Appendix C: Glossary, Acronyms, and Time-Distance-Shielding Aid

C.1 Glossary

ALARA. As Low As Reasonably Achievable. Foundational dose-reduction principle.

Background. The radiation level present at a location absent any specific source of interest; varies with geology, building materials, and altitude.

Bremsstrahlung. "Braking radiation." X-rays produced when a charged particle (e.g., a beta) decelerates in matter. Why pure beta sources produce some gamma signal.

Confidence (RIID). A score or label indicating how well the spectrum matches a library entry.

Arthur Holly Compton, Nobel laureate whose 1923 discovery of photon-electron scattering underpins the Compton continuum in every gamma spectrum. — Arthur Holly Compton (1892-1962), 1927 Nobel laureate in Physics. His discovery that X-rays scatter off electrons with a measurable energy shift (the Compton effect) explains the broad continuum below every photopeak in a gamma spectrum.

Compton continuum. The smooth low-energy slope below a photopeak in a spectrum, from photons that scattered before being detected.

Cordon. A perimeter excluding non-essential personnel from an area.

Decay chain. A sequence of radioactive isotopes, each transforming into the next, until reaching a stable element.

Dose rate. Energy deposited in tissue per unit time; the operator's safety indicator.

FWHM. Full Width at Half Maximum. A measure of energy resolution; smaller is better.

Gamma ray. Penetrating electromagnetic radiation emitted by atomic nuclei.

HVL. Half-Value Layer. Material thickness that halves the dose rate.

A handheld identifier reads the spectrum of a source and matches its photopeaks to a known isotope.

A sodium iodide scintillation detector crystal used to identify gamma-emitting isotopes. — A sodium iodide (NaI) scintillation detector. Gamma rays striking the crystal produce light pulses proportional to their energy, which a photomultiplier tube converts to voltage pulses for isotope identification.

Isotope. A specific form of an element distinguished by mass number (number of neutrons + protons in the nucleus).

MCA. Multichannel Analyzer. The electronics that sort detector pulses into an energy spectrum.

N42.42. ANSI/IEEE standard XML format for radiation spectra and event data.

NORM / TENORM. Naturally / Technologically Enhanced Naturally Occurring Radioactive Material. Routine background sources.

Photopeak. A peak in a spectrum at the full energy of an emitted gamma; the diagnostic feature for identification.

PRD. Personal Radiation Detector. Wearable alarm-only unit.

Reachback. Channel for accessing radiological expertise during a live event.

RIID. Radioisotope Identification Device.

Scintillator. A material that flashes light in response to ionizing radiation, used as the gamma-detecting heart of a RIID.

SNM. Special Nuclear Material. Plutonium, uranium-233, uranium enriched in U-235, materials of weapons interest.

A gamma-ray energy spectrum places counts against energy, with photopeaks marking each isotope.

Energy resolution formula: R equals FWHM divided by E, multiplied by 100 percent. — Detector energy resolution R, expressed as the full width at half maximum (FWHM) of a photopeak divided by its centroid energy E, in percent. A lower R means sharper peaks and better isotope discrimination.

Spectrum. Histogram of detector counts vs. energy; the operator's working canvas.

Survey meter. A handheld dose-rate meter (typically GM tube or scintillator probe).

C.2 Acronyms

Every acronym used in this guide, spelled out.

Acronym	Meaning
ALARA	As Low As Reasonably Achievable
ANSI	American National Standards Institute
BNC	Berkeley Nucleonics Corporation
CBRN	Chemical, Biological, Radiological, and Nuclear
CeBr	Cerium bromide, a scintillator crystal (CeBr₃)
DHS	Department of Homeland Security
DOE	Department of Energy
EPA	Environmental Protection Agency
FBI	Federal Bureau of Investigation
FEMA	Federal Emergency Management Agency
FRMAC	Federal Radiological Monitoring and Assessment Center
GM	Geiger-Muller, as in a GM-tube survey meter
HazMat	Hazardous Materials
HEU	Highly Enriched Uranium
HPGe	High-Purity Germanium, a high-resolution detector
IAEA	International Atomic Energy Agency
IC	Incident Commander
IEC	International Electrotechnical Commission
LaBr	Lanthanum bromide, a scintillator crystal (LaBr₃)
LE	Law Enforcement
MCA	Multichannel Analyzer
NORM	Naturally Occurring Radioactive Material
NRC	Nuclear Regulatory Commission
PPE	Personal Protective Equipment
PRD	Personal Radiation Detector
RAP	Radiological Assistance Program
RCP	Radiation Control Program (state)
RDD	Radiological Dispersal Device (a "dirty bomb")
RIED	Flagged for review: not defined elsewhere in this guide, likely a typo for RIID. Confirm or remove.
RIID	Radioisotope Identification Device
SNM	Special Nuclear Material
TDS	Time, Distance, Shielding
TENORM	Technologically Enhanced Naturally Occurring Radioactive Material
WIPP	Waste Isolation Pilot Plant

C.3 Time-Distance-Shielding Quick Aid

If at distance d₁ the dose rate is D₁, then at distance d₂ the dose rate is approximately the inverse-square estimate:

Inverse-square law: D sub 2 equals D sub 1 times the quantity d sub 1 divided by d sub 2, squared. — The inverse-square law. Double the distance and the dose rate falls to one quarter; ten times the distance drops it one hundredfold. Point source, no change in shielding.

Examples (point source, no shielding change):

100 mR/hr at 1 m → 25 mR/hr at 2 m → 4 mR/hr at 5 m → 1 mR/hr at 10 m
1,000 mR/hr at 1 m → 250 at 2 m → 40 at 5 m → 10 at 10 m → 1 at 31 m
Want to drop 100× from the current dose rate? Move 10× farther.

If you must add shielding, match the material to the threat:

Lead. Best stopping power per inch for high-energy gammas. Expensive and heavy.
Concrete and earth. Widely available. Half-value layers are larger, but the mass accumulates quickly.
Steel. Moderate. Vehicle panels and structural members add modest protection.
Water. Surprisingly effective. A few feet of water shields well.
Lead aprons. Built for diagnostic X-ray (low keV). They give little benefit against Co-60 or Cs-137.

If you must reduce time:

Plan the task before entering. Rehearse it cold.
Run, do not walk. (Within reason, do not trip.)
Rotate teams. Two teams at half time each beats one team at full time.