We report on experimental confirmation of the non-classical rotational inertia (NCRI) in solid helium samples originally reported by Kim and Chan. The onset of NCRI was observed at temperatures below ≈ 400 mK. The ac velocity for initiation of the NCRI suppression is estimated to be ≈ 10 µm/sec. After an additional annealing of the sample at T = 1.8 K for 12 hours, ∼ 10% relative increase of NCRI fraction was observed. Then after repeated annealing with the same conditions, the NCRI fraction was saturated. It differs from Reppy's observation on a low pressure solid sample.

Detailed studies of ac velocity V_{ac} and T dependence of torsional oscillator responses of solid 4He are reported. A characteristic onset temperature T_{0} approximately 0.5 K is found, below which a significant V_{ac}-dependent change occurs in the energy dissipation for the samples at approximately 32 bar and for one at 49 bar. A V_{ac} dependence of the so-called "nonclassical rotational inertia" fraction also appears below approximately T_{0}. The log(V_{ac}) linear dependence, which suggests involvement of quantized vorticies, was examined in the nonclassical rotational inertia fraction. We find a common 1/T;{2} dependence for this linear slope change in all of the samples for 30

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