Radionuclides determination neutron activation products

Table II summarizes the parameters which relate to the measurement of each element neutron activation products, half-lives, y-ray energies, lengths of irradiation, decay, and counting. Also listed are the possible interfering radionuclides and interfering reactions producing the same isotopes from another element which were necessarily evaluated. This table is subdivided into three sections representing the elements determined during each of the three counting intervals.

Radionuclides classified as activation products are created in nuclear reactors and other nuclear devices by the reactions of neutrons with fuel and construction materials. Activation products include the isotopes of the transuranic elements and radioisotopes of hydrogen, carbon, caesium, cobalt, iron, manganese, zinc, and a host of other radionuclides, all of which should be recognised and considered in determining the environmental pathways to human exposure. 

By the collision of fast neutrons with hydrogen atoms in the coolant H2O, recoil protons are produced which can react with 0 (isotope abundance in natural oxygen 0.20%) to form F. This radionuclide is a emitter with a halflife of 109.7 minutes. Its activity concentration in the coolant depends directly on the prevailing neutron flux and amounts to about 5 lO Bq/ml in a ISOOMWe PWR operating at design power level. In a BWR plant, Lin (1983) determined a F production rate of about 2 10 atoms/s MWth (corresponding to 2 10 Bq/ s MWth) which is consistent with a theoretically estimated value of about 2.6 10 atoms/s MWth. 

The prompt gamma-rays emitted following neutron or charged particle interactions with the target nuclide may be used as a basis for non-destructive analyses. The important advantage of this technique is that the determination does not depend in any manner on the half-life of a product radionuclide. In fact, using this technique, the product nuclide need not even be radioactive. Many conventional activation determinations are limited in their sensitivities by short half-life product radionuclides, or the fact that the most abundant or highest cross section isotope of the element to be determined leads to a stable product on irradiation. 

In classical activation analysis a material to be analyzed is bombarded with neutrons, charged particles, or photons (gamma-rays). By this bombardment radionuclides are produced from elements of the target material. These radionuclides can be analyzed qualitatively and quantitatively by radioassay methods. From the results and the knowledge of the nuclear reactions during the bombardment an analytical determination of the target material can be achieved. The radioactive products of the bombardment can be measured after the irradiation and the emitted types, energies, and half-lives provide information used for qualitative analysis and the radiation intensity supplies data for the quantitative composition of the material to be analyzed. 

Similarly, Baers and Harsanen (1993) have determined the specific Nb activities in reactor pressure vessel steel (containing niobium in the ppm range) and plating ( 1% Mb). Niobium was isolated from the other radionuclides by ion exchange chromatography and ""Nb measured by liquid scintillation spectrometry niobium mass in the samples was determined by inductively-coupled plasma mass spectrometry. In this way, it was possible to rule out interferences caused by other radionuclides. However, the data to be used for the calculation of fast neutron fluence can be impaired by ""Nb which is formed by decay of Mo which is an (n,y) product of stable Mo. This interference becomes significant when the... 

When information on the production and transport of the radionuclides in the primary system is requested, it is not sufficient to limit the analyses to those isotopes that are relevant for dose rate buildup such as °Co, Co, and Mn. As will be discussed in the following sections, there are two different possible sources of radionuclides in the primary circuit of light water reactors the materials located permanently in the core region and those located outside the neutron field from which corrosion products are transported to the reactor core and are temporarily deposited there. With regard to the production of radionuclides, the main difference between these two sources is the residence time of the substances in the neutron field, which is equivalent to its activation period for this reason, determination of the element specific activity, i. e. the activity of a given long-lived radionu-... 

The second method for distinguishing between the two mechanisms responsible for contamination buildup is radiochemical and is based on the measured element specific activities of appropriate radionuclides such as °Co/Co, Ni/Ni, and Fe/Fe. These ratios can be determined in the corrosion products collected from the fuel rod surfaces as well as in those isolated from the primary coolant (see Fig. 4.25.). From these analytical results and from the neutron flux density known from the design of the reactor core, apparent residence times in the neutron field... 

Because the water produced is not radioactive, methyl acetate foms by the first reaction, where all of the oxygen-18 ends up in methyl acetate. 55. 2 neutrons 4 / particles 57. Strontium. Xe is chemically unreactive and not readily incorporated into the body. Sr can be easily oxidized to Si +. Strontium is in the same family as calcium and could be absorbed and concentrated in the body in a fashion similar to Ca. The chemical properties determine where radioactive material may be concentrated in the body a how easily it may be excreted. 59. a. unstable beta production b. stable c. unstable positron production or electron capture d. unstable, positron production, electron capture, or alpha production. 61. 3800 decays/s 63. The third-life will be the time required for the number of nuclides to reach one-third of the original value (No/3). The third-life of this nuclide is 49.8 years. 65. 1975 67. 900 g 5u 69. 7 X 10 m/s 8 X 10- J/nu-clei 71. All evolved 02(g) comes from water. 79. 77% and 23% 81. Assuming that (1) the radionuclide is long lived enough that no signiheant decay occurs during the time of the experiment, and (2) the total activity is uniformly distributed only in the rat s blood, V = 10. mL. 83. a. 1 C b. N, c, N, UQ, and =N c. -5.950 X 10 J/mol H 85. 4.3 X 10- 87.-H Ne - g Bh -H 4 Jn 62.7 s [Rn 7 5f 6d ... 

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