X-ray tomographic studies of Stardust
samples: a track and individual particles
A. Tsuchiyama1, K. Uesugi2, T. Nakano3, T. Okazaki1,T. Nakamura4, A. Takeuchi2, Y. Suzuki2, and M. Zolensky
1 Department of Earth and Space Science, Osaka Univ.
2 SPring-8/JASRI, 3 GSJ/AIST
4 Department of Earth and Planetary Sciences, Kyushu Univ., 5 JSC/NASATwo types of tomographic studies
at BL47XU/SPring-8
1. 3-D structures of impact tracks
SUBTEAM: Bulk-composition
Projection tomography (high resolution)
Resolution: 0.5 or 0.195 μm/pixel
Samples: 4 tracks* in keystones
with XRF (T. Nakamura)
2. 3-D structures of individual particles
SUBTEAM: Mineralogy-Petrology
Imaging tomography (ultra-high resolution)
Resolution: 0.0425 μm/pixel
Samples: 4 particles removed from 2 tracks*
with XRD at BL17/PF (T. Nakamura)* Different tacks

3D structures of impact tracks
Projection tomography (0.5 or 0.195 μm/pixel)
Samples: 4 tracks (C2126,2,68,0; 32,0; 67,0; 47,0)
Photon energy: 10 keV
No. of projection: 1500
3-D image: 2000x2000 matrix, 1312 slices

XRF
Photon energy 15 keVBeam size:
40x40 to 400x260 μm

Procedure(1) Optical microscopy(2) Radiography
Whole 2-D image of keystone(3) XRFCoarse mode: cover whole track
Fine mode: individual particles

Optical microscopy(4) Tomography
Coarse mode: cover whole track
Fine mode: details of a track

Tomography(vertical slice: 5 tiles)

XRF
Tomography(CT slice)

Radiography(7.090 keV: tile image)Sample: C2126,2,68,0

CT slice images (C2126,2,68,0)4a/0564

4b/1008

subtrack-1
condensed aerogel
radial crack
particleparticle

subtrack-5(terminal particle)
subtrack-3

main track
condensed aerogel

Dark space: track hole with radial cracks
Bright wall: condensed aerogel (melted?) with very fine particles?
White: captured particles
Track is bifurcated into main and sub-tracks.
Particles are present along tracks and radial cracks as well as themain track terminal.

CT images parallel to the track (C2126,2,68,0)
radial crackbifurcation

C2126,2,68,0
subtrack-1
CT images nearly parallel tothe trackmain trackmain trackmain trackmain trackslice 219

slice 229

slice 239

terminal particleMany particles are present along the main and subtrack-1.

Track: Bird’s eye view (C2126,2,68,0)

Gray:
Gray track hole and radial cracks
Blue:
Blue condensed aerogelRed:Red captured particles
Track is bifurcated into 5 or 6.
Main and subtracks have terminal particles, respectively.
Many particles are present along the bifurcated tracks.

Track size vs. XRF data (C2126,2,68,0)
volume(μm3)

mode(%)

track

7.788E+06

78.75

particles

3.155E+04

0.32

diameter (μm)
entrance

79.9x60.5
length (μm)

main track

2484

subtrack-11672

condensed
aerogel

2.070E+06

20.93

subtrack-21353

total

9.889E+06

100.00subtrack-31107

subtrack-41027

subtrack-5(?)

756

Whole Fe mass: 6.66x10-11 g XRF data
Estimated mass (whole grain): 7.6x10-10 g
Fe mass/track volume:
volume 8.56x10-6 g/cm3
Estimated whole mass/track volume: 9.7x10-5 g/cm3
if density=1 g/cm3 : 0.01 vol.%If track volume is proportional to mass, we may
evaluate volatile/solid ratio among different tracks.
track volume ↔ kinetic E = 1/2mv2 (v∼const.)

Track bulb: Bird’s eye view (C2126,2,68,0)
dcefbaU-shaped radial crack (main: arrow-a and sub: arrow-b)
Crack along the central axis of the U-shaped crack: arrow-c
Subtrack-4 grows from the central crack: arrow-d(each subtrack seem to grow from a crack)crack
Wavy radial crack: arrow-e
Some particles are in radial cracks: arrow-f

3D structures of individual particles
Imaging tomography (0.0425 μm/pixel)
Samples: 4 particles (C2004.1.44.3, C2054.0.35.6; .5,; .4)
Photon energy: 8 keV
No. of projection: 3600
3-D image: 2000x2000 matrix, 1312 slices

XRD
BL17/Photon Factory, JapanThe results are presented by T.Nakamura

Conclusions• Whole dust particle
less fragile particles + fragile aggregate of fine particles← 3-D structure of track← 3-D structures of individual particles
less fragile particles: crystalline
fragile aggregate: amorphous-rich (mixture with aerogel)•Not easy to reconstruct whole dust particle texture completelyby tomography alone• Fe mass/track volume→ whole dust particle/track volueme: ~ 0.01 vol.%→ may estimate volatile/solid ratios of whole dusts particles
among tracks•

Crystalline particles
evidence of melting? (SEM/EBSD or TEM study required)fractured surface