<gamma> - <gamma> Perturbed Angular Correlation Study of dense Kondo effect.

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By means of perturbed angular correlation technique, spin fluctuations of Ce 4f electrons have been studied in Ce compounds which exhibit dense Kondo effect. Perturbed angular correlations can afford information about Ce spin dynamics without limitations encountered in inelastic neutron diffraction and NMR.The four detector system for time differential measurements have been remodeled by replacing two detectors with 1 1/2" NaI(Tl) scintillaters and RCA 8575 photomultipliers by two with 2" scintillaters and Phillips XP-2020 photomultipliers so that all four detectors are the same. An interface for computer control of the whole system and newly designed two channel digital pulse hight analysers were assembled to improve accuracy, stability, efficiency and time resolution of the apparatus.In addition to supplementary measurements on (La-Ce)Si system and (La-Ce) <Al_2> system, perturbed angular correlations were measured on (La-Ce) <Ni_2> system. Having pronounced fluctuations in the whole composition range and the temperature range, the (La-Ce) <Ni_2> compounds were found to have relatively high Kondo temperatures. The correlation time obtained from the attenuation facors of angular correlations were analysed on the basis of multiorbital Anderson model. An interpolation formula consistent with the perturbation theory at high temperatures and with the Hnzawa-Yamada theory at OK was deduced taking into account of crystalline field splitting. The experimental data were fitted to the interpolation formula for the evaluation of <T_K> . The obtained <T_K> values are substantially lower than those evaluated by other methods. The hyperfine coupling constant in the singlet ground state of Kondo system which is a possible origin of the discrepancy is an interesting future problem.