Question

Electrons with energy 80 keV are incident on the tungsten target of an X-ray tube. K shell electrons of tungsten have ionization energy 72.5 keV. X-rays emitted by the tube contain only

• A. A continuous X-ray spectrum (Bremsstrahlung) with a minimum wavelength of $\sim 0.155\dot{A}$
• B. A continuous X-ray spectrum (Bremsstrahlung] with all wavelengths
• C. The characteristic X-rays spectrum of tungsten
• D. A continuous X-ray spectrum (Bremsstrahlung) with a minimum wavelength of $\sim 0.155\dot{A}$ and the characteristic X-ray spectrum of tungsten

Answer 1

The correct option is D A continuous X-ray spectrum (Bremsstrahlung) with a minimum wavelength of $\sim 0.155\dot{A}$ and the characteristic X-ray spectrum of tungsten

Minimum wavelength of continuous X-ray spectrum is given by
${\lambda }_{min}\left(in\dot{A}\right)=\frac{12375}{E\left(eV\right)}=\frac{12375}{80\times {10}^3}\approx 0.155$. Also the energy of the incident electrons (80 KeV) is more than the ionization energy of the K-shell electrons (i.e. 72.5 KeV). Therefore characteristic X-ray spectrum will also be obtained because energy of incident electron is enough to knock out the electron from K or L shells.