Jr-meson

CoNVERSi et al. used a magnetic lens to separate (cosmic ray) /. -mesons from [jL -mesons. They measured the number of electrons emitted when mesons stopped in Fe and C. They found that / -mesons stopping in iron predominantly underwent nuclear capture. However, those mesons stopping in carbon mainly underwent free decay instead of capture. If they were the mesons proposed by Yukawa, they should have also been captured in the carbon (see Tomonaga and Araki ). The experiment of Conversi, Pancini, and Piccioni thus established that / -mesons have a weak interaction with nucleons (like the beta decay interaction) instead of the strong interaction that one now finds existing between jr-mesons and nucleons. 

Reactions of jr-mesons with nuclei. The remark at the end of the last section holds true as regards the reactions of r/r-mesons with nuclei. The values of the cross-sections and the angular distributions in scattering are a result of pion-nucleon interactions and nucleon-nucleon interactions. Most of the experimental and theoretical investigations were motivated by a desire to study the pion-nucleon interaction however it is frequently found that the interpretation of data involves nucleon-nucleon interactions. 

Only brief mention is made here of the large number of radiochemical and photographic emulsion studies of the capture of jr -mesons. An excellent review of this work up to 1953 has been given by Turkevitch and mofe recent work can be found in the bibliography of Winsberg s article . The main conclusion is that the 7r -meson when it is captured gives up its entire rest mass to the nucleus and a cascade and nuclear evaporation ensue (see Sects. 11 and 12). The end products have distribution similar to those described for nucleon reactions (Sect. 36) and photon reactions (Sect. 47). Meson induced fission has been studied by Al-Salam , Sugarman , and John and Fry . 

There is the possibility that the initial reaction involved in jr -meson capture may more closely resemble high energy photon reactions than high energy nucleon reactions in that two particles may initiate the cascade. Brueckner,... 

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