xray

Slide 1: 

Production of X-rays Parable of some Frazzled Electrons and Very Energetic Photons

What is an X-ray photon? : 

What is an X-ray photon? High energy, high frequency, short  light located between UV and gamma rays in the EM spectrum Behave very much like particles because of short  First discovered by Wilhelm Roentgen (used to be called “Roentgen rays”)

Full model of multi-electron atom : 

Full model of multi-electron atom Electrons exist in 3-d standing wave orbitals around the nucleus No two electrons can have all 4 quantum properties (n, m, l, s) the same or else “waves” interfere destructively (Pauli exclusion principle) Two electrons can be in the ground state (known as the “K-shell)

To create X-rays in the lab : 

To create X-rays in the lab

What happens when electrons strike the metal surface? : 

What happens when electrons strike the metal surface? Bremsstrahlung (“braking” radiation) produces wide spectrum of X-rays when electrons careen past the nucleus and decelerate without striking another electron K and K lines

K and K lines : 

K and K lines K line is produced when incoming electron strikes electron from ground state and ejects it… an electron from the n = 2 state “drops down” into open spot and emits X-ray (K line). When an n = 3 electron drops into the now open n = 2 spot another X-ray (K line) is produced Any electrons that continue dropping down into open spots produce photons, but not X-rays…

Characteristic lines : 

Characteristic lines Each metal target will have different energy levels and thus different K and K lines

The maximum energy of an X-ray photon is determined by the maximum KE of the incoming electron (cutoff frequency) : 

The maximum energy of an X-ray photon is determined by the maximum KE of the incoming electron (cutoff frequency)

Shielding effect : 

Shielding effect Since the n = 2 electron that is “dropping down” still sees one electron in the n = 1 state, the nucleus is partially shielded… This means we use Z - 1 in Bohr formula to determine energy levels

Sample problem : 

Sample problem What is the minimum voltage that must be applied to a tube in order to give an electron enough energy to knock a ground state electron out of a copper (Z = 29) target?