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.At first, it seemed as though the new radiation was similar to the then recently discovered X-rays.
(See List of nuclides for a list of these sorted by half-life.) 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.
Alpha decay is one type of radioactive decay, in which an atomic nucleus emits an alpha particle, and thereby transforms (or "decays") into an atom with a mass number decreased by 4 and atomic number decreased by 2.
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy (in terms of mass in its rest frame) by emitting radiation, such as an alpha particle, beta particle with neutrino or only a neutrino in the case of electron capture, or a gamma ray or electron in the case of internal conversion.
By contrast, there are radioactive decay processes that do not result in a nuclear transmutation.
The energy of an excited nucleus may be emitted as a gamma ray in a process called gamma decay, or that energy may be lost when the nucleus interacts with an orbital electron causing its ejection from the atom, in a process called internal conversion.
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.
Further research by Becquerel, Ernest Rutherford, Paul Villard, Pierre Curie, Marie Curie, and others showed that this form of radioactivity was significantly more complicated.
Rutherford was the first to realize that all such elements decay in accordance with the same mathematical exponential formula.
Rutherford and his student Frederick Soddy were the first to realize that many decay processes resulted in the transmutation of one element to another.