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

Alpha particles from a polonium-210 source

Answer

Beta particles from a strontium-90 source

Answer

X-rays from a tungsten filament

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

EPA (Environmental Protection Agency)

Answer

OSHA (Occupational Safety and Health Administration)

Answer

FHWA (Federal Highway Administration)

Question 3

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

Accepted Answer

Class 7 – Radioactive Material

Answer

Class 2 – Compressed Gas

Answer

Class 5 – Oxidizers

Answer

Class 9 – Miscellaneous Hazardous Materials

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

To count the number of tests permitted per shift under the radiation license

Answer

To determine the number of roller passes required for compaction

Answer

To set the depth of measurement for direct transmission mode

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

The full pavement depth regardless of lift thickness

Answer

Exactly 150 mm (6 inches) below the surface

Answer

Only the surface texture layer at 5–10 mm

Question 6

What is the most likely corrective action when nuclear density readings show significantly lower density at one end of a freshly paved mat?

Accepted Answer

Investigate roller pattern, breakdown temperature, and compaction uniformity in that zone

Answer

Average all readings across the mat and report the mean value only

Answer

Immediately reject the entire paving lot without further investigation

Answer

Recalibrate the gauge to match the lower density readings

Question 7

What minimum separation distance from the nuclear gauge is generally required for non-essential bystanders during measurement?

Accepted Answer

2.0 m (approximately 6.6 ft)

Answer

0.5 m (approximately 1.6 ft)

Answer

1.0 m (approximately 3.3 ft)

Answer

5.0 m (approximately 16.4 ft)