Which of the following is a downside of using nuclear density gauge meters?

The correct answer highlights a significant consideration when using nuclear density gauge meters: the requirement for special training and licensing. This is essential because these devices use radioactive materials to measure density and moisture levels in various materials, such as soil or construction materials. Due to the potential risks associated with radiation exposure, operators must undergo specific training to understand how to safely handle the equipment, interpret the data obtained, and comply with regulatory requirements surrounding the use of radioactive substances. Licensing typically ensures that only qualified personnel can operate these gauges, thereby protecting both the users and the public from unnecessary exposure to radiation.

Considering the other choices, calibration does not necessarily require special equipment; it can be achieved through standardized processes or tools that are commonly available. The lightweight and portable nature of these gauges is generally seen as an advantage rather than a downside, as portability facilitates their use in various field conditions. Lastly, while nuclear density gauges can be quite accurate, stating that they are always accurate without maintenance is misleading; like all instruments, they require regular maintenance and calibration to ensure continued accuracy over time.