Question

A $K_{\alpha }$ X-ray emitted from a sample has an energy of $7.46keV$. Of which element is the sample made?

• A. $\text{Calcium (Ca, Z = 20)}$
• B. $\text{Cobalt (Co, Z = 27)}$
• C. $\text{Cadmium (Cd, Z = 48)}$
• D. $\text{Nickel (Ni, Z = 28)}$

Answer 1

The correct option is B $\text{Cobalt (Co, Z = 27)}$

Electron Transition

Energy of emitted photon due to electron transition $h\nu =E\left(n_2\right)-E\left(n_1\right)$ $=13\cdot 6\times Z^2(\frac{1}{n_1^2}-\frac{1}{n_2^2})eV$

So,
$K_{\alpha }$ rays, from (n=2) to (n=1)
$7.46\times {10}^3=13.6\times Z^2(1-\frac{1}{2^2})$
$Z^2=731.37$
$Z=27$