Cosmic Ray Exposure Age Determinations of Cosmic Spherules from Marine Sediments

AbstractThe cosmic ray exposure ages of deep sea metalic lie spherules were determined by various methods; low level countings (Ni-59), neutron activation analysis (Mn-53), high energy accelerator mass spectrometry (Be-10, Al-26) and mass spectrometry (K isotopes). The exposure ages of 0.3 - 50 Ma were obtained. According to Poynting-Robertson effect, the starting points (supplying sources) are located at inner region of the orbit of Saturn.

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3. Fragmentation of Asteroids and Delivery of Fragments to Earth

International Astronomical Union Colloquium ◽

10.1017/s0252921100070184 ◽

1977 ◽

Vol 39 ◽

pp. 283-291 ◽

Cited By ~ 1

Author(s):

G. W. Wetherill

Keyword(s):

Cosmic Ray ◽

Asteroid Belt ◽

Combined Effects ◽

Iron Meteorites ◽

Exposure Age ◽

Impact Rate ◽

Dynamical Time ◽

Spectrophotometric Data ◽

Exposure Ages ◽

Cosmic Ray Exposure Ages

Earth-impacting meteoroids are derived from both comets and asteroids, and some uncertainty still exists regarding with which of these bodies some stone meteorites should be identified. In contrast, the long cosmic ray exposure ages of iron meteorites strongly suggest a long-lived asteroidal source capable of providing ~108 g/yr of this material to the earth’s surface over at least much of solar system history. Spectrophotometric data show that differentiated asteroids are concentrated in the inner portion of the asteroid belt. The orbital histories of fragments of inner belt asteroids are investigated, considering the combined effects of close planetary encounters, secular perturbations, and secular resonances. Particular attention is given to the low inclination (<15°) objects with small semimajcr axis (2.1 to 2.6 A.U.), which can make fairly close approaches to Mars (<0.1 A.U.). It is found that the annual yield and dynamical lifetime of collision fragments of these asteroids is in agreement with the observed impact rate and exposure age of iron meteorites. A smaller yield of stone meteorites (-107 g/yr) is expected, because elimination of these objects by collision is probable on the long dynamical time scaTe. Achondrites could be produced in this way; the yield is probably too low to account for chondrites. Chondrites could possibly be derived indirectly from these bodies insofar as these asteroids are also sources of Apollo and Amor objects.

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γ-spektroskopische Untersuchungen an Steinmeteoriten

Zeitschrift für Naturforschung A ◽

10.1515/zna-1962-1012 ◽

1962 ◽

Vol 17 (10) ◽

pp. 921-924

Author(s):

C. Mayer-Böricke ◽

M.M. Biswas ◽

W. Gentner

Keyword(s):

Single Crystal ◽

Specific Activity ◽

Cosmic Ray ◽

Mean Value ◽

Exposure Age ◽

Specific Activities ◽

Exposure Ages ◽

Cosmic Ray Exposure Age ◽

Coincidence Spectroscopy

Cosmic ray produced Al26 and Na22 activities in chondrites have been studied by nondestructive γ (511 keV) — γ coincidence spectroscopy. The values of the Αl26 specific activities of the four measured hypersthene chondrite samples are nearly equal, and have a mean value of 0.061 Αl26 e+-decays/min. g.The Na22 specific activity of the Bruderheim chondrite was found to be 0.094 Na22 disint./min. g in agreement with the results obtained by other authors using different methods. From the Na22 activity and the Ne22 content of our sample we have calculated a cosmic ray exposure age of 26 × 106 y for Bruderheim. Exposure ages of other chondrites are discussed.Single crystal γ-spectroscopy of Bruderheim shows in addition to Al26 and Na22 the presence of Mn54 and K40.

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6. Mixing Process of the Lunar Surface Materials and their Cosmic-Ray Exposure Age

International Astronomical Union Colloquium ◽

10.1017/s0252921100070214 ◽

1977 ◽

Vol 39 ◽

pp. 301-306

Author(s):

J. Iriyama ◽

M. Honda

Keyword(s):

Lunar Surface ◽

Formation Rate ◽

Cosmic Ray ◽

Population Data ◽

Mixing Process ◽

Exposure Age ◽

Surface Materials ◽

Meteoroid Impact ◽

Exposure Ages ◽

Cosmic Ray Exposure Age

From the cosmic ray exposure age data, (time scale 107 - 108 years), of the lunar surface materials, we discuss the mixing process of the lunar surface layer caused by the meteoroid impact cratering. The gardening effect calculated using a crater formation rate slightly modified from the current population data is consistent with observed exposure ages of the lunar samples.

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Cosmic Ray Exposure Age Determinations of Cosmic Spherules from Marine Sediments

Properties and Interactions of Interplanetary Dust - Astrophysics and Space Science Library ◽

10.1007/978-94-009-5464-9_38 ◽

1985 ◽

pp. 179-181

Author(s):

Kazuo Yamakoshi

Keyword(s):

Marine Sediments ◽

Cosmic Ray ◽

Exposure Age ◽

Cosmic Spherules ◽

Cosmic Ray Exposure Age ◽

Age Determinations

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On Cosmic-Ray Exposure Ages of Terrestrial Rocks: A Suggestion

Radiocarbon ◽

10.1017/s0033822200014971 ◽

1995 ◽

Vol 37 (3) ◽

pp. 889-898 ◽

Cited By ~ 3

Author(s):

Devendra Lal

Keyword(s):

Cosmic Ray ◽

Cosmogenic Nuclides ◽

Clear Definition ◽

Erosion Rates ◽

Exposure Age ◽

Exposure History ◽

Definition Of ◽

Exposure Ages ◽

Cosmic Ray Exposure Ages

An important recent development in the field of geomorphology has been the application of in-situ cosmic-ray-produced nuclides to obtain model erosion rates and surface exposure ages. These concepts emerged some four decades ago in studies of cosmogenic nuclides in meteorites, but cannot generally be used analogously for terrestrial rocks. The differences in the two cases are outlined. For the case of steady-state erosional histories, the terrestrial surface exposure ages depend on the half-life of the radionuclide studied. A suggestion is made for presenting the surface exposure ages, which allows a clear definition of the meaning of the estimated exposure ages. In the case of a discrete exposure history, the meaning of “exposure age”—which should more appropriately be called “event age”—is however quite unambiguous.

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