Transcript EATING DISORDERS AND THEIR EFFECTS ON ORAL HEALTH

Radiation Physics II
X-rays
Weightless bundles of energy without an
electrical charge that travel in waves with a
specific frequency at the speed of light. X-ray
photons interact with the materials they
penetrate and cause ionization
X-Rays Properties
1.
2.
3.
4.
5.
6.
Appearance
Mass
Charge
Speed
Wavelength
Path of travel
X-Rays Properties
7.
8.
9.
10.
11.
12.
13.
Focusing capability: X-rays cannot be focused to a point and always
diverge from a point
Penetrating power: X-rays can penetrate liquids, solids, and gases. The
composition of the substance determines whether x-rays penetrate or pass
through, or are absorbed
Absorption: X-rays are absorbed by matter; the absorption depends on the
atomic structure of matter and the wavelength of the x-ray
Ionization capability
Fluorescence capability: X-rays can cause certain substances to fluoresce
or emit radiation in longer wavelengths (e.g., visible light and ultraviolet
light).
Effect on film
Effect on living tissues
The X-ray Machine Component
1.
2.
3.
4.
Control Panel
Extension Arm
Electrical connector (plug)
Tubehead
support arms
tubehead
control panel
6
support arms
control panel
tubehead
7
Control Panel
Exposure Time
exposure time
adjustment
70 kVp 7 mA
8
Control Panel
9
Tubehead
1.
2.
3.
Metal housing, or the metal body of the tubehead that
surrounds the x-ray tube and transformers and is filled with
oil
Insulating oil, the oil surrounds the x-ray tube and
transformers inside the tubehead; it prevents overheating by
absorbing the heat created by the production of x-rays
Tubehead seal, or the aluminum
a. Permits the exit of x-rays from the tubehead
b. Seals the oil in the tubehead
c. Acts as a filter to the x-ray beam
Tubehead
4.
5.
6.
7.
8.
Aluminum disks, 0.5-mm thick aluminum placed in the path of the
x-ray beam; they filter out the non-penetrating, longer
wavelength
Lead collimator (lead plate) with a central hole that fits
directly over the opening of the metal housing where the
x-rays exit; it restricts the size of the x-ray beam
Position-indicating device (PID), it is lead-lined cylinder that
extends from the opening of the tubehead
X-ray tube, is the heart of the x-ray generating system
Transformer is a device that alters the voltage of incoming
electricity
X-ray tube

Is the basic apparatus for generating x-rays, is
composed of leaded-glass tube, cathode, and
an anode
X-ray tube- leaded-glass tube



The glass tube is leaded to prevent x-rays from escaping in all
directions
One central area of the leaded-glass tube has a “window” that
permits the x-ray beam to exit the tube
The x-ray tube is evacuated to:
1. Prevent collision of the moving electrons with gas
molecules, which would significantly reduce their speed
2. Prevents oxidation and "burnout" of the filament
X-ray tube- Cathode
1.

Filament
It is a coil of tungsten wire about 2 mm in
diameter and 1 cm or less in length

It is mounted on two stiff wires that support it
and carry the electric current

The filament produce electrons when heated
X-ray tube- Cathode
2.

Focusing Cup
The filament lies in a focusing cup, a negatively charged
concave reflector made of molybdenum

The focusing cup focuses the electrons emitted by the filament
into a narrow beam and directs the beam toward a small
rectangular area on the anode called the focal spot

The electrons move in this direction because they are repelled
by the negatively charged cathode and attracted to the
positively charged anode
X-ray tube- Anode

Positive electrode, consists of a thin tungsten plate (target)
embedded in a copper stem

A tungsten target serves as a focal spot and converts
accelerated electrons into x-ray photons

The copper stem, which functions to dissipate the heat away
from the tungsten target.

X-ray tube- Anode

The target is made of tungsten because it has a high
atomic number, high melting point, and low vapor
pressure at the working temperatures of an x-ray tube

The purpose of the target is to convert the kinetic
energy of the electrons generated from the filament
into x-ray photons
X-ray tube
Electricity and Electric Currents






Electricity is the energy that is used to make x-rays
Electrical energy consists of a flow of electrons through a conductor; this
flow is known as the electric current
Amperage is the measurement of the number of electrons moving through
a conductor. Current measured in amperes or milliamperes (mA)
Voltage is the measurement of electrical force that causes electrons to
move from a negative pole to a positive one. Voltage is measured in volts
or kilovolts (kV)
In the x-ray tube, the amperage can be increased or decreased by the
milhiamperage (mA) adjustment on the control panel of the x-ray machine
The voltage of the x-ray tube current is controlled by the kilovoltage peak
(kVp) adjustment on the control panel
Circuits
1.
2.
Low- voltage or filament circuit: the filament circuit
uses 3 to 5 volts, regulates the flow of electrical
current to the filament of the x-ray tube, and is
controlled by the milliamperes settings
High-voltage circuit: the high-voltage circuit uses
65,000 to 100,000 volts, provides the high voltage
required to accelerate electrons and to generate x-rays
in the x-ray tube, and is controlled by the kilovoltage
settings
Transformers

A transformer is a device that is used to either
increase or decrease the voltage in an electrical
circuit

In the production of dental x-rays, 3
transformers are used to adjust the electrical
circuits: the step-down transformer, the step-up
transformer, and the autotransformer
Transformers

The filament circuit uses 3 to 5 volts, a step-down transformer
is used to decrease the voltage from the incoming 110 or 220
line voltage to the 3 to 5 volts required

The high-voltage circuit requires 65,000 to 100,000 volts and
uses both a step-up transformer and an auto- transformer. A
step-up transformer is used to increase the voltage from the
incoming 110 or 220 line voltage to the 65,000 to 100,000
volts required. An auto- transformer serves as a voltage
compensator that corrects for minor fluctuations in the current
kVp
3-5 volts
65-90 volts
<110 volts
110 volts
65,000 to
90,000 volts
filament
23
Production of Dental X-rays
1. Electricity from the wall outlet supplies the power to generate x-rays
2. The current is directed to the filament circuit and step-down transformer in
the tubehead. The transformer reduces the 110 or 220 entering line voltage to
3 to 5 volts
3. The filament circuit uses the 3 to 5 volts to heat the tungsten filament in the
cathode portion of the x-ray tube. Thermionic emission occurs; thermionic
emission is the release of electrons from the tungsten filament when the
electric current passes through it and heats it up. The outer shell electrons of
the tungsten atom acquire enough energy to move away from the filament
surface, and an electron cloud forms around the filament. The electrons stay
in an electron cloud until the high-voltage circuit is activated
Thermionic Emission
Release of electrons from hot filament when
current flows after depressing exposure
switch
x-section
hot
of
filament
filament
electrons
The hotter the filament gets, the greater the number
of electrons that are released.
25
Production of Dental X-rays
Production of Dental X-rays
4. When the exposure button is pushed, the high-voltage circuit
is activated. The electrons produced at the cathode are
accelerated across the x-ray tube to the anode. The
molybdenum cup in the cathode directs the electrons to the
tungsten target in the anode
5. The electrons travel from the cathode to the anode. When the
electrons strike the tungsten target, their energy of motion
(kinetic energy) is converted to x-ray energy and heat. Less
than 1% of the energy is converted to x-rays; the remaining
99% is lost as heat
Production of Dental X-rays
6. The heat produced during the production of x-rays is carried away from the
copper stem and absorbed by the insulating oil in the tubehead. The x-rays
produced are emitted from the target in all directions; however, the leadedglass housing prevents the x-rays from escaping from the x-ray tube
7. The x-rays travel through the unleaded glass window, the tubehead seal, and
the aluminum disks. The aluminum disks remove or filter the longer
wavelength x-rays from the beam
8. Next, the size of the x-ray beam is restricted by the lead collimator. The
x-ray beam then travels down the lead-lined PID and exits the tubehead at
the opening of the PID
X-ray Production
3
29
Types of X-rays Produced

Not all x-rays produced in the x-ray tube are the
same; x-rays differ in energy and wavelength

The energy and wavelength of x-rays varies based on
how the electrons interact with the tungsten atoms in
the anode. The kinetic energy of the electrons is
converted to x-ray photons via one of two
mechanisms: general (Bremsstrahiung) radiation
OR characteristic radiation
1. General Radiation

General radiation is produced when an electron
hits the nucleus of a tungsten atom or when an
electron passes very close to the nucleus of a
tungsten atom
Bremsstrahlung X-ray Production
High-speed
electron from
filament enters
tungsten atom
+
Electron slowed
down by positive
charge of nucelus;
energy released in
form of x-ray
Electron continues on to other
atoms until all of its energy is
lost
33
Bremsstrahlung X-ray Production
Maximum energy
+
High-speed electron
from filament enters
tungsten atom and strikes
nucleus, losing all its
energy and disappearing
The x-ray produced has energy equal
to the energy of the high-speed
electron; this is the maximum energy
possible
34
2. Characteristic Radiation

Produced when a high- speed electron displaces an electron
from an inner shell of a tungsten target atom and causes
ionization of that atom

When this happens, another electron in an outer shell of the
tungsten atom is quickly attracted to the void in the deficient
inner shell. When the displaced electron is replaced by the
outer-shell electron, a photon is emitted with an energy
equivalent to the difference in the two orbital binding energies
Characteristic X-ray Production
Ejected electron
leaves atom
vacancy
High-speed electron with
at least 70 keV of energy
(must be more than the
binding energy of k-shell
Tungsten atom) strikes
electron in the K shell
M
L
K
Recoil electron
(with very little
energy) exits atom
36
Characteristic X-ray Production
X-ray with 59 keV
of energy
produced. 70
(binding energy of
K-shell electron)
minus 11 (binding
energy of L-shell
electron) = 59.
Outer-shell electron
drops into vacant spot
M
L K
37
Characteristic Radiation