The decay rate of ${}^7\mathrm{Be}$ electron capture in ${\mathrm{C}}_{70}$ and Be metal was measured employing a reference method. The half-life ($T_{1/2}$) of ${}^7\mathrm{Be}$ endohedral ${\mathrm{C}}_{70}$ (${}^7\mathrm{Be}$@${\mathrm{C}}_{70}$) was found to be $T_{1/2}=52.49\pm 0.04$ d at room temperature ($T=293$ K) and $T_{1/2}=52.42\pm 0.04$ d at liquid helium temperature ($T=5$ K). Furthermore, the $T_{1/2}$ of ${}^7\mathrm{Be}$ in Be metal was $T_{1/2}=53.25\pm 0.04$ d at room temperature ($T=293$ K) and $T_{1/2}=53.39\pm 0.03$ d at liquid helium temperature ($T=5$ K). These values for ${}^7\mathrm{Be}$@${\mathrm{C}}_{70}$ at $T=5$ K are approximately $1.6\%(1.8\%$) smaller than those for ${}^7\mathrm{Be}$ in Be metal at $T=293$ K ($T=5$ K), indicating the difference in the electron wave functions for ${}^7\mathrm{Be}$ inside ${\mathrm{C}}_{70}$ and ${}^7\mathrm{Be}$ in ${\mathrm{C}}_{60}$ and Be metal. The average charge transfer from the $L\left(2s\right)$ electrons of the ${}^7\mathrm{Be}$ atom influences such variations in the decay constant ($\lambda =ln2/T_{1/2}$) in the environment. The experimental and theoretical investigations revealed that the change in the EC-decay rate of ${}^7\mathrm{Be}$ could be largely related to the potential configurations and the environment inside ${\mathrm{C}}_{60}$ and/or ${\mathrm{C}}_{70}$ cages. The motion of ${}^7\mathrm{Be}$ inside cages was found to be restricted according to temperature.

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• Atomic & molecular collisions
• Beta decay
• Electron & muon capture
• Lifetimes & widths
• 6 ≤ A ≤ 19