How did Becquerel discover the connection between phosphorescence and X-rays?

[PainterGuy]

Hi,

I was reading about the discovery of radioactivity and found the text quoted below important but couldn't properly understand the part in boldface. I would really appreciate if you could help me with it. Thank you.

Radioactivity was discovered in 1896 by the French scientist Henri Becquerel, while working with phosphorescent materials.[8] These materials glow in the dark after exposure to light, and he suspected that the glow produced in cathode ray tubes by X-rays might be associated with phosphorescence. He wrapped a photographic plate in black paper and placed various phosphorescent salts on it. All results were negative until he used uranium salts. The uranium salts caused a blackening of the plate in spite of the plate being wrapped in black paper. These radiations were given the name "Becquerel Rays".

It soon became clear that the blackening of the plate had nothing to do with phosphorescence, as the blackening was also produced by non-phosphorescent salts of uranium and by metallic uranium. It became clear from these experiments that there was a form of invisible radiation that could pass through paper and was causing the plate to react as if exposed to light.

Source: https://en.wikipedia.org/wiki/Radioactive_decay#History_of_discovery

Henri Bacquerel was suspecting a connection between phosphorescence and X-rays. I believe that X-rays could easily penetrate through materials such as paper and could affect the photographic plate. I'm not sure if a phosphorescent material could affect a photographic plate assuming no other material lies between the plate and phosphorescent material. Could you please confirm it?

Anyway, Henri Bacquerel found that phosphorescence could not penetrate the paper therefore 'phosphorescence' was not X-rays since X-rays could penetrate a paper.

Was there any particular reason that black paper was used? I understand that black color absorbs all visible light but I don't think it can absorb all electromagnetic waves such as radio waves or X-rays.

Thanks for your help!

 

[shjacks45]

Silver photographic plates in the 1800s were typically wrapped in brown butcher paper. White paper is translucent unless thick like cardstock, allowing enough light to fog the film.
Know the terms. Fluorescence, like in real time xray screens, is energy absorbed then re-emitted as a lower energy e.g. xray>light or blue>orange (the yellow dot on white LEDs). Phosphorescence (1st noted in White Phosphorus) means absorbs a photon then re-emits a lower or same energy photon at a later time. Being vague because extra energy can be stored in atom or in molecule. Basically Flourescence is very fast Phosphorescence.
Pure Uranium isn't very radioactive. However on sitting a long time its more radioactive daughters proliferate. Uranium emits a 4.5 million electron volt alpha which is almost immediately destroyed giving multiple xrays that do go through stuff. Xrays don't add energy to atoms or molecules, rather semiconductor scintilators like in Zinc Sulfide the xray forms hole-electron pairs. Bacquerel didn't quite have the mechanism down, but his experimental results were great.
There are some great Youtube videos about flourescent Uranium glassware and "glow in the dark" paint; nile red is one of the channels.

 

[shjacks45]

Light Amplification by Stimulated Emission (Laser) is dye like Rhodamine Red 6B absorbs light more energetic than red, and re-emits it in the same direction as another same photon hits it. Delayed emission.