Radiation Quantities and Units

RADIATION QUANTITIES

Measure of the amount of radiation

RADIATION QUANTITIES

Measures a radiation beam

Radiation Exposure

Radiation travelling through air; Total radiation delivered to a body

Radiation Exposure

Measure of the radiation that emanates from the source and delivered to a specific target

Radiation Dose

Radiation travelling through a medium

Radiation Dose

Concentration of radiation at some point or to a specific tissue or organ

Exposure

RADIATION QUANTITIES AND THEIR UNITS OF MEASURE:

(X)

Activity

RADIATION QUANTITIES AND THEIR UNITS OF MEASURE:

(A)

Effective Dose

RADIATION QUANTITIES AND THEIR UNITS OF MEASURE:

(E)

Equivalent Dose

RADIATION QUANTITIES AND THEIR UNITS OF MEASURE:

(H)

Absorbed Dose

RADIATION QUANTITIES AND THEIR UNITS OF MEASURE:

(D)

EXPOSURE

Measure of ionization produced in air by photons; Measured using ionization chamber

EXPOSURE

Quantity of charge released during the ionization of air by passage of radiation under strictly defined conditions

IONIZATION

Removal of an orbital electron from an atom

IONIZATION

Produces an ion pair

Negatively charged electron; Positively charged ion

Ion pair produced in ionization

IONIZATION

The removal of electron from an atom causes the deposition of energy to the interacting medium

IONIZATION

the energy of the incident radiation is usually transferred to the ejected electron, and will eventually be absorb by the medium as the recoil electron undergoes a series of interaction and eventually come to rest

Primary Standard Instrument

Free air ionization chamber

Secondary Instrument

Instruments designed for field use, such as the Victoreen R meteR

Secondary Instrument

Mimics the primary standard instrument, but they are smaller and suitable for field use

FREE AIR IONIZATION CHAMBER

Measurement of the exposure according to the definition of Roentgen (old unit of exposure)

IONIZING RADIATION

Form of radiation w/ sufficient energy to excite and/or ionize atoms

Roentgen

Quantity of charge released during the ionization of air by passage of radiation under strictly defined conditions

temperature decreases, and as pressure increases

Exposure increases as

3 MeV energy

Limited to the measurement of beam w/

very bulky

Confined to national standards laboratories bc it is

Directly Ionizing

Includes all charged particles; Interact w/ electrons thru long-range Coulombic charged-particle interactions and deliver to matter directly

Directly Ionizing

Alpha and beta

Indirectly Ionizing

Includes x-rays, gamma rays, and all uncharged particles

Indirectly Ionizing

Interact via a transfer of energy to a single charged particle, and

Indirectly Ionizing

It is the secondary charged particle that delivers energy to the absorbing material

Indirectly Ionizing

Photons and neutrons

CAPACITOR ION CHAMBER

Secondary instrument

CAPACITOR ION CHAMBER

Suitable for field use (radiotherapy department)

1. Thimble Chamber

2. Stem Capacitor

3. Measuring System (Electrometer)

4. Power Supply

CAPACITOR ION CHAMBER PARTS

ABSORBED DOSE

Measure of the amount of energy imparted to an interacting material

UNITS OF EXPOSURE

Unit of charge divided by a unit of mass

ABSORBED DOSE

Differs w/ different interacting material for the type and energy of the beam

ABSORBED DOSE

Energy absorption per unit mass

medium

As ionizing radiation passes through an object, some of the energy of that radiation is transferred to that

ABSORBED DOSE

Energy absorption of 100 ergs per gram of matter

EQUIVALENT DOSE

Transfer of photon energy to orbital electrons

EQUIVALENT DOSE

Absorption by the medium of energy released by the primary electrons as they ionize and excite atoms along their paths

Absorbed Energy

Responsible for any biologic damage resulting from the tissues being exposed by radiation

UNITS OF ABSORBED DOSE

Conventional Unit: radiation absorbed dose (Rad)

Roentgen

Old unit of exposure

Gray

Pioneer in the field of measurement of radium radiation and x-rays and their effects on living tissue; Louis Harold Gray

Medium Composition

Photon Energy

related tp mass energy absorption coefficient of the medium relative to air which is affected by:

EQUIVALENT DOSE

Takes into account the variation in biologic harm that is produced by diffy types of radiation

EQUIVALENT DOSE

Commonly used to express the biological impact of radiation on persons receiving occupational or environmental exposures

relative biological effectiveness (RBE)

Different types of radiation have diffy efficiencies known as

EQUIVALENT DOSE

This quantity is for radiation protection purposes

EQUIVALENT DOSE

Both the type and energy of the radiation of concern are considered

RADIATION WEIGHING FACTOR

Some types of radiation, such as alpha articles are more biologically damaging to living tissues than other types of radiation when the absorbed dose from both is equal

RELATIONSHIP OF Gy and Sv

In x-rays and other photons where the radiation factor is 1

EFFECTIVE DOSE

Quantity for expressing relative radiation risk to specific tissues or organs in humans, both patients and other personnel

EFFECTIVE DOSE

This is due to the different radio sensitivities of different tissues and organs in the body

EFFECTIVE DOSE

Take into account the sensitivity of the tissue where radiation was absorbed

TISSUE WEIGHING FACTOR

Takes account of the sensitivities of different organs and tissues for induction of pababilistic effects from exposure

Weighing Factor

Given to all individual organs and tissues that kown to demonstrate cancer or hereditary effects is such a way that all weighing factors, when combined, result in a value of 1

COLLECTIVE EFFECTIVE DOSE

Considers the amount of radiation delivered to a specific geographical population

COLLECTIVE EFFECTIVE DOSE

Sum of all individual effective doses within a certain population within a particular time frame

ACTIVITY

Measure of the number of disintegration per seconds

ACTIVITY

Amount of radioactive element in a particular energy state at a given time that wll decay to another state at a given time interval

∆N

is the expectation value of the number of spontaneous nuclear transitions from a given excited state of an isotope in a time ∆�

RADIATION INTENSITY

Rate of emitted energy from unit surface area

RADIATION INTENSITY

Total number of photons or particles that comprises the beam per given time

ATTENTUATION

Removal of photons from a beam of x-rays or gamma rays as it passes through matter

ATTENTUATION

The total reduction in the number of x-rays remaining in an x-ray beam after penetration thru a given thickness of tissue

ATTENTUATION

Caused by both absorption and scattering of the primary photons

Linear Attenuation Coefficient

Actual fraction of photons interacting per 1-unit thickness of material

Linear Attenuation Coefficient

Describes the fraction of a beam of x-rays or gamma rays that is absorbed or scattered per unit thickness of the absorber

Linear Attenuation Coefficient

Quantity that characterized how easily a material or medium can be penetrated by a beam of light, sound, particles, or other energy or matter

ENERGY

ATOMIC NUMBER

DENSITY

The rate at which photons interact (attenuation coefficient value) is determined by:

Mass Attenuation Coefficient

The linear attenuation coefficient normalized to unit density

Mass Attenuation Coefficient

Rate of photon interactions per 1-unit area mass

Mass attenuation coefficient value

are normalized w/ respect to material density, and therefore do not change w/ changes in density

DIRECT

Material density does have a _____ effect on linear attenuation coefficient values

HALF-VALUE LAYER (HVL)

Thickness of absorbing material necessary to reduce the x-ray intensity to half of its original value

X-RAYS

are attenuated exponentially, high-energy x-rays are more penetrating than low-energy x-rays

DIAGNOSTIC X-RAYS

usually has HVL 3 to 5 mm Al or 3 to 6 of soft tissue

10-keV x-rays

are attenuated at 15%/cm of soft tissue

100-keV x-rays

are attenuated at rate of 3%/cm of soft tissue

WAVELENGTH

ENERGY

Photon Interaction W/ Matter is Dependent on the ________ of electromagnetic radiation and ______

PHOTON INTERACTION W/ MATTER

Also dependent on the density, thickness, and atomic number of interacting material

Absorbed

interact w/ matter and be completely absorbed by depositing its energy

Scattered

Interact and be scattered or deflected from its original direction and deposit part of its energy

Penetrate

Penetrate the body w/o interaction to expose the image receptor

Electromagnetic radiation

interacts w/ structures w/ similar size to the wavelength of the radiation

HIGHER

SHORTER

The ______ the energy of the EM radiation, the ____ the wavelength

CLASSICAL SCATTERING

Occurs when an incident photon changes direction w/o losing energy

Incident photon

is momentarily absorbed either by a shell electron (Thomson Scatter) or the atom (Rayleigh Scatter)

Backscatter

Low amount of energy los

Side Scatter

Responsible occupational exposure

Side Scatter

Moderate amount of energy lost

Forward Scatter

Low amount of energy lost

0-angle

deflection means that no energy is lost

ENERGY LOST

The direction of scatter radiation is dependent on the amount of ____

GREATER

GREATER

the ______ the energy lost, the _____ would be the divergence from its original path