Conversation started Oct 25, 2018 at 21:57.
sammy gerbil
sammy gerbil
Oct 25, 2018 21:57
@Abcd The PD is that between the cathode (where electrons are produced by heating) and the anode (to which they are attracted and accelerate). Increasing PD increases the KE of electrons arriving at the anode. This increases the energy and intensity of X rays produced by bombardment.
Abcd
Abcd
@sammygerbil didnt get last sentence.
sammy gerbil
sammy gerbil
Higher energy electrons can knock out electrons which are more tightly bound to atoms.
Other electrons fall back into the vacant energy level and emit an X photon.
Another way intensity can increase is when the current from the cathode has not reached saturation.
Then the increased PD drags more electrons away from the cathode, and they reach the anode quicker because they are moving faster. So there are more X photons generated per second.
@Abcd So there are 2 ways in which increased PD can increase intensity of X rays : (1) increase in energy of each X photon emitted, (2) increase in the number of photons emitted per second.
Abcd
Abcd
@sammygerbil i think you mean electron
sammy gerbil
sammy gerbil
Oct 25, 2018 22:14
@Abcd No I do mean the number of photons emitted by the anode. Which of course equals the number of electrons reaching the anode.
The intensity of any beam of EMR depends on the energy of each photon and the density of photons.
Abcd
Abcd
@sammygerbil what happens to electron after striking another electron during x ray emission.
sammy gerbil
sammy gerbil
@Abcd It loses energy and wanders around inside the metal anode. It might fall into an atom which has a vacancy in its energy levels. Otherwise it is conducted back to the cathode. The anode is connected back to the cathode via a power supply, so these electrons are dragged back to the cathode where they can be 'evaporated' again and be accelerated towards the anode etc.
Abcd
Abcd
@sammygerbil nice
sammy gerbil
sammy gerbil
@Abcd The bombarding electron ejects a bound electron from the atom which it strikes. An X photon is not emitted until a free electron in the metal falls into the vacant energy level.
Abcd
Abcd
@sammygerbil y
sammy gerbil
sammy gerbil
Oct 25, 2018 22:36
@Abcd I have missed out the most important process for X ray generation : braking radiation. Most of the X rays are produced when the fast electrons are rapidly decelerated in the anode. The X rays which come from the ejection of electrons from atoms is a minor process, but it is responsible for the spikes in the energy spectrum.
See radiologycafe.com/radiology-trainees/frcr-physics-notes/…
 
Conversation ended Oct 25, 2018 at 22:36.