Download Study Notes for Test 1

Study Question for Test 1 NRad
1. Can the AgBr on the XRay film be ionized by both xray protons and visible light
protons
YES
2. Direction of travel of electrons in the xray tube?
CATHODE -, ANODE +
3. What is the purpose for using intensifying screens?
When intensifying screens are used, 40 times less radiation is needed this is both
cost efficient and safer for the patient.
4. What controls the energy of xray protons?
Speeds of electrons
5. What effect does voltage have on the electrons?
Voltage determines the direction of flow and speed of electrons
6. What is voltage?
The electric potential and driving force of electrons through conductor
7. What is current?
The amount of electricity flowing through the conductor
8. What is resistance?
Tendency of atoms of conductor to hang on to the electrons (ohms)
9. How many pulses are in a 60hz AC
One Hz is a round trip per second. Each pulse is a one way trip. There are twice
as many pulses as # of Hz (60Hz = 120 pulses)
10. What factors is the electric power (watt) directly related to?
Current and voltage (force of electron flow and amount of flow)
11. State the first law of thermodynamics?
An electronic current will be induced to flow in a circuit if some part of that
circuit is in a changing electric field
12. With regards to question #11, what factors affect the induced voltage?
Length of conductor passing through the magnetic field, speed of rotation of
conductor through the field, strength of the magnetic field, angle between
conductor and magnetic field.
13. At what angel (between conductor and field) do we get max voltage?
90 angle = max voltage
0 angle (parallel) = least (zero) voltage
14. In an AC generator, what is the relation between conductor and field?
Mechanical force is applied to the system to move one part in relation to the other
one (which is fixed) in order to generate electrical force (energy). Conductor may
rotate within a magnetic field or the magnetic field may rotate around a fixed
conductor.
15. How is an AS motor and a transformer similar/different in their relation between
conductors and magnetic field?
They both use AC power source in order to rotate on part in relation to the other
(fixed one) (ie: electricity  mechanical energy). AC motor has a fixed magnetic
field and a rotating conductor. Transformer has a fixed conductor and a rotating
magnetic field.
16. How many changes of magnetic field are in a 60Hz transformer?
120 changes in the field
17. What is a step up transformer?
higher # of 2 windings than # of 1 windings (voltage higher)
18. How are the ratios of voltages in a transformer circuit related to the # of
windings?
directly – this means a straight line
19. If a transformer has 8 primary and 4 secondary coils, what happens to the
voltage?
decreased by ½
20. # of 1 coils held contant and #2 coils increase, what happens to voltage and
current?
voltage and increases but current decreases
21. What can a variable auto transformer do?
Both increase and decrease the voltage
22. What kind of current is needed for xray tube?
DC current
23. What kind of current is produced from a transformer?
AC
24. What is a rectifier?
It allows the current to flow in only one direction (cathode anode +) It can
convert AC to  DC
25. In a rectifier, where is heat applied to?
to the cathode ()
26. What is thermionic emission?
When heat is applied to the cathode in a rectifier, it will boil off excess electrons
from its surface
27. How does a rectifier convert AC to DC?
AC  DC means a two way current - one directional current in question #26
we saw how electrons can boil off at hot cathode and go to anode. If voltage is
reverse (as it happens w/ AC) electrons build up at anode, but since anode is cold,
they stay there.
28. How many pulses of AC pass thru a rectifier?
½ the original # of pulses. Because ½ of pulses are in one direction and the other
½ in opposite direction and rectifier allows only one direction to be passed
29. What is the effect of rectifier?
Since only ½ of the pulses of an AC current pass through, half of the original AC
energy is lost. The DC produced is called a pulsating DC current. A rectifier
bridge can avoid the 50% loss of energy.
30. What is full wave rectification?
When a rectifier bridge is used to avoid loss of energy, (due to loss of ½ the AC
pulses, the pulses in wrong direction) all the pulses are used. We still get a
pulsating DC current, but now we have more DC pulses per second which gives
the same xray exposure in a shorter time. It reduces chance of patient movement.
31. What is the shortest length of time we can have for a pulse?
1/120 second. One Hz=one cycle/sec = 2 pulses / sec
60 Hz (U.S.) = 60 cylces/sec = 120 pulses/sec
so each pulse in US takes 1/120 sec
The higher the Hz, the less time it would take for a pulse
32. What is a focusing cup?
It is a metal cup with a negative charge (repells electrons), and is used to redirect
and focus the electrons onto a focal spot (anode)
33. Why is the tungsten disc of anode rotate rapidly?
to avoid heat build up in one spot
34. What is the difference between primary beam and leakage radiation?
The xray beam that leaves the protective housing through the window is called the
primary beam. The xrays that leave the housings at any other place are called
leakage
35. Describe the voltage and amperage of an xray tube circuit?
High voltage, low amperage
36. Explain Kvp?
Voltage of tube (xray tube) is from a rectified AC circuit (ie: AC  pulsating
DC). The pulsating DC goes from 0 to peak and back to 0 again. So Kvp – Killo
volts peak that it kilo volts at the peak of the pulse
Kvp gives the highest xray energy possible (xrays are hetero energstic). Most of
xray photons have 1/3 the max energy
37. Describe the voltage and amperage in the filament circuit?
Low voltage, high amerage
38. Compare and contrast the tube circuit vs. filament circuit?
Tube Circuit
Filament Circuit
Kvp (kilovolt at peak)
MAS (milliamp second)
High voltage low amperage
Low voltage high amperage
 Kvp =  electron speed
 current = more e- boiled off
 electron speed =  photon energy
more e- boiled off  more
photons
 photon energy = penetration
more photons made  
exposure
penetrating power = quality
number of photons = quantity
(quantity = density)
39. Explain exposure
Exposure is the number of xrays produced this depends on intensity (=quantity =
milliamps = mA) and time (sec)
exposure = # of xray photons = (intensity)(time) = mAs
mA gives the # of xrays made in one pulse
number of pulses per second are also important
40. Explain a choke coil?
It adjusts the filament current independent of step down transfromer