A muoniated radical in selenium

We report new 0.3 T transverse-field muSR experiments in crystalline Se which show only a small, slowly relaxing muon signal at 300 K, accounting for about 30% of the incoming muon polarization. However, at 90 K signals are observed around 74 and 157 MHz, characteristic of a radical with a hyperfine coupling of 231 MHz. Very fast relaxation which increases with temperature makes these signals impossible to follow beyond 200 K. Above 400 K a quickly relaxing diamagnetic signal becomes visible, its relaxation falling with increasing temperature. In the melt (> 490 K) just a single non-relaxing diamagnetic signal is seen. These observations may be explained by electron spin-exchange with a muoniated radical. (C) 2002 Elsevier Science B.V. All rights reserved.