Chapter 3

Question 1

Define Transformer

Answer 1

two windings that are separated by
some distance that allow you to
alter the voltage and current based
on the ratio of the number of
windings
Vs/Vp = Ns/Np=Ip/Is

Question 2

What material is an anode usually
made of? What about the filament?
why? what is its Z?

Answer 2

Tungsten (Z=74) has a high
melting point of 3,370°C

is the element of choice for withstanding intense heat produced in the target by the electronic bombardment.

Question 3

typical focal spot size for :

1) CT
2) RT

Answer 3

1) 0.1mmx0.1mm
2) 5mmx5mm

Question 4

Ballpark the volt and current
through the filament

Answer 4

6Amps at 10V

Question 5

why is the Choke coil or rheostat
used in the filament circuit?

Answer 5

small variations in mA or kVp
cause a large change in electron
emmision, this eliminates small
variations

Question 6

Draw a diode and draw the flow
the electrons through the diode.
what is the voltage drop across a
forward biased diode?

Answer 6

Electrons flow in (forward) through
the point of the triangle and out
through the base ofthe triangle.
0.7V

Question 7

Two ways X-rays are created?

Answer 7

Bremsstrahlung and characteristic
x-rays

Question 8

What type of target is used in
therapy? Why?

Answer 8

Transmission-type Bremsstrahlung
is very forward directed as energy
increases

Question 9

Equation Bremsstrahlung efficiency
When does it apply

Answer 9

9x10^-9ZV
Up to a few MV

Question 10

Draw a circuit diagram for and xray
tube

Answer 10

high-voltage circuit
to provide the accelerating potential for the electrons and the low-voltage circuit to supply heating current to the filament

The high voltage to the x-ray tube is supplied by the step-up transformer

The primary of this transformer is connected to an
autotransformer and a rheostat. The function of the autotransformer is to provide a stepwise adjustment in voltage

Question 11

Schematic diagram of a therapy x-ray tube with hooded anode

Answer 11

The apparent size of the focal spot can be reduced by the principle of line focus

apparent focal spot ranges between 5 ×
5 mm and 7 × 7 mm

Since the x-rays are produced at various depths in the target, they suffer varying amounts of attenuation in the target. There is greater

attenuation for x-rays coming from greater depths than those from near the surface of the target. Consequently, the intensity of the x-ray
beam decreases from the cathode to the anode direction of the beam. This variation across the x-ray beam is called the heel effect.

Question 12

What is the unfiltered
Bremsstrahlung spectrum
1)non-relativistic
2) relativistic

Answer 12

1) Kramers’ rule I(E) =
KZ(Emax-E)
2)Bethe-Heitler is proportional to
f(E)/E

Question 13

define:

1) superficial Therapy
2) Orthovoltage therapy

Answer 13

1) 50-150 kVp 2)150-500kV

(usually at 20mA)