Question 2: What are radioactive substances? There are too many of them.
Everything made of radionuclides is radioactive.
How many radionuclides are there? There are many radionuclides. Humans can make radionuclides through nuclear reactions. As for natural radioactivity, there are mainly three series, namely, uranium series headed by U238, actinide series or actinide series headed by U235, and thorium series headed by Th232. They all have quite a long half-life. You can check the number of nuclides in the periodic table. There are some that are not in the above three series, such as potassium 40 and so on.
Question 3: What are the main radionuclides in edible radionuclides pollution? They are also called unstable radionuclides, which are relative to stable radionuclides. Refers to the unstable nucleus, which can spontaneously emit rays (such as alpha rays and beta rays). ) and form stable nuclides through decay. The energy released during decay is called decay energy, and the time required to decay to half the original number is called decay half-life, ranging from 10 15 to 10- 12 seconds.
The source of radioactivity on the earth is the residue of primary nuclear synthesis and various subsequent nuclear combustion processes. Long-lived radionuclides exist in natural rocks, and cosmic rays will also form a small amount of radionuclides in nature. The decay of nuclides in the earth's crust contributes to the generation of heat on the earth.
There are less than 300 stable or extremely long-lived nuclides. With the development of science, more radioisotopes are synthesized by nuclear reaction in accelerators or reactors. There are about 2,000 known radionuclides, and it is theoretically predicted that there are more than 8,000 radionuclides in drip line, which is called artificial radioactivity.
Question 4: How many types of radionuclide examination are there? What are the advantages of each? Hello! First of all, the same element has different isotopes. For example, hydrogen has three isotopes, deuterium and tritium. When all isotopes of an element are radioactive, we call it a radioactive element, such as uranium. If not, you can't. For example, C 14 is radioactive, and C 12 cannot be called radioactive elements, but only radioactive isotopes. Hope to adopt, thank you!
Question 5: The law of constant decay of various radionuclides refers to the law that the atomic number or activity of radionuclides changes with time (see Radioactivity and Radionuclides). The radioactive decay theory put forward by e Rutherford and f Soddy in 1903 reveals the instability of radioactive materials for the first time, and puts forward a quantitative negative exponential relationship when studying the radioactive decay rate of thorium X(224Ra).
( 1)
Integral:
(2)
When both sides of formula (2) are multiplied by λ, the corresponding activity relation is obtained:
(3)
Where: decay rate of radionuclide atoms; NO and n are the number of nuclide atoms at initial time (t = 0) and time t; AO and a are the activities at the starting time and t time; λ is a decay constant, and its physical meaning is the decay probability of nucleus in unit time.
Formula (2) shows the statistical law of nuclear decay, that is, the number of radioactive nuclei decreases exponentially with time. Each radionuclide decays independently and obeys this basic law, but each has its own characteristic decay constant. For example, the λ of uranium 238 is 1 .55x10-1,and the λ of radium 226 is1.
The parent substance (nuclide 1) decays into a daughter substance (nuclide 2), which decays into a stable nuclide, and the parent substance and daughter substance are in the same system. At this time, formulas (1) and (2) can calculate the atomic numbers of nuclide 1 coexisting with nuclide 1 * * and isolated nuclide 2 at different times.
(4)
(5)
At first, there were only parent nuclides. In a given sample N 1, 0, the change of N2 with time only depends on λ 1 and λ2. There are three situations:
① The activity (A2) of λ 2λ 1 nuclide 2 increases with time at first, then reaches a certain saturation value, which is equal to the activity (A 1) of nuclide 1, and then the activity of nuclide 2 decreases according to the half-life of nuclide 1, showing a long-term balance (Figure/kloc-0) Curve a is the initial activity of pure nuclide 1, curve b is the activity of pure nuclide 1 gradually accumulated nuclide 2, and curve b' is the state that the activity of isolated nuclide 2 decays with time. Thorium 234 is produced from uranium 238 and radon 222 is produced from radium 226. In addition, when radionuclides are generated by nuclear reaction using neutrons in the reactor or ion beams generated by accelerators,
② The activity of λ 2 > λ1nuclide 2 initially increased with time. After tm reaches a certain maximum, the activity of nuclide 2 is greater than that of nuclide 1, and then gradually tends to decay according to the half-life of nuclide 1, and a temporary equilibrium appears (Figure 2). The descriptions of curves A, B, B' and C are the same as those in figure 1.