Chapter 9: Basic Radiation Protection and Radiobiology

Vocabulary flashcards covering fundamental terms, radiation units, cellular response theories, interactions with matter, and monitoring devices from Chapter 9.

Air Kerma

SI quantity used to measure energy transferred from radiation to matter, which may be at the surface of a patient's or radiologic and imaging sciences professional's body; measured in joules per kilogram ($\text{J/kg}$), where $1\,\text{J/kg} = 1\,\text{Gray}\ (\text{Gy}_{a})$.

ALARA

Mnemonic meaning to keep all radiation exposure as low as reasonably achievable.

Becquerel (Bq)

Unit of radioactivity in the International System of Units, equal to one disintegration per second ($1\,\text{d/s} = 1\,\text{Bq}$).

Classic Coherent Scattering

Interaction with matter in which a low-energy photon (below $10\,\text{keV}$) is absorbed and released with its same energy, frequency, and wavelength but with a change of direction, resulting in no energy transfer to the patient.

Compton Scattering

Interaction with matter in which a higher energy photon strikes a loosely bound outer electron, removing it from its shell, and the remaining energy is released as a scattered photon; responsible for the majority of occupational workers' exposure to radiation.

Curie (Ci)

Unit of radioactivity defined as the quantity of any radioactive nuclide in which the number of disintegrations per second is $3.7 \times 10^{10}$.

Exposure (X)

The amount of radiation delivered to a point, measured in coulombs per kilogram ($\text{C/kg}$).

Germ Cells

Cells of an organism whose function is to reproduce the organism (e.g., ovum, spermatozoa), possessing $23$ chromosomes and reproducing through meiosis.

Gray (Gy)

Unit in the International System used to measure the amount of energy absorbed in any medium; $1\,\text{Gy} = 100$ radiation absorbed doses ($\text{rad}$).

International System (SI) of Units

System of units based on metric measurement developed in 1948 and officially adopted in 1985 to measure radiation.

Kiloelectron Volts (keV)

Units of energy equal to $1000$ electron volts.

Photoelectric Interaction

Interaction with matter in which a photon strikes an inner shell electron, causing its ejection from orbit with the complete absorption of the photon's energy; constitutes the greatest hazard to patients in diagnostic radiography.

Radiation

Forms of energy emitted and transferred through matter.

Sievert (Sv)

Unit in the International System used to measure the dose equivalence, or biologic effectiveness, of differing radiations ($1\,\text{Sv} = 100\,\text{rem}$); defined as the product of the absorbed dose in Gray and the quality factor.

Somatic Cells

All of the body's cells except germ cells, containing $46$ chromosomes ($23$ pairs) and dividing through mitosis.

X-rays

Form of human-made electromagnetic radiation traveling at the speed of light, possessing the ability to penetrate matter.

Thermionic Emission

The process by which a cathode filament composed of thoriated tungsten boils off electrons when electric current (milliamperage) is applied.

Direct Hit Theory

Theory proposing that any type of radiation transfers its energy directly to a key molecule (such as DNA), resulting in ion pair formation or excitation that disrupts cellular function.

Indirect Hit Theory

Theory proposing that radiation deposits energy in non-critical molecules (primarily water, which makes up approximately $80\%$ of the cell), creating chemical changes that alter the internal environment and injure or kill the cell.

Target Theory

Theory stating that certain key molecules existing in limited supply (specifically DNA in the nucleus) are essential to cellular viability, and direct or indirect damage to these targets has serious consequences for cell survival.

Hematopoietic Syndrome

Acute radiation syndrome occurring at total body doses of $2$ to $10\,\text{Gy}$, characterized by bone marrow damage leading to infection, hemorrhage, and anemia, with a mean survival of $6$ to $8$ weeks.

Gastrointestinal (GI) Syndrome

Acute radiation syndrome occurring at total body doses of $10$ to $50\,\text{Gy}$, caused by damage to the epithelial lining of the GI system and resulting in massive diarrhea, nausea, vomiting, and fever, with a mean survival of $3$ to $10$ days.

Central Nervous System (CNS) Syndrome

Acute radiation syndrome occurring at total body doses above $50\,\text{Gy}$, leading to brain edema, increased intracranial pressure, seizures, coma, and death within a few hours to $2$ to $3$ days.

Inverse Square Law

Principle stating that the intensity of radiation varies inversely with the square of the distance from the source.

Optically Stimulated Luminescence (OSL) Dosimeter

Personnel monitoring device containing aluminum oxide crystals; dose is determined by exposing the crystals to laser light, causing luminescence proportional to radiation exposure.

Thermoluminescent Dosimeter (TLD)

Personnel monitoring device containing lithium fluoride crystals that trap valence electrons when irradiated; the dose is measured by heating (annealing) the crystals to release light photons.

Direct Ion Storage (DIS) Dosimeter

Personnel monitoring device consisting of a gas-filled ionization chamber connected to an EEPROM solid-state memory, allowing instant exposure readout when connected to a computer via USB.

Geiger-Müller Counter

Field survey instrument constructed of an electrode housed within an ionization chamber that detects x-radiation, gamma radiation, and beta radiation by measuring free electrons produced by air ionization.