the isotopes of neon, krypton, rubidium, xenon and mercury. Phys. Rev. '!..J_, 450-454.
Paneth, F . .A., R. Reasbeck and K. I. Mayne (1952) Helium-3 content and age of meteorites. Geochim. Cosmochim. Acta~· 300-303.
Pepin,R. 0. (1967) Trapped neon in meteorites. Earth Planet. Sci. Letters 2, 13-18. 43
Pepin, R. 0. (1968) Neon and xenon in carbonaceous chondrites. In: Origin and Distribution of the Elements, editor L. H. Ahrens, 379-386, Pergamon, London.
Reasbeck, P. and K. I. Mayne (1955) Cosmic radiation effects in mete orites. Nature 176, 733-734.
Reynolds, J. H. {1956) High sensitivity mass spectrometer for noble gas analysis. Rev. Sci. Instr. !:2_, 928-934.
Reynolds, J. H. {l960a) Determination of the age of the elements. Phys. Rev. Letters 4, 8-10.
Reynolds, J. H. {1960b) Isotopic composition of primordial xenon. Phys. Rev. Letters 4, 351-354.
Rowe, M. W., D. D. Bogard, C. E. Brothers and P. K. Kuroda {1965) Cosmic -ray-produced xenon in meteorites. Phys. Rev. Letters 15, 843-845.
Rowe, M. W. (1968) On the origin of excess heavy xenon in primitive chondrites. Geochim. Cosmochin1. -----Acta 32, 1317-1326. Signer, P. and H. E. Suess (1963) Rare gases in the sun, in the atn1os phere and in meteorites. In: Earth Science and Meteoritics, editors J. Geiss and E. D. Goldberg, Chap. 13, pp. 241-272, North Holland, Amsterdam.
Srinivasan, B., E. C. Alexander, Jr., 0. K. Manuel and D. E. Troutner {1969) Xenon and krypton from the spontaneous fission of Californium-252. Phys. Rev. 179, 1166-1169.
Srinivasan, B. and 0. K. Manuel (1970) On the isotopic composition of trapped helium and neon in carbonaceous chondrites. Pre print, University of Missouri-Rolla.
Stoenner, R. W. and J. Zahringer (1958) Potassium-argon age of uon meteorites. Geochim. Cusmochim. Acta 15, 40-50.
Suess, H. E. (1948) On the radioactivity of K 40• Phys. Rev. 73, 1209.
Suess, H. E. {1949) Die Haufigkeit der Edelgase auf dere ErdL• und im Kosmos. -J. ---Geol. --57, 600-607. Suess, H. E. and H. C. Urey {1956) Abudances of the elements. Rev. ~ Phys. 28, 53-74. 44
Strutt, R. J. (190Ba) Note on the association of helium and thorium in minerals. Proc. Roy. Soc. London ABO, 56-57.
Strutt, R. J. (190Bb) Helium and radioactivity in minerals. Proc. Roy. Soc. London ABO, 572-594.
Strutt, R. J. (1909) The accumulation of helium in geological time. Proc. Roy. ~· London ABl, 272-277.
Verniani, F. (1966) The total mass of the earth's atmosphere. J. Geophys. Res • .z.!., 3B5 -391.
Weizsacker, C. F. (193 7) Uber die Moglichkeit eines dualen Beta Zerfalls of Kaluim. Phys. ~- 3B, 623-624. 45
VITA
Edward William Hennecke was born on September 28, 1945 in
Cape Girardeau, Missouri. He received his primary and secondary
education in Jackson, Missouri. He attended the University of Mis
souri at Rolla, Missouri where he obtained his B.S. in chemistry in
January 1968.
He has been enrolled in the Graduate School of the University of
Missouri-Rolla since September 1968. He had held teaching assistant ships continuously from September 1968 to January 1971 and received a research assistantship from the National Science Foundation, NSF-GA-
16618 in January 1971.