Iodine radioactive decay

Radical trapping studies, 14 277 Radicidation, 8 655 Radioactive decay, 21 287—288 particles associated with, 21 291 Radioactive decay properties of uranium isotopes, 25 393 Radioactive emission, interaction with tracer molecules, 21 276 Radioactive iodine, protection from,... 

This same relationship between shift and coordination number is found with iodine compounds (38, 40), Tetrahedrally coordinated in KIO4 has a higher value of octahedrally coordinated F ion in IOe . If we extend this concept to Sn, the Mossbauer data 7,11) indicate that AR/R for Sn is positive and not negative as Gordanskii has recently proposed 4, 27). This conclusion agrees with that of Bocquet et al. (5), who showed by means of electron conversion in the radioactive decay of that il/ o) was larger in white tin than... 

Chemists of the early twentieth century tried to find the existence of element 85, which was given the name eka-iodine by Mendeleev in order to fill the space for the missing element in the periodic table. Astatine is the rarest of all elements on Earth and is found in only trace amounts. Less than one ounce of natural astatine exists on the Earth at any one time. There would be no astatine on Earth if it were not for the small amounts that are replenished by the radioactive decay process of uranium ore. Astatine produced by this uranium radioactive decay process soon decays, so there is no long-term build up of astatine on Earth. The isotopes of astatine have very short half-lives, and less than a gram has ever been produced for laboratory study. 

In some cases it is recommended to take radioactive iodine drugs such as iodotop (NaT ). It accumulates in the thyroid gland along with L-thyroxine and L-triiodothyronin, where radioactive decay takes place—weak 8-radiation destroys thyroid gland follicle cells, which leads to a gradual decline in thyroid hormone secretion. 

Like all first-order processes, radioactive decay is characterized by a half-life, f]/2, the time required for the number of radioactive nuclei in a sample to drop to half its initial value (Section 12.5). For example, the half-life of iodine-131, a radioisotope used in thyroid testing, is 8.02 days. If today you have 1.000 g of I, then 8.02 days from now you will have only 0.500 g of remaining because one-half of the sample will have decayed (by beta emission), yielding 0.500 g of MXe. After 8.02 more days (16.04 total), only 0.250 g of will remain after a further 8.02 days (24.06 total), only 0.125 g will remain and so on. Each passage of a half-life causes the decay of one-half of whatever sample remains, as shown graphically by the curve in Figure 22.2. The half-life is the same no matter what the size of the sample, the temperature, or any other external condition. 

Figure 3.2 shows results of the experiment in which the initial concentration of stable I2 was 0.013 /ug m-3. The scrubber was not in operation. All results are corrected for radioactive decay of 132I. The airborne concentration rose initially as the source was mixed in the air within the containment shell. The activity on the charcoal-loaded papers was due mainly to inorganic iodine, and this declined with a half-life of about 30 min, as 132I was adsorbed on surfaces. Plaques of various materials were exposed periodically to monitor the deposition. In other experiments with more iodine carrier, loss by deposition was more rapid. 

Iodine is lost from herbage by the same processes which cause field loss of Sr, 137Cs and other nuclides (Section 2.13). There is also the possibility of revolatilisation of iodine. If XG is the rate constant of field loss (fraction of iodine per unit area of ground lost from vegetation per second) and X1 the rate constant of radioactive decay, the combined apparent or effective loss rate is XE = XG + Xt. The effective half-life is Te = 0.693/A . The use of the term half-life implies that field loss is exponential and TE invariant with time, which is not always true. 

Aging the spent fuel to reduce by radioactive decay the 8-day iodine-131 that would be released to the atmospheric during dissolution... 

Iodine is obtained by oxidizing iodides from seawater or brines using Cl2, concentrated H2S04, Fe3+, or other oxidizing agents. Astatine is produced naturally by the radioactive decay of uranium or thorium. Production of At is also accomplished by bombarding Bi with alpha particles,... 

Several chlorine isotopes exist with mass numbers ranging between 32 and 40. The two stable isotopes are Cl and Cl with natural abundances of 75.77% and 24.23% respectively, while the others are radioactive. Bromine also has two stable isotopes, Br and Br, with natural abundances of 50.69% and 49.31% respectively, while the others are radioactive. Iodine has only one stable isotope, and numerous radioactive ones are known. Astatine is known only as its radioisotope see Radioactive Decay). 

About lO becquerels of iodine-131 were released in the accident. Iodine is mainly absorbed by a person s thyroid gland after inhalation or after consumption of contaminated foodstuffs such as milk products its short-range beta particles irradiate the gland from the inside. Uptake of iodine by the thyroid is very easy to prevent, for example by banning consumption of contaminated food for a few weeks until the iodine-131 decays sufficiently or by administering small amounts of non-radioactive iodine prophylactic-ally to block the thyroid gland. 

Generally, the more unstable a nuclide is, the shorter its half-life is and the faster it decays. Figure 15 shows the radioactive decay of iodine-131, which is a very unstable isotope that has a short half-life. 

The increase is caused by the sudden reduction in the overall removal rate constant for xenon when the reactor is shut down, whereas the rate of production of xenon from its main source, the decay of 1, decreases only slowly with time as the iodine decays. For low neutron fluxes ( < 10 ) prior to shutdown the xenon buildup after shutdown is less important because the xenon burnout by neutron capture is then small relative to xenon removal by radioactive decay. 

Unlike the hghter noble gases, xenon is not produced by nucleosynthesis within stars. It is made dnring snpernova explosions. It is also formed on Earth through radioactive decay (e.g., of iodine-135) and in fission reactions, and it is sometimes fonnd in gases emitted from mineral springs. It has nine stable isotopes, of which xenon-129 and xenon-132 are the most abundant (26.4% and 26.9%, respectively). 

To determine an age from an initial iodine isotopic composition, we can rewrite the equation of radioactive decay as... 

Iodine-131 undergoes radioactive decay to form an isotope with 54 protons and 77 neutrons. What type of decay occurs in this isotope Explain how you can tell. 

Iodine-129 has a half-life of 15.7 million years iodine-131 has a half-life of about 8 days. Both emit beta particles upon radioactive decay. 

Americium-241 is used in smoke detectors. It has a first order rate constant for radioactive decay of k = 1.6 X 10" yr . By contrast, iodine-125, which is used to test for thyroid functioning, has a rate constant for radioactive decay otk = 0.011 day", (a) What are the half-lives of these two isotopes (b) Which one decays at a faster rate (c) How much of a 1.00-mg sample of each isotope remains after 3 half-lives (d) How much of a 1.00-mg sample of each isotope remains after 4 days ... 

C. It occurs naturally by radioactive decay from uranium and thorium isotopes. Astatine forms at least 20 isotopes, the most stable astatine-210hasahalf-lifeof8.3 hours. It can also be produced by alpha bombardment of bismuth-200. Astatine is stated to be more metallic than iodine at least 5 oxidation states ate known in aqueous solutions. It will form interhalogen compounds, such as Atl and AtCl. The existence of At2 has not yet been established. The element was synthesized by nuclear bombardment in 1940 by D. R. Corson, K. R. Mac-Kenzie, and E. Segre at the University of California. 

Example 2-8. Radioactive iodine is used to image the thyroid gland. Typically, a saline solution of Na l is administered to the patient by an IV drip. Predict the most likely type of radioactive decay for this nuclide and calculate Q for the reaction. Given that the half-life of l is 8.025 days, what percentage of the isotope will have decayed during the 2.0-h procedure ... 

Solution. According to the Nuclear Wallet Cards, the only stable isotope of iodine is 1. Therefore, l lies to the higher side of the band of stability and will need to increase Z in order to become a stable isotope. The only form of radioactive decay that increases Z is the emission of a beta particle. Using the principles of conservation of mass number and conservation of atomic number during a nuclear reaction, the nuclear equation for beta decay is... 

The most widely used radioactive tag in RIA is iodine 125. Iodine 125 decays by electron capture. It emits a single gamma ray having an energy of 35.48 keV. Four tellurium K x-rays with energies between 27.5 and 31.8 keV are also emitted. In addition there are L and M x-rays with energies of about 4 and 0.5 keV, respectively, as well as a variety of conversion and Auger electrons. Measurement of these relatively weak photons by... 

A variety of radiotracers are used in clinical work, the most used isotopes being technetium-99m, iodine-131, tantalum-201, xenon-133, and indium-113m. The use of technetium, Tc, dominates, since it can be made to react with many substances having specific biological behavior. Tc is obtained from an isotope generator, which is based on the radioactive decay of radioactive molybdenum, Mo. Pharmaceuticals containing Tc are usually introduced by intravenous injection. Some radiopharmaceuticals may also be introduced orally, e.g., for those containing iodine this is the common procedure. 

Pathways for venting the containment atmosphere may be provided for a number of reasons, and these pathways may be equipped with filters to remove iodine from the vented gas. Filters for iodine removal can be present in both passive systems (in which flow continues only as long as there is a pressme difference) and active systems (in which there is a continuous forced flow at a controllable rate). Dry filters intended for the removal of aerosol particles are not likely to be effective for the removal of gaseous forms of iodine, especially organic iodides. Even if gaseous iodine will absorb on the filter mediiun, heat loads on the filter medium caused by radioactive decay can lead to revaporization of the absorbed iodine. Filters that involve water must be maintained at high pH to avoid the formation of volatile forms of iodine by processes identical to those that occur in reactor containment smnps. 

Even with identical decontamination factors, the operation of the purification system affects the activity concentrations of the individual iodine isotopes in the primary coolant to a different extent. The purification effect results in an effective halflife Terr of the iodine isotopes in the coolant which is shorter than the halflife of radioactive decay and can be calculated according to... 

By the radioactive decay of the iodine isotopes that are accumulated on the ion exchanger beds, radioactive xenon isotopes are produced. These radionuclides are released to the coolant again and are transported back to the primary circuit in periods when the degasification system is not being operated their contribution to the total xenon activity in the primary coolant was discussed in Section 4.3.2.1.1. When the degasification system is in operation, the xenon isotopes are removed from the purified coolant flow and are transported to the gas delay line. 

Once Csl (as well as CsOH) is deposited on the surfaces of the primary system under high-pressure accident conditions it can potentially revaporize as a consequence of heatup from its radioactive decay and from the system thermohydraulics, which means it would be released to the containment. Usually, it is assumed that the re-released material remains in the form of Csl however, the question arises of whether or not a fraction of the revaporized Csl is converted to HI. Calculations performed by Kress et al. (1993) showed that at 1000 K even in the absence of H2 and excess CsOH, only < 3.8% of the Csl was converted to HI under the conditions of different accident sequences. This result demonstrates that revaporization is not likely to produce significant amounts of volatile forms of iodine under such conditions. 

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