Radioactivity - Biophysics S1

Flashcards covering the fundamental concepts of radioactivity, atomic and nuclear structure, types of radioactive decay, kinetics, and related phenomena based on the provided lecture notes.

Röentgen

Discovered X-rays in 1895.

Henri Becquerel

Discovered radioactivity in 1896, observing that uranium salts impressed photographic plates in the dark.

Pierre and Marie Curie

Pioneered work on natural radioactivity and coined the term 'Radioactivity' in 1898.

Atom

An electrically neutral edifice composed of a nucleus and electrons, with a diameter of approximately 10^-10 m.

Nucleus

The central part of an atom, with a diameter of approximately 10^-15 m, containing protons and neutrons.

Electron

A subatomic particle with a mass of 0.9 x 10^-27 g (1800 times weaker than a nucleon's mass) and a charge of -1.6 x 10^-19 C.

Proton

A stable nucleon with an atomic mass unit (uma) of 1.007596, found in the nucleus, carrying a positive charge.

Neutron

A nucleon with an atomic mass unit (uma) of 1.00896, found in the nucleus, with no charge. Spontaneously decays into a proton, an electron, and an antineutrino.

Atomic Number (Z)

The number of protons in a nucleus, which also equals the number of electrons in a neutral atom.

Mass Number (A)

The total number of nucleons (protons + neutrons) in a nucleus. A = Z + N.

Nuclide

A specific type of atomic nucleus, characterized by its atomic number (Z) and mass number (A).

Isobars

Nuclides that have the same mass number (A) but different atomic numbers (Z).

Isotones

Nuclides that have the same number of neutrons (N) but different atomic numbers (Z).

Isomers

Nuclides that are identical in composition but exist in different energy states.

Isotopes

Nuclides that have the same atomic number (Z) but different numbers of neutrons (N), leading to different mass numbers (A).

Nuclear Forces

Strong attractive forces that hold nucleons together in the nucleus at very short distances (R ~ 10^-12 cm), alongside repulsive forces at even shorter distances.

Electrostatic Repulsive Forces

Forces of repulsion between positively charged protons within the nucleus.

Mass-Energy Equivalence

Expressed by E = MC², stating that mass can be converted into energy and vice versa, fundamental to nuclear processes.

Binding Energy (L)

The energy required to dissociate a nucleus into its constituent nucleons (protons and neutrons); calculated as L = Δmc².

Mass Defect (Δm)

The difference between the sum of the masses of individual nucleons and the actual measured mass of the nucleus, corresponding to the binding energy.

L/A (Average Binding Energy per Nucleon)

The binding energy per nucleon, typically ranging from 6 to 8 MeV, indicating the stability of a nucleus.

Aston Curve

A graph representing the average binding energy per nucleon (L/A) as a function of the mass number (A), showing nuclear stability trends.

Segré Diagram (Stability Diagram)

A plot of the number of neutrons (N) versus the number of protons (Z) for nuclides, illustrating the zones of nuclear stability and instability.

Valley of Stability

The region on the Segré diagram where stable nuclei are located, often with N ≈ Z for light nuclei and N > Z for heavier nuclei.

Radioactive Transformation

A spontaneous, inevitable, and random process where unstable nuclei (radioactive nuclides) change to achieve greater stability by emitting particles and/or electromagnetic radiation.

Deselectation

A type of nuclear transformation that liberates energy without modifying the structure of the nucleus, such as gamma deexcitation, internal conversion, or pair creation.

Disintegration

A type of nuclear transformation that liberates energy with modification of the nuclear structure and emission of a particle, such as alpha, beta, or fission.

Decay Law

Describes the exponential decrease in the number of radioactive atoms over time, given by N(t) = N0
e-λt.

Radioactive Constant (λ)

The probability per unit time that a radioactive nucleus will disintegrate, characteristic of a specific radionuclide and independent of external conditions.

Activity (A)

The rate of disintegration of radioactive nuclei in a source per unit time, given by A(t) = λN(t) or A(t) = A0
e-λt.

Becquerel (Bq)

The current SI unit of radioactivity, defined as one disintegration per second (1 d.p.s.).

Curie (Ci)

An older unit of radioactivity, equivalent to the activity of 1 gram of Radium 226, or 3.7
x 10^10 disintegrations per second.

Specific Activity

The ratio of the activity of a radioactive sample to its mass at a given instant, typically expressed in Ci/g or Bq/Kg.

Radioactive Period (T_phy)

The time required for half of the radioactive atoms in a sample to decay, a characteristic property of each radioisotope, calculated as T = Ln2 / λ.

Effective Period (T_eff)

The combined period accounting for both physical radioactive decay (Tphy) and biological elimination (Tbio) from a living system, calculated as 1/Teff = 1/Tbio + 1/T_phy.

Alpha Radioactivity (α)

A type of nuclear disintegration where an unstable nucleus emits an alpha particle (a helium nucleus, 4He), primarily observed in heavy isotopes (A > 150).

Beta-Minus Radioactivity (β-)

A type of nuclear disintegration where a neutron transforms into a proton, emitting an electron (β- particle) and an antineutrino from a nucleus rich in neutrons, resulting in a continuous energy spectrum.

Beta-Plus Radioactivity (β+)

A type of nuclear disintegration where a proton transforms into a neutron, emitting a positron (β+ particle) and a neutrino from a nucleus rich in protons, requiring an energy threshold of 1.022 MeV.

Annihilation

A secondary phenomenon of β+ decay where the emitted positron encounters an electron, resulting in their mutual destruction and the emission of two 0.511 MeV gamma photons in opposite directions.

Electron Capture (CE)

A type of nuclear disintegration where a nucleus captures an inner atomic electron (usually from the K shell), transforming a proton into a neutron and emitting a neutrino, in competition with β+ decay.

X-ray Emission (Secondary to CE)

Following electron capture, the vacant electron shell is filled by an electron from a higher shell, releasing characteristic X-rays.

Auger Electron

A secondary electron emitted when the energy released from an electron transition to fill an inner shell vacancy is transferred to another peripheral electron, ejecting it from the atom.

Gamma Radioactivity (γ)

The emission of electromagnetic radiation (gamma photons) from an excited nucleus as it transitions to a lower energy state, often accompanying other nuclear transformations.

Metastable Nucleus

A nucleus in an excited state with a measurable half-life for gamma emission (delay > 0.1s).

Internal Conversion (CI)

A process where an excited nucleus transfers its excess energy directly to an orbital electron, causing its ejection from the atom without emitting a gamma photon.

Internal Pair Production

A deexcitation process in highly excited nuclei (E ≥ 1.022 MeV) where the nucleus directly creates an electron-positron pair, typically followed by positron annihilation.

Fission

The fragmentation of very heavy nuclei into two or more smaller nuclei, often accompanied by the emission of neutrons and the production of radioactive nuclides.

Radioactive Filiation

A series of radioactive transformations where a parent radionuclide decays into a daughter product, which may itself be radioactive, leading to a decay chain.

Secular Equilibrium

A state in a radioactive decay chain where the half-life of the parent nuclide (T1) is much longer than that of the daughter nuclide (T2), and the daughter's activity approaches and decays with the parent's activity (A2 ≈ A1).

Transient Equilibrium

A state in a radioactive decay chain where the parent nuclide's half-life (T1) is longer than the daughter's (T2), but not vastly, leading to the daughter's activity peaking and then decreasing with an apparent half-life close to the parent's.