CCIL Hot Mix Asphalt Field Density Testing 2

Question 1

Nuclear density gauges use which radiation source to measure material density?

Accepted Answer

Gamma rays from a cesium-137 source

Answer

Most nuclear density gauges use cesium-137 as the gamma radiation source; gamma photons interact with material electrons and the backscatter or transmission count rate is related to density.

Question 2

Which regulatory body in the United States governs the licensing and use of nuclear density gauges?

Accepted Answer

NRC (Nuclear Regulatory Commission)

Answer

The Nuclear Regulatory Commission (NRC) — or an Agreement State equivalent — regulates the possession, use, and transport of radioactive materials including nuclear density gauges.

Question 3

Under which DOT hazardous materials classification are nuclear density gauges transported?

Accepted Answer

Class 7 – Radioactive Material

Answer

Nuclear gauges are classified as Class 7 Radioactive Material under DOT regulations, requiring proper packaging (Type A package), labeling, and shipping documentation.

Question 4

What is the purpose of taking a 'standard count' before using a nuclear density gauge in the field?

Accepted Answer

To establish a baseline reading on a reference block for drift detection and quality control

Answer

Standard counts are taken on a manufacturer-supplied reference block before field use; deviations from historical counts indicate instrument drift, source decay issues, or malfunction.

Question 5

In backscatter measurement mode, approximately how deep does a nuclear density gauge measure from the pavement surface?

Accepted Answer

Approximately 50–75 mm (2–3 inches) from the surface

Answer

In backscatter mode, gamma photons scatter back from the near-surface zone, giving density measurements primarily in the top 50–75 mm, making it suitable for thin HMA lifts.

CCIL - Canadian Council of Independent Laboratories Practice Test

CCIL - Canadian Council of Independent Laboratories Practice Test

CCIL Hot Mix Asphalt Field Density Testing 2