Why is radiation visible on cameras? like a radioactive object would have loads of white dots around it?
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Cameras operate either by having pixels on something like a CCD, or grains of light-sensitive chemicals embedded in a film. In both situations the actual radiation, charged particles or high energy rays, interact with small areas of the film or pixels of the CCD. The radiation triggers them as if a large amount of light struck them, producing white spots on that one frame. As many frames of a video affected by radiation are played these spots are visible as very brief speckles.
The cloud chamber was about the first way of making radiation visible, and having done that you could use a camera to take pictures of the effect.
> Cloud chambers were invented in the early 1900s by the Scottish physicist Charles Thomson Rees Wilson. They played a prominent role in experimental particle physics from the 1920s to the 1950s, until the advent of the bubble chamber.
https://en.wikipedia.org/wiki/Cloud_chamber
Gamma radiation is super high energy photons. They hit the photosensitive camera lens and overloads that one tiny point where it hits, which shows up as a bright white dot
You’re the greeter at a venue, counting how many visitors in your line shake your hand, give you a high five, or a fist bump.
One particularly busy day, a visitor punches you in the gut. There’s no spot on the form for “assault”, so you just mark all three interactions.
It just gets worse from there—people are now pushing their way through other lines just so they can punch you. No spot on the form to mention that you’re going to the hospital, so you just mark all three hand gestures, or throw away the form.
The sensor on a camera is only designed to measure red, green, or blue light from a specific direction, but will also react to being struck by a high-energy particle or photon.
Radiation is just “moving energy”. Light is a type of radiation. Your camera absorbs that energy and produce an image by counting the energy absorbed, just like a large 2D thermometer.
Radioactive materials emit radiation that has very high energy, and the sensor thinks that very intensive light is hitting it, and thus white spots appear.
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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