# On characteristic X-ray spectra and relative intensity

I am looking at the following image (from http://www.schoolphysics.co.uk/age16-19/Atomic%20physics/X%20rays/text/X_ray_spectra/index.html):

and I want to know, of the two curves, which one represents the element with the higher atomic number. That is, I understand that X-rays are scattered and that the peaks are characteristic of a material. What I am less clear on i why one curve should be above another relative to their atomic numbers (I am going to assume the cutoff voltage on the left is identical even though in this picture it isn't).

The reason I am confused is that I am told that that $\frac{1}{\sqrt{\lambda}} \propto Z$ which is all very well, but on this graph it would seem to indicate that the upper line is a heavier (higher Z) material. Is hat the case, or is intensity actually proportional to $\frac{1}{\sqrt{\lambda}}$ as well? I would have thought the lower curve would be a higher Z since it usually take less energy to knock electrons off of elements further up the periodic table.

Anyhow, what clarification might be offered is appreciated.

• I think you're misreading the graph, which is why you're getting confused. The two curves are actually for the same element as a target material. What's different between the two curves is the acceleration voltage; the higher curve uses a larger accelerating voltage. The reason the larger accelerating voltage curve is above the low-voltage curve is because more energy is being imparted to the accelerated electrons in the high-voltage situation, and so the x-ray light emitted upon striking the target is more intense. – DumpsterDoofus May 17 '14 at 20:01
• I get that part, but let's assume for the moment we used the same accelerating voltage on two different elements. What would we expect to see in that case? – Jesse May 17 '14 at 20:16
• For the continuous bremsstrahlung see Kramer's Law. Intensity $I \propto Z$ (Atomic number). – peanut_butter May 17 '14 at 22:03
• Moseley found an empirical law relating the frequency of the characteristic lines to the atomic number of the target element. Quantum theory then provided an explanation of the law. en.wikipedia.org/wiki/Moseley%27s_law – Farcher May 8 '16 at 19:49