Irradiation Histories of Iron Meteorites

Honda, M.; Nagai, Hiroki; Nagao, Keisuke; Bajo, K.; Takaoka, N.; Oura, Y.; Nishiizumi, K.

doi:10.1143/jpsjs.78sa.12

Cited by 4 publications

(6 citation statements)

References 8 publications

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“…By way of example, assuming a Rh/Pd elemental ratio of about 1 and an exposure age of 650 Ma, the cosmic-ray shift in 104 Pd/ 106 Pd is up to 1 e-unit, i.e., well detectable with present-day analytical precision. Note that Chen and Papanastassiou (2005) found no anomalies in a Pd isotope study of various iron meteorites despite the fact that some of them are known to have relatively long cosmic-ray exposure ages, e.g., 300 Ma for Gibeon (Honda et al 2009). However, the finding of a normal Pd isotope composition despite long cosmic-ray exposure ages is due to low Rh/Pd ratios.…”

Section: Modeling Resultsmentioning

confidence: 99%

“…Note that Chen and Papanastassiou () found no anomalies in a Pd isotope study of various iron meteorites despite the fact that some of them are known to have relatively long cosmic‐ray exposure ages, e.g., 300 Ma for Gibeon (Honda et al. ). However, the finding of a normal Pd isotope composition despite long cosmic‐ray exposure ages is due to low Rh/Pd ratios.…”

Section: Modeling Resultsmentioning

confidence: 99%

“…Assuming now an exposure age for Gibeon of about 300 Ma (Honda et al. ), the maximum shift in 108 Pd/ 104 Pd and 106 Pd/ 104 Pd (normalized to 110 Pd/ 104 Pd) is −0.15 and −0.24 ε‐units, respectively, i.e., hardly detectable. Consequently, Pd isotopes can only serve as neutron‐dose monitors for samples with relatively high Rh/Pd ratios (Rh/Pd > 0.5).…”

Section: Modeling Resultsmentioning

confidence: 99%

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Thermal neutron capture effects in radioactive and stable nuclide systems

Leya

Masarik

2013

Meteorit & Planetary Scien

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Abstract-Neutron capture effects in meteorites and lunar surface samples have been successfully used in the past to study exposure histories and shielding conditions. In recent years, however, it turned out that neutron capture effects produce a nuisance for some of the short-lived radionuclide systems. The most prominent example is the 182 Hf-182 W system in iron meteorites, for which neutron capture effects lower the 182 W/ 184 W ratio, thereby producing too old apparent ages. Here, we present a thorough study of neutron capture effects in iron meteorites, ordinary chondrites, and carbonaceous chondrites, whereas the focus is on iron meteorites. We study in detail the effects responsible for neutron production, neutron transport, and neutron slowing down and find that neutron capture in all studied meteorite types is not, as usually expected, exclusively via thermal neutrons. In contrast, most of the neutron capture in iron meteorites is in the epithermal energy range and there is a significant contribution from epithermal neutron capture even in stony meteorites. Using sophisticated particle spectra and evaluated cross section data files for neutron capture reactions we calculate the neutron capture effects for Sm, Gd, Cd, Pd, Pt, and Os isotopes, which all can serve as neutron-dose proxies, either in stony or in iron meteorites. In addition, we model neutron capture effects in W and Ag isotopes. For W isotopes, the GCR-induced shifts perfectly correlate with Os and Pt isotope shifts, which therefore can be used as neutron-dose proxies and permit a reliable correction. We also found that GCR-induced effects for the 107 Pd-107 Ag system can be significant and need to be corrected, a result that is in contrast to earlier studies.

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Section: Modeling Resultsmentioning

confidence: 99%

Section: Modeling Resultsmentioning

confidence: 99%

Section: Modeling Resultsmentioning

confidence: 99%

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Thermal neutron capture effects in radioactive and stable nuclide systems

Leya

Masarik

2013

Meteorit & Planetary Scien

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“…Size-reducing collisions of meteoroids can also raise production rates. For example, Lavielle et al (1999) identify Bendego as an iron that may have undergone multiple periods of exposure, presumably initiated by collisions, and there are others, such as Canyon Diablo (Michlovich et al, 1994) and Gibeon (Honda et al, 2009). In general, we expect collisions to reduce the sizes of meteoroids and thereby tend to increase production rates, that is, to have the same qualitative effect as would an increase in the cosmic-ray flux.…”

Section: Ironsmentioning

confidence: 94%

Cosmic-Ray Exposure Ages of Meteorites

Herzog

Caffee

2014

Treatise on Geochemistry

153

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“…Based on this estimation, the San Juan A2 mineral phases studied here experienced 29-32 times lower fluence than Campo del Cielo silicates, or about 6.5 × 10 17 thermal equivalent neutrons per cm 2 , compared to values reported for lunar soils (Burnett et al 1972;Curtis and Wasserburg 1975) and large chondrites (Bogard et al 1995). Campo del Cielo apparently experienced a simple single-stage irradiation history, without any mechanical damage (constant exposure geometry) for more than 180 Ma (Honda et al 2009). Assuming the neutron flux spectra are identical for MURR and Campo del Cielo (certainly not true but good for an estimate), the average thermal equivalent neutron flux for these fragments is about 1.2 × 10 2 n cm −2 s −1 .…”

Section: Xenonmentioning

confidence: 43%

Neutron capture ¹²⁸Xe and ¹²⁹Xe in the San Juan mass of the Campo del Cielo IAB iron meteorite: Evidence for a high fluence of thermalized neutrons

Pravdivtseva

Varela

Meshik

et al. 2021

Meteorit & Planetary Scien

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The petrographic study of the San Juan A2 polished section demonstrated textural and compositional similarities with the Campo del Cielo IAB iron meteorite, with trace element abundances in metal following the pattern of bulk Campo del Cielo. Xenon, neon, and helium isotopic compositions have been measured in radial graphite rims, massive graphite inclusions, fine-grained graphite aggregates, cliftonite, and platy graphite. Two silicate inclusions and two areas of metal were also analyzed. 3 He/ 4 He versus 4 He/ 21 Ne data for San Juan metal plot next to the values reported for the El Taco fragment of Campo del Cielo, supporting San Juan being a part of the Campo del Cielo meteorite shower. Based on the Ne isotopic composition of its components, and the observed correlation between 128 Xe and 129 Xe, the San Juan A fragment of Campo del Cielo was well shielded from the primary galactic cosmic ray high-energy irradiation. Its size allowed the secondary neutrons to be fairly well thermalized, receiving an equivalent (normalized to the research reactor with highly thermalized neutron spectrum) fluence of thermal and epithermal neutrons of 6.6 × 10 17 n cm −2 . Considering 1.8 × 10 8 years single-stage and constant exposure geometry irradiation history for Campo del Cielo, and assuming the identical neutron flux spectra for the research reactor and Campo del Cielo, the average thermal equivalent neutron flux for San Juan is about 1.2 × 10 2 n cm −2 s −1 . Xe isotopic composition in the radial graphite rims and platy graphite shows evidence of live 129 I in San Juan and is consistent with a mixture of iodine-derived and tellurium-derived Xe.

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Irradiation Histories of Iron Meteorites

Cited by 4 publications

References 8 publications

Thermal neutron capture effects in radioactive and stable nuclide systems

Thermal neutron capture effects in radioactive and stable nuclide systems

Cosmic-Ray Exposure Ages of Meteorites

Neutron capture ¹²⁸Xe and ¹²⁹Xe in the San Juan mass of the Campo del Cielo IAB iron meteorite: Evidence for a high fluence of thermalized neutrons

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Irradiation Histories of Iron Meteorites

Cited by 4 publications

References 8 publications

Thermal neutron capture effects in radioactive and stable nuclide systems

Thermal neutron capture effects in radioactive and stable nuclide systems

Cosmic-Ray Exposure Ages of Meteorites

Neutron capture 128Xe and 129Xe in the San Juan mass of the Campo del Cielo IAB iron meteorite: Evidence for a high fluence of thermalized neutrons

Contact Info

Product

Resources

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Neutron capture ¹²⁸Xe and ¹²⁹Xe in the San Juan mass of the Campo del Cielo IAB iron meteorite: Evidence for a high fluence of thermalized neutrons