Question

State four properties of Becquerel rays.

Answer 1

Becquerel used an apparatus similar to that displayed below to show that the radiation he discovered could not be x-rays. X-rays are neutral and cannot be bent in a magnetic field. The new radiation was bent by the magnetic field so that the radiation must be charged and different than x-rays. When different radioactive substances were put in the magnetic field, they deflected in different directions or not at all, showing that there were three classes of radioactivity: negative, positive, and electrically neutral.The term radioactivity was actually coined by Marie Curie, who together with her husband Pierre, began investigating the phenomenon recently discovered by Becquerel. The Curies extracted uranium from ore and to their surprise, found that the leftover ore showed more activity than the pure uranium. They concluded that the ore contained other radioactive elements. This led to the discoveries of the elements polonium and radium. It took four more years of processing tons of ore to isolate enough of each element to determine their chemical properties.

Answer 2

Henri Becquerel tried to expose potassium uranyl sulphate crystals to sunlight and then placed them on photographic plates wrapped in black paper, believing that the uranium 238 absorbed the sun’s energy and then emitted it as X-rays. This hypothesis was disproved and his experiment "failed" because it was overcast in Paris on the day of the experiment. For some reason, Becquerel decided to develop his photographic plates anyway. To his surprise, the images were strong and clear, proving that the uranium emitted radiation without an external source of energy such as the sun. He had discovered radioactivity.

Becquerel showed that the radiation he discovered could not be X-rays because X-rays are neutral and cannot be deflected by a magnetic field. The new radiation was deflected by a magnetic field - turned out to be alpha particles with a very long half life - showing that the radiation must be charged. Additional work on thorium and polonium yielded the familiar three types of radiation, alpha, beta and gamma.