Rays In Meteorites Research Articles

Meteorite Ablation Evaluated from the Data on the Density of Cosmic-Ray Tracks

We determined the form of the functional dependence of the rate of formation of tracks of galactic cosmic rays in meteorites (ρ/t) on the shielding degree for ordinary chondrites with preatmospheric radius R > 5 cm based on published semiempirical data on ρ/t. The resulting dependence was used to construct a nomogram which allowed us to estimate the ablation of a meteorite according to the average rate of track formation in it and its recovered mass. The calculated ablation of meteorites agrees with the estimates obtained by other methods. The average ablation for 83 ordinary chondrites was found to be equal to 78.4+3.1–3.4%. The analysis of the data obtained demonstrated that the average preatmospheric mass of chondrites is M ∼ 90 kg, and for 95% of the meteorites, the preatmospheric masses fall in the interval ∼2–3500 kg, which corresponds to radii from ∼5 to ∼60 cm. It was found that meteorites with a small preatmospheric mass tend to higher ablation.

Oral histories in meteoritics and planetary science: III. Robert M. Walker

Abstract— In this interview, taped in 2000 August, during the meeting of the Meteoritical Society in Chicago, Robert Walker recalls that he began studying meteorites when he realized that they should display particle tracks caused by their bombardment by cosmic rays. Walker was much intrigued by the idea of finding fossil tracks from old cosmic rays. Among his more important accomplishments, he lists the discovery of tracks of extremely heavy cosmic rays in meteorites and those of very lowenergy solar flare particles in lunar samples. He has played a leadership role in research on interplanetary dust particles and on presolar grains in meteorites in an effort to learn more about the origins of the elements. Walker has spent most of his career at Washington University in St. Louis where he established the McDonnell Center for Space Science. In 1993, the Meteoritical Society presented him with the Leonard Medal.

Helium produced by cosmic rays in meteorites

Helium produced by cosmic rays in meteorites

Measurement of44Ti(44Sc) in meteorites

The measurement of44Ti produced by spallation reaction of cosmic rays in meteorites fell in the last hundred years can be used for investigations on century-scale variations of solar activity. The low specific activity and the interferences of natural background and of meteorite gamma emitters are the main difficulties to be surmounted in this measurement. A selective γ-spectrometer consisting of a HP Ge and a NaI(T1) detectors in coincidence and anticoincidence has been set up in the underground (70 m w.e.) Laboratory of Monte dei Cappuccini, which allows to obtain a reliable measurement of44Ti(44Sc).

Deconvolution of the effects of solar and galactic cosmic rays in meteorites on the basis of improved interaction data

Abstract The interaction of galactic protons with small meteorites was simulated by isotropically irradiating artificial meteorites with radii of 5, 15, and 25 cm with 600 MeV protons. The depth dependent production of a wide range of spallation products was measured and compared with HETC calculations. On the basis of the new data a deconvolution of SCR and GCR effects in small meteorites was performed.

Half‐life of 26Al

The half‐life of 26Al has been redetermined because of suggestions of an error in the accepted value based on its use in calculating 21Ne production rates from cosmic rays in meteorites. Two solutions of 26Al were analyzed for the specific radioactivity and mass spectrometric determination of the 26Al concentration. The half‐life obtained for 26Al was 7.05×105 years ±3.4%. This is identical to the accepted value of 7.16×105 years and indicates that problems with the 21Ne production rate is not due to an erroneous half‐life.

Tracks of heavy primary cosmic rays in meteorites

Tracks of primary cosmic rays with atomic number ≳20 have been identified in 23 out of 42 meteorites of various types. They satisfy the criteria of rapid attenuation with depth, directional anisotropy, proper length distribution, proper absolute number, and equal numbers in adjacent minerals with widely different uranium contents. From measurements of track densities in samples of meteorites with known cosmic-ray age, the original depths of the samples below the preatmospheric surfaces of the meteoroids were obtained. These ranged from ∼3 to 50 cm. Minimum values of the preatmospheric radii ranging from 10 to 55 cm were also obtained. Using a computed relationship between track lengths and particle mass, the observed distribution of track lengths was used to infer the existence of cosmic rays that are considerably heavier than iron. The relative abundance of cosmic rays with Z ≳ 32 was estimated to be ∼1:4000 that of the iron group (20 ≤ Z ≤ 30).

Determination of trace elements in meteorites

For some years, the meteorites, being aggregations of extra-terrestrial matter, have stimulated world-wide interest. This is connected with continuously expanding space research, especially because, until now, no space probes have transferred any interplanetary or interstellar matter to Earth, except minute amounts of micrometeorites. Furthermore, the determination of certain radionuclides produced by cosmic rays in meteorites allows derivation of their “ages”, i.e. of the time since their impact on Earth, or of the time, respectively, during which they have been exposed to cosmic rays.Much interest is caused by the trace elements, especially because from their contents conclusions can be drawn concerning the cosmic abundance of the rarer elements. Many elements of the periodic system, being trace constituents in meteorites, are determinable by neutron activation analysis.In Vienna a research project has been developed by some academic institutions, concerning the determination of main, minor, and trace constituents of the various types of meteorites, using modern separation and determination methods.We have begun to investigate an iron meteorite from Magura (Czechoslovakia) and a hypersthene-olivine chondrite from Mocs (Rumania). The iron meteorite was investigated by gamma-spectrometry and the stone meteorite by gamma-spectrometry as well as spectrochemically.The preliminary results are the following: Magura iron: Main and minor constituents: Fe, Ni (6, 35%), Co (0, 80%), C (0, 38%)Trace constituents: Mn, Cr, Cu, Ga, V, Ag, Sb, Sn, Hf, Ir, Au; not yet made sure: Sm, Eu, Tb, Dy, Ho, Cp, Re, Os, Ru Mocs chondrite: Main constituents Si (38, 2%), Mg, Fe, CaMinor and trace constituents: Ni, Al, Na, Mn, Cr, Ga, Sc, Sb, Cu, Co, Ti, V, Au, Tr, not yet made sure: Sm, Dy, Ho, Yb, Cp, Re.

Nuclear Effects of Cosmic Rays in Meteorites

Following a major shortage of 99Mo in the 2009–2010 period, concern grew that the aging reactor production facilities needed to be replaced. Most producers were using highly enriched 235U (HEU) as the target material. The Organisation for Economic Co-...Read More