  RADMON is a small radiation monitor designed and assembled by students of the
University of Turku and the University of Helsinki. It is flown on-board
Aalto-1, a 3-unit CubeSat in low Earth orbit at about 500 km altitude. The
detector unit of the instrument consists of two detectors, a Si solid-state
detector and a CsI(Tl) scintillator, and utilizes the \textDelta{E}-E technique
to determine the total energy and species of each particle hitting the
detector. We present the results of the on-ground and in-flight calibration
campaigns of the instrument, as well as the characterization of its response
through extensive simulations within the Geant4 framework. The overall energy
calibration margin achieved is about 5\%. The full instrument response to
protons and electrons is presented and the issue of proton contamination of the
electron channels is quantified and discussed.
