Chemistry International -- Newsmagazine for IUPAC

Energy production is not the only use for the energy of the atomic nucleus. Nuclear and radiochemistry and related sciences and technologies—like radioanalytical, radiopharmaceutical, and radiation chemistry—are frequently applied in many branches of science and through technology for the betterment of people around the world.

The Energy of the Atomic Nucleus
The popular perception of the energy released by nuclear processes—such as neutron induced fission of ²³⁵U, ²³⁹Pu (bred from natural U), or ²³³U (bred from natural ²³²Th) or nuclear fusion of hydrogen isotopes—is that it is used for energy production (i.e., heat, and from that electricity and, in the future, nuclear-hydrogen or hydricity) or nuclear weapons. Indeed, scientists knew as early as the 1940s that the energy release from 1 kg of ²³⁵U is equal to that of the combustion of either 2 000 tonne of oil equivalent or 3 000 tonne of coal equivalent. In a nuclear weapon, this energy corresponds to the detonation of 20 000 tonne of TNT (1 tonne TNT = 4.184 GJ). During the nuclear fission of this mass of ²³⁵U, a mass of roughly 1 g (less than 0.1 percent of the initial mass)—calculated through the equation ΔE = Δm c²—is converted into energy. Therefore, nuclear fission has an enormous advantage as a clean source of energy and with the further advantage that there are no greenhouse gas emissions.

Presently—in spite of the negative perception of nuclear technologies—only 441 nuclear power plants (NPPs) produce 16 percent of worldwide electricity (33 percent in the 22 countries of the OECD, with maxima of 80 percent and 82 percent in France and Lithuania). At the present time, 34 to 40 NPPs are under construction in 12 countries, while around 30 are planned in several countries <www.world-nuclear.org>. The environmentalist James Ephraim Lovelock, creator of the Gaia hypothesis, says “opposition to nuclear energy is based on irrational fear” <www.ecolo.org/lovelock>.

According to the International Energy Outlook 2004 of the OECD, the worldwide demand for energy will double by 2050, while the demand for electricity will double by 2025. Large and densely inhabited developing countries such as China and India will place a particular burden on resources. Electricity produced from nuclear power represents a sustainable solution to the global energy problem that will result from this demand, especially considering the very small level of radioactive wastes produced annually by the global nuclear industry (i.e., 200 000 m³ of medium and intermediate level nuclear wastes and 10 000 m³ of high-level wastes). It is noteworthy that the global amount of energy presently consumed worldwide in one year—corresponding to an “equivalent” power of 13 TW thermal—could be produced by the fission of merely 5 million kg of either ²³²Th (in thermal breeder reactors), ²³⁵U or ²³⁹Pu. Compare this to the burden on ecosystems of CO₂ released by the combustion of fossil fuels at a rate of 0.8 million kg.s^-1. It should be noted that ²³²Th is present in the Earth’s crust in amounts four to seven times greater than U.

Non-Energetic Applications of the Energy of the Atomic Nucleus
Nuclear materials, however, are used for more than energy production. Non-energetic applications of the energy of the nucleus affect the biomedical field, the environment, cultural heritage, research, advanced technologies, security issues, and human wellbeing. Nuclear processes, such as the decay of radioactive species (i.e., radionuclides), are widely used for combating human diseases (i.e., radiopharmaceutical chemistry), foodstuff irradiation for sterilization and preservation purposes (i.e., radiation chemistry), and the safeguarding of cultural heritage and the environment (i.e., radioanalytical and radiation chemistry). They are also used for heating and lighting in difficult environments and for an extensive range of other, often surprising, applications.^1,2 The American Nuclear Society <www.ans.org> recently estimated that the number of employees and scientists engaged worldwide in the non-energetic use of the energy of the nucleus in research, industry, government, hospitals, transportation and safety, environmental protection, life sciences, materials sciences, bio- and nano-technologies, and space exploration is much larger than the number of people working in the nuclear power industry.

Radionuclides, Labelled Compounds, and Radiopharmaceuticals
Table I shows a select list of relevant discoveries and related Nobel Prizes in Chemistry and Physics associated with the nuclear sciences, emphasizing those with significant applications in the diagnosis and treatment of illness. Since the discovery of radioactivity in 1896, just after the discovery of X-rays in 1895 by Wilhelm C. Röntgen, there has been a wide range of beneficial applications of nuclear technology to human health.

Even excluding all the radiodiagnostic and radiotherapeutic techniques based on the use of X- and gamma rays (radiography, CT, cobaltotherapy, gamma-knife), or accelerated particle beams that irradiate pathological tissues (electron beams, IMRT, proton and heavy ion hadrontherapy), there are many techniques based on the use of both sealed and unsealed internal radioactive sources. Among these are endocavitary radiotherapy and brachytherapy of tumors and other tissues, which have been in use for half a century. More recently, brachytherapy of prostate cancer has involved using Ti or stainless steel seeds containing ¹²⁵I—or ¹⁰³Pd—that are inserted permanently into a patient’s body, and cause minimal discomfort.

More relevant for the nuclear and radiochemistry community are the applications of radiopharmaceutical compounds labelled with radioactive nuclides produced either by a nuclear reactor or an accelerator. The first are obtained by neutron capture or fission and are neutron rich and in general decay by beta minus (negatron) emission; they are suitable for metabolic radiotherapy after being administered to humans (and animals) as labelled chemical species. The latter are normally neutron poor and decay by electron capture and/or positron emission; these are used for radiodiagnostic and molecular imaging in 2D by gamma-camera, and more recently by SPET, PET, PET/CT, and spiral-PET tomographic equipment with 3D capability. In addition, a number of novel alpha emitters recently have been proposed for high-LET radionuclide targeted radioimmunotherapy, while applications of a range of low energy monoenergetic Auger and IC emitters (⁶⁴Cu, ¹¹¹In, ¹¹⁷mSn) are under investigation for selective irradiation of DNA inside cell nuclei, after internalization of properly labelled species through cellular and nuclear membranes.^2,3 Table II shows the primary specifications of a labelled compound to be used on living organisms, humans, animals, and cells.

Since the discovery of X-rays a century ago, the application of radionuclides and labeled compounds in many branches of nuclear science and technology has led to a vast array of improvements in both energy production and quality of life. The role of different branches of nuclear and radiochemistry proved fundamental to this purpose.²

References
1. Radiation and Modern Life, Fulfilling Marie Curie’s Dream, Waltar A.E., Prometheus Book, New York, USA, 2004.
2. Handbook on Nuclear Chemistry, 5 Vols, Vértes A., Nagy S., Klencsár Z., Eds., Kluwer Academic, Amsterdam, The Netherlands, 2003.
3. Handbook of Radiopharmaceuticals: Radiochemistry and Applications, Welch M.J., Redvalny C.S., Eds., Wiley, New York, USA, 2003.

Mauro L. Bonardi <[email protected]> is a professor at the Universita degli Studi di Milano, Accelerators and Applied Superconductivity Laboratory, in Segrate, Italy. David S. Moore <[email protected]> is at the Los Alamos National Lab, in Los Alamos, New Mexico, USA.

*Part II focusses on issues related to terminology; later published in the Jan-Feb 2008 CI.