Room temperature EPR spectra of (NH₄)₂SO₄ doped K₂SO₄ monocrystals irradiated with x-rays show the presence of NH₃⁺ radicals. The EPR parameters areg ‖=2.0037 andg ⊥ = 2.0068;¹⁴NA_XX=13.75;A_YY=24.5;A_ZZ=25.5 gauss;¹HA_XX=A_YY=22 andA_ZZ=25 gauss. From the¹⁴N and¹H coupling constants it has been inferred that at room temperature the planar NH₃⁺ radical undergoes rotation about theC₃ axis which corroborates with the equivalence of the protons, but the radical itself is in an asymmetric crystal field environment. The 77K spectra indicate a considerable reduction in the motion of the radical with the free motion almost completely stopped.