JOURNAL OF GEOPHYSICAL
RESEARCH, VOL. 96, NO. A11, PAGES 19,321-19,330, NOVEMBER
1, 1991
Compositionof Solar Flare Noble GasesPreservedin MeteoriteParentBody Regolith
M. N. RAO• D. H. GARRISON?
D. D. BOOARD
G. BADHWAR,
ANDA. V. MURALI
3
NASA JohnsonSpaceCenter, Houston,Texas
The isotopiccomposition(long-termaverage)of solar flare (SF) Ne has been determinedby three
isotope
correlation
techniques
applied
to datameasured
onchemically
etched
pyroxene
separates
•repared
fromtheKapoeta
meteorite,
whichis known
to contain
implanted
solargases.TheSF 2øNe/2"Ne
ratio
obtainedis 11.6+ 0.2 and confinns previousdeterminations
of this SF ratio in lunar and meteoritic
samples.The sameSF Ne composition
is alsoobtainedby applyingan ordinateintercepttechniqueto the
samedataset. The ordinateintercepttechnique
wasalsoappliedto theAr and He data,on whichthe threeisotopecorrelation
technique
cannotbe applied.The isotopiccomposition
of SF Ar andSF He so obtained
areSF36Ar/•Ar=4.9
+0.1andSF4He/3He
=3800_+200,whicharesignificantly
different
fromthesolar
wind(SW)ArandSWHevalues
of-5.35and-2500,re.spectively.
Correlation
between
2øNe/22Ne
and
36Ar/38Ar
forthesame
datasetalsogivesa similar
SF 36Ar/XAr
ratioof 4.8+ 0.2. Thedetermined
SF He,
NeandAr isotopicratiosdiffer from thosein SW by 52%, 17% and 9%, respectively,but the elemental
compositions
of 4Hed36Ar
and2øNe/36Ar
do notshowobvious
differences
between
SF andSW. The
concentration
of the SF component
in Kapoetapyroxenesis -20% that of the SW component,which is
ordersof magnitudehigher than expectedfrom SW and SF protonflux measurements.Variationsin
elementalandisotopiccomposition
of He, Ne andAr in SF relativeto SW arefoundto correlatewell with a
(Z/A)2 dependence,
indicating
a rigidity-dependent
particle
spectrum
in solarflares.
INTRODUCEION
meteoritesKapoeta and Fayetteville using stepwiseheating
methods
have better definedthe SF 2øNe•2Nevalue to be in the
Information about the composition of charged particle
emissionsfrom the ancientSun can be obtainedfrom analysis range of 11.3 to 11.6 for both the ancientSun and the recent
of helium, neon and argonimplantedinto fine-grainedregolith Sun [Venkatesanet al., 1981; Nautiyal et al., 1981, 1986;
(or soils) of small planetary bodies such as the Moon and Wider et al., 1983, 1986; Padia and Rao, 1989]. However, it
meteorite parent objects. Surface-implantednoble gases in hasnot beenclear whetheronly Ne showsisotopicdifferences
silicategrainsfrom theseregolithsare a mixture of low-energy between$W and $F composition,or if similar and possibly
existin He andAr isotopes
aswell.
solarwind (SW) and solarenergeticparticles,or solarflare (SF) relatedisotopicdifferences
Complete analytical decompositionof a four-component
gases,which reside in the outer micrometer and outer tens of
and cosmogenic
micrometers,respectively,of individualgrainsand are referred systemof implantedSW and SF components
to as implantedor surface-correlated
components.Noble gases GCR and SCR componentsthrough stepwisesampleheating
producedby in situ spallationreactionsfrom galactic cosmic aloneis not possiblewith the Ne, Ar and He isotopicsystems.
rays (GCR) and solar cosmicrays (SCR) residethroughoutthe However, chemical etching of the surfaces of grain-size
interior of grains in abundancesgoverned by the exposure separatesof selected minerals, using techniquesdeveloped
history, mineral-dependentproduction rates, and shielding earlier for lunar soils [Rao et al., 1979;Nautiyal et al., 1981],
SW gases(mostlypresentin
conditionsof the grains and are referredto as cosmogenicor can removethe surface-correlated
volume-correlatedcomponents. Meteorites such as Kapoeta, the outer micrometer of grains), thereby permitting
relatively rich in such solar gases, are ideally suited for decompositionof the SF, GCR and SCR componentsin the
mineral
residues.
studyingthe preservedrecord of the isotopic abundancesof
We have made mass spectrometricanalysesof noble gas
solar noble gas componentsfrom the early solar system,
whereasstudiesof grains from lunar soils and rocks usually componentsin acid-etchedpyroxene mineral separatesfrom
Kapoeta, a brecciatedmeteorite consistingof both light and
characterize more recent SW and SF irradiations.
Therecentsolarwindis represented
by a 2øNe/22Ne
ratioof dark phases. The light phasehas been shieldedfrom relatively
13.6 + 0.1 [Geiss et al., 1972], as measuredon the Moon. A low energySW and SF particleirradiation,with its noblegases
different Ne isotopic component (called Ne-C) having a being predominantly spallation products from deeply
2øNe/22Ne
ratio of 10.6 was first identifiedby Black [1972] penetratingGCR. The dark phaseconsistsof SW- and SF-
grainswhichcontainthevestigialrecordof ancient
from stepwiseheatingof bulk samplesof gas-richmeteorites irradiated
SW
and
SF
implantedions,aswell asGCR and$CR spallation.
and was attributedto SF Ne implantation. Further detailed
measurements
of Ne in lunar soilsandrocksand in the gas-rich Using three-isotopecorrelationsand•ordinateintercept
techniques,
we confirmpreviousresultsof otherlaboratories
thattheisotopic
composition
of SFNe is different
fromthat
1Also
atPhysical
Research
Labaratory,
Ahmedabad,
India.
in SW. Themajorpurpose
of thepresent
study,
however,
2Alsoat Lockheed
Engineering
& Sciences
Company,
Houston, found
Texas.
3AlsoatLunarandPlanetary
Institute,
Houston,
Texas.
is to extendthe techniques
usedto determine
the SF Ne
composition
to determine
the SF Ar andSF He isotopic
Paper number91JA01948.
compositions[Rao et al., 1990]. Additionally, we discussa
rigidity-dependentsolar flare particle spectrumas a possible
explanationfor the observedisotopic and elementalSF SW
0148-0227/91/91JA-01948505.00
correlations.
Copyright1991by the AmericanGeophysical
Union.
19,321
19,322
RAO ET AL.: SOLARFLARENOBLEGASES
EXPERIMENTAL METHODS
Sampleswere taken from a large piece of Kapoetawherethe
contact surface between light and dark portions was clearly
distinguishable.The light sample(gas-poor)was takenfrom a
clearwhite portion,while the dark sample(gas-rich)was taken
from a portion which appeareduniformly grey. Extra dark
grainsfound in the dark matrix were removedby hand-picking
undera microscope.The light anddark sampleswere separately
disaggregated by gentle crushing followed by mild
ultasonication of remaining large aggregates. Mineral
fractionsenrichedin pyroxeneand feldsparwere then prepared
by repeatedheavy liquid separationfollowed by dry-sieving
into 10-35 !.tm, 35-125 !.tm and 125-200 !.tm grain-size
fractionsusing nylon sieves. Using energy dispersiveX-ray
measurementson a scanningelectronmicroprobe,purity was
determinedfor pyroxene separatesto be 98% for the 125-200
I.tm size fractionand 93% to 96% for both 10-35 I.tm and 35125 I.tm size fractions.
The minor elemental composition was determined in
aliquants of Kapoeta pyroxenes and feldspars by neutron
activationanalysis,and the major elementalcompositionwas
determined by microprobe measurements (by alternately
scanningsamplesand standardsunder similar conditions). For
the pyroxenes, we have found the following average
compositions(over different size fractions):SiO2= 51.89%;
A1203= 0.18%; MgO = 19.69%; CaO = 1.75%; FeO = 24.36%;
MnO = 0.81%; Ba = 36 ppm. The averagecompositions
from
feldsparsize fractionsare SiO2= 45.02%; A1203= 35.39%;
MgO = 0.4%; CaO = 18.6%;FeO = 0.52%;Ba = 68 ppm;U = 52
ppm;La = 1.52 ppm. Uncertainties
in thesedeterminations
are
8 to 10%.
To remove the SW gasesfrom the surfaceof the silicate
grains, aliquants of these mineral separateswere selectively
etchedby stirring an acid mixture of HF+H2SO,•+H20 (1:1:4)
underan infraredlamp for 30 to 60 s for the light etchandabout
2 to 2.5 min for the heavy etch. The chemicalreactionis
suddenlyfrozen after the stipulatedperiod by heavily diluting
the mixture with ultrapurewater. The etchedpyroxeneresidue
is then washed in ethyl alcohol and dried. This procedure
resultedin lightly etched(LE) andheavily etched(HE) samples
for each pyroxene size fraction. Two chemical etching
procedures
were considered,weak acid/longexposureor strong
acid/shortexposure. Long exposureis likely to enhancethe
effects of acid creeping into the crevices of the pyroxene
grains,dissolvingdeeperlayers and increasingthe amountof
etchant.This effect results in distortionof the etchingdepth
from the sieved fractions, while generally irregular in shape,
were determined by estimating the approximatesizes of
nonaggregate
grainsundera microscope
(about200 grainsper
sample)[Eberhardtet al., 1965;Rao et al., 1979]. The average
grainsizesare then--62 !.tmfor the 35-125 !.tmsize fractions
and~146 grn for the 125-200!.tinsize fractions.The thickness
of the surfacelayer removed from the pyroxenegrains was
estimated
usingthe amountof Fe, Si, andMg determined
in the
acidleachsolutionby atomicabsorption
spectrometry
(AAS)
usingstandard
procedures,
andthedetermined
average
chemical
composition
of pyroxenes. For the LE 35-125 !.tmand LE
125-200 I.tm size fractions,the weight loss of the original
samples
was~8%. For theHE 35-125I.tm and125-200!.tmsize
fractions,
the weightlosswas~25% and20%, respectively.In
the caseof the 10-35!.tmfraction,the weightlosswasfoundto
be ~25%. For purposesof calculation,we assumedthat the
grainshapesare approximately
sphericalandthe materialwas
removeduniformly from the surface. The averageetching
depthsthusdetermined
by procedures
givenby Eberhardtet al.
[1965] and Rao et al. [1979] for both pyroxenesize fractions
are 1-2 I.tm for thelightly etchedsamplesand8-10 I.tm for the
heavily etchedsamples. These representaverageetching
depthsand may vary amongindividualgrainsdependingon
graingeometryandetchingalongstructural
defects.Finally,
basedon the range-energyrelationshipgiven by Lal [1972]
and using the determined average etching depths, the upper
limit for the kinetic energyper nucleonof the implantedsolar
flare particleswas estimatedfor each sample. Lightly etched
sampleswith 1-2 !.tm removed containSF particlesof energy
>0.4 MeV/amu (plus cosmogenicgases). Heavily etched
sampleswith 8-10 !.tmremovedcontain SF particlesof energy
>1.2 MeV/amu (plus cosmogenicgases). The uncertaintyin
individual grain etching depths of 1-2 I.tm correspondsto
variationsin energyof 0.1-0.2 MeV/amu.
The noble gas compositionof the unetched(UE) samples
from eachsize fractionis dominatedby solarwind gaseswith
moderatecontributionsfrom SF and cosmogenicgases. While
not treatedwith acid, these sampleshave probably lost some
amount of surface material as a result of sample handling,
crushing,ultrasonictreatmentand mineral separationsusing
corrosivebromoformand acetyl bromide. The material lost is
estimatedto correspondto SF particleswith energy<0.005
MeV/amu.
Noble gas analyseswere made with a 6"-60ø sectormass
spectrometerequipped with a Nier source and an electron
multiplier. Gas extractionof ~100-mg sampleswas made by
radio frequencyinductionheatingin a low blank, differentially
information
derived from mass balance.
To minimize
this
pumped,Ta-tube furnace. Standarc'Zr/A1 gettersand charcoal
effect, we have adopted the strong acid/short exposure fingers were used for gas clean-up and noble gas separation.
approach. This permits the attack of the grain surfacesby Noble gas isotopicmeasurements
were then made by standard
strongacid for a shortperiodof time at an elevatedtemperature massspectrometrictechniquesin three temperatureextractions
(60øC)to etchaway the requiredamountof the surfacematerial. of 600øC, 1200øC and 1600øC. All data were corrected for
The HF + H2SOn+ H20 mixture chosenis commonlyused for blanksandmassdiscrimination.Typical 1600ø blanksfor the
etching of pyroxenes [Crozaz et al., 1970]. The pyroxene systemare 3He, 0.2; 4He, 160;2øNe,0.25;4øAt,7.5 (x10'lø
etching by HF + H2SO,• mixture is different from that by cm3STP).
concentrated HNO3 [Wieler et al., 1986]. The etching of
pyroxene grains by HNO3 seemsto take place along some
SOLARFLARENEON,ARGON,
AND HELIUM ISOTOPIC COMPOSITIONS
crystalplaneswhile otherplanesseemto remainunattackedby
the etchant[Haack, 1972]. Similar inferenceswere made earlier
Solar Flare Neon
in the case of olivine etching by HNO3 (D. Lal, private
communication,1989). The use of HF + H2SOnseemsto result
In this investigation we first show that three-isotope
in a relativelyuniformchemicalattackof pyroxenes.
correlationplots and the ordinate intercept technique,when
The averagegrain sizesof the individualpyroxenegrains appliedto stepwise-released
Ne data from etchedpyroxenesize
RAO ET AL.' SOLARFLARENOBLEGASES
19,323
16
14
I
SW
12• Lunar
12
lO
z
[]
6000
A
12000
o
1600C
0.0
SCR
2
2.O1
GCR lOO
0.0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
21Ne / 22Ne
Fig.1. Three-isotope
correlation
plotforNe fromstepwise
heating
of etched
grainsizeseparates
of Kapoeta
pyroxene.SW,
solarwindcomposition
experiment
[Geisset al., 1972]'Lunar, typicallunarfines;Air, terrestrial
atmosphere;
C.Ch,
carbonaceous
chondrites
(meteorites);
GCR, produced
by galactic
cosmic
rayspaRation;
SCR, produced
by solarcosmicray
reacttons.
CompOSitional
Nechanges
duetoshielding
variations
of0-100
gcm
'2and0-2g'cm-2
were
calculated
from
Hohenberg
et al. [1978] and are shownfor the GCR and SCR components,
respectively.The GCR value plotted
(2øNe/22Ne=0.92,
21Ne/22Ne=0.86)
represents
-15gcm
'2shielding
determined
from
track
data
calculations
ofpreatmospheric
radiiby Bhandari
etal. [1980]. The Kapoeta
datadefinea lineartrendproduced
by mixingof two components.
SF Ne is
represented
bytheintersection
of thetwotrendlines.Theinsertshows
thepossibility
of upto 2%residual
STMin the 600øC
extractions.Uncertainties
in isotopicratiosare within the symbols.
likelytocontain
residual
SW,yields
a SF2øNe/22Ne
ratioof
separates,yield similar and expectedcompositionsfor the less
surface-correlatedSF Ne component. We then apply the 11.5q-0.2. This SF valueof 11.5 wouldallow for up to 2% SW
ordinateintercept techniqueto He and Ar to determinethe to remain in the 600øC releases. Either value is consistent with
surface-correlated
SF Ar and SF He composition. Until now, previousdeterminationsof 11.3 to 11.6 for the SF Ne
three-isotope
correlationdiagrams(e.g., 2øNe/22Neversus compositionof both the ancientSun and the contemporarySun
21Ne/22Ne)
havebeen
theonlymethod
used
todetermine
thesF [Venkatesanet al., 1981;Nautiyal et al., 1981,1986;Wieler et
Ne isotopiccompositionin irradiated samples. In a three- al., 1983, 1986],indicating
thatthe long-termaverageSF Ne
isotope'plot for a systemconsistingof two distinct composition
hasnot changed
appreciably
overthe last4,5
component
in Kapoetapyroxene
is
components,generally surface-correlatedand volume- Gyr. The cosmogenic
consistent
with
either
SCR
Ne
produced
at
an
average
depth
of
correlated,
thedatafromdifferent
temperature
releases
lie on•
at an averageshieldingdepth
straight line joining the two end members. The relative ~0.3 gcm-2,or GCR Ne produced
proportionof these componentsin a given gas fraction of ~15 gcm'2 (Figure1).
An equivalent SF Ne composition is found using the
determines where along the line the data point falls.
Extrapolation
of the data alongthe mixing line until it crosses ordinateintercepttechniqueapplied to the samepyroxeneNe
theSW-air-planetary
mixinglinethendetermines
thesurface-databy plotting2øNe/22Ne
versus
thereciprocal
of the22Ne
concentration(Figure 2a). The ordinate intercept technique
correlatedcomponentcomposition.
Our Ne isotopicdatafrom step-wisetemperature
extractions [Eberhardt et al., 1970] has been widely applied to lunar
to determine
the isotopiccomposition
of
(600ø, 1200ø,and1600øC)of etchedpyroxeneseparates
of the regolithmaterials
10-35•tm, 35-125 •tm and 125-200•tm grain-sizefractionsfor two mixed gas components,a surface-co,elated(imp!anteed
anda volume-col'related
(cosmic
bothdarkandlight Kapoetaphasesareplo,ttedin Figure1. The solarwindor flare)component
component.
For a suiteof grainsizes,a plotof
pronounced
lineartrenddefinedby theNe data(R2=0.991) rayproduced)
of
indicates
mixingof a SF component
alongtheupperleft of this an isotopicratio versusthe reciprocalof the concentration
line and a cosmogenic
componentat the lower right. an elementdominatedby the variable (surface)component
results
in a lineartrend.Theintercept
of thistrend
Extrapolation
of thislineartrendintersects
the SW-lunar-air
tie generally
to infiniteconcentration
of thesurface-correlated
line at 2øNe/22Ne= 11.6 q- 0.2 and 2aNe/22Ne= 0.030 q- 0.001 extrapolated
definesthe isotopicratiø of that surface
andder'roes
theSFNe composition.
TheFigure1 insertshows component
that at low-temperatureextractionsthere is a very slight component.Sampleswith differentdegreesof etchh•goughtto
to the ordinateintercepttechnique,
because
like
deviationof the 600øCdatafrom the mixing line, possiblydue be amenable
to thepresence
of verysmallamounts
of SW Ne. A best-fitline samples of different grain sizes, etched samples vary in
of the surface-correlated
gasper unit volumeof
through
onlythe 1200øCand1600øCdatapoints,whichare concentration
19,324
RAo ETAL.' SOLAR
FLARENOBLEGASES
14
0.8
(a)
0.6
ß
10
z
•.
8
z
c•
TEMP.
6
r•
600
0.2
.46
1600
r•
600
0.036
/•
1200
0.030
o
'1600
-
ß SUM
ß SUM
.52
I
2
TEMP, 21/22
.71
A 1200
o
....
20/22
0
0.027
.
I
I
I
I
0.2
0.3
0.4
0.5
0
0
0.6
I
I
I
I
I
0.1
0.2
0.3
0.4
0.5
-8
0.6
1 / [22Nex 10'sccSTP/g]
/ [22Ne x 10 ccSTP/g]
5.5
4,000
(c)
5.0
i
i-i
(d)
i
TEMP.
[] 600
/• 1200
ß SUM
3,000
4.5
TEMP. 36/38
•
600
• 1200
o 1600
ß SUM
SW
2.5
2.0
0
-• 2,000
4.82
..!-
5.06
4.87
4.94
5.35
i
i
I
i
2
4
6
8
4/3
3770
--3990
1,000
0
10
I
0
5
10
15
,
I
,
20
I
,
25
3O
1/ [3He
x10'SccSTP/g]
1 / [38Arx 10'eccSTP/g]
Fig.2. Ordinate
intercept
plotsfor(a)2øNe/22Ne,
(b)21Ne/22Ne,
(c)•Ar/38Ar,
and(d)4He/3He.
Dataarefrom600øC,
1200øC,
and1600øCtemperature
extractions
of five etchedKapoeta
pyroxenes
(threegrain-size
separates
andtwodegrees
of etching).
Wholedata,reconstructed
fromthe sumof the temperature
data,are alsoshown(twodatapointsoverlapin someplots).
Uncertainties
are contained
withinthe symbols,exceptwhereindicatedfor a few concentrations.
the samplebut not in the concentration
of volume-correlatedextrapolation. Since bulk analysesof grain-sizeseparates
gas. Additionally,increasingtemperatureextractionsare ratherthanstepwise
temperature
releases
are thepreferreddata
datafor all
expectedto preferentiallyreleasesurface-correlated
gas first to usewith theordinateinterceptplot,thecombined
and volume correlated gas later. The 600øC and 1200øC extractions
of eachetchedpyroxenegrain-sizeseparateare also
extractions (each as a data subset) release predominantly
surface-correlatedgas. To the extent that both of these
extractionsof individualsamplesshowa spreadon the ordinate
intercept plot because of variations among samples in
concentrationof surface-correlatedgas (and not becauseof
variations in relative proportions released of surface- and
volume-correlated gas), these temperature data sets
independentlyqualify for the ordinateintercepttechnique. The
distributionof Ne data for each temperatureextractionthen
indicatesa mixture of surface-correlated(solar) and volumecorrelated(cosmogenic)components.
The 600øCextractionsall havemeasured2øNe/22Nelessthan
or equal to 11.7, much lower than the SW value of 13.6.
plottedin Figure2a. Thesedatadefinea line (R2= 0.943)
whichyieldsan intercept
valueof 11.52for the2øNe/22Ne
SF
composition.An analogousplot, shownin Figure 2b, of
2XNe/22Ne
versus1/[22]is wellbehaved
andyields2XNe/22Ne
SF
TABLE 1. KapoetaPyroxene
SolarFlare(SF)Isotopic
Compositions
Determined
by the OrdinateIntercept(OI) Three-Isotope
Correlation,
andTwo-ElementCorrelationTechniques
Method
4Hed3Fe 2øNed22Ne21Ned221•
3990+100
3770+200
11.52+0.1
11.71+0.1
11.46+0.2
0.027+.001
0.036+.003
0.030+0.002
component,
yieldsa 2øNe/22Ne
valueof 11.7. The 1200øC Three-isotope
3150+150
temperature
data(R2 =0.921)definean intercept
valueof 11.46. Two-element
11.60+0.1
0.030+0.001
Furthermore,they define a line (R2=
extrapolatedto infinite concentration
of
OI; 600øC
0.969) which, when OI; 1200ø C
the surface-correlatedOI; 1600øC
Both of these values are within errors of the SF 2øNe/22Ne
composition
of 11.6 + 0.2 determined
by the three-isotope
Ne
correlation
technique
usingall of thedata.The 1600øCdataare
36Ar/38Ar
4.94+.1
4.82+.2
5.06+0.2
4.87+.2
SF value a
3800__+200 11.6+0.2
0.030+0.001
4.80+.2
4.90+0.1
SW value•'
2500+100
0.029+0.001
5.35+0.02
13.6+0.2
a AverageSF valueobtainedfrom all methods.
SW valuesfrom Geisset al. [ 1972]andEberhardt
etal.
dominatedby the volume-correlatedcosmogeniccomponent bMeasured
and have a lever arm too long to permit meaningful [1972].
RAO ET AL.: SOLARFLARENOBLEGASES
values similar to those obtained in the three-isotope
correlationplot. A summaryof SF Ne values obtainedby
differentmethodsis given in Table 1.
19,325
contain small amountsof residual SW. An 3eAr/38Arvalue of
4.9 + 0.1 is obtained by averaging the four independently
derived values, giving greater weight to the more precise
summedtotal data, and is taken to representthe compositionof
the surface-correlated
SF Ar component.
Yet anothermethodfor deducingthe isotopiccomposition
of a surface-correlated component is to utilize elemental
correlationsand determine one surface-correlatedcomposition
knowing the other. Figures 3a and 3b show the correlation
The solar flare 2øNe/22Necompositionwas previously
determinedto be 11.6 :k 0.2 by Nautiyal et al. [1981, 1986] and
Padia and Rao [1989] from stepwisepyrolysisof acid-etched
pyroxeneand plagioclasemineral separatesfrom both lunar
samplesand the Kapoeta and Fayetteville meteorites. A
slightly lower value (though within errors) of 11.3 :k 0.3 was
2øNe/22Ne
and36Ar]38Ar
and4He/3He,
respectively.
In
reportedby Wieler et al. [1986, 1989] for lunar samplesusinga between
closedsystemstepwiseetching (CSSE) technique. The reason such a plot the summeddata def'memixing lines between a
solar component,variable by grain size and
for the small difference in the value determined in Ahmedabad, surface-correlated
India, and in this Kapoeta investigation versus the value degree of etching, and a volume-correlated cosmogenic
determinedby Wider et al. [1986, 1989] is not clear and may component(which in the case of nHe/3He also contains
be analyticalor procedural. Subtle fractionationeffects in SF radiogenic 4He). The intersectionof the SF 2øNe/22Ne
Ne may exist amongsamples,as Wieler et al. [1986] found the compositionwith the trend line definedby the summeddata in
for 36Ar/3SAr
and
2øNe/22Ne
ratio in five plagioclase
samplesfrom Apollo 16 eachfigurei• usedto infertheSFcomposition
in theseSF
soilsto vary from 10.9 + 0.1 to 11.6 + 0.2, with an averageof nHe/•He(seeFigures3a and3b). The uncertainties
compositions
are shownby the width of the shadedbarsand are
assignedfrom a projectionof the uncertaintyin the derivedSF
2øNe/22Neratio onto the correlation of the summeddata. A
direct "straight-line" correlation between Ne and Ar and
especiallybetweenNe and He releasedat specifictemperatures
generallygood agreementon data for solar-derivedgases is not expectedon theseplots becauseof different diffusion
between their CSSE experiment and single-stage i•tching rams of both the solar and cosmogeniccomponentsof the
followedby total samplefusion. It is conceivablethat a small noble gas elements. This is particularlypronouncedin Figure
amount of SW Ne remained in all samples analyzed in
Ahmedabadand in this investigation,but we would not expect
the five of 11.3 + 0.3. A small mineral-dependent
effect may
alsoexistfor the SF Ne composition,as feldsparandpyroxene
are knownto differ in their retentionpropertiesof SW Ne. We
have no reasonto expect different resultsfrom the CSSE and
single-stageetching techniques,as Wieler et al. [1986] found
the amount of SW Ne to remain so constant between lunar and
meteoritic samples and different etching experiments. The
CSSE experimentsof Wieler et al. [1986] releasedsubstantial
quantitiesof SW Ne in the earlieretchingsteps;the specificSF
Ne compositionderived thus subtly dependson the fact that
specificdata representinggreateretchingdepthswere selected
for extrapolation. There is no real evidencein the collective
data of a temporalvariation in the SF Ne composition. It is
established,however,that this energeticsolarNe composition
is quite distinctfrom the solar wind Ne compositionwhich has
a 2øNe/22Ne
ratio of 13.6 + 0.1.
(a)
SF 36Ar/38Ar = 4.8 +- 0.2
f
o
•
ß
',::::::::
3
-
a,•
SolarFlareArgon
With the conclusionthat the isotopic compositionsof SF
Ne and SW Ne are substantiallydifferent, we now examine
whetherany differencesexist in the isotopiccompositionof Ar
li.•:-.-'::.:
Cosmog,
I
•
•
o
o
2
$F
20Ne/22Ne
= 11,6
-20,2iiiiiii!i
•
I
•
I
•
I
, ,"-'",•
,
I
4
6
8
lO
12
14
20Ne / 22Ne
and He in solar flares comparedto solar wind. BecauseAr has
onlytwo isotopes
(masses
36 and38) withpredominantly
4,000
(b)
_
solar contributions(mass40 is dominatedby the decay product
ß
OF 4Ho/3Ho = 3150 + 150
of 4øK), a three-isotope
correlationplot cannotbe usedto
determine the Ar composition.
Having established the
consistency
betweenthe three-isotopecorrelationand ordinate
intercepttechniquesin determiningthe SF Ne composition,we
now apply the ordinateintercepttechniqueto the Ar data from
3,000
ß
:i:i:i:i:i:i:i:i:i:i.•!:!:i:!:i:i:i
::::::::::::::::::::::::::::::::::::::::
::::::::::::::::::::::::::::::::::
'•' 2,000
...................
....................
/•
the sameetchedpyroxenegrain-sizefractionswith a view to
deducingthe surface-correlated
SF Ar composition(see Figure
2c). Best-fit lines throughtemperaturedata setsof 1200øC,
1600øCandthesummed
totaldata(R2= 0.993)yield36Ar/38Ar
-:.:-:-:.:-:.:.:.:.:.:-:.:.:-:-:.:-:.:.
....................
:::::::::::::::::::::::::::::::::::::::
1,000 --
/•
•
0
9
I
,
I
':':':':"::':':':':':':':':':':':':':'
SF 20Ne/22Ne = 11.6 + 0.2
•
I
•
I - , :::::¾:::::::::::::::::::::::::::
10.5
11
11.5
12
intercept values of 5.06, 4.87 and 4.94, respectively. Data
20Ne / 22Ne
obtainedin the 600øC extractionsfit to a line with essentially
zero slope. This indicatesthat variable concentrations
of the
36
38
Two-element,isotopecorrelationplotsfor (a) Ar/ Ar versus
SF componentwere released in the 600øC extraction with Fig. 3.
22
4
3
22
2øNedNe and(b) He/ He versus2øNe/Ne. Stepwise
temperature
virtually no cosmogeniccomponentreleased. An averageof extractions(open symbols)of five etched Kapoetapyroxenesand
the 600øCdata yields a SF value of 36Ar/3SAr= 4.82. As
mentionedfor the 600øCNe, theseextractionsmay or may not
9.5
/X
10
whole sampledata (solid symbols)reconstructed
from the sumof the
temperature
dataareplotted.
19,326
lL•o ET AL.: SOLARFLARENOBLEGASES
3b, Wheresignificant
amounts
of nonsolar
He wasreleased
in
Figure3b is a two-element,
isotoperatioplot of '•He/3He
the 600øCextraction,
andall He wastotallyextracted
by versus
2øNe/e2Ne
similarto the36Ar/38Ar
versus
2øNe/eZNe
plot.
1200øC.
Intersectionof the SF 2øNe/22Nefield of 11.6 + 0.2 with the
TheSFComposition
of2øNeffZNe
= 11.6+ 0.2intersects
the trendlinedefined
bythesummed
temperature
datayieldsa SF
trendlinedefined
by thesummed
etched
pyroxene
dataandthe '•He/3He
composition
of 3150+ 150,considerably
lowerthan
GCRc0smogenic
endpoint
in Figure
3aata sF36Ar/3SAr
value thatobtained
bytheordinate
intercept
method.
Thistrendline
of 4.8 + 0.2, which is within the limits of the SF 3•Ar/38Ar is not anchoredto the cosmogenic
He composition
because
of
value
of4.9+ 0.1derived
fromtheordinate
intercept
plot.The thedominance
ofradiogenic
'•He.Also,thefivesummed
data
are
600,øC
and1200øC
datapointsplotneartheregionwherethese pointsusedin Figure3b to derivethis4He/aHecomposition
trendlinesintersect,
indicating
a minorcontribution
fromthe not highly linear, and the uncertaintyon this ratio is probably
cosmogenicComponent,whereasthe 1600øCpoints indicate considerablygreater than the shaded'•He/3He field would
significant
contributions
from the cosmogenic
component.indicate. In addition,He and Ne differ considerablyin the rate
Consistentresults from the two techniquesindicate that the of releaseof their surface- and volume-correlatedcomponents
long-term average SF Ar compositionimplanted in etched with increasingtemperature,as evidencedby the apparently
releasesof
Kapoeta pyroxene grains is significantly lower than that of curvedmixing line definedby individualtemperature
othertrapped
argon
reservoirs
suchasSW(3•Ar/38Ar
= 5.35)or the etchedsize separatesin Figure 3b. Becauseof the greater
terrestrial
"air"andis bestrepresented
by a 3eAr/38Ar
ratioof tendencyfor He to be diffusivelylost from the samples,it is
4.9 + 0.1.
possible
thattheHe/Neratiosvaryevenamongthesummed
A fewattempts
havebeenmade
earlier
todetermine
theSF data,which might explainthe differentSF '•He/3He value
Ar compositio
n usinglunarandmeteorite
samples.
Usingthe derivedfrom Figure3b comparedto Figure2d. We placemore
ontheordinate
intercept
technique
andpreferthelohgCSSE techniqu
e on mineralseparates
from lunarfines71501, reliance
term
average
SF
'•He?He
ratio
of
3800
+
200
for etchedKapoeta
Wieleretal. [1986]reported
nodifference
in the3eAr/38Ar
ratio
pyroxene grains, although it is clear that a considerable
uncertaintyexists in this value.
Earlier,Benkertet al. [ 1988]reporteda valueof greaterthan
reporteda valueof 4.94 + 0.1 for the36Ar/38Ar
ratioby fitting
4200
for the'•He/3Heratioin SF He by fittingcurvedmixing
curvedmixing lines to selectedtemperaturefractions. Earlier,
Rao and Mathew[1987] reporteda valueof 5.2 for the same linesto selectedtemperaturefractiondata from the CSSE study
from lunar fines 71501. In
ratio basedon the 600øC gas releasefrom two orientedrocks of pyroxeneand ilmeniteseparates
from the lunar Surface.
anothercontext,Nier and Schlutter[1990] observedan average
betweenSW, SF and air. While using the sametechniqueon
mineral separatesfrom the same soil, Benkert et al. [1988]
Solar Flare Helium
The isotopic compositionof He measuredin solar flares
'•He?Heratioof 4160+ 520 whilestudying
He andNe isotopic
ratios in interplanetary dust particles (IDPs).
Thus there
appearsto be significantevidencethat the '•He/3Heratio in
variesfromonetypeof flareto another.I n 3He-richflares, solar flares is substantially greater than the SW value of
generally
smallevents,
the4He/3He
ratioranges
from1 to 100,
-2500.
and in larger, "normal"flares the sameratio is 1000 or greater
Summarizing,new data presentedin this studyindicatethat
at energiesof about 10 MeV/amu [Webberet al., 1975]. As the long-termaverageNe, Ar and He isotopiccompositionsin
this '•He/3He ratio in solar flares is known to be energy solarflaresare 11.6 + 0.2 for •Ne?ZNe, 4.9 + 0.1 for 3aAr/3SAr,
dependent,
the'•He/aHeratioaveraged
overmanylargeevents and3800 + 200 for '•He/3He. TheseSF compositions
are
canbe ashigh as a few thousandat low energiesof ~1 MeV/amu significantly
differentfromtheSW ratiosof 13.6for •øNe/ZeNe;
[Black, 1983; Hurford et al., 1975]. The average isotopic 5.35 for 3•Ar?SArand 2500 for '•He?He.
composition
for He in a "normal"flare wouldseemto be a
ELEMENTAL
ABUNDANCES
AND(Z/A)2DEPENDENCE
bettercandidatefor comparisonwith lunar and meteoritedata.
We now considerthe SF elementalcompositionof He, Ne
Based on correlationsbetween trapped He and Ne isotopic
compositionsin gas-richmeteorites,Black [1972] suggesteda andAr, i.e., '•He?•Arand2øNe?•Ar,usingthe samedatabase.
valueof ~2500 for He-C whichwastentativelyidentifiedas SF At the outsetit may be noted that the SF componentcannotbe
He at 1 MeV/amu. On the other hand, Yaniv and Marti [ 1981] derived by simple diffusive fractionation of SW into these
reported
a valueof ~12 for theSF'•He?Heratioin thelunarrock grainsbecausethe SF componentis enrichedin heavy isotopes
68815 at an energyof ~10 MeV/amu.
relativeto the light isotopes(Table 1). If it were a diffusive
Finding consistentresults between the ordinate intercept process,light isotopesshouldbe enrichedrelativeto the heavy
and the two-elementisotoperatio techniquesin the caseof SF isotopes.This argumentwas madein moredetailby Wieler et
Ne and SFAr leadsus to applythesetechniques
to the He data. al. [1986]. Here we have studiedthree samplesets,unetched
A He ordinateinterceptplot of 600øC, 1200øC and summed (UE), lightlyetched(LE) andheavilyetched(HE) fractionsfrom
temperature data from each of the etched pyroxene size two pyroxenegrain size separates,
35-125 grn and 125-200gm
fractionsis shownin Figure2d. The 1200øCdataare dominated (see experimentalsection). The data are given in Table 2 as
by cosmogenic
He, whereasvirtually no 3He remainsby the measuredtotals,i.e., summeddatafrom all temperature
stepsof
1600øC extraction. The summedand the 600øC data points a given pyroxene fraction. The LE and HE samplescontain
define best-fit lines (R2=0.992, 0.994) which, upon contributionsfrom SF particlescorresponding
to E >0.4 and E
extrapolationto infinite surface-correlated
gas concentrations, >1.2 MeV/amu, respectively, and small amounts of
yield surface-correlated
SF '•He/3Hevaluesof 3990 and3770, cosmogenic gases. SF abundances were estimated by
respectively(averagevalue: 3800 + 200). These values are subtracting
thegasconcentration
measured
in the SF shielded
muchhigherthanthe accepted
SW '•He/3Heratioof ~2500 light pyroxenesamplefrom the measuredtotal abundancesin
measuredin Kapoetabulk samples[Schultzand Kruse, 1989] the LE and HE dark pyroxenesamples. The UE samplesare
and lunarfines [Eberhardtet al., 1970, 1972].
dominatedby SW gases of E > -0.005 MeV/amu. SW
RAO ET AL.: SOLAR FLARE NOBLE GAS•ES
19,327
TABLE2. Measured
Elemental
Abundances
in units10-scrn3STP/g
Etch
3I-Ie
4I-Ie
2øNe
2•Ne
22Ne
3aAr
38Ar
2004.9
1045.6
810.1
264.1
205.1
245.2
8.26
5.32
5.49
4.26
3.92
3.99
165.3
86.2
73.5
37.7
21.7
24.7
56.53
36.23
15.60
13.87
5.06
7.15
10.72
7.71
3.51
3.19
1.37
1.83
3.9
0.89
4.2
1.6
0.06
PyroxeneDark
35-125 grn
125-200•
35-125 •
125-200•
35-125 •
125-200Wain
PyroxeneLight
125-200•
UE
UE
LE
LE
HE
HE
LE
44.39 116,900
31.01 69,600
35.26 88,000
27.33 55,600
25.74 37,500
21.91 36,700
4.11
2,804
Estimateduncertaintiesfor Ne and Ar are 5-7% and for He, 10-12%.
UnetchedCLIE)samplescontainprimarilySW gaseswith moderateamountsof SF gasesand small
amountsof cosmogenic
gases.Unetchedsampleswerenot treatedwith the acid etchant. However,these
samplesmay have lost somesurfacematerial (estimatedE <0.005 MeV/amu) as a result of sample
handling,crushingand ultrasonictreatment. SW abundances
comparableto literaturedata [Shultz and
Kruse, 1989] are obtainedby subtracting
the heavily etchedsampleconcentrations
from the unetched
sample concentrations.
Lightlyetched(LE) samples
had-1-2 prnof surfacematerialremovedby acidetching. They containSF
gaseswith E >0.4 MeV/amu, plus smallamountsof cosmogenic
gases.
Heavilyetched(HE) samples
had-8-10 [xmremovedby acid-etching.They containSF particleswith E
>1.2 MeV/amu, plus smallamountsof cosmogenic
gases. SF abundances
were obtainedby subtracting
the SF shieldedlight sampleabundances
from the HE darksample.
abundanceswere obtainedby subtractingthe calculatedSF
still possiblethat there has been a factor of 2-3 diffusive loss
of SF He, relative to At, from theseKapoetagrains.
A comparison of the long-term average isotopic
samples,and are shownTable 2. These SW abundances
are
abundancesfrom the total He, Ne and Ar measured in the UE
of SF 3He/4He,
2øNe/22Ne
and36Ar/3SAr
ratiosto the
comparable
to thosefrom Kapoetaliteraturedata [Schultzand composition
Kruse, 1989] except for SW He, which shows large losses corresponding
SW ratios showsthat the enrichmentof heavier
relative to At, possibly due to diffusion from shallow grain- isotopesover lighter isotopesis greater in SF than SW by
surfaceimplantation.The observed
SW 4He/36Arratiosof 626- about52%, 17% and 9%, respectively(Table 3). Theseheavy
1540 are a factorof 7 to 10 lower thanthe SW 4He/36Arratio of ion enhancements
for He, Ne, and Ar fit the empiricalequation
-7500 obtained from lunar fines [Eberhardt et al., 1970]. The AM/Mp = K, whereM refersto the isotopicmass, AM refersto
SF 4He/36Arratiosrangefrom4300 to 10,030with an average the massdifferencebetweentwo adjacentisotopesof a given
valueof 6640, whichis closeto the SW 4He/36Arratio of -7500
from lunar fines. There has apparentlybeenmuchlessdiffusive
lossof SF He than SW He, relativeto At. This greaterretention
of SF He is likely due to the higher-energySF particlesbeing
more deeplyimplantedin the grain surfacesthan SW. The SW
element,p is the enhancementfactor (SF/SW), and K -0.68 is a
constant. This heavy ion enhancementbetween the two
isotopesof a given elementdecreasesmonotonicallyas the
mass increases from He to Ar in solar flares.
Table 3 lists the isotopic and ele•nental fractionation
2øNe/36Ar
ratiosrangefrom 27.5 to 35.0 with an averageof
31.7, which is similar to the "solar system average" SW
2øNe/36Arvalue of ~37 determined from meteorites and lunar
sampleslandersand Ebihara,1982]. The SF 2øNe/36Ar
ratios
TABLE 3. IsotopicandElementalFractionation
Factors,for
example,
36
36
(2øNe/Z2Ne)sw/(•e/•e)sFand(2øNed
Ar)sw/(2øNe/
Ar)sl•
range from 29.2 to 49.6 with an averagevalue of-41, also
Elemental
similar to the "solar system"SW value of-37. This suggests
Isotopic
that therehas been no significantlossof SF Ne, relative to At.
3/36
4/36
20/36
22/36
3/4 20/22
36/38
We concludethat the4He/36Arand2øNe/36Ar
ratiosin solarflares
are similarto thosein SW within experimentalerrors.
SW/SF a 1.52
1.17
1.09
0.4-1.5 0.7-1.7 0.8-1.3 0.5-1.0
We can alsocomparethe long-termaverageSF He/At andSF (Z/A)2b 1.79 1.21 1.10
1.80 1.00 1.00 0.80
Ne/Ar values derived here with direct satellite measurements of
(l/A)2c 1.79 1.21 1.10
144
81
3.20 2.70
contemporarysolar energetic particles (SEP) summarizedby
Mason [1987]. This comparisonrequiresconsideringtotal SF
aSolarFlare (SF) isotopicratios are derivedfrom three-isotopeand
elementalabundanceratios of (3He+4He)/(3aAr+3SAr)and
(2øNe+22Ne)/(3aAr+38Ar),
whicharedetermined
fromTable2. SF
contributions
of 2XNeand4øAtarenegligible.The observed
SF
Ne/Ar ratiosof ~45 are in excellentagreementwith the satellite
SEP Ne/Ar ratio of 42. However, the observed SF He/At values
of 4-7 x 103are lowerthanthe valueof ~17 x 103givenby
Mason [1987]. While SF He does not show the same order of
magnitudelossesrelative to Ar as SW He, noted above, it is
ordinateintercepttechniques(see Table 1); SF elemental ratios are
derivedfrom heavyetchconcentrations
(seeTable 2); solarwind (SW) He
andNe isotopicratiosare from Geisset al. [1972]; SWAr isotopicratios
are from Eberhardt et al., 1972. The SW He/Ar elemental ratios are from
Geiss et al. [1972]; the SW Ne/Ar ratio is from Anders and Ebihara
[1982]. Estimated elemental ratio uncertaintiesare He/At -35%; Ne/Ar
-25%.
t,(Z/A)2 factorrepresents
rigidity
dependence.
c(1/A)2
factorrepresents
mass
dependence.
19,328
RAOET AL.: SOLARFLARENOBLEGASES
factors
obtained
fromSw/sFratiosfor He, Ne, andAt. It
It has been shown [Lal, 1972; McGuire et al., 1981] that the
by an exponential
shouldbe clearlyunderstood
thatbecauseof thenatureof these SF particlespectrumcan be well represented
rigidity,J(R)= ke-R/Ro,whereJ is thedifferential
measurement
techniques,theseratiosare basedon essentially in particle
the same energy per nucleon and reflect rather long term flux and Ro is a characteristicrigidity. This rigidity spectrum
averages
of theseelements.The isotopicratiosgivenin Table can be transformedinto a spectrumin kinetic energy per
3, which are less affectedby relative diffusionrates, show a nudeonJ(E)= AE-• At very high energies(> 100 MeV/amu,Ro
near-perfect
correlation
with (Z/A)2 and(l/A) 2. In orderto ~100 MV) theslopebecomessteepwith ¾~3,while remaining
distinguish
betweentheserelations,one can examinethe essentially flat at low energies (<10 MeV/amu) with •'-1
elementalfractionationfactors. It is quite clear from these [Blanfordet al., 1975]. This low-energyvalueis in agreement
ratiosthata (Z/A)2 proportionality
is favoredover the simpler with observationsof Lal and Rajah [1969] and Pellas et al.
(l/A) 2 dependence,
particularlywhenoneconsiders
the higher [1969], who found¾=1.2 + 0.2 for $F Fe groupnucleiin the 1diffusion rates of He relative to At.
to 10-MeV/amurange in Kapoetapyroxenes. However,there
The excess22Ne over 2øNe in SF comparedto SW, as may be somecontributionto the flatteningof the observedFe
discussedat the beginning of this section, can easily be group $F particle spectrum at low energies, i.e., 0.1-10
understoodif one assumesthat the SF particle spectrumis a MeV/amu, from shieldingof Kapoeta grain surfaces[Zinner,
function of rigidity alone. There is significantexperimental 1979]. For Kapoeta,we can use a $F flux ratio as an indication
evidence (next section) to suggest that this assumptionis of the spectral shape of the implanted $F ions in the 1valid. If we now recall that the measurements are made at the
Mev/amuenergyregion. This ratio is definedto be thetotal SF
samekinetic energy per nucleon,the rigidity spectrum,J(R), particleflux with E > 0.4 MeV/amu to the totalSF flux with E >
can be convertedinto a kinetic energy per nucleon spectrum, 1.2 MeV/amu, i.e., (•E>0.4 MeV/amu)/(•E>l.2 MeV/amu).
J(E). This transformationfor very low energyparticles(E<< The observedflux ratios and the theoreticallypredictedflux
protonrestmass,m) is simplygivenby J(E) = J(R) (Z/^)2 ratios determined for both rigidity and kinetic energy
((E+m)/R). Thus the conversionfrom a rigidity to a kinetic dependentspectraare listed in Table 4. The resultsshowthat
energy per nucleonbasis leads to the observed(Z/A)2 the solar flare particle flux spectrumdeterminedin Kapoeta
proportionality. This is consistent with the explanation does indeed flatten out at low energy, i.e., •' approaches1 at
offeredby Meyer and Casse [ 1979], in which they proposed particleenergiesof a few MeV/amu.
that the particle acceleration selectively enhances the
abundance
of heavierisotopesdue to their greaterrigidity at the
TABLE 4. Measured and Theoretical Solar Flare Flux Ratios:
sameenergyper nucleon.
ß (E>0.4 MeV/amu)/•(E>l.2 MeV/amu), DerivedFrom
LighfiyEtehedand Heavily EtchedGas Concentrations
Basedon orderingof our isotopicdataby (Z/A)2, as first
suggested
by Meyer and Casse[1979], one would expectsolar
particle accelerationto selectively enhancethe abundanceof
heavier isotopes. In a review of satellite-basedmeasurements
of a largenumberof isotopesin recentsolarflares,Mewaldt et
al. [1984] found no such abundanceenhancement. There are,
however, three significant differences between our
measurementsand these satellite-basedmeasurements: (1) our
data include particleswith significantlylower kinetic energy
per nucleon (<~1 MeV/n) compared to the measurements
summarized by Mewaldt et al. [1984]; (2) although it is
observedthat the isotopic compositionis relatively constant
over a very small time interval, our measurements
correspond
35-125gm
125-200
gm
3•Ar
22Ne
4He
lae-a/•o
3.08
1.94
3.40
1.53
2.35
1.51
1.49a
1.49a
!• '•
1.41•'
1.41•'
SeeTable2 for samplegasconcentrations.
"Integralflux determined
from a rigidity-dependent
particlespectrum;
R=54.8 MV at E=0.4 MeV, R=94.9 MV at E=l.2 MeV, Ro=100 MV.
•'Integral
fluxdetermined
froma kineticenergy
dependent
particle
spectrum;
?--1.4for E<15 MeV and ?=3for E>15 MeV [Blanfordet al,
1975].
to an extremelylargetime averageandincludemany3He-rich
flares; and (3) Mewaldt [1979] pointed out that the isotopic
Up to 25% of the total trappedsolarNe and Ar in Kapoeta
compositionof solar wind and solar flaresmay be significantly
canbe attributedto SF (Table 2). Similarly,SF Ne observedin
different. Althoughno modelsexist for thesedifferencesor for
the isotopiccomposition
in 3He-richflares,we simplypoint
out that our measurementsof noble gasesover a very large
(Z/A) 2 can mosteasilybe understood
in termsof a rigiditydependentmechanism.
ENERGY SPECTRUM OF SOLAR FLARE NEON AND ARGON
By calculatingthe approximatedepthsto which the grain
surfaces have been etched and utilizing a range-energy
relationship [Lal, 1972], the grain-etchingtechniquecan be
used to samplethe incident particle energy spectrumabove a
given kinetic energy per nucleon. The kinetic energy per
nucleonfor the trappedsolar flare particlesremainingin each
sample after etching is estimated to be greater than -0.4
MeV/amu in the lightly etchedsamples,and greaterthan -1.2
MeV/amu in the heavily etched samples(see experimental
section).
pyroxenesfrom lunar fines accountfor -20-30% of the total
retainedsolar Ne [Nautiyal et al., 1986; Wieler et al., 1986].
This resultled Wieler et al. [1986] to point out that theratio of
the averageSW protonflux to the SF protonflux (E >10 MeV)
is six ordersof magnitudehigherthantheir observedlunarsoil
SW/SF Ne flux ratio. In order to explain this apparentlarge
flux of SF ions, Wieler et al. [1986] invoked the presenceof
10- to 50-keV/amu "suprathermalions" in concentrations
sufficientlyhigh to bring the SW/SF flux ratio down to ~3.
KapoetaSW/SFNe andAr flux ratiosof ~10, inferredfrom the
measuredabundanceratios listed in Table 5, were determinedin
the acid-etchedgrain separateswhere particlesof energyless
than-1.2 MeV/amu were quantitativelyremoved.This implies
that the measuredSF componentin gas-richmeteorites(as well
as in lunar soils)doesnot seemto be dominatedby ions from
the 10- to 50-keV/amu range, althoughthe presenceof such
ions at much lower concentrations
cannot be ruled out.
At
RAG ET AL.' SOLAR FLARE NOBLE GASES
19,329
TABLE 5. Ratios of Solar Wind (SW) to Solar Flare (SF) Abundances,
of trappedgasesin the meteoriteKhor Temiki, J. Geophys.Res.,
70, 4375-4378, 1965.
Eberhardt, P., J. Geiss, H. Graf, N. Groegler, U. Kraehenbuehl, H.
Schwaller,J. Schwarzmueller,and A. Stetfler, Trappedsolarwind
4I-Iea
22Ne
3•Ar
ProtonFluxt'
noblegases,exposureage, and K/Ar age in Apollo 11 lunar fine
material,Proc. Apollo 11 Lunar Sci. Conf., 2, 1037-1070, 1970.
Eberhardt, P., J. Geiss, H. Graf, N. Groegler, U. Kraehenbuehl,H.
35-125gun
2.12
6.62
10.17
-106
Schwaller,and A. Stettler, Trapped solar wind noble gases in
125-200gun
0.90
2.49
4.07
Apollo 12 lunar fines 12001 and Apollo 11 breccia10046,Proc.
Lunar Sci. Conf., 3rd, 1821-1856, 1972.
See Table 2 for SW and SF abundances.
Geiss, J., F. Buehler, H. Cerutti, P. Eberhardt, and C. Filleux, Solar
aSeetext for discussion
of SW He lossfrom the unetchedsamples.
wind compositionexperiment,Apollo 16 Preliminary Science
t'SWproton
fluxtoSFproton
fluxratio[Weileretal., 1986].
Report,NASA SP-315, 14.1-14.10, 1972.
Haack U., Systematicsin the fission track annealingof minerals,.
Contrib. Mineral. Petrol., 35, 303-312, 1972.
Hohenberg,C. M., K. Marti, F. A. Podosek,R. C. Reedy, and J. R.
presentthe reasonfor the large differencesbetweenthe proton
Shirck,Comparisons
betweenobservedand predictedcosmogenic
SW/SF flux ratio and the He, Ne and Ar SW/SF ratios measured
noblegasesin lunar samples,Proc. Lunar Planet. Sci. Conf., 9th,
ForExample,
22Ne
sw/•sv
in theseKapoetapyroxenesis unclear.
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(ReceivedFebruary4, 1991;
revised June 21, 1991;
acceptedJuly 2, 1991.)