RT 1303 REVIEW QUESTIONS
CHAPTER 8 X-RAY PRODUCTION
Where does the electron traveling from the cathode to the anode get it=s kinetic
energy?
Ans:
From the high voltage
How much of the kinetic energy is lost in the form of heat?
Ans:
99%
How does the anode handle all of the heat generated?
Ans:
Spread it over a large surface areaC
rotating anode
Larger anodes for high capacity output
High rotation of the anodeB--10000 rpm vs. 3600 rpm
Use of line focus principle
Use tungsten 90%, and rhenium 10% to handle all of the hear produced
Draw the heat quickly from the anodeCtube housing with cooling fans
(Above questions were answered in ch.7)
What are the two ways x-rays are produced?
Ans:
Brems X-ray production
Characteristic X-Ray production
Describe Bremsstrahlung X-Ray production
Ans:
The kinetic electron from the cathode is attracted toward the nucleus of the
tungsten atom. When it turns toward the + charge of the nucleus, it releases
kinetic energy in the form of electromagnetic energy, most of it in the form of
heat, but some in the energy of x-rays. The energy of the x-rays is polychromatic,
which means that the energy is from the applied KVP down to where it is heat,
hence the use of the term KVP and not just KV. The average energy of the x-ray
beam is 1/3 to 2 of the applied kv and this is why we will need to use a filter to
increase the mean energy of the beam. (next chapter)
Describe characteristic X-Ray production
Ans:
The kinetic electron comes into the tungsten atom and if it has 69,.5 kv of energy, it can
eject an electron from the k shell of the tungsten atom. This hole is filled from an outer
shell electron. The excess kinetic energy of the electron is given up in the form of an x-ray.
The energy of the x-ray depends upon where the two electrons came from.
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Example:
INITIAL ELECTRON
EJECTION
K Shell
K Shell
K Shell
L Shell
L Shell
L Shell
→
→
→
→
→
→
WHERE SECOND
ELECTRON CAME
FROM
L Shell
M Shell
Out of Atom
K Shell
M Shell
Out of Atom
RESULTING X-RAY ENERGY
→
→
→
→
→
→
57.5 KV
67.5 KV
69.5 KV
Cannot Happen
10 KV
12 KV
What is the maximum energy which can be produced characteristically in a tungsten
atom and why?
Ans:
The answer is in the question above, 69.5 KV. The reason is that the K shell
binding energy of the tungsten atom is 69.5 KV and that is where the x-ray
receives it=s energy from.
What is the maximum energy which can be produced by the Brems process?
Ans:
As high as is placed on the KVP selector. If the x-ray can go to 20 MEV, then 20
MEV x-rays will be produced by the Brems process.
Where does polychromatic energy production come from?
Ans:
It comes from both Brems and Characteristic production processes. Brems is
from the applied KVP down to where it is not considered x-ray energy anymore
and is considered heat. Characteristic x-ray production comes in discrete
energies, see the energies listed above.
What percentage of x-ray production comes from where?
Ans:
On average 70% comes from Brems and 30% comes from Characteristic.
What is the maximum energy which can be produced by the following and why?
Ans:
BremsCAs high as the machine is designed to produce.
CharacteristicC The K shell of the target atom. That is why they use tungsten is
because it has a high K shell binding energy, 69.5 KV.
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