DECK 12 — RADIATION & CONTAMINATION SURVEYS

What is the purpose of a radiation survey?

A radiation survey measures exposure levels or checks for radioactive contamination on surfaces or personnel.

What is contamination in radiation work?

Contamination is unwanted radioactive material present on surfaces, clothing, skin, or equipment.

What is exposure rate?

Exposure rate is the intensity of radiation being emitted in an area, independent of contamination on surfaces.

Why is contamination different from exposure?

Contamination involves loose radioactive material; exposure involves radiation fields that exist even without contamination.

What types of radiation can handheld survey meters detect?

Depending on the probe, meters can detect alpha, beta, gamma, or a combination.

What is a GM pancake probe used for?

A GM pancake probe is used for beta and gamma contamination surveys due to its large sensitive window.

Why are GM pancake probes poor for alpha detection?

The mica window is thick relative to alpha range, so most alpha particles are stopped before reaching the gas.

What type of detector is used for alpha contamination surveys?

Alpha surveys use zinc sulfide (ZnS) scintillation probes or gas-flow proportional detectors.

Why must alpha probes be close to the surface during surveys?

Alpha particles have very short range in air and cannot travel far.

What is frisking?

Frisking is the method of scanning personnel or objects with a detector to check for contamination.

What is the recommended frisking speed?

Frisking speed is about 1–2 inches per second to ensure adequate sensitivity.

Why must the detector be close to the surface during frisking?

Keeping the probe close maximizes geometric efficiency and allows detection of weak contamination.

Why are gloves worn during contamination surveys?

Gloves prevent the spread of contamination and protect skin from contact.

Why are wipes used during contamination checks?

Wipes sample surfaces for removable contamination that may not be easily detected directly.

What is a wipe test?

A wipe test collects removable contamination and measures it with a low-background detector such as an LSC or NaI well counter.

Why must background be measured in contamination surveys?

Background establishes the baseline count rate so contamination can be identified above it.

What indicates contamination on a survey meter?

A sustained count rate significantly above background indicates contamination.

Why should the survey meter be checked before use?

Functional checks ensure the meter responds to a check source and the battery is adequate.

Why must you know the detector efficiency?

Detector efficiency is needed to convert counts into activity for contamination assessments.

What factors affect detector efficiency in contamination surveys?

Distance, probe type, window thickness, and radiation energy affect efficiency.

Why does distance matter in surveys?

Increasing distance reduces geometric efficiency and may cause missed contamination.

Why are beta sources easy to detect with pancake probes?

Betas penetrate the thin mica window and produce strong GM avalanches.

Why are gamma sources detected with lower efficiency in GM probes?

Gammas have low interaction probability in thin gas volumes.

Why is calibration required for survey instruments?

Calibration ensures accurate response to known radiation levels and maintains regulatory compliance.

Why are energy response differences important?

Survey meters may respond differently to low- vs high-energy radiation, affecting accuracy.

What is fixed contamination?

Fixed contamination adheres strongly to surfaces and cannot be removed easily by wiping.

What is removable contamination?

Removable contamination can be transferred or removed by wiping or touch.

Why is distinguishing fixed from removable contamination important?

Removable contamination poses greater spread risk; fixed contamination may be stable but still require decontamination.

Why must frisking be done slowly near edges and folds of clothing?

Edges trap contamination and require careful scanning.

Why is shielding generally not used in contamination surveys?

Shielding reduces sensitivity and may interfere with detecting weak signals.

Why must the detector be oriented properly?

Probe face orientation maximizes exposed window area and improves efficiency.

What is the purpose of an audible output during surveys?

An audible output allows the worker to hear count increases without looking at the display.

Why do survey meters use batteries?

Battery operation allows portability but requires regular battery checks.

Why can GM detectors saturate at high contamination levels?

High rates create dead time losses and may produce underreporting.

What is the primary safety goal during contamination surveys?

The goal is early detection and prevention of contamination spread.