homework and exercises - X-ray: Observation of absorption edge

So I am working on this experiment on X-ray and kinda stuck on this last and following section.

I have done the measurements and plotted the graph as required in 1. and 2. See below,

However, I am afraid my graph doesn't look much similar to the graph from Kaye and Laby[3,p. 4.2.2 graph], the one below.

I would be very grateful if someone can please help me with and explanation to point 3. of the task and also the following 2 questions, Question 2 and Question 3. Thanks in advance.

Link to Kaye and Laby [3,p. 4.2.1 table]: http://www.kayelaby.npl.co.uk/atomic_and_nuclear_physics/4_2/4_2_1.html

Answer

The $\rm K_\alpha$ X-ray emission is due to an $\rm L$-shell electron falling into the $\rm K$-shell with the emission of a photon.
The $\rm K_\beta$ X-ray emission is due to an M-shell electron falling into the $\rm K$-shell with the emission of a photon with a higher energy than that of a $\rm K_\alpha$ photon.

As the atomic number increases so does the energy of the $\rm K$-photons.

In the reverse process an incoming photon, if it has enough energy, can knock out an electron which is in the $\rm K$-shell.
You will note that the energy of an incoming photon has to be greater than $\rm K_\alpha$, $\rm K_\beta$ etc photons because the incoming photon has to remove the electron in the $\rm K$-shell from the atom completely not just promote the electron into a higher energy level.
So for a given element, the energy of the $\rm K$-edge is greater than the $\rm K$-photons.