Which of the following actions is strictly prohibited during exposure?

Holding the film or sensor during exposure is strictly prohibited because it increases the risk of unnecessary exposure to radiation for the person holding it. The film or sensor should be securely positioned before the radiation exposure begins to ensure that there is no movement, which can lead to blurry images and the need for re-exposure. Furthermore, by holding the film or sensor, an individual places themselves in a position where they are exposed to radiation, which goes against safety protocols designed to minimize exposure to both patients and operators.

The other listed actions are more about ensuring safety and achieving accurate imaging results. Adjusting the tubehead and altering the machine's settings, when done properly, are essential for ensuring correct exposure settings and patient positioning. Using the collimator is important for directing the beam and reducing unnecessary radiation exposure to surrounding tissues. Therefore, holding the film or sensor during an exposure stands out as a critical action to avoid for safety reasons.