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Il Nuovo Cimento (1943-1954)

, Volume 10, Issue 3, pp 308–318 | Cite as

Nuclear capture of negative μ mesons in photographic emulsions

  • H. Morinaga
  • W. F. Fry
Article

Summary

Ilford C-2 emulsions have been exposed to negative μ mesons from the University of Chicago cyclotron. The μ mesons were separated from the π mesons of the same momentum by utilizing the difference in the ranges of the μ and π mesons in Cu. About 24 000 meson tracks which stopped in the emulsion have been studied. In 591 cases (2.4 percent) the stopped meson is accompanied by the emission of one or more charged particles. A large percentage of these «stars» are one prong stars. The energy distributions of protons and alpha-particles from the one prong stars have been obtained. The general shapes of the energy distribution curves indicate that the protons and alpha-particles from these stars are mostly evaporation products from a moderately excited nucleus such as silver or bromine. The average energy of the charged particles from these stars is lower than from negative π meson stars. The negative π meson contamination is found to be less than 0.3 percent. In several cases the characteristics of the star make it possible to identify the nucleus in which the meson was captured and to evaluate the energy given to the nucleus. In these cases the energy given to the nucleus is found sometimes to be as high as 45 MeV.

Riassunto

Delle emulsioni Ilford C-2 sono state esposte a mesoni μ negativi prodotti dal ciclotrone dell'Università di Chicago. I mesoni μ si separavano dai mesoni π di pari impulso utilizzando la differenza di range dei mesoni μ e π nel Cu. Si sono studiate circa 24 000 tracce che si arrestano nell'emulsione. In 591 casi (2,4%) l'arresto dei mesoni è accompagnato dall'emissione di una o più particelle cariche. Una larga percentuale di dette stelle è formata di stelle a 1 ramo. Si sono ricavate le distribuzioni delle energie dei protoni e delle particelle α delle stelle a 1 ramo. L'andamento generale delle curve di distribuzione dell'energia indicano che i protoni e le particelle α derivati da queste stelle sono, generalmente, prodotti di evaporazione di un nucleo moderatamente eccitato, come l'Ag o il Br. L'energia media delle particelle cariche originate da queste stelle è minore di quella delle analoghe particelle derivate da stelle di mesoni π negativi. La contaminazione da parte di mesoni π negativi si trova essere inferiore al 0,3%. In alcuni casi le caratteristiche della stella permettono di identificare il nucleo in cui il mesone è stato catturato e di calcolare l'energia ceduta al nucleo. In questi casi, si constata, a volte, che l'energia ceduta al nucleo ammonta fino a 45 MeV.

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Copyright information

© Società Italiana di Fisica 1953

Authors and Affiliations

  • H. Morinaga
    • 1
  • W. F. Fry
    • 2
  1. 1.Department of PhysicsIowa State CollegeAmes
  2. 2.Department of PhysicsUniversity of ChicagoChicago

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