A Search for Penetrating Showers from Hydrogen at Sea Level Using a Cloud Chamber

The extent to which multiple production of $\pi$-mesons takes place in local sea-level penetrating showers was studied with a counter controlled cloud chamber in a magnetic field. The rates at which penetrating showers occur under carbon, aluminum, and lead were determined and a search was made for them under liquid hydrogen. In a total operating time of 626 hours with an average thickness of 2.28 g/${\mathrm{cm}}^2$ of liquid hydrogen above the chamber, no penetrating showers were found which could have originated in the hydrogen. On the basis of the rates at which such showers occur in heavier materials and the number of them formed in the material of the Dewar while operating with hydrogen, one would have expected to detect a minimum of 6 showers from the hydrogen if the cross section for the production of penetrating showers were the geometric area of the nucleus (taken as 6×${10}^{-26\mathrm{}}$ ${\mathrm{cm}}^2$ for hydrogen). It can then be concluded that the majority of sea-level local penetrating showers detected below heavy materials by an apparatus of this kind can be attributed mainly to plural production. From momentum measurements in the magnetic field, the minimum value which can be assigned to the momentum of the incident nucleons which causes the average penetrating shower detected with this apparatus was estimated at 6 B ev/c. It follows that the multiple production of charged mesons in a single nucleon-proton collision at about 6 Bev probably does not occur in more than 15 percent of the cases.