Also, there are different things that mechanism of the radiation.
"Alpha decay" and the "beta disintegration" in it are introduced.
　　

Alpha decay

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Alpha decay means radioactive nuclei alpha line is taken out and collapses, and it changes to a more stable nucleus.
Alpha decay is the atomic mass number which add two protons and two neutrons is a helium nucleus
of 4.
Since, it changes to the atom of other kinds because when alpha decay is caused once, an atomic number decrease two times.
For exaple,
As for the thorium of the atomic mass number 232, an atomic mass number changes to radium of 228
because if alpha decay is caused once, one alpha particle will be emitted.
The element which causes alpha decay is restricted in the decay chain.
　　

Beta dicay

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Beta dicay means radioactve nuclei beta line is taken out and collapses, and it changes to a more stable nucleus.
At this time, change that a neutron emits an electron and a neutrino and changes to a proton has occurred inside the nucleus.
In beta disintegration, unlike alpha decay, an atomic mass number does not change.
But one atomic number becomes large.
As the example from which beta dicay arises,
If the radium element of the atomic mass number 225 carries out beta disintegration once,
changes to the actinium element of 225 that atomic mass number same.
The element which carries out beta disintegration is also restricted.