Antoine Henri Becquerel -

Becquerel's most famous achievement was an accidental discovery involving uranium salts.

: He was the first to realize that beta particles were identical to the high-speed electrons recently discovered by J.J. Thomson. antoine henri becquerel

: In 1899, he demonstrated that some radioactive rays (beta particles) could be deflected by magnetic fields, proving they were charged particles rather than waves. antoine henri becquerel

: Days later, he developed the plate and found a clear, dark image of the crystals—meaning they were emitting "penetrating rays" spontaneously, without any external energy source like the sun. antoine henri becquerel