The wavelength of `K_alpha` X-ray of tungsten is `21.3` pm. It takes `11.3` keV to knock out an electron from the L shell of a tungsten atom. What shoulb be the minimum accelerating voltage across an X-ray tube having trungsten target which allows production of `K_alpha` X-ray?

Explanation

`E_(K)-E_(L)=(hc)/lambda_(K_(alpha))`
`lambda_(K_(alpha))=21.3 pm=0.0213 nm`
`E(eV)=1242/(lambda(nm))=1242/0.0213=58.3 ke V`
`E_(K)-E_(L)=E`
`E_(K)-11.3=58.3`
`E_(K)=69.6 ke V`
Acceleration potential `=69.6 kV`