Fission products half-lives

The use of technetium-99m (half-life = 6.006 h) in diagnostic medicine , particularly for brain and heart imaging " , has became widespread since the availability of macroscopic quantities of the long-lived technetium-99 isotope from fission products (half-life =2.13 X 10 yr, weak j8"-emiter, = 0.292 MeV, = 85keV. Normal glassware... 

Fission product Half-life Thermal 235U Fast 235U High 238U Fast Pu Thermal Cf Spontaneous... 

Fission product Half-life Thermal "35u Fast "35u High "38U Fast " Pu Thermal " "Cf Spontaneous... 

Fission product Half-life Decay constant (s ) Effective yield (atoms per fission) Thermal absorption cross section (b)... 

The situation became seemingly more complicated by an observation of Curie and Savitch (Curie and Savitch 1938a, b), of an activation product (half-life of about 3.5 h "that behaved like lanthanum. Today it is known, the authors had observed the fission products La (3.9 h) with an admixture of La (92 min). This observation led however to the resolution of all the problems, namely to the discovery of nuclear fission. 

Krypton and Xenon from Huclear Power Plants. Both xenon and krypton are products of the fission of uranium and plutonium. These gases are present in the spent fuel rods from nuclear power plants in the ratio 1 Kr 4 Xe. Recovered krypton contains ca 6% of the radioactive isotope Kr-85, with a 10.7 year half-life, but all radioactive xenon isotopes have short half-Hves. 

Uranium-239 [13982-01 -9] has a half-life of 23.5 min neptunium-239 [13968-59-7] has a half-life of 2.355 d. Recycling or reprocessing of spent fuel involves separation of plutonium from uranium and from bulk fission product isotopes (see Nuclearreactors, chemical reprocessing). 

The Natural Reactor. Some two biUion years ago, uranium had a much higher (ca 3%) fraction of U than that of modem times (0.7%). There is a difference in half-hves of the two principal uranium isotopes, U having a half-life of 7.08 x 10 yr and U 4.43 x 10 yr. A natural reactor existed, long before the dinosaurs were extinct and before humans appeared on the earth, in the African state of Gabon, near Oklo. Conditions were favorable for a neutron chain reaction involving only uranium and water. Evidence that this process continued intermittently over thousands of years is provided by concentration measurements of fission products and plutonium isotopes. Usehil information about retention or migration of radioactive wastes can be gleaned from studies of this natural reactor and its products (12). 

Approximately 25—30% of a reactor s fuel is removed and replaced during plaimed refueling outages, which normally occur every 12 to 18 months. Spent fuel is highly radioactive because it contains by-products from nuclear fission created during reactor operation. A characteristic of these radioactive materials is that they gradually decay, losing their radioactive properties at a set rate. Each radioactive component has a different rate of decay known as its half-life, which is the time it takes for a material to lose half of its radioactivity. The radioactive components in spent nuclear fuel include cobalt-60 (5-yr half-Hfe), cesium-137 (30-yr half-Hfe), and plutonium-239 (24,400-yr half-Hfe). 

Y emits a 2.28 MeV ft particle with a half-life of 64. lh and is suitable for radiotherapy applications. 90Y is available from a 90Sr/90Y generator system. The 90Sr is produced as a fission product. 

Rh is a ft emitting radionuclide suitable for therapeutic applications. It has a 35.4-h half-life and emits 0.566 MeV and 0.248 MeV ft particles and a 319 keV gamma photon. It is a reactor-produced radionuclide that is also potentially available from the separation of fission products in... 

The same problems of separating radioactive materials occur of course with the fission products of uranium where the task is often to separate a much larger number of different carrier-free radio-elements than occurs in normal targets. The mixture is complex and consists of elements from zinc to terbium and several hundred radioactive isotopes of varying half-life. 

TEA chloride See tetraethylammonium chloride., te,e a klorjd ) technetium chem A transition element, symbol Tc, atomic number 43 derived from uranium and plutonium fission products chemically similar to rhenium and manganese isotope Tc has a half-life of 200,000 years used to absorb slow neutrons in reactor technology. tek ne-she-om ... 

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