Analysis of energy deposition in water around the site of capture of a negative pion by an oxygen or carbon nucleus

Abstract

A study was made of the energy deposited in water spheres and cylinders of increasing size around the site at which an oxygen or carbon nucleus captures a stopped negative pion. No great differences were found either between results for O and C or between results for spheres and cylinders. As known from the literature, approximately 100 MeV is released as kinetic energy of secondary products after capture, about 60 MeV to neutrons and 40 MeV to charged particles. Most of the neutron energy is transported away from the immediate capture site. Calculations here show that 50% of the charged-particle energy is deposited within a distance of 0.1 cm from the site and 90% within 2 cm. Practically all charged particles with an LET ⩾ 170 MeV cm-1 in water lose their energy within ~0.2 cm. The calculations also show that, on the average, 30 NeV of energy is deposited inside a sphere of 1 cm radius per π- capture by oxygen and 35 XeV per capture by carbon.