Moseley’s law for characteristic x-rays is $\sqrt{v}=\mathrm{a}(Z-\mathrm{b})$. In this

Here, a depends on type of transition. For given pair of pair of principle quantum numbers, a is same of all the elements. b is screening constant, which depends on transition series. For different series of transition, b is different. e.g, for K-series, b=1 ; for L-series, b=7.4 etc.

So, a nd b are independent of the material.