Isotopes short-lived

In the early years of this century the periodic table ended with element 92 but, with J. Chadwick s discovery of the neutron in 1932 and the realization that neutron-capture by a heavy atom is frequently followed by j6 emission yielding the next higher element, the synthesis of new elements became an exciting possibility. E. Fermi and others were quick to attempt the synthesis of element 93 by neutron bombardment of but it gradually became evident that the main result of the process was not the production of element 93 but nuclear fission, which produces lighter elements. However, in 1940, E. M. McMillan and P. H. Abelson in Berkeley, California, were able to identify, along with the fission products, a short-lived isotope of... 

These isotopes are sometimes used as tracers of natural terrestrial processes and cycles. Long-lived isotopes, such as Rb and Sm are used for precise dating of geological samples. When the solar system formed it also contained several short-lived isotopes that have since decayed and are now extinct in natural systems. These include Al, Fe, Pu, Pd, and Al with a half-life of less than a million years is particularly important because it is a potentially powerful heat source for planetary bodies and because its existence in the early solar system places tight constraints on the early solar system chronology. 

The two Mossbauer levels of Pt, 99 keV and 130 keV, are populated by either EC of Au(fi/2 = 183 days) or isomeric transition of Pt(fi/2 = 4.1 days). Only a few authors, e.g., [323, 324] reported on the use of Pt, which is produced by thermal neutron activation of " Pt via " Pt(n, y) Pt. The source used in the early measurements by Harris et al. [322, 325] was carrier-free Au diffused into platinum metal. Walcher [326] irradiated natural platinum metal with deuterons to obtain the parent nuclide Au by (d, xn) reactions. After the decay of short-lived isotopes, especially Au(fi/2 = 6.18 days), Au was extracted with ethyl acetate, and the Au/Pt source prepared by induction melting. Buym and Grodzins [323] made use of (a, xn) reactions when bombarding natural iridium with... 

B.) In steady state, the mobile pool of nuclides is constant. For a long-lived nuclide (solid circles), the adsorbed abundances are determined by exchange with the groundwater. For a short-lived isotope that has a decay constant that is comparable to the desorption rate constant k i, decay of sorbed atoms is a significant flux, and so the steady state sorbed abundance is lower (see Eqn. 3). 

Once uranium is incorporated into buried bone, shell, coral, or speleothems, the isotope uranium-235 decays, initially into the short-lived isotope (thorium-231) and then into long-lived protoactinium-231. Uranium-238, on the other hand, decays first into two successive short-lived isotopes (thorium-234 and protoactinium-234) and only then into a long-lived isotope, uranium-234 (see Fig. 12). The decay of uranium-235 to long-lived protoactinium-231 is used to date events up to 150,000 years in age that of uranium-234 (derived from uranium-238) to thorium-230 is of use for dating events within the time range 1000-500,000 years. 

In the future, when nuclear fusion power plants are in operation, most of these disadvantages will not be a concern. Fusion reactions produce only short-lived isotopes and so there would be no long-term storage problems. An added advantage is that there is a virtually inexhaustible supply of deuterium fuel in the world s oceans. 

Technetium-99m and other short-lived isotopes used as radiopharmaceuticals... 

Characteristics of the Reactions with Short-Lived Isotopes. 205... 

The article has been organized around the different labelled precursors available directly from a cyclotron ([ F]p2 and [ F]fluoride) and the main F-reagents easily prepared from them and developed for the synthesis of radiopharmaceuticals. A short introduction will present first some characteristics of the chemistry with short-lived isotopes. 

Another difficulty arises from the chemical properties of the actinide metals. They are chemically reactive, rapidly corroded by moist air, pyrophoric, and, when in the molten state, dissolve common crucible materials. The radioactivity of short-lived isotopes of Am and Cm makes their long-term storage difficult small amounts can be stored successfully under ultrahigh vacuum. Large amounts of isotopes such 238pu with a Ti/2 of only 87.7 years are best stored under a pure inert... 

Actinium decays via a series of short-lived isotopes, eventually ending with stable lead. The presence of these radioactive daughters, particularly Th (which is a strong y-emitter), necessitates the use of lead-lined gloved boxes and remote control manipulators. Consequently, the metallurgy of actinium has been little studied and, due to the great expense and trouble involved, probably will not be studied extensively in the future. 

Astatine is one of the rarest elements in nature. Extremely small amounts of short-lived isotopes At-215, At-217, At-218 and At-219 are naturally found occurring in equilibrium with uranium, neptunium and thorium isotopes. The element was named hy Corson, MacKenzie and Segre who produced the first of its isotope At-211 in 1940 hy homharding bismuth with alpha particles. Since then many isotopes in the mass range 200 to 219 have been synthesized. All isotopes, however, are unstable, their half-lives ranging between a few microseconds to less than ten hours. The most stable ones are At-210, At-211 and At-209. No use of this element is known so far. 

Radon-222 may be transported with a carrier gas into an ionization chamber and its alpha particles counted. Short-lived isotopes in a carrier gas stream are measured this way using a flow-type ionization chamber. 

As the half lives of isotopes become shorter, they get more difficult to study. This is because short-lived isotopes are highly radioactive, which causes the emitted radiations to produce redox reactions, even in dilute solutions. Special apparatus is needed to study them, because of their intense radioactivity and the need to work rapidly. Further, due to limited quantities of the heavier elements, they can be studied only in very dilute solutions which sometimes behave strangely. 

The first observation of Zn NMR in zinc metal was by Abart and coworkers in a measurement at 4.2 K, using a field sweeping technique, which yielded a value of = 12 73(4) MHz. No subsequent NMR observation has been reported. A measure of the temperature dependence of the Zn nuclear quadrupole coupling in zinc metal has been obtained from time differential perturbed angular correlation (TDPAC) measurements using an excited state of Zn (/ = 9/2 605 keV). However, the use of liquid helium temperatures and exotic short-lived isotopes precludes the adoption of these techniques for general material characterization. 

Another short-lived isotope of beryllium, 7Be, decays to 7Li by electron capture with a half-life of —53 days. This half-life is so short that any atoms present in chondrite components must have been produced in the solar system essentially immediately before the host object formed. A hint of the presence of 7Be in the form of large excesses of 7Li in an Allende CAI was presented by Chaussidon et al. (2006). However, these authors were not able to demonstrate a tight correlation with the 9Bc/ Li ratio. 

The eastward movement of the nuclear debris injected into the atmosphere at Lop Nor (90°E and 40°N) can be computed as shown in Figure 3 (10). Whenever the fresh nuclear debris completes one cycle around the earth, there is usually a sudden increase in the concentrations of short lived isotopes such as 33-day 141Ce, 50.4-day Sr, 65-day 95Zr, as well as the number of single fallout particles in the unit volume of air, as shown in Figures 4 and 5 (1, 16,17). 

Decay time was critical to the determination of elements from the 5- and 30-min decay counts, so we decided to use the rabbit irradiation facilities with the highest thermal neutron flux (1014 n/cm2/sec) to build up the specific activity of short-lived isotopes. The higher flux also provided a greater sensitivity. 

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