The decay rate of ${}^7\mathrm{Be}$ has always been measured by either forming a beryllium compound or implanting ${}^7\mathrm{Be}$ in a medium. We can quantitatively understand the measured changes of ${}^7\mathrm{Be}$ decay rates in different environments as well as its L/K orbital electron capture ratio using tight-binding linear muffin-tin orbital method calculations. We find that ${}^7\mathrm{Be}$ loses a very substantial fraction of its $2s$ electrons in a medium. As a result of this loss of $2s$ electrons, the extracted nuclear matrix element of the ${}^7\mathrm{Be}$ electron capture reaction from terrestrial decay rate measurements should increase by 2–2.7%, thus decreasing the calculated ${}^8\mathrm{B}$ solar neutrino flux from the Standard Solar Model by 2–2.7%.

• Received 2 September 2004

DOI:https://doi.org/10.1103/PhysRevC.71.025801