Herein, Selenium (Se) nanoparticles (NPs) have been synthesized in the host matrix of a neat room temperature ionic liquid (RTIL) via rapid, one-pot electron beam (EB) mediated approach. A dark red coloured solution was obtained, which exhibited absorption bands at 520, 620 and 730 nm. The Se NPs were predominantly amorphous, as was indicated from the XRD and TEM studies. This was further evident from the Raman mapping of the NPs. The NPs extracted from the RTIL showed assembling of the primary units (flake and spherical shaped) into an interconnected porous nanostructure. Interestingly, the well-known amorphous to crystalline phase transformation of Se NPs was found to be much slower (>2 months) in RTIL compared to few minutes-to-days as reported in earlier studies. Further, the interplay of dose rate was found to have significant impact on the morphology of the Se NPs. An equivalent dose of gamma-ray irradiation (low dose rate) produces largely globular and less interconnected NPs. Based on the results obtained, it can be inferred that the RTIL simultaneously played the role of a solvent, a stabilizer and an in-situ source of radicals for the reduction of precursors. The underlying mechanism for the formation and subsequent morphological evolution of Se nanostructures in the two methods (EB and gamma-irradiation) has been proposed, and was rationalized in the viewpoint of dose rate difference in addition to the existence of innate structural and fluidic aspects of the RTIL. (C) 2017 Elsevier B.V. All rights reserved.