When it decays, a radionuclide transforms into a different atom - a decay product. The atoms keep transforming to new decay products until they reach a stable state and are no longer radioactive. The majority of radionuclides only decay once before becoming stable.
Those that decay in more than one step are called series radionuclides. The series of decay products created to reach this balance is called the decay chain decay chain The series of decays or transformations that radionuclides go through before reaching a stable form. For example, the decay chain that begins with Uranium culminates in Lead, after forming intermediates such as Uranium, Thorium, Radium, and Radon Also called the "decay series.
Each series has its own unique decay chain. The decay products within the chain are always radioactive. Only the final, stable atom in the chain is not radioactive. Some decay products are a different chemical element. Every radionuclide has a specific decay rate, which is measured in terms of " half-life half-life The time required for half of the radioactive atoms present to decay or transform.
Some radionuclides have half-lives of mere seconds, but others have half-lives of hundreds or millions of years. The processes inside the nuclei involve very high energies, much higher than those reached at normal temperatures. From the point of view of those radioactive nuclei, the temperature of liquid nitrogen or of liquid water are both effectively zero.
The decays occur via quantum tunneling, not thermal activation. So you can't freeze the process to a halt. The half-life of radioactive decay can also be altered by changing the state of the electrons surrounding the nucleus. In a type of radioactive decay called "electron capture", the nucleus absorbs one of the atom's electrons and combines it with a proton to make a neutron and a neutrino. The more the wavefunctions of the atom's electrons overlap with the nucleus, the more able the nucleus is to capture an electron.
Therefore, the half-life of an electron-capture radioactive decay mode depends slightly on what state the atom's electrons are in. By exciting or deforming the atom's electrons into states that overlap less with the nucleus, the half-life can be reduced. Since the chemical bonding between atoms involves the deformation of atomic electron wavefunctions, the radioactive half-life of an atom can depend on how it is bonded to other atoms.
Simply by changing the neighboring atoms that are bonded to a radioactive isotope, we can change its half-life. However, the change in half-life accomplished in this way is typically small. For instance, a study performed by B. Wang et al and published in the European Physical Journal A was able to measure that the electron capture half-life of beryllium-7 was made 0.
In addition to altering the chemical bonds, the half-life can be altered by simply removing electrons from the atom. In the extreme limit of this approach, all of the electrons can be ripped off of a radioactive atom. For such an ion, there are no longer any electrons available to capture, and therefore the half-life of the electron capture radioactive decay mode becomes infinite.
Certain radioactive isotopes that can only decay via the electron capture mode such as rubidium can be made to never decay by ripping off all the electrons. Other types of radioactive decay besides electron capture have also been found to have the decay half-life depend on the state of the surrounding electrons, but the effects are smaller.
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