Dose mean lineal energy for fast neutrons in small spherical targets.

The calculation of microdosimetric distributions for neutrons, has so far been performed for target sizes in the micrometre region, where the LET approximation is valid. In small spherical targets straggling and δ ray effects strongly influence the energy deposition. The dose mean lineal energy ȳ(D) can, however, be calculated using Kellerer's proximity function approach from a computer simulated ion track event pattern. In such tracks, different structural components can be distinguished. The calculation was performed for the main constituents of secondary charged particle spectra produced by 14.1 MeV neutrons in tissue. The influence of δ rays on the energy deposition in small targets of 1 to 100 nm diameter is shown and the deviation from the LET approximation is discussed