Rare earth minerals are usually associated with natural radioactive elements such as uranium, thorium, and in the process of production, the enrichment of nuclear elements are often in the intermediate product and waste, most of the radioactivity throughout the production process (especially the pre-treatment process), in the workplace and the surrounding environment caused by pollution. Therefore, understanding and grasp of the dangers of radioactive and protection knowledge, the correct understanding of rare earth in the production of radioactive, neither exaggerate radioactive harm and influence of rare earth production, and to pay much attention to radiation protection, is is determined attitude should be taken. This is of great significance to promote the sustainable and stable development of the rare earth industry, ensure the safety and health of the production workers, and strengthen the awareness of environmental protection.
Basic knowledge of radioactivity.
Radioactive elements and their rays.
The isotopes of atoms with equal number of protons and unequal neutrons make a great difference in the stability of the nucleus because of the number of neutrons in the same element. Unstable nuclei emit invisible to the naked eye ray, and then into another element isotopes, this process is called nuclear decay (or change), said this can emit radiation elements (isotopes) is a radioactive element (isotopes), composed of such elements (isotopes) substances called radioactive material. The radiation released by a radioactive substance is divided into alpha, beta, and gamma rays.
The alpha particle is a high speed helium nucleus, consisting of two protons and two neutrons, with a mass of 4 and a positive charge of two units. The alpha particles emitted by ordinary radioisotopes are all below 7 million electron volts. The range is short (about 2 ~ 12cm in the air), weak in penetration, with very few materials, such as a piece of paper, to block the alpha particles.
The beta ray is a fast moving negative electron or positron, and the mass is small. In almost all radioactive decay, the beta rays are associated with other radioactive decay. If there is too much neutron in the nucleus, the neutron will decompose into a proton and a negative electron, and the beta-ray is a negative electron that is decayed by the neutron. Instead, it is the positron emission that is emitted when protons in the nucleus are too numerous to decompose into neutrons and positrons. Normally, radioactive isotopes emit less than 5 million electron volts. The beta ray has a longer range than the alpha particle (for example, the beta rays emitted by phosphorous 32 can shoot up to 7m in the air). Although the penetrating capability is higher than the alpha particle, it can absorb the beta rays completely with a 5mm thick aluminum plate.
Gamma ray is a kind of electrically neutral, without rest mass, a short wavelength (below 10-8 cm) of electromagnetic wave, is the nucleus from the energy of high excited state to a more stable ground state, the release of excess energy. The atomic number and atomic weight of the element are invariable after the gamma ray is released, but its half-life and other nuclear properties have changed. The gamma rays are normally emitted at the same time as the alpha or beta rays. The gamma rays have a very strong penetrating power, not as easy to be blocked by matter as the alpha and beta rays, and the range is quite large. In general, the larger the density of matter, the better the blocking effect. Generally, the nuclear reaction and accelerator laboratory are built with a reinforced concrete wall of about 250cm thick to ensure the safety of outdoor staff. The radiation produced by radioactive isotopes has a power of less than 3 million electron volts, and 1.27cm thick lead plates can be reduced by half.
The intensity of radioactivity and the intensity of the unit's radioactivity (also known as radioactivity) are expressed in the number of atomic nuclei that occur in each second. That is:
I = - dN = lambda N
I -- radioactivity intensity, Bq; Lambda -- decay constant; N -- decay number, times; T -- time, s.
Therefore, the international unit of radioactive intensity is decay/second, called Bq, called becquerel or becquerel. The special unit used in the past is Curie, which is denoted as Ci, lCi=3.7 * 1010Bq. The radioactive intensity in the mass of the material unit is called the radioactive intensity, and the unit is Bq/kg. A unit of radioactivity in a liquid or gas is expressed in Bq/L. A dose is a measure of the amount of energy absorbed by a unit mass (or volume) of matter or an organism that is absorbed by radiation, also known as absorbed dose. The unit of dose is J/kg, which is called Gy, or gray, or ge. The relationship with a dedicated unit (rad) used in the past is lGy=100rad. The radiation dose per unit time is called the dose rate. Its unit is Gy/s, rad/s, etc. Cumulative dose is the total dose received by the human body or organism under a continuous irradiation of various rays or repeatedly. The cumulative dose should be dated. If the staff accumulated dose in one year, the accumulated dose in the lifetime. The biological response to the same absorbed dose was related to the type of radiation and the exposure conditions. For example, in the same radiation dose, the damage to the organism is 10 times as much as the X-ray, which is called the linear coefficient Q. Available dose equivalent (H) to express the harm of various kinds of rays, defined as: a little on the study of the biological tissues is open the absorbed dose of D, the quality factor Q and other correction coefficient N the product of the (external radiation source N = 1). In other words, H=DQN when the unit of absorbed dose D is Gy, the unit of H is Sv(xi, hewert, sievet). When the unit of D is rad, the unit of H USES rem(rem). Q=1 when x-rays, gamma rays, and x-rays, gamma rays, and beta rays are irradiated. When the alpha rays are irradiated, Q=10.
Although the detailed mechanism of radiation induced biological damage is not quite clear, people have basically realized the various human effects caused by radioactivity. Because the rays causes ionization of atoms or molecules, when organisms by radiation exposure, its some macromolecular structure even cells in body structure and organization structure will directly destroyed, cause protein molecules, RNA or DNA acid chain rupture. Rays can damage some has important significance on metabolic enzymes, can make the water molecules within the biology ionization and generate some free radicals, and through the radical indirectly affect some of the components of the body. These disruptions can cause cell mutations, such as cancer, and trigger a variety of radioactive diseases. The most sensitive to radiation is the proliferation of cells and tissues, the blood system, the reproductive system, the digestive system, the lens of the eye, and the skin cells and tissues. The human body is divided into external irradiation and internal irradiation. External irradiation is the external radiation of the body to the body, and the internal irradiation is through inhalation, feeding, infiltration and other channels, and the radioactive isotopes enter into the body.
The human body caused by radiation should include somatic effects (damage to somatic cells) and genetic effects (damage to germ cells and are reflected in offspring). Body effect and can be divided into acute injuries (caused by high doses of radiation in a short time), chronic injury (long) caused by the light exposure, forward effect (in a long time to emerge after irradiation). The damage effect depends not only on the total exposure, but also on the irradiation rate, the area and site of the exposure, and the body's own conditions (age, health status, etc.). In rare earth production, it is mainly to prevent chronic injury and long-term effects caused by long time low dose, as well as the internal irradiation injury caused by excessive radioactive substances entering the body.
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