Answer
No radiation is emitted below a wavelength of $6.2\times 10^{-10}~m$
Work Step by Step
We can find the wavelength of a photon with an energy of $2.0~keV$:
$E = \frac{hc}{\lambda}$
$\lambda = \frac{hc}{E}$
$\lambda = \frac{(6.626\times 10^{-34}~J~s)(3.0\times 10^8~m/s)}{(2.0\times 10^3~eV)(1.6\times 10^{-19}~J/eV)}$
$\lambda = 6.2\times 10^{-10}~m$
No radiation is emitted below a wavelength of $6.2\times 10^{-10}~m$.
