K X-Ray Production in PIXE: 2 MeV vs. 4 MeV

[Silviu]

Homework Statement

In PIXE (Proton-Induced X ray Emission), if you increase the beam energy from 2 MeV to 4 MeV, do you expect that the factor of increase in the cross section for the K X ray production from Ni is higher than that from S, or vice-versa?

Homework Equations

The Attempt at a Solution

The professor didn't give us any equation, just a conceptual explanation of the process. It makes sense that the cross section increases with the energy of the incident particle but I am not sure how this increase depends on different elements. So I am not sure how to approach this problem. Any idea?

 

[Fred Wright]

Which atom has more electrons that can make the transition $h\nu_{x-ray}$?

 

[Silviu]

Which atom has more electrons that can make the transition $h\nu_{x-ray}$?

Hello! I guess the one with more electrons has a higher cross section. My question was more how do you calculate the change in the ratio of the cross sections. Like if the cross section of the one with more electrons is a and for the other one is b, when the energy is 2 MeV, of course when you go to 4 MeV the one with more electrons will still have a higher cross section, but I am not sure what happens to the ratio $\frac{a}{b}$ because the ration can both increase or decrease while its value to be greater than 1

 

[Fred Wright]

If atom a has much fewer electrons which can be ionized, increasing the energy will have a smaller effect on the observed crossection.You observe a certain prosecution for atom a at 2 Mev but increasing the energy will not have much of an effect because all of it's electrons were ionized at the lower energy. Where as atom b still has electrons which can be ionized at the higher energy.