Electron-capture decay rate ofB7e@C60by first-principles calculations based on density functional theory

Abstract

Carrying out a first-principles calculation assuming linear relationship between the electron density at Be nucleus and the electron-capture ͑EC͒ decay rate, we explained why 7 Be@C 60 shows higher EC decay rate than 7 Be crystal, which was originally found experimentally by Ohtsuki et al. ͓Phys. Rev. Lett. 93, 112501 ͑2004͔͒. From the results of the calculation, we found that there are inequivalent four stable ͑i.e., lower energy͒ Be sites inside C 60 and that center of C 60 ͑C_C 60 ͒ is the most favorable site. For C _ C 60 , the electron density at the Be nucleus is the highest. It is also much higher than that at the Be nucleus in a Be crystal. Also, we estimated the expected electron density at the Be nucleus at room temperature by taking statistical average of the electron densities at the four Be nucleus sites using the Boltzmann distribution. The results of the calculation show fairly good agreement with the experimental results. In this paper, we focus on the detail of calculation, which was not fully demonstrated in the paper by Ohtsuki.

Electron captureβdecay ofBe7encapsulated inTkalya1, Bibikov2, Bodrenko3 2010Phys. Rev. C17010View full textAdd to dashboardCite

“…at the Be nucleus. the DFT calculations[5,6]. However, our value is in excellent agreement with the experimental data of Kraushaar et al[16] of the direct measurement of the 7 Be half-life in the metal source T…”

“…The corresponding relative decrease of the electron density in our calculations is 0.28%, in qualitative accord with the value of 0.17% in Refs. [5,6]. The reason for the enhanced electron density in Be@C 60 might be a slight hybridization of Be's and C 60 's orbitals, as suggested in Ref.…”

“…A density functional theory (DFT) basing numerical calculations of the electron density at the Be nucleus was presented in Refs. [5,6] along with the experimental data. It was found that, in accordance with the experiment, the electron density at Be encapsulated in the center of C 60 is larger than the one at the nuclei in metallic Be.…”

Half-life measurement of 7Be in host beryllium metal

“…This implied that the 7 Be atoms are located in a unique environment inside C 60 . This large change in the half-life is firmly caused by the electron dens-ity at the nucleus position and the magnitude of the change has also been explained theoretically [18].…”

Measurement of Neutron Lifetime and Purcell Effect

“…The authors interpreted the observations by calculating the electron density at the position of 7 Be inside C 60 . Based on these experiments, Morisato et al used density functional theory to calculate and explain why 7 Be@C 60 shows higher EC decay rate than 7 Be metal found in the above experiments in detail, and found that there are inequivalent four stable Be sites inside C 60 and that center of C 60 is the most favorable site [59]. Recently, a similar analysis was published in 2012 [60].…”