Highly excited neutron-rich nuclei, formed as the product of other types of decay, occasionally lose energy by way of neutron emission, resulting in a change from one isotope to another of the same element.The nucleus may capture an orbiting electron, causing a proton to convert into a neutron in a process called electron capture.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 metallic uranium.
All results were negative until he used uranium salts. This shows that the population decays exponentially at a rate that depends on the decay constant. However, for a collection of atoms, the collection's expected decay rate is characterized in terms of their measured decay constants or half-lives. The half-lives of radioactive atoms have no known upper limit, spanning a time range of over 55 orders of magnitude, from nearly instantaneous to far longer than the age of the universe.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.Another type of radioactive decay results in products that vary, appearing as two or more "fragments" of the original nucleus with a range of possible masses.