Cosmic and solar radiation allow us to investigate myriad phenomena in astrophysics and heliophysics, and we can use them to study the surface composition of the Moon and other planets in the solar system. At the same time, mitigating the exposure of spacecraft and their crew to high-energy radiation is one of the greatest challenges of human spaceflight. This thesis presents the development of two instruments for studying cosmic and solar particles and the secondary radiation created by them. One is the RadMap Telescope, a radiation monitor designed for characterizing the environment inside the International Space Station. It is the first detector providing spectroscopic capabilities in a form factor small enough for use as an area dosimeter. The other is an instrument that can help detect sub-surface water-ice deposits on the Moon via neutron spectroscopy.