The Lyman-alpha gap is $3Z^2(\mu/m_e)\mathrm{Ry}/4$, giving $\lambda=4hc/[3Z^2(\mu/m_e)\mathrm{Ry}]$. For heavy lithium nucleus and $Z=3$, $\boxed{\lambda\simeq13.5\ \mathrm{nm}}$. A specified lithium isotope would permit the small reduced-mass correction; no isotope is supplied.


Solution

Past exam of the short options paper shared by Prelims and Parts A and B of the physics course of the University of Oxford / 2016 / S3 / 3 / 5 / a / Solution

 Solution (source code)