Table of Definitions
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Term | Definition |
Absorbed dose | The amount of energy absorbed by an object or person per unit mass. This reflects the amount of energy that ionizing radiation sources deposit in materials through which they pass, and is measured in units of Gray. |
Accuracy | A measure of how close a measured value is to the true or accepted value. |
Average dose model | A statistical model used to calculate the De value of a sample that was fully bleached prior to burial and affected by a heterogeneous dose rate environment. |
Age-depth profile | In the context of rock surface dating, a plot of luminescence age (y-axis) vs slice depth into the rock (x-axis). Ages are most commonly obtained from sub-millimeter slices cut from a core extracted from the rock or artefact. |
Alpha efficiency | A measure of the efficiency with which alpha radiation generates a luminescence signal relative to beta radiation. Specifically it is the ratio of luminescence per unit alpha track length to the luminescence per unit absorbed beta dose. |
Alpha particle | A composite particle consisting of two protons and two neutrons tightly bound together. Emitted from the nucleus of some radionuclides during a form of radioactive decay, called alpha-decay. |
Alpha spectrometry | High-resolution measurement of the energy and intensity of alpha particles emitted by radioactive substances. |
Aliquot | Subsample of grains: 1 grain (single-grain aliquot or single-grain dating), n ≲ 100 (small aliquot), 100 to 1000 grains (medium aliquot), n ≳ 1000 (large aliquot). |
Aliquot rejection criteria | Criteria that are used to reject aliquots with suboptimal luminescence characteristics from further analysis. |
Anomalous fading | The loss of luminescence signal over time at ambient temperatures. Affects most feldspars and some quartz minerals. Attributed to the loss of electrons from traps that should be thermally stable at ambient temperatures over geological time, to other defects and centers in the crystal lattice. |
Atomic absorption spectroscopy (AAS) | Detects elements in a sample through the application of characteristic wavelengths of electromagnetic radiation from a light source. Individual elements will absorb wavelengths differently, and these absorbances are measured against standards. |
Beta microdosimetry | Refers to the heterogeneity of the ambient dose rate field within a sample site at the grain level that cannot be captured by current routine methods of dose rate measurement. Grain-to-grain variations in microdosimetry can lead to increases in the measured sample overdispersion (OD). |
Beta particle | A high energy, high speed electron (β-) or positron (β+) that is ejected from the nucleus by some radionuclides during a form of radioactive decay called beta-decay. Beta-decay normally occurs in nuclei that have too many neutrons to achieve stability. |
Central age model (CAM) | Also known as the central dose model, a statistical model used to calculate the De value of a sample. Assumes that the luminescence signal of minerals in the sample have been completely reset by sunlight prior to burial. |
Cosmic ray | A high-speed particle—either an atomic nucleus or an electron—that travels through space. Most of these particles come from sources within the Milky Way Galaxy and are known as galactic cosmic rays (GCRs). The rest of the cosmic rays originate either from the Sun or, almost certainly in the case of the particles with the highest energies, outside the Milky Way Galaxy. |
Cutheat | A step in the SAR protocol where a sample is heated to a desired temperature, then allowed to cool immediately. Often applied prior to the measurement of a test dose signal for quartz. |
Equivalent dose (De) | The laboratory radiation dose required to produce a luminescence signal equivalent to the signal produced by the natural dose of radiation the target mineral absorbed since last exposure to heat or light. Expressed in Grays (Gy), where 1 Gy = 1 Joule/kg. |
Dose response curve (DRC) | Plots the relationship between absorbed radiation dose of a mineral and its luminescence signal brightness. Created by measuring the luminescence response of a grain or multi-grain aliquot to a series of increasing laboratory-induced radiation doses. |
Dose rate (Dr) | The rate of exposure to alpha (α), beta (β), and gamma (γ) radiation from radioisotopes of potassium (K), uranium (U), thorium (Th), rubidium (Rb), and incoming cosmic rays (attenuated for depth below surface). Expressed in Gray (Gy) per thousand years (Gy/ka), (1 Gy = 1 Joule/kg). |
Feldspar | An aluminosilicate mineral containing varying amounts of potassium, sodium and calcium. Constituting about 60% of the Earth’s crust, it is the most abundant mineral group. Compositional end-members include potassium (K) feldspar (orthoclase or microcline, KAlSi3O8), sodium (Na) feldspar (albite, NaAlSi3O8) and calcium (Ca) feldspar (anorthite, CaAl2Si2O8). |
Flame photometry | Also known as flame emission spectroscopy. Used to determine the elemental composition of a sample by measuring the light emitted when the sample is subjected to a flame. |
Finite mixture model (FMM) | A statistical model used to identify distinct De components in samples that have experienced mixing between two or more sedimentary units of different age. |
g-value | A parameter used to quantify the rate of fading of the luminescence signal from feldspar. Specifically, it is the slope of the line of a signal vs delay time plot with units of percent per decade, where a decade is a 10-fold increase in delay time (i.e., one increment on a logarithmic scale). |
Gamma ray | A packet of electromagnetic energy (photon) emitted by the nucleus of some radionuclides following radioactive decay. Gamma photons are the most energetic photons in the electromagnetic spectrum. |
Gamma spectrometry | Used for the qualitative and quantitative determination of radionuclides that emit gamma radiation. Most of the radionuclides send out gamma radiation during their transformations to stable decay products. |
Gray (Gy) | One of the two units used to measure the amount of radiation absorbed by an object or person, known as the "absorbed dose," which reflects the amount of energy that radioactive sources deposit in materials through which they pass. One gray (Gy) is the international system of units (SI) equivalent of 100 rads, which is equal to an absorbed dose of 1 Joule/kilogram. |
Inductively coupled plasma optical emission spectrometry (ICP-OES) | An analytical technique used to determine how much of certain elements are in a sample. Uses an optical spectrometer to measure the light emitted from elements as they pass through a plasma. |
Inductively coupled plasma mass spectrometry (ICP-MS) | A technique used to identify the elemental composition of a substance. Uses an argon (Ar) plasma – the ICP – to convert the sample into ions that are then measured using a mass spectrometer – the MS. Offers lower detection limits than ICP-OES and is a better choice for trace element analysis. |
Ionizing radiation | A type of energy released by atoms that travels in the form of electromagnetic waves (gamma or X-rays) or particles (neutrons, beta or alpha). Emitted during the spontaneous disintegration of atoms. |
Luminescence | Photons of light that are emitted when electrons, evicted from their traps by light or heat, recombine into luminescence centres at lower energy states. The intensity is directly proportional to the number of trapped electrons, which is, in turn determined by burial duration, and Dr. |
Luminescence age | Time since the last exposure of a sample to light or high heat. Calculated by dividing De (Gy) by Dr (Gy/ka). Expressed in a (annum), ka (kiloannum), or Ma (mega annum). Datum is the date of sample collection, not yr B.P. (used only for radiocarbon dating). |
Luminescence-depth profile | In the context of rock surface dating, a plot of the luminescence signal (y-axis) vs slice depth into the rock (x-axis). Most commonly measured from sub-millimeter thick slices of a core extracted from the rock or artefact. |
Luminescence reader | An instrument designed to measure the luminescence signal of minerals while stimulating the sample with heat or light. Consists of light emitting diodes (LEDs) and/or lasers for light stimulation as well as a radiation source to irradiate samples. An attached photomultiplier tube fitted with light filters detects luminescence within desired light wavelength ranges. |
Minimum age model | Also known as the minimum dose model, calculates the De value from a sample that was partially bleached prior to deposition. |
Neutron activation analysis (NAA) | A non-destructive technique to determine the elemental composition of a material that relies on the measurement of gamma rays emitted from a sample that was irradiated by neutrons. |
Optically stimulated luminescence (OSL) | Luminescence that results from stimulation of the sample using photons of any wavelength. The OSL dating method was invented by D.J. Huntley in 1985. |
Overdispersion (OD or σ) | Spread in De values beyond that expected based on analytical uncertainties. Causes include: partial bleaching, microdosimetry, intrinsic sensitivity, and/or post-depositional mixing. σb specifically refers to the scenario where all grains have received the same dose. |
Partial bleaching | Incomplete resetting of a luminescence signal due to insufficient sunlight or heat exposure. |
Post-depositional mixing | The displacement or remobilisation of grains in a sedimentary column through disturbance (e.g., soil processes, freeze-thaw processes, insect or animal burrowing). |
Precision | A measure of how close a set of repeated measurements are to one another. |
Preheat | A step in the SAR protocol that holds the sample at a desired elevated temperature for a period of time. Typically applied just prior to measurement of the natural, regenerative dose, or test dose signal to eliminate thermally unstable charge. |
Radionuclide (radioisotope) | An unstable element which disintegrates and emits ionizing radiation. All radionuclides are uniquely identified by the type of radiation they emit, the energy of the radiation, and their half-life. |
Recuperation | Luminescence signal that has not been sufficiently depleted at the end of each SAR cycle, as well as excess accumulated charge as a result of thermal transfer during the preheat. Samples that behave well should have recuperated signals that are ~5% or less of the natural signal. |
Recycling ratio | The ratio between the two repeat regenerative dose measurements in a SAR protocol. If this ratio is within 2σ or 10% of unity, we can be assured that the test dose has adequately corrected for luminescence sensitivity changes in the sample. |
Regenerative dose | A laboratory radiation dose administered to the sample, typically for the purpose of generating a dose response curve during the SAR protocol. |
Rock surface burial dating | In the context of luminescence dating, a determination of the burial age of a rock surface. |
Rock surface exposure dating | In the context of luminescence dating, a determination of how long a rock surface has been exposed to daylight. |
Saturation | Occurs when larger radiation doses to a mineral no longer induce increases in luminescence intensity; the saturation dose of a mineral will determine its upper age limit. |
Secular equilibrium | A state in which the rate of formation of each radioisotope in a decay series is equal to its rate of decay, resulting in a stable concentration of each isotope. |
Sensitivity | Luminescence intensity per unit mass per unit radiation dose of a given mineral. A mineral’s sensitivity is often related to the source geology and sediment history. |
Single aliquot regenerative-dose protocol (SAR) | A measurement protocol used to determine De, where the sensitivity-corrected natural luminescence signal (Ln/Tn) is interpolated onto a dose response curve. |
Statistical models | Used to calculate the De value(s) of a sample. Common models include minimum age model, central age model, finite mixture model, and average dose model. |
Thermoluminescence (TL) | The luminescence emitted from a sample that is stimulated with heat. TL dating is the predecessor of OSL dating and was originally performed on pottery. |
Quartz | A silica mineral with the formula SiO2. The second most abundant mineral in Earth's continental crust, behind feldspar forming a significant portion of many igneous, metamorphic and sedimentary rocks. |
X-ray fluorescence | Determines the elemental composition of a sample by measuring the fluorescent (or secondary) X-rays emitted from a sample when it is excited by a primary X-ray source. |