PP-W Physics

A fundamental unit of matter

• Central nucleus: Contains the protons (+) and neutrons (no charge) particles AND
• Orbiting electrons: Contains negatively charged particles

Process of converting an atom into ions

ion

electrons

Radiation that is capable of producing ions by removing or adding an electron to an atom

• Particulate Radiation 
• Electromagnetic Radiation

Tiny particles of matter that possess mass and travel in straight lines at high speeds.

• Propagation of wavelike energy(without mass) through space or matter
• Man-made or occur naturally

beta or cathode rays

streams of high-speed electrons that originate in the x-ray tube

fast moving electrons emitted from the nucleus of radioactive atoms

• Cosmic rays
• Gamma rays
• X-rays
• Ultraviolet rays
• Visible light
• Infrared light
• Radar waves
• Microwaves
• Radio waves

Electromagnetic Spectrum

cosmic, gamma, and xrays

discrete bundles of energy called photons

• bundles of energy with no mass or weight
• travel as waves at the speed of light- move thru space in a straight line

• waves
• velocity, wavelength, and frequency

speed of the wave

distance between the crests of the waves/determines the penetrating power of the radiation

higher

• The number of wavelengths that pass a given point in a certain amount of time
• Long

• Low
• Less
• High
• More

• High-energy, ionizing electromagnetic radiation
• Possess properties of both waves and particles
• Defined as weightless bundles of energy (photons) without an electrical charge that travel in waves with specific frequency at the speed of light
• X-ray photons interact with the materials they penetrate causing ionization

• Invisible
• No weight or mass
• Have no charge
• Short wavelengths, high frequency
• Travel in waves; at the speed of sound through space in a straight line that can be deflected/scattered
• Cannot be focused to a point, always diverge from a point

• Penetrates liquids, solids and gasses
• Absorbed by matter
• Causes ionization with materials they penetrate (process of converting an atom into ions)
• Causes certain substances to fluoresce (Barium, Magnesium)
• Can cause biological changes in living cells
• Can produce an image on photographic film

• Control Panel: On/Off switch and Control devices for time, kilovoltage and milliamperage
• Extension Arm: Allows movement and positioning of tubehead, extends from control panel to tubehead and houses the electrical wires
• Tubehead: Contains the xray tube where xrays are produced

• Metal housing
• Insulating oil
• Tubehead seal
• X-ray tube
• Transformer
• Aluminum disks
• Lead collilmator
• PID (extends out from the tubehead)

Protects the x-ray tube and grounds the high voltage components

Prevents overheating by absorbing the heat created by the production of x-rays

Seals the oil in the tubehead and acts as a filter to the x-ray beam

x-ray tube

Alters incoming electricity

Filter out non-penetrating, longer wavelengths

Restricts the size of the x-ray beam

Open-ended, lead-lined cylinder that aims and shapes the xray beam

• glass vacuum-sealed tube
• Critical in the production of x-rays

• Leaded Glass Housing
• Negative Cathode
• Positive Anode

• Vacuum tube prevents x-rays from escaping in all directions
• One central area has a window that permits xray beam to exit the tube
• Directs beam toward the aluminum disks, lead collimator, and PID

• Tungsten wire filament
• Produces electrons when heated
• Molybdenum (focusing) cup
• Focuses the electrons into a narrow beam and directs it across the tube toward the tungsten target of the anode

• step-down
• cathode

• Consists of a wafer-thin tungsten plate embedded in a solid copper rod
• Tungsten plate (target) serves as a focal spot where bombarding electrons are converted into xray photons

• step-up
• speed of electrons

Dissipates the heat away from the tungsten target

• Electricity
• conductor
• electrical current

Decreases the voltage from the incoming 110 or 220 line voltage to 3 to 5 volts used by the filament circuit (Cathode)

increase the incoming 110 – 220 volts 65,000 to 100,000 volts

Voltage compensator that corrects for minor fluctuations in the current flowing through the xray machine

• 1. Electricity enters the control panel from the wall outlet
• 2. Current travels from the control panel to the tubehead through the electrical wires in the extension arm
• 3. Current is directed to the filament circuit and the step down transformer (110 or 220V to 3-5V) in the tubehead
• 4. Filament circuit uses the 3-5volts to heat the tungsten filament in the cathode
• 5. “Thermionic Emission” occurs: the release of electrons from the tungsten filament when the electrical current passes through it and heats the filament (“boiling-off” of electrons creates an electron cloud)
• 6. Outer-shell electrons of the tungsten atom acquire enough energy to move away from the filament surface and an electron cloud forms 
• 7. Electrons stay here until the high voltage circuit or step up transformer (110-220V to 65,000-100,000 V) is activated

• 1. When the exposure button is pushed, the high voltage circuit is activated (step-up transformer)
• 2. Electrons produced at the cathode are accelerated across the xray tube to the anode
• 3. Electrons strike the tungsten target and are converted to xray energy (<1%) and heat (>99%)
• 4. A small number of xray photons exit through the unleaded glass window
• 5. X-ray beam then travel to the tubehead seal, and the aluminum disc (filter).
• 6. Aluminum discs remove (filter) the ineffective low energy, non-penetrating longer wavelength xrays from the beam
• 7. The size and shape of the xray beam is next restricted by the collimator and travels down the lead-lined PID (aims and shapes the xray beam) and exits the tubehead

• General (Braking) Radiation 
• 2) Characteristic Radiation

• Speeding electrons slow down due to interaction with tungsten target in the anode (hits or near-misses nucleus of tungsten atom) thus producing xray photons
• Braking Radiation=“Bremsstrahlung”(German term that means braking radiation)
• 70%

• a high speed electron dislodges (ejects) an inner-shell electron from tungsten atom and causes ionization from that atom
• Remaining electrons are rearranged to fill the vacancy, resulting in the production of an xray photon
• Accounts for a very small part of xray production and only at 70 kVp and above

x-ray beam that exits the PID

created when the xray beam interacts with matter (soft tissues, bones, teeth) Less penetrating than primary

a form of secondary radiation that results from an x-ray that has been deflected from its path due to interaction with matter. Deflects in all directions and is detrimental to pt. and operator

• X-ray photons can pass thru pt. w/ no interaction:   leaving atoms unchanged and producing densities/ images on receptors
• Completely absorbed by pt. (photoelectric effect/ionization): 30%
• Scattered (changes direction): most of scatter radiation is Compton scatter (ionization): 62%)
• Coherent/unmodified scatter (photon is not modified and no ionization or change in the atom occurs; xray photon just changes direction : 8%)

• X-ray photon collides with a loosely bound outer-shell electron and gives up part of its energy to eject the electron from its orbit
• X-ray photon loses its energy and continues in a different direction at a lower energy level
• Ionization occurs
• Partial absorption occurs

• X-ray photon collides with a tightly bound inner-shell electron
• Gives up all its energy to eject the electron from its orbit
• All of the energy of the photon is absorbed
• Ionization occurs
• Total absorption occurs

• Path of a low-energy xray photon interacts with an outer-shell electron
• No change in the atom occurs
• No ionization occurs, xray photon just changes direction and is unmodified

Unit of measure to describe number of electrons (or current) passing through the cathode filament

temperature of the cathode filament and the QUANTITY (#of xrays)

exposure time

increase (darker image)

decrease (lighter image)

penetrating ability of the x-ray beam

kilovoltage

speed

65 to 100kV

• how sharply dark and light areas are differentiated or separated on an image
• high contrast (few shades of gray, mostly black and white)
• low contrast (many shades of gray)

• Impulses
• 60

• decreased by half
• doubled

kVp, mA, exposure time and distance

Exposure time (as with mA)

source of radiation to patient’s skin

• Less divergent xray beam
• Decreased radiation exposure to pt
• Less image magnification

¼

4

• penetrating capability
• intensity