production of X Rays pt 2

Question 1

Electricity:

Answer 1

Electricity: Flow of electrons through an electrical conductor.

Question 2

Current

Answer 2

Current: Amount of electrons flowing through a conductor per second. Measured in amperes (A)

Question 3

Circuit:

Answer 3

Circuit: Path of electrical current

Question 4

Voltage (Potential difference) V).

Answer 4

Voltage (Potential difference): Difference in electrical potential energy between two points in an electric circuit. Measured in volts (V).

Question 5

AC

Answer 5

alternating current, used in US
flow 1 direction then the other
60 cycles per second

Question 6

issues with x ray machine and AC

Answer 6

machine needs 1 direction of current to work: cathode to anode
1. During each half-cycle (1/120 of a second), anode is positive and attracts the electrons from
the cathode (x-radiation is produced).
2. During each alternate half-cycle (1/120 of a second), anode is negative, therefore, no
attraction for electrons exists and no x-radiation is produced (inverse voltage).

Question 7

DC

Answer 7

1 direction of current, allows continuous production of x rays

Question 8

how can we use AC to make continuous x rays

Answer 8

via rectificator/full wave rectification, allows constant flow from cathode to anode (always from filament to target)
drawing in notes
XRAY TUBES ARE SELF RECTIFYING

Question 9

stabilizing kVp (constant E level)

Answer 9

1. Changing alternating current into direct current
2. Full-waive rectification, high frequency power supply
3. Essentially constant potential between cathode and anode via multiple phases
4. Higher mean energy of beam compared to AC.
   creates a constant potential

Question 10

constant potential and direct current benefits

Answer 10

1. Shorter exposure times
2. More consistent beam intensity
3. Higher mean energy of beam
4. Decreased radiation dose

Question 11

How are x-ray produced?

Answer 11

X-rays are produced whenever high-speed electrons are suddenly decelerated or brought to a stop when they pass close to the nuclei of a high Z # absorbing material (in this case tungsten 74W)

Question 12

mechanisms of x ray formation

Answer 12

1.Bremsstrahlung radiation

2. Characteristic radiation

Question 13

1.Bremsstrahlung radiation
AKA?

Answer 13

◦ AKA Breaking radiation
◦ Electron to nucleus interaction
◦ The fast-moving electrons either slow down or stop when they come close to the nucleus of the atoms and part of their energy is transferred as X-rays.

Question 14

2. Characteristic radiation

Answer 14

◦ Electron to electron interaction
◦ A few electrons interact with tungsten target orbital electrons, imparting enough energy to ionize the tungsten target.
◦ When electrons displace inner shell electrons, characteristic radiation is produced.

Question 15

Bremsstrahlung radiation
what is directed toward the target material?
constant e velocities?
KE and velocity?
Bremsstrahlung radiation increases with?

Answer 15

 High-velocity electrons directed toward the target material.
 All electrons do not attain the same velocity. Some move at higher velocity(ies) than others (depending on kV)
 KE = ½ mV2. The higher the velocity, the greater the KE of electrons.
 Bremsstrahlung radiation increases with increasing the voltage (kV) and the atomic number of the target ( Z#)

Question 16

Bremsstrahlung radiation defelctions and collisions

Answer 16

1. Impinging electron is deflected and decelerated. Kinetic energy lost is emitted as an x-ray photon.
2. Head-on collision with nucleus: Electron brought to rest producing a maximum energy photon.

Question 17

Bremsstrahlung radiation
◦ wavelengths?
◦ Electron energy loss with interaction?
◦ interactions btwn Tungsten and e?

Answer 17

◦ This type of radiation has a wide distribution of wavelengths (heterogeneous).
◦ Electrons lose their energies in random fashion when they interact with tungsten atoms.
◦ Multiple interactions between electrons and tungsten atoms.

Question 18

Characteristic Radiation
1. Arises when?
2. Atom is now?
3. the hole left by the electron? result?
4. The energy emitted by the electron is equivalent to?

Answer 18

1. Arises when cathode electron collides with inner orbital electron of tungsten atom (target) and removes it from orbit.
2. Atom is now ionized and unstable.
3. Immediately, the hole left by the electron is filled by an electron from an outer shell, and energy is emitted from this electron in the form of x-radiation characteristic of tungsten and the involved shell.
4. The energy emitted by the electron is equivalent to the difference in the binding energies of the two shells/orbitals

Question 19

tungsten
L to K transition → energy released?
M to K transition →energy released?

Answer 19

L to K transition →69,500 – 12,100 ev = 57,400 ev
◦ M to K transition →69,500 – 2,800 ev = 66,700 ev

Question 20

_____% of diagnostic x-ray beam is characteristic radiation

Answer 20

30%

Question 21

Summary of Characteristic Radiation mechanism

Answer 21

◦ Electron strikes and ejects an inner shell electron of a tungsten atom.
◦ This creates a hole or vacancy in the atom that makes it unstable.
◦ The atom responds by shifting electrons inward to fill the vacancy. Whenever an outer shell electron is shifted inward it must give up some of its energy in the form of radiation called a characteristic photon.
◦ In this manner discrete energy is imparted to the newly formed radiation which is “characteristic” of the atom type and orbital from which it came, thus the name characteristic radiation.

Question 22

Bremsstrahlung radiation makes up the _______of the x-ray beam and produces a ______ beam of varying photon energies.

Answer 22

Bremsstrahlung radiation makes up the majority of the x-ray beam and produces a heterogeneous beam of varying photon energies.

Question 23

Characteristic radiation is only a______ source of radiation from the x-ray tube and produces photon energies ______ for the target material.

Answer 23

Characteristic radiation is only a minor source of radiation from the x-ray tube and produces photon energies specific for the target material.