Ionizing Radiation and Radiation Quantities/Units Flashcards
what are the sources of radiation?
- Natural that are always present in the environment
- Manmade created by humans for specific purposes
what are sources of manmade (artifical) radiation?
- Consumer products containing radioactive material
- Air travel
- Nuclear fuel for generation of power
- Atmospheric fallout from nuclear weapons testing
- Nuclear power plant accidents
- Medical Radiation
what are sources of natural radiation (background)?
- Terrestrial radiation
- Cosmic radiation (solar and galactic)
- Internal radiation from radioactive atoms (also called radionuclides)
Terrestrial radiation
decay of radioactive materials in the earth (soil, water, vegetation)
- internal or through the skin
Cosmic radiation
from space (stars)
- typically beta and gamma radiation
Internal (ingestion, inhalation or natural)
decay of radioactive materials in the body naturally or through ingestion or inhalation (uranium for ingestion or inhalation, breaks down into radon)
Consumer product radiation
tobacco, building materials, older televisions, airport x-ray systems, smoke detectors and construction materials
Air Travel
- cosmic radiation
- depends on length, altitude and latitiude
flying coast to coast - 0.035 mSv
Nuclear fuel for generation of power
- small amounts of radioactive gases and liquids
Atmospheric Fallout from nuclear weapons testing
- more than 500 nuclear weapons tests took place in the 40’s, 50’s and 60’s
- radioactive particles and gases were spread in the atmosphere
- these particles and gases still continue to fall to the earth
Nuclear power plant accidents
- Three mile island
- Chernobyl
- Fukushima
Medical radiation
- radiography, nuclear medicine, radiation therapy, etc.
sources of medical radiation broken up by specialty
- CT - 65.2%
- General Radiography - 8.7%
- Nuclear Medicine - 17.4%
- Interventional Procedures - 8.7%
what is the major change in sources of radiation from 1990 - 2006?
medical radiation went from 0.5 mSv to 3.2 mSv
which medical procedure is the highest source of radiation?
CT
what are the 2 largest sources of artificial radiation?
- Diagnostic medical x-ray (which includes computed tomography (CT), interventional fluoroscopy, and conventional radiography or fluoroscopy)
- Nuclear medicine procedures
what radiation are we unable to control?
natural background radiation
If a patient has a chest X-ray, how much exposure do they actually receive?
2 exposures/procedure - PA and Lateral
- approximately 0.08 mSv
Energy
the ability to do work - to move an object against resistance
How radiation relates to energy
Radiation is kinetic energy that passes from one location to another and can have many manifestations (light, heat, nuclear, electromagnetic)
- many types of radiation exist
what is ionizing radiation
Ionizing radiation is radiation with kinetic energy that has the ability to produce charged particles (ions) when passing through matter.
all ionizing radiation can be classified into what 2 categories?
Electromagnetic radiation
Particulate radiation
What is ionization
- Conversion of atoms to ions
- Valuable for creating images
- Has the undesirable result of potentially producing some damage in the biologic material
what are 2 examples of non ionizing radiation?
ultrasound and MRI
what are photons?
X-ray and gamma rays - no mass no charge
Electromagnetic waves are characterized by their?
wavelength and frequency
what is wave particle duality
the dual nature of electromagnetic radiation
- this form of radiation can travel through space in the form of a wave but can interact with matter as a particle of energy
what are forms of particulate radiation?
- alpha particles
- beta particles
- neutrons
- protons
what are the characteristics of particulate radiation?
- All these are subatomic particles that are ejected from atoms at very high speeds.
- They possess sufficient kinetic energy to be capable of causing ionization by direct atomic collision.
- No ionization occurs when the subatomic particles are at rest
what are alpha particles?
- Alpha rays
- Emitted from nuclei of very heavy elements such as uranium and plutonium during the process of radioactive decay
- Are simply helium nuclei (minus their electrons)
what is the makeup of an alpha particle?
- Each Alpha Particle contains two protons and two neutrons
what is the mass and charge of an alpha particle?
- Have a large mass (approximately 4 times the mass of a hydrogen atom) and a positive charge twice that of an electron
Ability of alpha particles to penetrate matter?
- Alpha particles are less penetrating than beta particles (fast electrons).
- They lose energy quickly as they travel a short distance in biologic matter
- Are considered virtually harmless as an external source of radiation. A piece of ordinary paper can absorb them or function as a shield.
- As an internal source of radiation, they can be very damaging.
- If emitted from a radioisotope deposited in the body, such as in the lungs, alpha particles can be absorbed in the relatively radiosensitive epithelial tissue and are very damaging to that tissue.
beta particles weight and charge?
8000 times lighter than alpha particles and have only one unit of electrical charge (-1) as compared with the alpha’s two units of electrical charge (+2).
beta particle characteristics
- Identical to electrons except their origin; emitted from the nucleus of a radioactive atom
- Beta particles will not interact as strongly with their surroundings as alpha particles do.
- Capable of penetrating biologic matter to a greater depth than alpha particles with far less ionization along their paths.
How many types of radiation do we produce? How are these x-rays produced?
- 2 – characteristic and bremsstrahlung radiation
- Characteristic is 1 value from K shell – ionizes k shell electron – replaces it
- Bremstrahlung ranges from minimum to maximum energy – changes direction
- X-rays use more Brems than characteristic
What are radiation units? and why are the important?
- Need to develop standards for measuring and limiting radiation exposure
- Awareness of potential harmful effects of ionizing radiation
- Desire of the medical community to reduce radiation exposure throughout the world by developing standards for measuring and limiting this exposure
Radiation Exposure
Radiation travelling through the air
- Charge produced in a unit mass of air
- Amount of charge created/kg of air by the x-ray beam
- Used only for photons (not particulate) less than 3 MeV
what does radiation exposure not give you information about?
- how much energy is absorbed by tissues being irradiated
- Where in the body absorption takes place
- Tissue sensitivity to radiation
Radiation Dose
radiation travelling through a medium
- energy absorbed within an object/medium
SI unit
Coulomb/Kg
- coulomb is charge per kg
Conventional unit
Roentgen (R) or milliroentgen (mR)
conversion between conventional and SI units
1R = 2.58 x 10^4 C/kg
Why bother with a unit that deals with radiation traveling through the air
attenuation processes for air, soft tissue, and H2O is very similar, meaning that a number of dosimetric experiments and measurements can take place quite easily in air to represent what might be happening in the human body.
What is Air Kerma?
- Replacing ‘Exposure’
- Used to express how much energy is transferred/deposited from x-rays to air
KERMA = Kinetic Energy Released in Air = Total kinetic energy released in a unit mass (kg) of air
SI unit of Air Kerma?
gray (Gy) = J/kg - Joule is energy per kg
Kerma vs. absorbed dose in X-ray?
- Kerma and absorbed dose are basically the same at the diagnostic x-ray level
Dose Area Product (DAP)
- An estimation of the total amount of energy delivered to a patient (at the entrance surface) during an exposure
- Sum of the total Air Kerma over the exposed surface area of the patient.
DAP units
Expressed using Gy-cm2 or mGy-cm2
If a patient receives an Air Kerma dose of 20 mGy over a surface area of 100 cm2, what Is the DAP?
2 dGy*cm^2
What is absorbed dose? and what does it measure?
- baseline quantity from which other dose units are derivded
- absorbed does measures the amount of energy that is imparted to a medium
- It is defined as the mean energy deposited to a medium by ionizing radiation divided by the mass of that medium
units for absorbed dose?
1J/kg =1 Gy = 100 rads
What is equivalent dose?
- Absorbed dose does not differentiate between different types of radiation
- Equal absorbed doses of different types of radiation produce different amounts of biologic damage in body tissue.
-The concept of dose equivalence takes this biologic impact into consideration by using a specific modifying, or quality, factor to adjust the absorbed dose value. - Radiation Weighting Factor (WR) is a dimensionless factor (a multiplier) used for radiation protection purposes to account for differences in biologic impact among various types of ionizing radiation
Units for equivalent dose
1 J/Kg = 1 Sv = 100 rems
How do you calculate equivalent dose
The product of the absorbed dose (Gy) in a tissue or organ and its Radiation Weighting Factor (WR)
EqD = D x WR
Sv = Gy x WR
What is effective dose?
A further measure that takes into consideration the differing sensitivities of exposed tissue to radiation
- It is the tissue-weighted sum of the equivalent doses in all specified tissues and organs of the human body and represents the stochastic health risk to the whole body
- Incorporates both the effect of the type of radiation used and the variability in radiosensitivity of the organ or body part irradiated through the use of appropriate weighting factors
annual dose limit radiation workers
whole body - 20 mSv/year averaged over 5, max of 50 mSv in any single year
lens of eye 20 mSv/year averaged over 5, max of 50 mSv in any single year
skin - 500 mSv equivalent dose
hands and feet - 500 mSv equivalent dose
annual dose limit members of the public
whole body - 1 mSv effective
lens of the eye - 15 mSv
skin - 50 mSv equivalent dose
what are weighting factors?
Factors that determine the overall harm to those biologic components for risk of developing a radiation-induced cancer or, for the reproductive organs, the risk of genetic damage.
how do you calculate effective dose?
EfD = D x Wr (radiation weighting factor) x Wt (tissue weighting factor)
what is the tissue weighting factor?
Takes into account the carcinogenic sensitivity of each organ
E.g. If the lungs receive an absorbed dose of 0.5 Gy, from exposure to alpha radiation, what is the effective dose in Sv?
EfD = 0.5 Gy x 20 x 0.12 = 1.2
what are the 5 types of interaction possible between X-ray and matter?
- Coherent scatter
- Photoelectric absorption
- Compton scatter
- Pair production
- Photodisintegration
What does Photoelectric absorption depend on?
- Energy (E) of the incident x-ray photons
- Atomic number (Z) of the atoms comprising the irradiated object
- Physical density
- Thickness
What causes the probability of photoelectric absorption to increase markedly?
- E of the incident photon decreases
- Z of irradiated atom increases
