Nuclear chemistry
The nuclear chemistry , and nuclear chemistry known is how the radiochemistry is part of the chemical, radioactive substances has as its object. In particular, she deals with the technical implementation of analyzes and syntheses, taking into account radiation protection and often tight deadlines. Areas of application are basic research, industrial production, medical diagnostics and therapy (see nuclear medicine ) and environmental analysis .
history
Historically, it was chemists who were the first to investigate either naturally occurring alpha decay series (based on the radioactive Th and U isotopes) or (in terms of nuclear physics) induced nuclear reactions. The resulting transformations of elements ( transmutation , the age-old dream of the alchemists ) can only be studied with highly developed chemical analysis methods, especially since the reaction products often only occur in minimal quantities. Examples include the separation of radium and polonium from pitchblende by the chemist Marie Curie and her husband, the physicist Pierre Curie, and the discovery of nuclear fission by the chemists Otto Hahn and Fritz Straßmann .
Basic research in nuclear chemistry
Decay series
When a nuclide decays, there is often no stable decay product, but a radioactive nuclide. This means that even an isotopically pure element becomes a mixture of several elements over time. The radiation emanating from such a mixture is naturally more difficult to identify than that of an individual element. By chemically separating the elements from one another, the individual elements can then be identified based on their radiation. This also clarifies the reaction mechanism, i.e. the order in which the different types of decay take place. The result is a decay series . The nuclear chemistry thus enables the radiation to be assigned to a specific nuclide.
External influences on half-life
In the case of radioactive decay through electron capture, there are measurable influences of external conditions such as the state of aggregation, pressure or chemical bond on the half-life , because the decay rate depends on the internal properties of the mother nucleus as well as the probability of the electrons being at the location of the nucleus.
One case that has been discussed since the late 1940s is the EC decay of Be-7 to Li-7. T. Ohtsuki and colleagues investigated the half-life of radioactive Be-7 on the one hand in Be metal and on the other hand in C60 cages ( Buckminster fullerene ). They found the half-lives 52.68 ± 0.05 days (metal) and 53.12 ± 0.05 days (C60), i.e. H. a difference of 0.83%.
Under extreme pressure conditions as in the outer layers of neutron stars or briefly during particle collisions in terrestrial particle accelerators occur otherwise unstable neutron-rich iron isotopes are stable.
Continuation of the periodic table
In the case of elements with atomic numbers greater than about 100, rearrangements in the periodic table could occur due to quantum mechanical effects . It is therefore a current research topic in nuclear chemistry to determine the chemical properties of the heaviest elements synthesized to date. Physico-chemical experiments sometimes have to be carried out with just one atom. The heaviest elements investigated so far ( Dubnium , Seaborgium , Bohrium ) do not yet show any fundamental changes compared to their homologues (Ta, W, Re).
literature
- C. Keller: Fundamentals of Radiochemistry, Salle & Sauerländer 3rd edition 1993, ISBN 3-7935-5487-2 .
- KH Lieser: Introduction to nuclear chemistry . 3rd edition, VCH-Verlag, Weinheim 1991, ISBN 3-527-28329-3 .
- M. skull: chemistry of superheavy elements . Angewandte Chemie 2006, 118, 378-414.
Individual evidence
- ^ GT Emery, Perturbation of Nuclear Decay Rates, Annu. Rev. Nucl. Sci. 22 (1972) pp. 165-202
- ^ E. Segrè, CE Wiegand: Experiments on the Effect of Atomic Electrons on the Decay Constant of Be-7 , Physical Review, Volume 75, Issue 1, pp. 39-43 (1949).
- ↑ T. Ohtsuki et al .: Enhanced Electron-Capture Decay Rate of 7Be Encapsulated in C60 Cages , Physical Review Letters, vol. 93, issue 11, id. 112501 (2004).
- ↑ Jerome Novak: Neutron stars: Ultradichte Exoten , Spectrum of Science, March 2004, pp. 34-39.