Becquerel like many physicist in early 1896. was intrigued by Rondgen’s discovery of X-rays.He wondered whether fluorescent and phosphorescent salts those that emitelight after apsorbing it, would also emit X-rays and began a series of experiments to find out. His experiments showed that the radiation persisted whether or not he excited the salt in any way, and wasn’t diminished when the salt was melted or dissolved. He also showed that the radiation produced ionisation in the air that could discharge an electroscope. The phosphorescent materials he used were uranium salt and he concluded that it was essential to the emission of radiation but the uranium. He discovered that it consisted of two parts – highly ionising rays with little penetration, which he called “alfa rays” and less strongly ionising but more penetrating rays which he called “beta rays”. (Villard were discovered gamma rays).
Marie Sklodowska Curie discovered radium and polonium and showed that radioactive decay must be an atomic process. Marie and Pierre Curie shared the 1903 Nobel Prize for Physics with Becquerel.
Radioactive decay is a nuclear process. It involves the decay of nuclei from one element and their transformation into nuclei of another element. Spontaneous decay occurs when the transformation results in a release of energy. This can be calculated using Einstein’s mass-energy equation.
Alfa decay is common in heavy nuclei with too many protons.Beta decay seems easier to explain using a proton-electron model then proton-neutron model.
How electrons are emitted?
Beta decay caused major problems for theoretical physicists….
The main problems were these:
– Where do the electrons come from?
– The emitted electrons have a continuous energy spectrum, what happens to the missing energy’?
How can a nuclear containing an even number of spin -1/2 particles emit another spin -1/2 particle?
The solution to these problems needed new physics and wonderful new discovery…..