RADIATION PHYSICS - 2
8 November 1895, produced and
detected electromagnetic radiation in
a wavelength range today known as Xrays or Röntgen rays,
an achievement that earned him the
first Nobel Prize in Physics in 1901.
BORN-
Wilhelm Conrad Röntgen
27 March 1845
Lennep, Rhine
Province,Germany
DIED - 10 February
1923 (aged 77)
Munich, Germany
Specific learning Objective
• To know about the components of X-ray tube
• To know about the electricity specification of
Xray machine.
• To know about transformer and its type.
FORMAT
Introduction
Components of X-ray Tube head
Electricity specification
Transformer
Auto transformer
Step Up and Step Down Transformer
Effect of mA, Kvp and exposure time on Xray beam
support arms
Tube head
control panel
-- - - - - - - - - - - - -- - - - - - -TRANSFORMER
- -STEP
- -UP- ---------------OIL
-- - - - - - - - - - - - - ----------------------------------- --------------STEP DOWN
- - - - - - - TRANSFORMER
- - - - - ---------------- - - - - - -- - - - - --
ALTERNATE CURRENT (AC) MACHINE- SELF OR HALF WAVE RECTIFIED
60-cycle Alternating Current
+ 110, 220
positive
0
- 110, 220
INVERSE VOLTAGE
OR
REVERSE BIAS
negative
Direct Current (Constant Potential): 800 cycles/sec.
DIRECT CURRENT (DC) MACHINE - FULL WAVE RECTIFIED
1/60
Number of Impulses
=
60
60 impulses/60 = 1.0 second
30 impulses/60 = 0.5 second
15 impulses/60 = 0.25 second
1 Second
X-ray Production
-
+
+
8mA
70Kvp
LOW VOLTAGE CURRENT – 8 Ma
– for tungsten filament
HIGH VOLTAGE CURRENT – 70 Kvp – for potential difference between cathode
and anode
Transformers
• Electromagnetic devices that allow a voltage of alternating
current to be changed.
Principle operation of a transformer is based on induction.
When current is passed through a conductor, a magnetic
field
is
established
in
and
around
the
conductor.
This magnetic field can be used to induce a voltage and
current flows in a conductive material that is placed close by.
Step-Down Transformer
current flow
110 volts
Primary
current flow
3-5 volts
LOW VOLTAGE CURRENT
Secondary
Autotransformer
110 V
current flow
65
80 V
Step-Up Transformer
current flow
110 volts
Primary
current flow
Secondary
65,000 to
90,000 volts
mA (milliamperes)
↑QUANTITY
Number of X-rays
100
10 mA
50
average energy
(no change)
5 mA
maximum energy
(no change)
X-ray Energy (keV)
70
Exposure time
↑QUANTITY
Number of X-rays
100
1 sec
50
average energy
(no change)
0.5 sec
maximum energy
(no change)
X-ray Energy (keV)
70
Increasing mA or Exposure Time ( E.T) results in:
• An increase in the number of x-rays produced
• No change in the energy of the x-ray beam
milliamperes (mA) x seconds (s) = mAs
10 mA x .5 seconds = 5 mAs
20 mA x .25 seconds = 5 mAs
↑mA → ↑electrons → ↑x ray photon → ↑ quantity of Xrays
↑ E.T → ↑electrons → ↑x ray photon → ↑ quantity of Xrays
↑ QUALITY
Number of X-rays
kVp (kiloVolt peak)
average energy
90 kVp
70 kVp
maximum energy
70
90
X-ray Energy (keV)
↑Kvp → ↑speed of electron →↑energy of Xray photon →↑ penetration
Incorrect exposure factors
(too many x-rays or too much energy;
-film too dark)
Correct exposure factors
-Good density
Incorrect exposure factors
(not enough x-rays or energy too low;
-film too light)
Constant patient size
1.
2.
3.
4.
5.
A
B
A
C
A
B
Proper kVp, mA, exposure time (e.t.)
Increase mA; no change in kVp, e.t.
Decrease e.t.; no change in kVp, mA
Increase kVp; no change in mA, e.t.
Double mA, halve e.t.; no change in kVp
B
C