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Il Nuovo Cimento (1955-1965)

, Volume 8, Issue 4, pp 539–548 | Cite as

Cosmic-ray evidence on the origin of meteorites

  • S. F. Singer
Article

Summary

The birth of a meteorite coincides with the breakup of its parent body and also with the beginning of the meteorite’s exposure to cosmic rays. This continued exposure creates through nuclear evaporations definitely calculable amounts of3He, about 2/3 of it by way of tritium. Hence the date of breakup can be obtained from the3He content; or better still, from the3He and tritium content measured in the. same sample. However, the latter method has only limited applicability. The two methods give good accord; of six meteorites dated, all are found to be about 300 million years old. This agreement establishes confidence in the calculations of the3He production rate and leads to some considerations concerning the process of nuclear excitation. The age is also in good accord with Öpik’s calculation of the mean lifetime of meteoritelike bodies against capture by the inner planets. From this agreement conclusions can be drawn concerning the mechanism of meteorite creation and concerning the relative constancy of cosmic-ray intensity as far back as 300 million years.

Riassunto

La nascita di un meteorite coincide con la frantumazione del corpo che gli dà origine nonchè con l’inizio della sua esposizione ai raggi cosmici. Tale esposizione continuata crea attraverso evaporazioni nucleari quantitativi esattamente calcolabili di3He, circa 2/3 dei quali passando per il tritio. La data di nascita del meteorite può quindi essere desunta dal contenuto di3He; o meglio ancora dal contenuto di3He e di tritio misurati nello stesso campione. Tuttavia, quest’ultimo metodo è di applicabilitá limitata. I due metodi danno risultati in buon aooordo fra di loro; sei meteoriti esaminati furono tutti trovati vecchi di circa 300 milioni di anni. Tale accordo convalida i calcoli del tasso di produzione dell’3He e porta a qualche considerazione sul processo d’eccitazione nucleare. L’età riscontrata è anche in buon accordo coi calcoli di Öpik per la vita media dei corpi meteoritici rispettp alla cattura da parte dei pianeti interni. Da questo accordo si possono trarre conclusioni sul meccanismo di oreazione dei meteoriti e sulla costanza relativa dell’intensità délia radiazione cosmica negli ultimi 300 milioni di anni.

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Copyright information

© Società Italiana di Fisica 1958

Authors and Affiliations

  • S. F. Singer
    • 1
  1. 1.University of MarylandCollege ParkUSA

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