Radiological Control and Nuclear Physics Lecture Notes

Vocabulary flashcards covering core concepts of nuclear physics, radioactive decay, radiation interactions with matter, radiological units, cellular radiobiology, acute radiation syndromes, and advisory organizations.

Nucleon

A constituent particle of the atomic nucleus, identified as either a neutron or a proton.

Nuclide

A specific atomic configuration characterized by its number of protons ($Z$) and number of neutrons ($N$).

Isotope

Atoms having the same number of protons but a different number of neutrons.

Mass Energy Equivalence Concept

The principle stating that mass and energy are interchangeable, and the mass of an object depends on its speed.

Pair Annihilation

A process occurring when two particles with mass—a positron and an electron (negatron)—collide and transform into two rays (photons) of electromagnetic energy.

Mass Defect

The condition where the total mass of an atom is less than the sum of the individual masses of its protons and neutrons; the slight difference between these masses.

Binding Energy

The energy that binds the nucleus together.

Nuclear Fission

A process occurring when a free neutron strikes and is absorbed by a nucleus, causing it to split into two smaller nuclei with an accompanying release of energy.

Criticality

The condition in a nuclear reactor in which the number of neutrons produced by fission equals the number of neutrons in the previous generation.

Subcritical

A reactor condition in which too many neutrons escape or are absorbed without causing fission, resulting in a neutron flux and power output that die off over time.

Supercritical

A reactor condition in which the number of neutrons increases exponentially, used to increase neutron flux and power levels.

Nuclear Fusion

The act of combining or fusing two or more low-mass atomic nuclei (such as hydrogen and helium) under extremely high temperatures and pressure.

Radioactivity

The spontaneous emission of energy from a nucleus in the form of particles and packets of electromagnetic waves (photons) to alter nuclear configuration toward a more stable ratio.

Radioactive Decay

The process by which a nucleus spontaneously disintegrates or transforms through one or more discrete energy steps until a stable state is reached.

Naturally Occurring Radioactive Families

The three decay chains comprising the uranium series, thorium series, and actinium series; each yields radioactive daughters (including radon) and ends in a stable isotope of lead ($\text{Pb-206}$, $\text{Pb-208}$, and $\text{Pb-207}$).

Curie (Ci)

A historical unit of radioactivity defined as $2.22 \times 10^{12}\,\text{dpm}$ or $3.7 \times 10^{10}\,\text{dps}$.

Becquerel (Bq)

The SI unit of radioactivity defined as $1\,\text{dps}$ or $60\,\text{dpm}$, where $1\,\text{Ci} = 3.7 \times 10^{10}\,\text{Bq}$ and $1\,\text{Bq} \approx 2.7 \times 10^{-11}\,\text{Ci}$.

Specific Activity

The activity per unit mass, expressed in curies per gram or millicuries per gram; it is inversely related to half-life (shorter half-life yields greater specific activity).

Half-Life

The time required for radioactive activity to be reduced to one-half of its original value.

Exposure

The measure of the ability of photons to produce ionization in air only, measured in the unit Roentgen ($R$).

Absorbed Dose

The radiation energy absorbed or deposited per unit mass of a material (air, tissue), measured in rad or gray ($\text{Gy}$).

Rad

Radiation absorbed dose, defined as $100\,\text{ergs}$ of energy deposited per gram of material.

Equivalent Dose

The product of the absorbed dose in rad (or gray) and a radiation weighting factor ($W_R$) or quality factor ($Q$) to reflect biological damage.

Rem

Roentgen Equivalent Man, the unit of equivalent dose representing biological effect, calculated as absorbed dose in rad multiplied by the weighting factor ($Q$ or $W_R$).

Sievert (Sv)

The standard international unit of equivalent dose, equal to $100\,\text{rem}$ and calculated as absorbed dose in gray multiplied by the radiation weighting factor.

Ionization

Any process that removes a bound electron from an electrically neutral atom or molecule by supplying sufficient energy to overcome its binding energy, creating an ion pair.

Electron Excitation

Any process that supplies enough energy to an atomic or molecular electron so that it occupies a higher energy state (smaller binding energy) than its ground state.

Bremsstrahlung

Radiative energy loss occurring when a moving charged particle slows down near a nucleus, emitting an X-ray photon outside the nucleus; prominent in high-$Z$ materials.

Specific Ionization

The number of ion pairs formed by a charged particle per unit path length.

Linear Energy Transfer (LET)

The average energy locally deposited in an absorber by a charged particle per unit distance traveled, expressed in $\text{keV/cm}$.

Stopping Power

The ability of an absorber to remove energy from a beam of charged particles, measured as the average energy lost per unit distance traveled ($\text{keV/cm}$).

Range

The average depth of penetration of a charged particle into an absorber before it loses all kinetic energy and stops.

W-Value

The average amount of energy needed to create one ion pair in a given medium.

Compton Scattering

An interaction where an incoming photon undergoes partial energy loss (ranging from $200\,\text{keV}$ to $5\,\text{MeV}$) by colliding with and ejecting a loosely bound electron.

Pair Production

An interaction where a gamma photon with an energy of at least $1.022\,\text{MeV}$ disappears in the strong electric field near a nucleus and converts its energy into an electron and a positron.

Neutron Activation

The process of converting a stable nucleus into its radioactive counterpart through bombardment and capture of slow neutrons.

Elastic Scattering

A neutron interaction occurring when a neutron strikes a nucleus of approximately equal mass (such as hydrogen), transferring kinetic energy without the emission of gamma radiation.

Inelastic Scattering

A neutron interaction occurring when a neutron strikes a heavy nucleus, temporarily penetrates, transfers energy to an internal nucleon, and re-emerges with reduced energy accompanied by gamma ray emission.

Law of Bergoni and Trebondo

The principle stating that the radiosensitivity of a tissue is directly proportional to its reproductive capacity and inversely proportional to its degree of differentiation.

Stochastic Effects

Radiation-induced effects for which the probability of occurrence increases with dose without a threshold, where any exposure involves some risk (e.g., cancer, leukemia).

Nonstochastic (Deterministic) Effects

Radiation-induced effects for which the severity varies with the dose and a practical threshold dose exists, below which the effect is not observed (e.g., cataracts, burns).

$$LD_{50/30}$$

The acute lethal radiation dose that causes death in $50\%$ of an exposed population within $30\,\text{days}$ without medical treatment, evaluated at $450\,\text{rad}$.

Hematopoietic Syndrome

An acute radiation syndrome induced by doses of $200\text{ to }1000\,\text{rad}$, characterized by damage to blood-forming cells and tissues, with death potentially occurring in $2\text{ to }6\,\text{weeks}$.

Gastrointestinal (GI) Tract Syndrome

An acute radiation syndrome caused by doses of $1000\text{ to }5000\,\text{rad}$, resulting from the death of crypt stem cells, sloughing of intestinal villi, and fluid/electrolyte loss, resulting in death within $3\text{ to }12\,\text{days}$.

Central Nervous System (CNS) Syndrome

An acute radiation syndrome caused by doses above $5000\,\text{rad}$, characterized by tremors, convulsions, coma, and inevitable death within approximately $30\,\text{hours}$ due to brain edema and respiratory failure.

ICRU

International Commission on Radiological Units and Measurements; formed in 1925 to establish standardized international radiation units, including the Roentgen.

ICRP

International Commission on Radiological Protection; formed in 1928 to issue guidance for radiation safety, including the 1934 tolerance dose recommendation of $0.2\,\text{rad/day}$.

NCRP

National Committee on Radiation Protection and Measurements; founded in the United States in 1929 to develop protection practices, including standards used during the Manhattan Project.