PIC Nuclear Density Gauge Operation 2

Question 1

What does the 'backscatter mode' of a nuclear density gauge measure compared to 'direct transmission mode'?

Accepted Answer

Backscatter measures surface density only; direct transmission measures full-depth density

Answer

In backscatter mode the gamma source and detector are both at the surface, measuring near-surface density, while direct transmission inserts the source rod to full depth for a through-material reading.

Question 2

Which federal agency regulates the possession and use of nuclear density gauges on construction sites in the United States?

Accepted Answer

NRC (Nuclear Regulatory Commission)

Answer

The NRC licenses radioactive material and sets the regulatory framework for nuclear gauge use; states with NRC agreements administer equivalent programs locally.

Question 3

A nuclear gauge reading shows a wet density of 142 pcf and a moisture content of 8%. What is the approximate dry density?

Accepted Answer

131.5 pcf

Answer

Dry density = wet density / (1 + moisture fraction) = 142 / 1.08 ≈ 131.5 pcf.

Question 4

When storing a nuclear density gauge in its transport case overnight, which position must the source rod be in?

Accepted Answer

Safe/shielded position fully retracted

Answer

The source rod must always be fully retracted into the safe/shielded position when the gauge is not actively taking a reading to minimize radiation exposure.

Question 5

What is the primary purpose of performing a 'count ratio' or 'standard count' at the beginning of each gauge use?

Accepted Answer

To calibrate the gauge against a known reference block to verify instrument stability

Answer

The standard count compares current detector output against a reference block to confirm the gauge is functioning consistently and results are comparable across days.

(PIC) Paving Inspector Certification Practice Test

(PIC) Paving Inspector Certification Practice Test

PIC Nuclear Density Gauge Operation 2