The spin relaxation time T-1 for short-lived beta emitters O-13 and Mg
-23 implanted in Pt have been measured for the first time; T1T(O-13) =
2.90 +/- 0.65 Ks and T1T( Mg) = 1665 +/- 140 Ks. The Knight shift for
O-13 in Pt was measured at 300 K to be K(O-13) = +(4.23 +/- 0.14) x 1
0(-3). In the case of O-13, the Knight shift is unusually large and th
e relaxation time is unusually fast compared with other interstitial i
mpurities in Pt. A KKR band-structure calculation reproduces the prese
nt large Knight shift fairly well.