Solid-state sucrose is a well-known dosimetric system, which is capable of reliable dose estimates only at a considerable time after exposure. Immediately after irradiation at room temperature, its electron paramagnetic resonance (EPR) spectrum is dominated by contributions from unstable radicals, which are studied here using continuous-wave EPR and electron-nuclear double resonance (ENDOR) spectroscopy. Four hyperfine tensors of proton couplings were determined, associated with two radical species, and subsequently compared to density functional theory calculation results, which led to the identification of the species with lower abundance (U2) as a radical formed by a H abstraction from C4. The more abundant center (U1) has not been definitively identified yet, but we present compelling evidence that it should be a C6 centered radical. Comparison of the simulated EPR spectra with all available data to the experimental ones suggests that the EPR spectrum of X-irradiated sucrose immediately after irradiation can now be almost entirely understood.