Which one of these things you see on the screen now is radioactive? Most kids think that anything that glows must be radioactive, but it turns out that there’s a lot of things that glow that aren’t radioactive at all. Many minerals (called phosphors) glow after being exposed to sunlight which contains UV light. In 1897, Henri Becquerel was studying phosphorescence when he accidentally discovered radioactivity. Naturally radioactive elements emit energy without absorbing it first. Let me explain…
Cold light refers to the light from a glow stick, called luminescence. A chemical reaction (chemiluminescence) starts between two liquids, and the energy is released in the form of light. On the atomic scale, the energy from the reaction bumps the electron to a higher shell, and when it relaxes back down it emits a photon of light. Glow sticks generate light with very little heat, just like the glow you see from fireflies, jellyfish, and a few species of fungi. Chemiluminescence means light that comes from a chemical reaction.
[am4show have=’p9;p52;p91;’ guest_error=’Guest error message’ user_error=’User error message’ ]
Fluorescence is what you see on those dark amusement-park rides that have UV lights all around to make objects glow. The object (like a rock) will absorb the UV light and remit a completely different color. The light strikes the electron and bumps it up a level, and when the electron relaxed back down, emits a photon, a light particle. Can you find the image with the glowing rocks? There’s two of them – one with the lights on and one with the lights off. Right – on the left side. The reason stuff glows is that fluorescent objects absorb the UV light and then spit it back almost instantaneously. Some of that energy gets lost during that process, and that changes the wavelength of the light, which makes this light visible and causes the material to appear to ‘glow’.
Sometimes things glow even after you turn off the UV light source. Phosphorescence light is the ‘glow-in-the-dark’ kind you have to ‘charge up’ with a light source. This delayed afterglow happens because the electron gets stuck in a higher energy state. Lots of toys and stick-on stars are coated with phosphorescent paints. Those are like the stars and planets you see in the middle of the slide. Atoms continue to emit light even after the electrons return to their normal energy states. While it looks like seconds to minutes that the glow lasts, some samples have been found to phosphoresce for years using highly sensitive photographic methods. Only a few minerals phosphoresce, such as calcite from Terlingua, Texas.
[/am4show]