Curie couple There are substances in natural products that can emit alpha, gamma and beta rays by themselves and are composed of atoms with the same atomic number. They are polonium, radon, francium, radium, actinium, thorium, protactinium and uranium.
Uranium and thorium are important nuclear fuels, and Ra and Ac can be used as radioactive sources and Radioactive standard source 。 The long-life isotopes U, U and Th of uranium and thorium are three Natural radioactive decay system The "ancestor" nuclide of. Some isotopes of polonium, radon, francium, radium, actinium, thorium, protactinium and uranium are the three Radioactive decay system Members of. Uranium and thorium often form paragenetic ore (such as monazite) with rare earth elements or other metals, and uranium also exists in coal, phosphorus and other deposits. Therefore, natural radioactive elements are the main source of radiation hazards in metallurgical, chemical and other industrial production. In the work of safety protection and environmental protection, their impact should be considered. When the content of uranium and thorium in ore is high, it should be recovered comprehensively. [2]
Natural radioactive elements refer to those originally found in natural products radioactive element 。 They are Polonium 、 radon 、 Francium 、 radium 、 Actinium 、 thorium 、 Protactinium and uranium 。 The number of nuclear charges of radioactive elements（ Atomic number ）Same radio isotope The elements that are composed of. It can be divided into natural radioactive elements (such as actinium, thorium, uranium, etc.) and artificial radioactive elements (such as plutonium, americium, curium, etc.). The application range of natural radioactive elements has expanded from early medicine and watch industry to nuclear power industry, aerospace industry and other fields. The main uses are: ① Nuclear fuel, except uranium 235, plutonium 239 produced by uranium 238 in the reactor after neutron irradiation and uranium 233 converted from thorium 232 in the reactor can be used as nuclear fuel. ② Neutron source, polonium 210 beryllium neutron source, radium 226 beryllium neutron source and plutonium 239 beryllium neutron source have important applications. ③ Radiation treatment of cancer, radium or radon sealed in tubes made of radium tube or radon tube can be used to treat cancer. In addition, thorium can be made into special welding rods, getters for ultra vacuum systems, and additives in structural metals; Thorium oxide can be used as catalyst for some organic chemical reactions and high-temperature ceramic materials, and can be mixed with tungsten to make filaments. [1]
(1) Uranium series: also known as uranium radium series, it starts from U, passes through 8 times of alpha decay, 6 times of beta decay, and finally generates stable Pb;
(2) Actinide series: also known as actinium uranium series, it starts from U, passes through 7 times of alpha decay, 4 times of beta decay, and finally generates stable Pb;
(3) Thorium series: starting with Th, it undergoes six alpha decays and four beta decays, and finally generates stable nuclide Pb.
(4) The products of interaction between cosmic rays and atmospheric elements or other substances mainly include H Be、Be、C、Al、Si， There are also P, P, S, Cl, Cl and Ar.
(5) Alone in the ocean and with stable isotope Long life nuclides, including K, Rb, In, La, Nd, Sm, Gd, Lu, Ht, Re, Pt, Pt, Sn, W, Ce, etc. Their half-life is roughly between 10 and 10 years. The application range of natural radioactive elements has expanded from early medicine and watch industry to nuclear power industry, aerospace industry and other fields. The main uses are:
① Nuclear fuel, except uranium 235, can be used as nuclear fuel, including plutonium 239 produced by uranium 238 through neutron irradiation in the reactor and uranium 233 converted from thorium 232 in the reactor.
② neutron source Polonium 210 beryllium neutron source, radium 226 beryllium neutron source and plutonium 239 beryllium neutron source all have important applications. ③ Radiation treatment of cancer, radium or radon sealed in tubes made of radium tube or radon tube can be used to treat cancer.
In addition, thorium can be made into special welding rods, getters for ultra vacuum systems, and additives in structural metals; Thorium oxide can be used as some organic chemical reaction The catalyst and high temperature ceramic material can be mixed with tungsten to make filament. natural radio isotope The important uses in marine research can be summarized in three aspects: ① Determine the age of seawater and speculate the circulation model of seawater;
② Study large-scale ocean mixing model;
③ Marine sediment Dating. 14C is widely used in the first two items. It is based on the phenomenon that the concentration of C in seawater is related to the age of the studied water body and the mixing degree of this water body with various water masses with different C contents. [3] 
