Why is radiation visible on cameras? like a radioactive object would have loads of white dots around it?
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Cameras nowadays operate with a photosensitive sensor (a sensor that is sensitive to light). Before, it used to be a photographic film that contained chemicals that would react to different intensities of light. This is why it had to be stored somewhere dark and also why “darkrooms” exist, where photographic film can be developed into a photo.
The type of ionising radiation (that is, electromagnetic waves with enough energy to ionise an atom by removing electrons) you are referring to is Gamma radiation, a very high-energy EM wave with a very short wavelength and a very high frequency. Because of the energy that this EM wave has, it can ionise atoms.
When a radioactive source like U-235 or Pu-239 decays, if it releases gamma radiation, the radiation would reach the film or sensor. Both work somewhat similar. Wherever it hits, the gamma ray overloads that spot on the film or sensor.
With the film, it is shown as a white dot, as if the film was held directly next to a light bulb. This is because the chemicals in the film have been excited by the high energy gamma rays like they would with high intensity light.
With the sensor, all it knows is that there is a lot of energy in that spot where the ray hit. So it translates the high energy of the ray as the brightness of that spot on the sensor.
Or, it interprets the high energy as the colour information (e.g. the arbitrary RGB values). White is always when those values are at their maximum level. So, it could interpret the energy as the colour information and set the information to their maximum values. This creates a white pixel.
I hope that explains it well.
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