[en] X-irradiation of a single crystal of bromonitrothiazole at 77 K leads to signals in both the g = 4 and the g = 2 regions of the ESR spectrum. The angular dependence of these signals is consistent with the formation of a radical pair which exhibits hyperfine structure with a ¹H and ¹⁴N nucleus. This structure together with the electron-electron dipolar interaction shows that irradiation probably causes a scission of the bond between the nitrogen group and the thiazole ring. The resulting radicals are pair-wise trapped up to 170 K; at higher temperature the NO₂ radical probably adds to a neighbouring undamaged molecule to form the azaallyl radical which is stable at room temperature. (author)