Question

Continuous X-rays are made to strike a tissue paper soaked with polluted water. The incoming X-rays excite the atoms of the sample by knocking out the electrons from the inner shells. Characteristic X-rays are analysed and the intensity is plotted against the wavelength. Assuming that only Kα intensities are detected, list the elements present in the sample from the plot. Use Moseley's equation v − (25 × 1014Hz)(Z − 1)2.
Figure

Answer 1

The elements present are Zirconium (Zr), Zinc (Zn), Copper (Cu) and Ferrous (Fe).

Explanation:

It is shown that

$f=(Z-1)^{2}\left(25 \times 10^{14} \mathrm{Hz}\right) \text { or } \mathrm{s} \lambda=1014(\mathrm{Z}-1) 2 \times 25$

(a) $3 \times 10-12 \times 10878.9 \times 1014 \times 25=(Z-1) 2 \text { or }(Z-1) 2=106 \times .0 .001520=1520$

⇒ Z = 39.98 = 40

So, it is found to be Zirconium (Zr).

(b) $-3 \times 10-12 \times 108146 \times 1014 \times 25=(Z-1) 2 \text { or }(Z-1) 2=106 \times 0.00082219 \text { or } Z=29.669$

= 30

So, it is found to be Zinc (Zn).

(c) $-3 \times 10-12 \times 108158 \times 104 \times 25=(Z-1) 2 \text { or }(Z-1) 2=104 \times 0.0007594 \text { or } Z=28.5589$

= 29.

So, it is found to be copper (Cu).

(d) $3 \times 10-12 \times 108198 \times 104 \times 25=(Z-1) 2 \text { or }(Z-1) 2=104 \times 0.000606 \text { or } Z=25.6162$

=26.

So, it is found to be Ferrous (Fe).