Radiation Production and Characteristics: Systems of Measurement and Mechanics

Flashcards covering systems of measurement, base and derived quantities, Newton's laws of motion, work, energy, and heat transfer principles relevant to radiologic technology.

Base Quantities

The three building blocks of all other quantities: mass, length, and time.

Mass

The quantity of matter contained in any physical object, represented by the standard unit kilogram ($kg$).

Kilogram ($kg$)

The standard unit of mass, represented by a platinum-iridium cylinder in Paris; originally defined as the mass of $1,000\,cm^3$ of water at $4^{\circ}C$.

X-rays and Gamma rays mass

Massless energy disturbances in space that are assigned mass equivalence values.

One meter (1960 definition)

The wavelength of orange light emitted from an isotope of krypton ($Kr\text{-}86$).

One meter (Current definition)

The distance travelled by light in $\frac{1}{299,792,468}$ second.

Caliper

An instrument used to measure a patient's thickness to calculate the appropriate kilowatt peak ($kVp$) or energy value of the x-ray.

Source-to-Image Receptor Distance ($SID$)

The technical factor in radiography measuring the distance from the x-ray tube to the receiving x-ray film.

Second ($s$)

The standard unit of time, currently based on the vibration of cesium atoms in an atomic clock.

Atomic clock

A device capable of keeping time correctly to about $1\,second$ in $5,000\,years$ based on the vibration of cesium atoms.

Secondary Quantities

Also called derived quantities, these are derived from a combination of one or more base quantities, such as volume ($l^3$) and mass density ($m/l^3$).

Velocity of light

A value given as $3.0 \times 10^8\,m/s$, which is also the speed at which x-rays and gamma rays travel.

Special Quantities

Quantities designed for specialized areas; in radiologic science, these include exposure, dose, effective dose, and radioactivity.

International Bureau of Weights and Measures

The organization in Paris, France, where standard units of mass, length, and time are kept.

Standard Units of Measure parts

Every measurement consists of two parts: magnitude and unit.

SI System

The International System (Le Systeme International d’Unites), which includes the MKS units (meter, kilogram, second) plus Ampere, Kelvin, mole, and candela.

Mechanics

A segment of physics dealing with objects at rest (statics) and objects in motion (dynamics).

Velocity

A vector quantity that measures the rate of change of an object's position with time, requiring both speed and direction.

Speed

A scalar quantity representing the number of meters per second or kilometers per hour an object is moving.

Acceleration ($a$)

The rate of change of velocity with time, expressed in the unit meters per second squared ($m/s^2$).

Law of Inertia (Newton’s First Law)

A body will remain at rest or continue to move with constant velocity in a straight line unless acted on by an external force.

Mass (as defined by inertia)

The property of a body that causes it to remain at rest or maintain a constant velocity; mass and inertia are the same thing.

Force ($F$)

The product of the mass ($m$) of an object multiplied by the acceleration ($a$) produced; $F = ma$.

Newton ($N$)

The SI unit of force, where $1\,N = 1\,kg \cdot m/s^2$.

Dyne

A unit of force equal to $1\,g \cdot cm/s^2$.

Law of Interaction (Newton’s Third Law)

For every action (force), there is an equal and opposite reaction.

Weight ($Wt$)

A force on a body caused by the pull of gravity, calculated as $Wt = mg$.

Acceleration due to gravity ($g$)

A constant rate of acceleration for falling objects, equal to $9.8\,m/s^2$ on Earth and $1.6\,m/s^2$ on the moon.

Momentum ($p$)

The product of the mass of an object and its velocity ($p = mv$); greater velocity results in more momentum.

Work ($W$)

Calculated as force times the distance over which it is applied ($W = Fd$), measured in Joules ($J$).

Power ($P$)

The rate at which work is performed or energy is expended, defined as $P = Work/t$.

Watt ($W$)

The SI unit of power, equivalent to one joule per second ($J/s$).

Law of Conservation of Energy

Energy may be transformed from one form to another, but it cannot be created or destroyed.

Kinetic Energy ($KE$)

The energy associated with the motion of an object, expressed as $KE = \frac{1}{2}mv^2$.

Potential Energy ($PE$)

The stored energy of position or configuration, expressed as $PE = mgh$.

Heat

The kinetic energy of the random motion of molecules.

Calorie ($cal$)

The heat necessary to raise the temperature of $1\,g$ of water by $1^{\circ}C$.

Conduction

The transfer of heat through a material or by touching.

Convection

The mechanical transfer of "hot" molecules in a gas or liquid from one place to another.

Thermal Radiation

The transfer of heat by the emission of infrared radiation; this is the primary way an x-ray tube cools.