Description of main materials and construction technology of radiation protection engineering in hospital
With the rapid development of science and technology, the diagnosis and treatment equipment of general radiology, nuclear medicine and radiotherapy are constantly updated, and various new technologies and equipment emerge. Radiation and radioisotopes play an important role in the medical diagnosis, disease treatment and medical research of these departments. At the same time, with the development of society and the improvement of people's cognitive level, more and more people can objectively understand and receive medical radiation. At present, the development of relevant departments in China also presents a rapid development trend. More and more people will be directly or indirectly exposed to medical radiation. For the safety consideration of the public and medical staff, radiation protection must be paid attention to, It will also become an important part of hospital safety management.
Description of main materials and construction technology of radiation protection engineering in hospital
This paper will discuss the basic principle of radiation protection, selection of protective materials and protective construction technology, focusing on the latter two aspects, analyzing and comparing the advantages and disadvantages of various common materials and technologies.
Basic principles
To explore the radiation protection in hospital, we should first know the classification and protection methods of radiation. According to the source of radiation, it can be divided into external radiation and internal radiation. External irradiation refers to the irradiation of human body caused by external radiation sources, mainly X-ray, γ - ray, β - ray and other high-energy charged ions and neutron beams; internal irradiation refers to the irradiation of radionuclides entering human body as radiation sources. In this paper, only the protection related to external radiation is discussed, and internal radiation protection is not included in this paper. For external exposure, the protection methods include time protection, distance protection and shielding protection. The specific protection principles are as follows, among which shielding protection will be the focus of this paper.
Principle of time protection: no matter what kind of exposure, the cumulative dose of human exposure is directly proportional to the exposure time. The longer the exposure time is, the more serious the radiation hazard is. In order to reduce the radiation dose, we should shorten the working time.
Principle of distance protection: the radiation dose rate of a certain place is inversely proportional to the square of its distance from the radiation source. The farther away it is from the radiation source, the smaller the dose rate there is. So we should try our best to stay away from the radiation source, that is to say, to work at a certain distance, so that the radiation dose received by people is below the maximum allowable value, so as to ensure personal safety and achieve the purpose of protection.
Principle of shielding protection: the intensity of ray will be weakened when it penetrates the substance, and the shielding substance with certain thickness can weaken the intensity of ray. Setting enough shielding substance (protective material) between radiation source and human body can reduce the radiation level, reduce the amount of agent received by people at work to below the maximum allowable dose, ensure personal safety, and achieve the purpose of protection. Shielding protection can be roughly divided into fixed protection, such as protective wall, door, window, lead glass observation window, protective screen, radioactive waste storage room, radioactive decay storage pool, etc.; mobile protection, such as lead tank, mobile protective screen, injection protection vehicle, etc.; personal protective equipment, such as protective cap, protective glasses, safety glasses, etc Protective gloves, etc.
Selection of shielding materials
As we all know, any substance can attenuate the ray passing through it more or less, but different substances have different degrees of attenuation to the ray, which means that not all materials are suitable for shielding materials. When choosing, we must consider the factors such as the protective performance (usually expressed as lead equivalent MMPB or specific lead equivalent MMPB / mm), structural performance and material source.
Shielding materials can be divided into four categories according to structural characteristics and purposes: heavy metal protective materials, such as: lead, iron, steel, copper, tungsten, etc.; wall protective materials for building, such as: concrete, brick, composite protective materials, soil, etc.; soft protective materials, such as lead rubber, lead plastic, etc.; transparent protective materials, mainly lead glass, organic lead glass, water, etc.
At present, the most commonly used materials in hospital protection engineering are concrete, barium sulfate, lead and lead glass.
Concrete (hereinafter referred to as concrete), with a density of 2.3-2.4g/cm 3, is composed of cement, sand and water. It is a kind of commonly used wall protection material, especially for high energy radiation. However, as a protective material, concrete has the disadvantages of large thickness, large volume, large self weight and high requirements for space and building structure.
Barium sulfate as a protective material, its protective performance is slightly higher than ordinary concrete, with high density, low strength and moderate cost. However, the requirements of its construction process conditions are high, especially for the proportion, hanging net and maintaining fullness, so it is necessary to ensure its adhesion, density and non cracking. In addition, the space occupied by the wall is slightly large and easy to crack (attention should be paid to the problem of annual inspection). Once there is a problem or the annual inspection is not qualified, the external decoration should be removed to solve the protection problem and then recovered again, causing great losses to the hospital; it can not be reused, so it needs to be treated as medical waste. Therefore, barium sulfate is often used as a coordination material.
As shielding materials, lead has a wide range of uses, including fixed protection, mobile protection and storage containers. The atomic number of lead is 82, the density is 11.34g/cm3, the melting point is 327.4 ℃, the Brinell hardness is 4.0, the compressive strength is 154kgf / cm2, and the elongation is 45%. With the characteristics of corrosion resistance and strong attenuation of X-ray and γ - ray, it is easy to process and shape, and is a good protective material. However, compared with other protective materials, the price of lead is more expensive. The attenuation ability of high-energy X-ray and gamma ray is decreased, and the mechanical strength is poor. As a protective material, it needs to be clamped and fixed on the iron plate or wood plate to prevent sagging under the action of gravity.
At present, the common density of domestic lead glass is 4.2g/cm3, 4.6g/cm3 and 4.8g/cm3. The specific lead equivalent of medical diagnostic X-ray (energy range 80-120kev) is about 0.2mmb/mm, 0.24mmpb/mm and 0.26mmpb/mm. The higher the lead content is, the higher the density is, the higher the lead equivalent is, but the color turns yellow, the surface hardness decreases, and it is easy to oxidize and change color, which results in the decrease of light transmittance. Lead glass is the necessary protective material for the observation window in the protection room and screen, and the required thickness shall be calculated and determined according to the actual situation.
Considering the advantages and disadvantages of each of the above four common materials, to do a good job of radiation protection in hospital, it is necessary to comprehensively consider the radiation production principle and protection principle, as well as the actual situation of the hospital itself (room space size, structure, equipment parameters, economic conditions) and other factors, and reasonably select the protection materials to achieve the optimization of protection effect and interests. In addition, advanced construction technology plays an indispensable role in the application of protective materials. The following will discuss some common construction technology of machine room protection.
Protective construction technology
Medical radiation protection covers a wide range of areas, including cyclotron area protection, nuclear medicine department overall protection, nuclide treatment ward protection, general radiology department room protection, radiotherapy department room protection, radioactive waste gas and liquid waste treatment, and each of them is a huge and complex systematic project. In this paper, we only focus on the hexahedral space of the radiation generating machine room to explore its existing common protective construction technology.
The protection inside the machine room shall be calculated scientifically according to the existing status of the machine room wall, the model and parameters of equipment and instruments, and then the protection construction shall be carried out for the walls, roofs, floors, doors and windows, pipeline cables, switches and sockets inside the machine room. For example, the scientific calculation results show that the original wall meets the protection requirements, which generally means that the material and thickness of the original wall can produce sufficient attenuation to the radiation, so there is no need to add additional protective layer; if it can not meet the protection requirements or precisely some walls can not meet the protection requirements, it is necessary to add additional protective layer.
Among them, compared with the top and ground, the wall surface has a wide range of construction technology, basically covering the top and ground construction technology. In addition, the protective door is the representative of the whole machine room, and it is also the weak link of the whole machine room protection, which requires high quality and technology. Therefore, the following will focus on the wall and protective doors involved in various processes, and the top, ground, protective windows, etc. are briefly described.
Wall protection construction technology
*Construction technology of barium sulfate wall protection
The surfaces of the walls to be decorated are all multi hole cement walls, whose drying speed is affected by many factors such as climate, temperature, humidity, material type and water retention. In addition, the infiltration of soluble salts and gas water in the walls will cause corrosion to the metal components, and if the wall adhesion is not enough, the barium sulfate layer may not be firm. In consideration of these problems, the corresponding substrate treatment (cleaning + roughening) should be taken first. That is to say, the surface particles and loose adherents shall be cleaned, and the small holes, depressions and gaps on the surface shall be filled with cement or putty, and then the cement and interface agent shall be fully stirred and evenly brushed on the wall once, so as to increase the roughness and improve the wall adhesion.
After the roughening layer is completely dry, the surface coating can be started. The barite sand containing more than 80% barium sulfate and cement shall be mixed in a certain proportion (generally 3:1 or 4:1) and fully mixed. According to the construction needs, a proper amount of clear water (generally no more than 10%) shall be added to dilute and then the application shall be started; after the first application, the second application shall be started after it is completely dried (at least 2 hours). In the process of application, it should be noted that once there is any leakage or uneven place, it should be repaired at any time. If there is any crack, it must be removed and reapplied. Follow the sequence of first horizontal plastering, slightly dry and then vertical plastering. The thickness of each plastering shall be controlled within 1.2cm. Repeat the plastering for many times to ensure that the wall does not crack, peel or fall off until it reaches the lead equivalent thickness required by the technology.
The price of this process material is relatively low, but the construction progress is very slow. Every time it is applied, it needs to wait for the second time to be completely dried, and the construction period is very long; the total thickness of the application is limited, which is 20-30mm (about 1-2mmpb); if it is more than 30mm, it must hang the steel mesh after every time it is applied for the next time. Even if hanging the steel mesh is adopted, the total thickness of the application is related to the base wall material , the total protection equivalent is about 5-6mmpb; if the required protection equivalent is larger, the technology of binding and supporting formwork with barium sulfate planting reinforcement can be used.
Barium sulfate coating is easy to crack and fall down. Once it cracks or falls down, it will produce ray leakage. Although the improved technology of hanging steel net wall with barium sulfate and binding and supporting formwork with barium sulfate planting steel bars increases the protection equivalent to a certain extent and reduces the possibility of irregular cracks, the cracks fall down, the protection equivalent is limited, the volume is large, the construction period is long, and it needs to be fixed The characteristics of annual inspection and low repetition rate have not changed substantially. Apart from the items that need special consideration of economic factors, they are not common in the wall protection construction of the machine rooms of major hospitals in China at present.
*Construction technology of direct wall protection with lead plate
Lead plate has better protection performance than barium sulfate, and electrolytic lead with purity no less than 99.9% should be selected.
The process of directly going to the wall is relatively simple, that is: first, according to the horizontal line of the floor elevation, snap the horizontal line of the ceiling elevation around the wall, find out the center point of the room, and draw the position line of the lead plate partition on the wall; then cut the lead plate and number it. When cutting, it is necessary to consider the reservation so that the lead plate can be overlapped (the length is not less than 20 mm), and the purpose of the number is to facilitate the rapid construction; next Add a small piece of lead plate as a gasket and fix the gasket and lead plate on the wall together with steel row nails, and then conduct lead back treatment to cover the nail tail to completely prevent radiation leakage. The space between steel row nails is generally 250mm * 250mm; for the overlap, use double-layer lead plate with the overlap amount of 10 mm ~ 20mm, and lead back treatment shall be carried out for the pipeline / wire box and other places requiring lead back treatment; finally, recheck the firmness Levelness, tight lap, etc.
With the way of direct fixation of lead plate and nails, the protection effect is good, the technological process is simple and the construction period is short. However, due to the large lead plate ratio, soft texture, and the higher the purity, the softer it is, it is difficult to control the firmness and levelness, and the treatment requirements for the overlap / nail hole / pipeline box and other fine parts are high. If this process is followed, it will fall off after a long time, resulting in radiation leakage and high maintenance cost. The external decoration needs to be disassembled and inspected, which is the same as the consequences caused by barium sulfate. At present, this process of lead plate directly onto the wall has been gradually eliminated.