Activator. Dopant atom (e.g., Tl in NaI(Tl), Ce in LaBr3:Ce) that produces a doped scintillator's light.
Afterglow. Residual light emission long after the nominal decay time, from delayed trapped-charge recombination.
Alpha pulser. Am-241 source in a detector housing, producing a known-energy peak for real-time gain reference.
Backscatter peak. Spectrum feature below the photopeak, from photons scattering off surroundings before depositing energy in the crystal.
Bialkali photocathode. The standard Cs-Sb-K PMT photocathode, peaking at 25 to 30 % QE between 400 and 420 nm.
Birks formula. Empirical relation describing reduced light yield per unit energy at high ionization density (ionization quenching).
Channel (MCA). One bin in a histogram of pulse heights.
CLLBC, CLYC, CLLB. Elpasolite scintillators (Cs2LiLa(Br,Cl)6:Ce, Cs2LiYCl6:Ce, Cs2LiLaBr6:Ce) detecting gamma rays and neutrons via PSD.
Compton edge. Maximum energy a Compton-scattered electron can acquire: \( \frac{2 E_g^2}{m_e c^2 + 2 E_g} \), about 477 keV for Cs-137.
Compton effect. Inelastic photon scattering off a quasi-free electron, transferring energy and changing direction.
CsI(Tl), CsI(Na). Cesium iodide doped with thallium or sodium, the standard non-hygroscopic and slightly hygroscopic alkali halide scintillators.
Cs2HfCl6 (CHC). Cesium hafnium chloride, a non-hygroscopic scintillator with light yield exceeding NaI(Tl) and roughly 2.8 to 4 % FWHM resolution at 662 keV.
Dark count rate (DCR). Spontaneous SiPM discharges in the absence of light, driven by thermal generation in the depletion region.
Decay time. The 1/e fall time of the scintillation light pulse.
Dead time. The interval after a detected pulse during which the system cannot register subsequent pulses.
Digital pulse processor (DPP). Electronics digitizing the preamplifier output for pulse-height analysis and PSD in firmware.
Displacements per atom (DPA). Unit of accumulated lattice damage from neutron flux.
Effective Z (Z_eff). A weighted average atomic number representing a compound's photoelectric absorption properties.
Elpasolite. Mixed-halide scintillator family (Cs2NaY(Cl,Br)6 type) detecting gamma rays and neutrons in one crystal via PSD.
Emission peak. The wavelength at which a scintillator's emission spectrum is maximum.
Energy resolution. The FWHM of a photopeak divided by its centroid energy, expressed as a percentage.
Figure of merit (FoM). PSD separation measure, \( \text{FoM} = \dfrac{|\mu_1 - \mu_2|}{\text{FWHM}_1 + \text{FWHM}_2} \); above 1.5 is clean separation.
FWHM. Full width at half maximum: the width of a peak measured at half its height.
GAGG:Ce. Cerium-doped gadolinium aluminum gallium garnet, Gd3Al2Ga3O12:Ce, a non-hygroscopic, high-light-yield scintillator emitting in the green band.
Gamma-equivalent energy. The energy at which a non-gamma event appears in a spectrum calibrated against gamma sources.
Geiger mode. Avalanche-photodiode operation above breakdown where each photon triggers a fixed-magnitude discharge; the basis of SiPM operation.
HALEU. High-assay low-enriched uranium, with U-235 concentration between 5 and 20 %.
HPGe. High-purity germanium detector, used at liquid nitrogen temperature for sub-keV energy resolution.
Hygroscopic. A material that absorbs moisture from the atmosphere.
LaBr3:Ce. Cerium-doped lanthanum bromide: a high-light-yield, fast, hygroscopic scintillator with La-138 intrinsic background.
Light coupling. The optical interface between a scintillator and its photodetector.
Light yield. The number of scintillation photons produced per unit of energy deposited.
List mode. Acquisition mode recording each event's pulse height, timestamp, and metadata for later reanalysis.
LSO:Ce, LYSO:Ce. Cerium-doped lutetium oxyorthosilicate and its yttrium-substituted variant, the dominant scintillators for clinical PET.
Mott-Seitz model. Empirical model of thermal quenching in scintillators.
MCA. Multichannel analyzer: the instrument that histograms pulse heights to produce a spectrum.
Multichannel analyzer. See MCA.
NaI(Tl). Thallium-doped sodium iodide, the most widely used general-purpose gamma spectroscopy scintillator; highly hygroscopic.
Non-proportionality. The deviation of a scintillator's light yield from linearity in energy deposited.
Pair production. Conversion of a photon above 1.022 MeV into an electron-positron pair in a nucleus's field.
PDE. Photodetection efficiency: the probability an incident photon produces a measurable signal in a SiPM.
Photoelectric effect. Absorption of a photon by an atom with full deposition of its energy and ejection of an electron.
Photopeak. The peak in a gamma spectrum corresponding to full energy deposition by photoelectric absorption.
PMT. Photomultiplier tube.
PSD. Pulse shape discrimination: distinguishing event types by the shape of the scintillation pulse.
Quantum efficiency (QE). The probability that a photon produces a measurable photoelectron in a photodetector.
Quenching. Reduction in light output from non-radiative pathways, including thermal, ionization, and chemical quenching.
Reflector. Material surrounding a scintillator's non-readout faces that redirects scintillation photons toward the photodetector.
SiPM. Silicon photomultiplier: a solid-state array of Geiger-mode avalanche photodiode microcells.
Spectrum stabilization. Compensation for gain drift caused by temperature, count rate, and PMT hysteresis.
TOF-PET. Time-of-flight PET with sub-200 ps coincidence resolution, partially localizing positron annihilation along the line of response.
Trapezoidal filter. Digital processing technique producing a trapezoidal pulse-height estimate from an exponentially decaying preamplifier pulse.
TTS. Transit time spread: the spread in photoelectron arrival time at a PMT's first dynode.
ADC Analog-to-digital converter ANSI American National Standards Institute APD Avalanche photodiode ASIC Application-specific integrated circuit BGO Bismuth germanate, Bi4Ge3O12 CCD Charge-coupled device CHC Cs2HfCl6 (cesium hafnium chloride) CHP Certified Health Physicist CLLB Cs2LiLaBr6:Ce CLLBC Cs2LiLa(Br,Cl)6:Ce CLYC Cs2LiYCl6:Ce CMOS Complementary metal-oxide-semiconductor CSP Charge-sensitive preamplifier CT Computed tomography CZT Cadmium zinc telluride DCR Dark count rate DPA Displacements per atom DPP Digital pulse processor dSiPM Digital silicon photomultiplier FoM Figure of merit FPGA Field-programmable gate array FWHM Full width at half maximum GAGG Gadolinium aluminum gallium garnet, Gd3Al2Ga3O12 HALEU High-assay low-enriched uranium HEU Highly enriched uranium HP Health physics or health physicist HPGe High-purity germanium HV High voltage HVL Half-value layer IAEA International Atomic Energy Agency IEC International Electrotechnical Commission IEEE Institute of Electrical and Electronics Engineers LBC LaBr2.85Cl0.15:Ce LSC Liquid scintillation counting LSO Lutetium oxyorthosilicate, Lu2SiO5 LYSO Lutetium-yttrium oxyorthosilicate LET Linear energy transfer MCA Multichannel analyzer MCP-PMT Microchannel plate photomultiplier tube MIP Minimum ionizing particle N42 ANSI N42 series of radiation-detection standards NaI Sodium iodide NIST National Institute of Standards and Technology (US) NPL National Physical Laboratory (UK) NPSS Nuclear and Plasma Sciences Society (IEEE) NRC Nuclear Regulatory Commission (US) NRRPT National Registry of Radiation Protection Technologists NSS-MIC Nuclear Science Symposium and Medical Imaging Conference OEM Original equipment manufacturer PDE Photodetection efficiency PET Positron emission tomography PMT Photomultiplier tube POI Probability of intercept PSD Pulse shape discrimination PTB Physikalisch-Technische Bundesanstalt (Germany) QA Quality assurance QE Quantum efficiency RIID Radioisotope identification device RSO Radiation safety officer RTBW Real-time bandwidth SCINT International Conference on Scintillating Materials and their Applications SiPM Silicon photomultiplier SMR Small modular reactor SNM Special nuclear material SPECT Single-photon emission computed tomography SPRD Spectroscopic personal radiation detector TIA Transimpedance amplifier TOF-PET Time-of-flight positron emission tomography TTS Transit time spread TRISO Tristructural isotropic (fuel particle) UV Ultraviolet XRF X-ray fluorescence Z Atomic number Z_eff Effective atomic number