Presolar grains in meteorites:Isotopic signatures and

timescales

earthly stellar celestial

the focus on isotopes

facts speculations

U. Ott Bern, April 14,2010

STARDUST grains in meteorites

silicon carbide (SiC)

diamond (C)

mostly solid (facts)

often speculative

carbonacoeus chondritesconstituents:-- chondrules-- Ca-Al-inclusions (CAIs)- matrix (w/ stardust)

Outline “earthly history” discovery story the inventory

stellar history “forward“ age

(timescales of nucleosynthesis, grain formation)

celestial history “backward“ age (“absolute age“)

Allendemeteorite: Xereleased in certain temperature steps: up to ~2x relative enhancement of lightest and heaviest isotopes

Xe-HL from presolar diamond

Earthly History….began in about 1964: Reynolds and Turner: stepwise

release and analysis of xenon isotopes in carbonaceous chondrite Renazzo

own similar “historical”analysis (1978): Allende DI #2

124Xe/130Xe [‰]

136Xe/130Xe [‰]

further characteristic of noble gas carriers: resistance to acids

characteristic noble gases

Xenon-HL - diamonds

Xe-S and Ne-E (almost pure 22Ne) - silicon carbide

(and graphite)

similarly, heat a primitive CM / CI meteorite, in certain temperature steps: enhancement of 22Ne

Maribo CM chondrite:fell in Denmark 2009

Terrestrial time-line 1964: discovery of strange Xe (now Xe-HL) 1969: discovery of Ne-E, (almost) pure 22Ne 1975: acid-resistance of noble gas carriers 1987: identification of pre-solar diamond as

carrier of Xe-HL;identification of pre-solar SiC ascarrier of Ne-E and s-process Xe

1990: identification of graphite (a gas carrier) 1994: identification of pre-solar oxides

(and later nitride), not carrying noble gases 2003/4: NanoSIMS: identification in situ of

pre-solar silicates in interplanetary dust and meteorites

mineral isotopic signatures stellar source contribution

diamond Kr-H, Xe-HL, Te-H supernovae ?

silicon carbide

enhanced 13C, 14N, 22Ne, s-process elements low 12C/13C, often enhanced 15N

enhanced 12C, 15N, 28Si; extinct 26Al, 44Ti low 12C/13C, low 14N/15N

AGB stars J-type C stars (?)

supernovae novae

> 90 % < 5 % 1 %

0.1 %

graphite enhanced 12C, 15N, 28Si; extinct 26Al, 41Ca, 44Ti Kr-S

low 12C/13C low 12C/13C; Ne-E(L)

SN (WR?) AGB stars

J-type C stars (?)novae

80 % (?) < 10 % (?)

< 10 % 2 %

corundum/spinel silicates

enhanced 17O, moderately depleted 18O enhanced 17O, strongly depleted 18O

enhanced 16O similar to oxides above

RGB and AGB AGB stars supernovae

> 70 % 20 % 1 %

silicon nitride

enhanced 12C, 15N, 28Si; extinct 26Al supernovae 100 %

Presolar grains in meteorites - Overview

1500 ppm

30 ppm

10 ppm

>50 ppm

> 200 ppm

0.002 ppm

major dust factories AGB stars (low mass < 8 Msun)and supernovae(high mass)

Hertzsprung-Russelldiagramm

courtesy V.V. Smith

-- C-O-core (from core He burning) -- alternate He and H burning in shells 12C, Ne-E (almost pure 22Ne from -captures on 14N), s-process -- (3rd dredge up) surface; winds grain condensation

major dust factories AGB stars (low mass < 8 Msun)

after J. Lattanzio

major dust factories supernovae (high mass > 8 Msun)

higher temperatures, densities higher burning phases

“onion shell”structure

explosion + explosive nucleosynthesis

Stellar History time-line forward ……e.g., AGB stars…

nucleosynthesis s-process (slow neutron capture);source of about half of the elements heavier than Fe

along

-stab

ility

s-process:in most cases, unstable nuclei have time for -decay before next neutron capture

taken from Rolf/Rodyney 1988

branching factor fn=n/(n+)n = n = nnvth

86Kr abundance sensitive to n density (85Kr branching),80Kr also to temperature (79Se branching)

neutron density in the s-process region shows up in certain isotopic ratios; where there is competition betweenneutron capture and -decay (branchings); e.g. krypton

half life of 85Kr ground state: ~ 11 a

after F. Käppeler

86Kr (and 80Kr) productionat variable ndensities

timescales forn capture onthe order of85Kr half life

from: Lewis et al. (1994)

Stellar History time-line forward …

……..from nucleosynthesis thatresulted in the characteristic isotopic patterns

information from radionuclides with suitable half-lives required: chemical separation between parent and

daughter element a favorable case: 26Al in silicon carbide

- aluminum is easily accommodated by silicon carbide,while daughter magnesium is not

Mg in SiC often virtually pure 26Mg (normal: 11%) others (restricted to supernova grains – X ):

44Ti 44Sc 44Ca (half-life 60 a)49V 49Ti (half-life 330 d)

26Al/27Al (SiC)at time of grain formation

0.001

0.01

0.1

1

main A

B

Y Z

X

grain formation within at most few half-lives of these nuclides

supernova grains

T½ = 7x105 a

T½ = 60 a

from E. Zinner

most stringent constrains (supernovae) V-Ti

supernova (X) SiC grains form within some monthsafter SN explosion (Hoppe and Besmehn, 2002, ApJ)

T½ (49V)= 330 d

the enigmatic diamonds

the diamond story is a lot trickier than that of thesilicon carbide, for two main reasons:

a) lack of significant concentrations of trace elementswith diagnostic isotopic features

b) small size, on average 2.6 nm (~ 1000 carbon atoms) no single grain analyses

12C/13C within range of “normal” Solar System matter question whether all are pre-solar

diagnostic elements essentially noble gases only – in particular xenon – and tellurium

isotopically strange Xe-HL released at higher temperature than ~normal Xe-P3

mass number

124 126 128 130 132 134 1360

50

100

150overabundance [%]

Xenon-HL vs. solar wind xenon

p-only

r-only

HL component –excesses in light (L)and heavy (H) nuclides

reminiscent of p- and r-process, but% enhancement atp-only 124Xe, 126Xe not equal; % enhancement atr-only 134Xe, 136Xe not equal

“observed HL”probably impure:high-T peak mostlikely a mixture of hi-T part of P3component and “pure HL” (s-process free, 130Xe ≡ 0)

m a ss n u m b e r1 3 0 1 3 2 1 3 4 1 3 6

iX e /1 3 6 X e

0 .0

0 .5

1 .0

1 .5

2 .0

2 .5

3 .0

3 .5

d ia m o n d X e

r-p ro c e s s

HL pure – the heavy part

clearly not the “average” r-process

some speculation

mass number129 131 133 135 137128 130 132 134 136

iXe/136Xe

0.0

0.2

0.4

0.6

0.8

1.0

Xe-H

Howard's n burst

Meyer's n-burst

r-process with separation

astrophysical “invention”: neutron burst (intermediate between s-and r-process in He shell of exploding supernova during passage of shock wave (not needed in standard description of abundances)

better fit: “classical” r-process with “early” separation (before full decay of precursors to the stable end products)

speculative

remember: nucleosynthesis of elements beyond “Fe peak“:predominantly by neutron capture processes (r = rapid; s = slow)

along

-stab

ility

taken from Rolf/Rodyney 1988

0 5000 10000 150000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Xe-R

134Xe/136Xe

Xe-H

time [sec]

time of separation determined by crucial ratio 134Xe/136Xe

precursors of 136Xe: fast decay

precursors of 134Xe:134I, 134Te with half-lives of 40-50 min.

required separation time: ~ 7000-8000 sec.

Suggested possibilities how to do it (?)(1) pre-condensation (of the less volatile precursors)

- requires early grain formation

(2) recoil loss from grains of decay products- requires early trapping of trace elements- in -decays (?) - experimental tests

(3) separation in strong magnetic field according tocharge / mass

(4) a combination

however:possible in environment of exploding supernova at such an early stage ?

speculative

Celestial Historyhow to date a presolar grain…. ? classical approach – radioactive decay:

D = daughter, P = parent element; 1, 2 = isotopes; 1= radiogenic / radioactive; 2 = stable nonradiogenic = decay constant

then: D1/D2 = (D1/D2)ini + (P1/D2) (et-1) for long-lived radioisotopes time information:

-- model age (initial assumed)-- age from slope of isochrone (contemporaneous samples)

= classical age dating

problem with stardust – unusual isotopic compositions model age: what was non-radiogenic ratio (D1/D2)ini ?

isochrone age can one assume the grains have the same age?

alternative (first suggested/applied by Andersand colleagues)- exposure to cosmic rays

( pre-solar cosmic ray exposure age, to be added to Solar System age for an absolute age)

applied to SiC, CR production of 21Ne from Si target

not so easy either…1. what is the abundance of non-cosmogenic 21Ne?2. what was the production rate (depending on flux and

spectrum of cosmic rays) >4.6 Ga ago ?

grain radius [m]

0.1 10

20

40

60

80

10021Ne retention [%]

I

II (1 m)

II(2.5 m)

I (corr)

3. significant error in first application: recoil loss of spallation 21Ne from µm-sized grains

- used curve 1 - but nuclear data on

which curve I is based were not applicable and in addition an error in the application- our experiment:

mean range ~2.5 µm

an experiment…1. take (terrestrial) SiC grains of various sizes

2. distribute homogeneously (and sufficiently separated) in a matrix where spallation does not produce 21Ne

3. irradiate with energetic protons (1.6 GeV)4. recover irradiated SiC, measure Ne in grains,

compare with production (from 22Na in SiC+paraffin)

paraffin waxparaffin wax

with SiC

later work recoil range for 126Xe (produced on Ba and REE) determined

on a Ba glass using the catcher technique:converted to SiC: ~0.2 µm

4 6 8 10 12 14

recoil range [µm]

0.0

0.1

0.2

0.3

0.4

0.5recoil range in Ba glass vs. mass difference

A (amu)

124

126

128129

130

131

132

retention of spallation xenon in SiC grains

grain diameter [µm]

retention [%]

0.512

5

10

2030

50

7080

90

95

0.3 1 3

124Xe

126Xe128Xe

21Ne

130Xe

losses for Xe much less than for Ne

Problem for application: how much cosmogenic Xein SiC? depends on assumptions about p-process 124Xe/126Xe

Xe data compatible with zero (!) age

most recent work / new possibilities new technology for high-sensitivity Ne analyses (ETH Zürich)

supply of “large” (> 5 µm) SiC grains

possibility of single grain analyses of grains with little loss

evidence for cosmic ray effects in such large grains first seen in Li isotopes (enhanced 6Li/7Li) – St. Louis

calculations of recoil energy distribution by F. Wrobel

DHORIN Code original aim of Wrobel’s work: material science, failures in

microelectronic devices

several numerical data sets supplied for our workenergy distribution ranges as function of size

grain diameter [m]

1 100

20

40

60

8021Ne retention [%]

fix 2.5 µm

Wrobel

retention calculated using the Wrobelenergy spectra agree very well with analytical (average) values

in addition describe distribution (in particular low E, short recoil part)

grain diameter [m]

1 10 100

20

40

60

80

10021Ne retention [%]

fix 2.5 µm

model Wrobel size range (except for one small grain)

New results: Jumbo grains

large grains: 5-35 µm (except for one small ~ 2 µm grain; not considered here)

recoil correction unproblematic

in this size range: perfect agreement of recoil losses for fixed range of 2.5 µm (experiment, Morisseyrelation similar) and from theoretical predictions of recoil energy distribution (Wrobel)

moreover: fraction of 21Ne that is cosmogenic is much larger than for the Lewis et al. (94) grain size separates

always more than 30%, mostly >50 %, up to 97% of 21Ne = cosmogenic

choice of (21Ne/22Ne)-G, whether 0.00059 (Lewis et al., 1994) or 0.0033 (for maximum 18O(,n)21Ne rate; Karakas et al, 2008) uncritical

for production rates in IS space

commonly used: predictions of Reedy (1989)

uses for flux and spectra geometric mean of the four spectra on the right (not the “source”spectrum; from Reedy, 1987)

additional input:nuclear cross sections

overall uncertainty~ 60 % (Reedy) (?)

Another suitable element (besides Ne, He): Lithium preferred estimate of recoil based on experiments of

Greiner (1975)

retention 6Li in SiC

diameter [µm]0.01 0.1 1 10 100 1000

rete

ntio

n (%

)

0

20

40

60

80

1006Li-Greiner 6Li-Wrobel6Li -Morissey

Greiner

Wrobel (Si)

Morissey (C)

The Greiner experiment fragmentation of C, O nuclei to produce He, Li, …

momentum distribution ~ Gaussian isotropic in system where C,O nuclei ~ at rest

important: do not integrate momentum including direction followed by calculation of recoil (result = essentially zero, error in Ray + Völ, 1983))

instead: calculate loss for given momentum and then integrate

best approach: fold momentum /energy distribution with energy-range relationship recoil losses

Li and Ne ages do not agree that well

only one Ne age clearly higher than 100 Ma (several, not shown, with low upper limits only);whereas many Li ages of several hundred Ma, in line with “typical” ages expected for IS grains

need same grain analyses

moreover: JUMBO grains are not “typical”, e.g. also low in Ne-E

Ne ages taken at face value: much shorter than estimated lifetime of interstellar grains

a possible explanation – inspired by Don Clayton’s suggestion of a galactic merger ~ 2 Gabefore solar system formation -:

~ 2 solar mass stars born during a starburst at this time would have entered the AGB (dust producing) phase shortly before formation of our Solar System

Extraction Temperature (oC)

400 800 12000.00

0.05

0.10

0.15

36Ar % R

elea

se o

f gas

/ o C

-50

0

50

100

132Xe

b.a. c.

84Kr

38Ar/36Ar 136Xe/132Xe

UDD1-4

86Kr/84Kr

[o

/oo]

Another speculation: age of the diamonds

ion implantation experiments using artificial nanodiamonds bimodal release

high-T part is isotopically fractionated relative to the (unfractionated) low-T part

3 He

/ 4 He

(x 1

04 )

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

200 400 600 800 1000 1200 1400 1600 1800

Temperature o C

He-P3

Orgueil DiamondsLeoville DiamondsBishunpur DiamondsFractionated He-P3

apply this and correct accordingly the high-T meteorite data; leads to apparent excesses oftypical cosmogenic isotopes 3He and 21Ne

after correction for meteoroid exposureexcess of ~ 200x10-8 cc/g (~ 5x1013 atoms/g) 3He

remarkable:

high ratio of excess 3He to excess 21Ne

3He/21Ne ~ 40 vs. ~10 for chondritic matter

Possible solutions1. diamonds in light-element-enriched chondritic-like matter

- or diamonds in organic mantles of chondritic-like matter- or variants of this theme

case of organic-enriched chondritic matter:e.g., increase C content to 70 wt % age increases factor ~4 (He, Ne consistent)however: need to take recoil also into account large size or even higher C content required for higher C even further age increase

mantles: needs exquisite fine tuning organic/anorganic ratio, size of both (Ne recoil into mantles, He recoil out of)

Possible solutions2. trapping of cosmic rays

3He and 21Ne are abundant secondary cosmic ray isotopesmeasured 21Ne/20Ne ~0.1measured 3He/4He ~0.2

overall : 3He/21Ne in cosmic rays ~300 (!!)high ratio because 3He produced not only by spallation of heavy (C and beyond) nuclei, but also abundantly produced from breakup of 4He

overall also: CR 3He/protonsomething like 0.019 (!!)

but does trapping work?

energy [GeV / amu]

0.2 0.4 0.6 0.8 1.0 1.2

3He / proton

0.010

0.015

0.020

0.025

0.030

what do the cosmic rays do?- imagine a setting like, e.g. a quiet molecular

cloud with dispersed diamondscosmic rays

recoil nuclei

pass through

stopped by grain

stopped by gas

product in grain

recoil in grain

pass through

recoil in gas

+ recoils produced by reactions with gas rather than grains+ recoils that leave the MC (negligible)

cosmic rays have typically energies many MeVs to GeVs will simply pass through nanodiamonds

only when slowed down do something like 300 eV, can they be trapped

further effect: being stopped hydrogen (gas) of ISM is ~6x more efficient than being stopped by C grains (in terms of resulting concentrations ccSTP He/g – gas or grain)

flux [cm-2 sec-1]

0.0001

0.001

0.01

0.1

0-9

9-30

30-90

90-300300-900 900-3,000

3,000-9,0009,000-30,000

3-15 GeV

> 15 GeV

energy [MeV]

results depend sensitively on (poorly known) low energy part of cosmic rays: Reedy (1987, 1989) mean proton spectra / inferred 3He

protons 3He (binned)

depth [g / cm²]

0.001 0.01 0.1 1 10 100 1000

3He rate [cc / g Ma]

10-11

10-10

10-9

10-8

10-7

GCR trapping

production in C (no recoil)

with the nominal values: 3He trapping in mass layers < 0.02 g/cm² more efficient than direct production in diamond (even neglecting recoil)

interestingly: such column densities in range typical for molecular clouds

SUMMARY

stardust in present in meteorites

preserves a record of nucleosynthesis in stars,as well as processes in the ISM and the ESS (early solar system)

here: concentrate on time scales nucleosynthesis: records timescales of s-process

formation: from presence of extinct radionuclides (SiC and others); indication / speculation from Xe-HL for possible early SN grain formation (and destruction)

pre-solar age: interaction with cosmic rays, needs knowledge of production rates and recoil losses

silicon carbide: up to several hundred Ma

nanodiamond: tricky, possible excesses of 3He and 21Ne may require association with larger carbon-rich assembly or trapped cosmic ray ³He