length - 1650763.73 times the length of one emission wave of the Krypton atom,
mass - how much matter an object contains - kg ito platinum-iridium cylinder kept in a vault in France, and
time - 9 192 631 770 vibrations of a Cesium atom.
Derived Units:
SI units
- Exposure, Coulomb per kilogram, C/kg, Roentgen, R, where 1 R = 2,58 x 10^-4 C/kg
- Dose, gray, Gy, rad, rad, 1 Gy = 100 rad
- Dose equivalent, sievert, Sv, rem, 1 Sv = 100 rem
- Activity, becquerel, Bq, curie, Ci, 1 Ci = 3.7 x 10^10 dps where dps is disintegrations per second
- Frequency, Hertz, Hz, cycles per second, cps, 1 Hz = 1 cps
Similar triangles are often used to calculate the object size with a known image size
Image = do/SOD = di/SID or
Image = object size / source object distance = image size / source image distance
Used mainly to calculate the size of the image
where,
do = 10cm, SID = 100 cm, SOD = 80 cm, di = ?
- do/SOD = di/SID
- 10/80 = di / 100, di = 10/80 x 100 = 12.3 cm
Magnification: the ratio of the image size to the object size is called magnification. Large Magnification require a short source object distance and large SID.
m=Si/So=SID/SOD
Newtons Laws of Motion:
- Newton's Law of Inertia.
- A body at rest will remain at rest and a body in motion will remain in motion unless acted upon by an external force.
- Newton's Law of Force.
- The force of a body is given by its mass times acceleration. F=ma
- Newton's Law of Equal Reactions
- For every action there is an equal and opposite reaction
Objects in Motion:
- s = vt, v=s/t
- v = Vo + at
- an object with a constant velocity has an acceleration of zero
Mass and Weight:
F=ma, Weight = mg, (gravity on earth 9.8 m/s^2, gravity Moon = 0 m/s^2)
Work and Energy: W= FS = kg/m^2 x m = Nm = j
Energy - mechanical
- kinetic and potential energy = 1/2 mv^2 and mgh
- law of conservation of energy = mgh = 1/2 mv^2
Momentum (p) = mv
Momentum is conserved in collisions; Mom before = Mom after or mv(before) = mv (after)
Heat - is energy of molecular motion. Heat transfer can occur through:
- conduction,
- convection and
- radiation.
Conduction is heat transfer from one end of a metal rod to the other end.
Heat transfer from the sun is radiation.
Heat transfer from fluid in motion is convection.
Convection energy is used by a fan to cool a room
Radiation is the emission of energy from a body. Radiation energy can be transferred through a vacuum and depends on the temperature of the body. Radiation is the principle means of heat transfer from x-ray anode to the tube housing.
Heat transfer from the sun is radiation.
Heat transfer from fluid in motion is convection.
Convection energy is used by a fan to cool a room
Radiation is the emission of energy from a body. Radiation energy can be transferred through a vacuum and depends on the temperature of the body. Radiation is the principle means of heat transfer from x-ray anode to the tube housing.
Temperature:
Convert 50 degrees Fahrenheit to Degrees Celsius
50F = 100/180 C -32 =10 Celsius
50F = 100/180 C -32 =10 Celsius
Electromagnetic radiation. All forms of electromagnetic ration travel with the speed of light, 3 x 10^8 m/s. the energy of electromagnetic radiation is related to the frequency f by:
- E=hf
h= Planck's consistant ( h= 6.6 x 10 ^34 j/sec). therefore higher frequency = higher energy
Only X-rays and gamma rays have enough energy to separate one or more electrons from the atom to produce an ion pair. X-Rays and Gamma rays are classified as ionizing radiation.
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| Wavelength of a sine wave, λ, can be measured between any two points with the same phase, such as between crests, or troughs, or corresponding zero crossings as shown. Frequency = 1 Hz = 1 cps.
Amplitude = V = fλ Velocity of an electromagnetic radiation c = fλ where c = velocity of light at 3 x 10^8 m/s - and c=k for all electromagnetic radiation Therefore: E = hf = h (c/λ) If the energy is measured in keV and the wave length is measured in Angstroms (symbol Å) 1 A = 10^-10 m, E(KeV) = 12.4 / λ (A) λ (A) = 12.4 / E(KeV) Intensity is defined as the energy passing through a unit area. It is measured in joules per meter2. The intensity of an x-ray beam is obtained by multiplying the number of photons passing through a given area by the energy of each x-ray photon. Radiation Units The photon fluence measures the number of photons per square meter. A more convenient measure of radiation is a measure of ionization produced in air (the exposure). The Roentgen was defined as the amount of radiation which would produce 2.58 x 10 ^-4 coulombs per kilogram of dry air. 1 roentgen (R) = 258 microcoulomb/kg (µC/kg) Radiation Dose The unit of dose measures the radiation energy deposited in the patients body. A grey is defined as a deposition of one joule of energy per kilogram. 1 Gy = 100 rad Other radiations: Alpha and beta particles - natural radiation Linear Energy Transfer Linear Energy Transfer is the amount of Ionization Energy Transfer by a particle along its particle track, measured in KeV per micron. The higher the LET the greater its biological effect keV/µm. Quality Factor To compare different sorts of radiation to each other we have to "adjust" the dose of radiation with a Quality Factor to get a "dose equivalent". 1 siervert = QF x Gray 1 rem = QF x rad For Medical X-rays QF = 1 and the units are adjusted so that 1 R = 1 rad = 1 rem and 1 Gy = 1 Sv In physics, an inverse-square law is any physical law stating that some physical quantity or strength is inversely proportional to the square of the distance from the source of that physical quantity. The inverse square law in radiography is: where I is intensity and r is distance (radius). 1. An object moving with a velocity of 12m/s travels 48 m in 4 seconds. 2. U=4m/s, a=?, v=25m/s t=7s a=3m/s^2 |
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