This article reviews radiation chemistry processes induced by high-linear energy transfer (LET) radiation. The first part gives a short historical introduction and defines the essential concepts of radiation chemistry. It is aimed at radiobiologists in search of basics in this discipline, to link to their biological observations. Then, special focus is done on LET effect, oxygen effect and nanoparticles as these parameters can influence the success of radiotherapy. The embraced point of view is the one from a chemist as involved molecular reactions in water are detailed and revealed, for example, how dioxygen can be produced in situ during high-LET irradiations, even in anoxic conditions. A step forward can be reached using nanoparticles in conjunction with radiation beams to enhance their effects. The last part of this review is thus devoted to the description of an original approach combining high-LET projectiles (3-MeV α-rays) and gold nanoparticles. Fluorescence microscopy was used to evaluate the formation yield of radicals in anoxic condition via scavenging by Ampliflu® Red. As with low-LET irradiations, an overproduction of radicals was obtained, encouraging to conduct a broader study and to consider nanoparticles in simulation as an additional source of radicals.