Range and Specific Ionization for High-Energy Protons in Nuclear Emulsions

Abstract

Stacks of nuclear emulsion varying in thickness from 18.35 g/${\mathrm{cm}}^{2}$ to 56.83 g/${\mathrm{cm}}^{2}$ were exposed in the external proton beam of the Berkeley cyclotron, and the average specific ionization $\frac{\mathrm{dT}}{\mathrm{dx}}$ [in Mev (${\mathrm{g}/{\mathrm{cm}}^{2})}^{\ensuremath{-}1}$] was measured by determining the equivalent thickness of Cu needed to remove the same amount of energy from the beam as a given thickness of emulsion. The energies range from 230 to 320 Mev. The emulsion stacks consisted of layers of 200-\ensuremath{\mu} Ilford C-2 stripped emulsions of average density 3.81\ifmmode\pm\else\textpm\fi{}0.01 g/${\mathrm{cm}}^{2}$. The specific ionization was found to be 1.5 percent higher for emulsion than for Cu measured over the same energy interval. From these data the ratio of the mean ionization potentials for emulsion and Cu was determined as $\frac{{I}_{E}}{{I}_{\mathrm{Cu}}}=0.89\ifmmode\pm\else\textpm\fi{}0.09$. The range of 342.5-Mev protons in emulsion was found to be 92.68\ifmmode\pm\else\textpm\fi{}0.25 g/${\mathrm{cm}}^{2}$, which is 1.1 percent lower than the measured range of the same beam in Cu (93.65\ifmmode\pm\else\textpm\fi{}0.20 g/${\mathrm{cm}}^{2}$). The measured range in emulsion is about 1.5 percent shorter than the value calculated by Vigneron (and extended to higher energies by Barkas). They assumed 332 ev as the mean ionization potential of emulsion.