Perturbed Angular Correlation Study of the Static and Dynamic Aspects of Cadmium and Mercury Atoms Inside and Attached to a C₆₀ Fullerene Cage

Abstract

30 keV ^111mCd and 50 keV ^199mHg beams from ISOLDE were used to implant on preformed targets of C₆₀ with a thickness of 1 mg cm^-2. Endofullerene compounds, viz. ^111mCd@C₆₀ and ^199mHg@C₆₀ formed during implantation were separated by filtration through micropore filter paper followed by solvent extraction. Dried samples of the endofullerene compounds were counted for the time differential perturbed angular correlation (TDPAC) measurement using the coincidence of the 151 - 245 keV cascade of ^111mCd and the 374 - 158 keV cascade of ^199mHg on a six LaBr₃(Ce) detector system coupled with digital electronics. The results for ^111mCd@C₆₀ indicate a single static component (27%) and a fast relaxing component (73%), the latter implying that the cadmium atom moves rapidly inside the cage at room temperature. The quadrupole interaction frequency and asymmetry parameter of the cadmium atom occupying the static site in C₆₀ are w_Q=8.21(36) Mrad s^-1 and η = 0.41(9), respectively. The fast relaxation constant is 0.0031(4) ns^-1. Similarly, mercury atoms also exhibit a single static and a fast component. The static site has a quadrupole frequency w_Q=283.0(12.4) Mrad s^-1 and η =0 with a fraction of 30%. The fast relaxation constant is 0.045(8) ns^-1 with a fraction of 70%, very similar to that of cadmium.