Radial gradient of galactic protons in the inner solar system

Numerical solutions of a realistic particle propagation model for the inner solar system are used to investigate the radial gradient of galactic protons with 50 Mev<E<2000 Mev. The model assumes anisotropic, energy-dependent diffusion in a stochastic interplanetary magnetic field whose average configuration is the Archimedian spiral pattern, and includes adiabatic deceleration as the dominant energy change mechanism. The results are compared with the Mariner 4 measurements of the energy-dependent earth-Mars gradient reported by O'Gallagher, and the possible role of particle transport in the solar colatitude (θ) direction is examined.