Electron capture is a variant on beta-radiation.  The lightest nucleus to decay by electron capture is 7Be -- beryllium-7.  The daughter nucleus is 7Li -- lithium-7.  The electron is transformed into a massless particle (a neutrino): e − + 7 B e + ⟶ 7 L i + ν The initial electron is bound in the atom, so the beryllium mass includes the electron.  In fact, since the electron starts bound in the atom, a more-accurate statement of the nuclear reaction is probably: 7 B e ⟶ 7 L i + ν The masses are beryllium: 7.016929 u, and lithium: 7.016003 u, and refer to the neutral atom as a whole.  (Use uc and uc2 as your momentum and energy units -- but carry them along in your calculation.) The initial beryllium atom is stationary.  Calculate the speed of the final lithium nucleus in km/s. (You will make life much easier for yourself if you recognize that practically all the energy released goes into the lighter particle.  c = 300,000 km/s)

Electron capture is a variant on beta-radiation.  The lightest nucleus to decay by electron capture is ⁷Be -- beryllium-7.  The daughter nucleus is ⁷Li -- lithium-7.  The electron is transformed into a massless particle (a neutrino):

e − + 7 B e + ⟶ 7 L i + ν

The initial electron is bound in the atom, so the beryllium mass includes the electron.  In fact, since the electron starts bound in the atom, a more-accurate statement of the nuclear reaction is probably:

7 B e ⟶ 7 L i + ν

The masses are beryllium: 7.016929 u, and lithium: 7.016003 u, and refer to the neutral atom as a whole.  (Use uc and uc² as your momentum and energy units -- but carry them along in your calculation.)

The initial beryllium atom is stationary.  Calculate the speed of the final lithium nucleus in km/s. (You will make life much easier for yourself if you recognize that practically all the energy released goes into the lighter particle.  c = 300,000 km/s)