Nuclear gauges

A nuclear gauge is a tool used in road construction and the petroleum industry. It consists of a radioactive source to measure the thickness and to measure the density of a liquid in a pipe.

For road construction a gamma source emitter such as ¹³⁷Cesium is used to produce gamma radiation. These isotopes are effective in analyzing the top 25 centimeters with high accuracy. ²²⁶Radium is used for depths of 300 meters. Such instruments can help find underground caves or identify locations with lower density that would make tunnel construction hazardous.

For petroleum industry if a nuclear gauge source is mounted on one side of a pipe and a detector on the other, the amount of radiation seen at the detector is dependent upon the shielding provided by the liquid in the pipe.

There are two types of nuclear gauges, fixed and portable.
Fixed nuclear gauges can be used in industry to make sure each item is the same. For example, paper mills use fixed nuclear gauges to measure the thickness of a sheet of paper and some bottlers use them to make sure that each bottle contains the right amount of liquid. 
Portable nuclear gauges are commonly used in industries such as agriculture, construction and civil engineering. They often measure soil moisture or other items, such as the density of asphalt in a paving mix. Portable nuclear gauges work by using direct transmission or backscatter. Direct transmission is the more precise of the two, it measures how much radiation passes through an object. Backscatter nuclear gauges measure how much radiation bounces back to the gauge after it hits the surface of an object.

Nuclear gauges are designed with worker safety in mind. They are lined with a lead shielding around the sealed source, which blocks the radiation. Workers usually receive little or no radiation from nuclear gauges. When properly used, nuclear gauges will not expose the public to radiation.

When no longer in use, nuclear gauges must be disposed of properly. They are hazardous waste and should not be treated as ordinary trash. Gauge manufacturers or state radiation control program staff can provide disposal instructions. Some manufacturers also accept gauges for disposal.

Finally; Nuclear gauges are as safe as using a power saw or a welding torch. As with those tools, safety precautions must be taken.

                       Mechanism of nuclear gauges                                                           

                                                          ( Source: American Portable Nuclear Gauge Association )