From the previous description, we have learned that rare earth minerals are usually accompanied by natural radioactive elements such as uranium and thorium . In the process of rare earth production, these nuclear elements are often enriched in intermediate products and wastes, and radioactivity runs through most of the processes of rare earth production ( Especially the pre-treatment process), causing pollution to the workplace and the surrounding environment. Therefore, understanding and mastering the knowledge of radioactive hazards and protection, and correctly understanding the radioactivity in the production of rare earths, not only exaggerating the radioactive hazards and affecting the production of rare earths, but also paying attention to the protection of radioactivity is a positive attitude. This is of great significance in promoting the sustainable and stable development of the rare earth industry, ensuring the safety and health of workers in the production of rare earths, and strengthening environmental awareness.
 Basic knowledge of radioactivity
 Radioactive elements and their rays
We know that elements composed of atoms with equal proton numbers and unequal numbers of neutrons are isotopes. The isotopes of the same element have great differences in the stability of their nuclei due to the difference in the number of their nuclei. An unstable nucleus emits a ray that is invisible to the naked eye and then becomes an isotope of another element. This process is called the decay (or metamorphosis) of the nucleus, and the element (isotope) that emits the ray is called a radioactive element ( Isotope), a substance consisting of such elements (isotopes) is called a radioactive substance. The rays emitted by the radioactive material are classified into α rays, β rays, and γ rays.
The alpha particle is a high-speed moving helium (He) nucleus composed of two protons and two neutrons with a mass of 4 and a positive charge of two units. Generally, the energy of alpha particles emitted by radioisotopes is below 7 million electron volts. The range is very short (about 2 to 12 cm in the air), the penetration ability is weak, and the alpha particles can be blocked with a small amount of material, such as a piece of paper.
The beta ray is a fast moving negative electron or positron with a small mass. In almost all radioactive decays, beta rays are associated with other radioactive decays. If there are too many neutrons in the nucleus, the neutrons will be decomposed into a proton and a negative electron, and the β - ray is the negative electron that decays from the neutron. Instead, β + rays because of the excessive number of nuclei is decomposed to protons emanating neutron and positron positrons. Typically, the radioactive isotope emits less than 5 million electron volts of beta ray energy. β-rays range is longer than the α particles (such as phosphorus 32 β rays emitted in the air can be emitted 7M), although higher than the penetration α particles, but using 5mm thick aluminum plate may β rays completely absorbed.
γ ray is an uncharged, non-resting mass electromagnetic wave with a very short wavelength (below 10 -8 cm ), which is the excess energy released when the nucleus retreats from a higher energy excited state to a more stable ground state. . After the γ-rays are released, the atomic number and atomic weight of the element are unchanged, but the nuclear properties such as half-life change. Gamma rays are generally emitted simultaneously with alpha rays or beta rays. Gamma rays have a strong penetrating power and are not easily blocked by substances like alpha particles and beta rays, and the range is also quite large. In general, the higher the density of the substance, the better the blocking effect on gamma rays. Usually, nuclear reactors and accelerator laboratories build reinforced concrete walls with a thickness of about 250 cm to ensure the safety of outdoor workers. Γ ray energy radioisotopes are produced in 3 million electron volts, 1.27cm thick lead plates can be reduced by half.
 Radioactivity intensity and dosage unit
Radioactivity (also known as radioactivity) is expressed as the number of nuclear decays occurring per second. which is:
Â
Where I - radioactivity, Bq;
I = - | dN | = λ N |
Dt |
λ - decay constant;
N - the number of decays, times;
t - time, s.
Therefore, the international unit of radioactivity is decay/second, denoted Bq, called becquerel or becquerel. The dedicated unit used in the past is Curie, which is recorded as Ci, lCi = 3.7 × 10 10 Bq.
The intensity of radioactivity in the mass of a substance is called the specific radioactivity, and the unit is Bq/kg. The unit of specific radioactivity of radioactive materials in liquids and gases is expressed in Bq/L.
A dose is a measure of the amount of energy absorbed by a unit mass (or volume) of a substance or organism by radiation, also known as the absorbed dose. The unit of dose is J/kg, denoted as Gy, called gray, referred to as Ge. The relationship with the dedicated unit rad used previously is lGy = 100 rad.
The radiation dose received per unit time is called the dose rate. Its unit is Gy/s, rad/s, etc.
The cumulative dose is the total dose received by a human or organism under one continuous illumination of various rays or repeated exposures. The cumulative dose should be indicated in time. Such as the cumulative dose of the staff within one year, the cumulative dose in a lifetime.
The biological response to the same absorbed dose is related to the type of radiation and the conditions of the exposure. For example, at the same irradiation dose, the degree of damage of the α-ray to the organism is 10 times that of the X-ray, and this multiple is called the linear coefficient Q. The dose equivalent (H) can be used to uniformly indicate the degree of damage of various rays, which is defined as the product of the absorbed dose D, the linear coefficient Q and other correction factors N at the point of the study in the biological tissue (for external radiation sources) N=1). which is:
H=DQN
When the unit of absorbed dose D is Gy, the unit of H is Sv (希, 希, sievet). When the unit of D is rad, the unit of H uses rem (rem). X-ray, γ-ray external irradiation, X-ray, γ-ray, and β-ray internal irradiation, Q=1; when α-ray internal irradiation, Q=10.
 Radioactive harm to the human body
Although the detailed mechanism of damage caused by radiation is not well understood, various human effects caused by radioactivity have been basically recognized.
Since radiation can cause atomic or molecular ionization of a substance, when the organism is irradiated with radiation, some macromolecular structures and even cell structures and structures in the body are directly destroyed, causing protein molecules, ribonucleic acids or deoxyribonucleic acid chains. fracture. Radiation can also destroy some enzymes that are important for metabolism. It can ionize water molecules in the body to produce some free radicals, and indirectly affect some components of the body through these free radicals. These damages can cause cell variability (such as cancer) and cause various radioactive diseases. The most sensitive to radiation in the human body are proliferating cells and tissues, cells and tissues that enter the blood system, the reproductive system, the digestive system, the crystals of the eyes, and the skin.
The human body is divided into external and internal radiation by radiation. External irradiation is the irradiation of the external radiation of the body to the body. The internal irradiation is the irradiation of the radioisotope into the body through inhalation, ingestion, infiltration and the like.
The human body caused by radiation should include somatic effects (damaged somatic cells) and genetic effects (damage of germ cells and reflected in the body of the offspring). The somatic effects can be further divided into acute injuries (caused by large doses of radiation in a short period of time), chronic injuries (caused by long-term exposure to small doses), and long-term effects (which appear long after exposure). The damage effect depends not only on the total exposure, but also on the irradiation rate, the area and location of the irradiation, and the body's own condition (age, health, etc.).
In the production of rare earths, it is mainly to prevent chronic damage and long-term effects caused by long-term small doses and internal radiation damage caused by excessive radioactive substances entering the body.
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