Radioactive iodine 131

Many people don’t know much about radioactive iodine 131 because we rarely come into contact with this knowledge in our lives. Radioactive iodine 131 is actually the product of nuclear fission. Of course, we don’t need to worry too much because extremely small amounts of radioactive substances will not have any impact on the environment and the body. Let’s take a closer look at radioactive iodine 131.

Iodine-131 is a radioactive isotope of the element iodine. It is an artificial radionuclide (a product of nuclear fission) with the symbol I-131 and a half-life of 8.3 days. Under normal circumstances, it does not exist in nature.

On March 26, 2011, extremely trace amounts of the artificial radioactive nuclide iodine-131 were discovered in the air in northeastern Heilongjiang Province, China. However, these trace amounts of radioactive substances will not have any impact on my country's environment and public health. Similar discoveries were subsequently made in the eastern coastal areas.

harm

Iodine mass number

Physical half-life

123

13.2 hours

125

60 days

129

1. 9th century 7

131

8.3 days

132

2.28 hours

133

20.3 hours

134

52.5 minutes

135

6.8 hours

Physical and chemical properties

A radioactive isotope of iodine-131. Symbol I-131, abbreviated as I. Its nucleus has 78 neutrons, while the stable nuclides of iodine have only 74 neutrons.

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Iodine 131 is a beta-decay nuclide, emitting beta rays (99%) and gamma rays (1%). The maximum energy of the beta rays is 0.6065 MeV, and the main gamma ray energy is 0.364 MeV. The half-life is 8.02 days. A 3.7×10 becquerel iodine-131 point source weighs 8.05×10 mg. The irradiation rate at a distance of 1 cm is 2.3 roentgens/hour, and it can be safely operated with a 5-cm thick lead shield. Iodine-131 is a highly toxic radionuclide, with the thyroid gland being the critical organ. Its effective half-life for humans is 7.6 days, and its maximum allowable accumulation in the body is 1.8×10 becquerels. The maximum permissible concentration of iodine-131 in the air of radioactive workplaces and in open water sources is 0.33 and 22 becquerels per liter, respectively.

The chemical properties of iodine-131 are the same as those of elemental iodine.

Generation and extraction

The nuclear reactions that produce iodine 131 are:

① Use tellurium metal or its compounds (such as tellurium dioxide) as target materials, irradiate in a reactor, generate tellurium 131 through (n, γ) reaction, and then tellurium 131 undergoes β decay to obtain iodine 131, namely Te(n, β)TeI;

②Use enriched uranium 235 as target material, and obtain iodine 131 through nuclear fission of U(n,f)I or U(n,f)TeI. The total fission yield of iodine 131 is about 0.82%.

method

① It can obtain relatively pure products without contamination by α impurities and other fission products. Many countries in the world use this method.

② ② When preparing iodine 131, in addition to possible contamination from other radioactive iodine isotopes, there are also α impurities and β impurities, which must be effectively purified. Only a few countries use it.

extract

There are several methods for extracting iodine-131 from the target material tellurium dioxide, including dry distillation, chromatography, extraction and distillation. Dry distillation and distillation are the most commonly used methods. The distillation method is to dissolve the irradiated tellurium dioxide in a sodium hydroxide solution, add hydrogen peroxide, molybdenum salt, etc., and then distill it in a sulfuric acid medium. The fraction containing iodine-131 is absorbed by sodium hydroxide with a reducing agent, and iodine-131 is obtained in the form of NaI solution. NaI solution is the primary product of iodine 131.

Production protection

When producing iodine 131 in large quantities, care must be taken to prevent the volatilization of iodine 131 to avoid causing serious pollution to the environment. The operation should be carried out in a shielded room with negative pressure and iodine removal equipment. Activated carbon, silver-coated activated carbon, silver-copper alloy mesh, silver mesh and alkaline solution are all good adsorbents for iodine 131.

use

In nuclear medicine, in addition to being used directly in the form of NaI solution for thyroid function tests and treatment of thyroid diseases, iodine-131 can also be used to label many compounds for in vivo or in vitro diagnosis of diseases. For example, iodine-131 labeled sodium rose bengal and sodium hippurate are commonly used scanning imaging agents for the liver, gallbladder, and kidneys. In addition to its applications in nuclear medicine, iodine-131 can also be used to find groundwater and measure the flow rate and direction of groundwater, locate underground pipeline leaks, and measure the water absorption capacity of each oil layer in oil field injection wells and its changes, so as to take timely and effective measures to adjust the distribution of water flow and maintain high and stable production of oil wells.