RTEC A - WEEK 4
GENERAL SCIENCE REVIEW
&
X-RAY PRODUCTION
IN THE TUBE
***FINAL***
ALERT
Please do not print the lecture until you see “FINAL” on the first slide.
Objectives
General Science review
Atomic interactions in the tube
Atomic Models
1.
BOHR model of the atom.
2. Electrons orbit around a nucleus (center)
ATOM
Differences in Binding Energy
K L M Shells
Electrostatic Laws
1. Repulsion/attraction
Like charges repel
Unlike charges attract
1. Inverse square relationship
Electrostatic force is very strong when objects are close together
It decreases rapidly as objects separate
How “X-rays” are created
TO PRODUCE X-RAYS
YOU NEED:
1.
A SOURCE OF ELECTRONS
2.
A FORCE TO MOVE THEM QUICKLY
3. SOMETHING TO STOP THEM SUDDENLY
How “X-rays” are created
1. Power is sent to x-ray tube via cables
2. mA (milliamperage) is sent to filament on cathode side.
3. Filament heats up – electrons “boil off”
•
Thermionic Emission
4. Negative charge
How “X-rays” are created
1. Positive voltage (kVp) is applied to ANODE
2. Negative electrons attracted across the tube to the positive ANODE.
3. Electrons “slam into” anode – suddenly stopped.
4. X-RAY PHOTONS ARE CREATED
Electromagnetic Energy Spectrum
1. Spectrum
Continuous range of energy
Although there are precise ranges defined, they often overlap
1. 3 most important to Radiologic technology:
Visible light
X-radiation
Radiofrequency
Electromagnetic Radiation
1. Photon is the smallest quantity of any type of EM radiation
It is a small bundle of energy traveling at the speed of light
Only visible light is naturally apparent to us
1. May be described as wavelike fluctuations of electric and magnetic fields.
Electromagnetic Radiation
1. These bundles of electric and magnetic fields travel at the same velocity:
Travel at the speed of light
3 x 108 m/s or 186,400 miles per sec
1. The Photons of EM radiation differ only in frequency and wavelength
General Characteristics of EMS
X-ray photons:
1. Have no mass or physical form
2. Travel in a linear path (until interaction occurs)
3. Dual nature:
wave vs. particle
4. Unaffected by
electric or magnetic fields
gravity
Wavelength
Wavelength is the difference between:
Crest to Crest
Valley to Valley
Frequency
Frequency is the number of wavelengths passing a point of observation per second
Wavelength and Frequency
1. Wavelength & frequency are inversely proportional
As Wavelength increases frequency decreases
As wavelength decreases frequency increases
1. Frequency and wavelength are closely associated with the relative energy of electromagnetic
radiations.
2.
More energetic radiations have shorter wavelengths and higher frequency.
The shorter the wavelength –
the higher the frequency
The Electromagnetic Spectrum
X-rays have wavelengths much shorter than visible light, but longer than high energy gamma rays.
What is Ionization?
When an electron is added or removed from the atom- it is ionized
Kinetic energy
1. Energy of motion
2. The electrons KINETIC energy is converted to electromagnetic or PHOTON energy
X-ray production begins
at the atomic level
Energy (photons) are released when
the electron collides with another electron,
or passes close to the nucleus of the atom –
the change in energy of the shells
–produces photons
X-ray Production
in the TUBE
INTERACTIONS IN THE TUBE
1. BREMS (Bremsstrahlung)
2. CHARACTERISTIC
3. HEAT
Tube Interactions
Heat = 99%
X-ray = 1%
Bremsstrahlung
(Brems) = 80%
Characteristic = 20%
Bremsstrahlung Radiation
Heat & Characteristic produces EM energy by e- interacting with tungsten atoms e- of the target
material
Bremsstrahlung is produced by e- passing by closely with the nucleus of a target tungsten atom – the
change in direction of the electron – releases a photon of energy
Heat
Most kinetic energy of projectile e- is converted into heat – 99%
Projectile e- interact with the outer-shell e- of the target atoms but do not transfer enough energy to
the outer-shell e- to ionize
Heat
Heat is an excitation
rather than an ionization
Bremsstrahlung
German
word meaning
slowed-down
or braking
radiation
Bremsstrahlung Radiation
Energy (photons) are released when
the e passes close to the nucleus, then changes direction
BREMS RADIATION
Electron
Passes by nucleus
Changes direction
Energy released as a PHOTON
Brem’s Radiation Animation
http://www.coursewareobjects.com/objects/mrophysics_v1/mod08/0816a.htm
Characteristic Radiation
Projectile e- with high enough energy to totally remove an inner-shell electron of the tungsten target
All tube interactions result in a loss of kinetic energy from the projectile eCharacteristic x-rays are produced when outer-shell e- fills an inner-shell void
Characteristic Radiation (Tube)
It is called
characteristic
because it is
characteristic of
the target element
in the energy of
the photon
produced
CHARACTERISTIC (in tube)
1. Electron hits inner shell e in orbit – knocked out & creates a hole
2. Other E’s want to jump in
3. Energy released as PHOTONS
Characteristic Radiation Animation
http://www.coursewareobjects.com/objects/mrophysics_v1/mod08/0808a.htm
Tungsten Atom