Effect of a synchrotron X‐ray microtomography imaging experiment on the amino acid content of a CM chondrite

Abstract

Abstract-X-ray microcomputed tomography and synchrotron X-ray microcomputed tomography (lCT) are becoming popular tools for the reconnaissance imaging of chondrites. However, there are occasional concerns that the use of lCT may be detrimental to organic components of a chondrite. Soluble organic compounds represent~2-10% of the total solvent extractable carbon in CI and CM carbonaceous chondrites and amino acids are among the most abundant compounds in the soluble organic fraction. We irradiated two samples of the Murchison CM2 carbonaceous chondrite under conditions slightly harsher (increased beam exposure time) than those typically used for x-ray lCT imaging experiments to determine if detectable changes in the amino acid abundance and distribution relative to a nonexposed control sample occurred. After subjecting two meteorite portions to ionizing radiation dosages of 1.1 kiloGray (kGy) and 1.2 kGy with 48.6 and 46.6 keV monochromatic X-rays, respectively, we analyzed the amino acid content of each sample. Within analytical errors, we found no differences in the amino acid abundances or enantiomeric ratios when comparing the control samples (nonexposed Murchison) and the irradiated samples. We show with calculations that any sample heating due to x-ray exposure is negligible. We conclude that a monochromatic synchrotron X-ray lCT experiment at beamline 13-BM-D of the Advanced Photon Source, which imparts 1 kGy doses, has no detectable effect on the amino acid content of a carbonaceous chondrite. These results are important for the initial reconnaissance of returned samples from the OSIRIS-REx and Hayabusa 2 asteroid sample return missions.

X‐ray computed tomography imaging: A not‐so‐nondestructive technique

“…A synchrotron CT apparatus imparted a dose of 1.1 and 1.3 kGy (110 and 130 krad) in two recent experiments using the microCT attached to the synchrotron beamline at the Advanced Photon Source at the Argonne National Laboratory, beamline and hutch 13‐BM‐D (Friedrich et al. ), which is similar to the values calculated here from the induced TL. According to government health reports (COMARE ), a typical X‐ray CT scan deposits in the human body a dose of about 1000 mrem.…”

Effect of polychromatic X‐ray microtomography imaging on the amino acid content of the Murchison CM chondrite

“…Friedrich et al. () found no significant effect on the amino acid abundance in 20 amino acids enantiomers or enantiomeric ratios in seven amino acids after irradiation. In this work, we are interested in the effect of benchtop μCT instrumentation where the total photon flux is order of magnitudes lower than found in synchrotron beamlines.…”

“…Friedrich et al. () explored the effect of high‐intensity synchrotron X‐ray radiation on the amino acids contained in the CM carbonaceous chondrite Murchison. The X‐ray beam used in synchrotron μCT imaging is brilliant (Nielsen ) but the X‐rays impinging the sample in the Friedrich et al.…”

“…The X‐ray beam used in synchrotron μCT imaging is brilliant (Nielsen ) but the X‐rays impinging the sample in the Friedrich et al. () experiments were at high monochromatic energies (25 or 50 keV). With these relatively high energies, Compton scattering dominates the interaction of the X‐rays with the molecular electrons rather than the photoelectric effect.…”

“…To examine the effect of tube‐based μCT using bremsstrahlung radiation on the amino acids in a carbonaceous chondrite, we performed a set of experiments similar to those in Friedrich et al. (). Since Murchison CM chondrite amino acid abundances have been well studied (e.g., Elsila et al.…”