Answer to Question #10795 Submitted to "Ask the Experts"

What is it that makes the atoms unstable? My family and I were discussing this over dinner and I decided to see if I could find out more information about it. My major question is what makes them unstable and how could we fix it? We have come to the conclusion that if we could shoot them with protons or neutrons then we could solve the problem and neutralize the atoms. It may seem slightly ridiculous but I'm trying to understand the major issues we have today and possible solutions to them.

Atoms become unstable when the number of protons is too large (greater than 83), the number of neutrons is too large (greater than 126), or the ratio of the number of neutrons to protons in the nucleus is greater than an acceptable value of about 1.5. In such cases the forces that hold the nucleus together in a stable configuration, which are often associated with the binding energy of the nucleus, are not sufficient and the nucleus will transform into another energy configuration by emitting some radiation. For example, most of the fission products produced by the fissioning of uranium have too large a neutron-to-proton ratio. Such a fission product is often unstable (i.e., radioactive) decaying by transforming a neutron in the nucleus into a proton plus a beta particle (equivalent to an electron) plus a near massless uncharged particle called an antineutrino.

Your inference about the possibility of transforming an unstable atom into an energetically stable atom is indeed valid to some degree. For example, radioactive ⁵⁸Co could be transformed into stable ⁵⁹Co by irradiating it with low energy neutrons with the hope that the radioactive species would capture a neutron to induce a simple (n,gamma) reaction. Similary one might attempt to transform radioactive ⁶⁰Co into stable ⁶⁰Ni by irradiating it with protons from an accelerator to induce the (p,n) reaction. Unfortunately, such reactions are not possible or feasible with all radionuclides and, when they are, the efficiency of the process is often extremely low so that only a small fraction of the radioactive atoms may be transformed during a reasonable irradiation time. Additionally, such irradiations are also often expensive to carry out because of the need for a prolific neutron source, such as a reactor, or a high proton flux accelerator. Some applications, however, are practical.

One practical application of the idea of transforming radiotoxic species into less hazardous products is well known and has been recommended for reducing some of the very long-lived and highly radiotoxic actinide elements (beyond uranium in the periodic table) and a few other long-lived nonactinides that are produced by the operation of nuclear reactors. These products remain in the spent fuel after it has been removed from the reactor. If the fuel were to be reprocessed, these radioactive species of concern could be separated from other species (most of the remaining fission products) and placed back into an operating reactor to be transformed by neutron capture that might lead to fission of the species in some cases or production of shorter half-life radionuclides by single or multiple neutron capture events. This would be a means for greatly reducing the inventory of long-lived species that govern very long-term waste disposal, a major problem impeding the further development/application of nuclear power.

So your idea is not so far-fetched. The problem with implementing it for reduction of reactor-produced waste in the United States has been the decision implemented during President Carter’s administration not to reprocess reactor fuel. Perhaps that will change in the future, but I don’t hold out much hope in that.

Keep the family discussion going. Who knows when the next great idea might develop.

George Chabot, PhD