Scintillation crystals: a series of colorful intraocular lenses
Source: Sinoma hi tech Release time: 2020-08-17
The reason why we can see the colorful light is that we can see only a part of the world around us. In nature, there are many high-energy rays or particles that can not be seen by naked eyes. Even ordinary sensors can not detect them directly. People must use a kind of special material called scintillator to perceive their existence.
What is a scintillation crystal
Scintillation crystal is a kind of functional crystal material which can transform the energy of Χ, γ - ray or other high-energy particles into visible light or ultraviolet light. It is vividly compared to the "eye" that can see high-energy rays or particles. The detection process of scintillation crystal is shown in the figure below. Firstly, Χ or γ - ray generated by the radiation source incident on the scintillation crystal, and the ray is absorbed by the scintillation crystal to produce flicker light. Then, the optical signal is transformed into electrical signal by the photodetector, and then the electric signal is collected, stored and displayed, so as to realize the energy, momentum, direction and duration of these invisible high-energy rays or particles Accurate measurement of multi physical parameters.
Since the scintillation effect of thallium doped sodium iodide (NAI: TL) crystal was discovered in 1948, extensive and in-depth studies have been carried out on the growth, performance and application of scintillation crystals at home and abroad. Hundreds of inorganic scintillation crystals have been developed by scientists and technicians. According to the chemical composition of crystals, they can be divided into two categories: one is oxide scintillators, such as bismuth germanate (BGO), lead tungstate (PWO), cerium doped yttrium lutetium silicate (lyso: CE) and cerium doped gadolinium gallium aluminum garnet (GAGG: CE), which have the characteristics of high density, short decay time and good chemical stability; the second is halide scintillators, such as Nai: TL, thallium doped cesium iodide (CSI: CE) Most of them have low melting point, small band gap and very high luminous efficiency, which can obtain good energy resolution and time resolution at the same time.
Application of scintillation crystal
Scintillation crystal is closely related to people's life, and has a broad application market in security inspection, nuclear medical imaging, geological exploration, industrial non-destructive testing, high-energy physics and environmental monitoring and other fields. It is one of the mainstream crystals with significant economic benefits in the field of crystal materials in the world, and its industrial scale is second only to semiconductor crystal and optical crystal. For example, the luggage security machines widely used in airports and subways use scintillation crystals to detect the X-ray penetrating luggage bags, so as to realize the inspection of firearms, controlled knives and other prohibited items without unpacking, so as to ensure the safety of passengers. In the hospital, the scintillation crystal is used to detect the high-energy gamma ray produced by radioactive tracer injected into the human body, and the functional and metabolic imaging of human body is obtained on PET / CT machine. Tissues with high metabolic rate or lesions show bright signals, and low metabolic rate shows dark signals. Doctors can quickly diagnose the lesions of human organs and the size and location of tumor tissues, which can be used for cancer and swelling Early diagnosis and treatment of tumor. In the oilfield, the scintillation crystal is used to obtain the data of the content and distribution of radioactive substances in the formation, so as to determine the content and location of the formation oil and gas. The Chang'e-2 satellite launched by China uses scintillation crystals to detect the contents of radioactive elements in the large impact craters on the lunar surface and its surrounding sputters, so as to study the geological history of the moon and provide relevant resource distribution data for the development and utilization of the moon.
The research and development of scintillation crystal in CCRI started in 1980, and has successively undertaken a number of scientific and technological research tasks, such as tackling key scientific and technological problems during the sixth Five Year Plan period, special supporting projects for the ninth five year plan, the Eleventh Five Year Plan and the twelfth five year plan, the state key research and development, the Ministry of science and technology, the Ministry of science and technology, and the enterprise R & D investment in Chaoyang District. The Nai: TL scintillation crystal has been successfully developed by hot forging technology in China for the first time. The shape of Nai: TL crystal has been changed, and its mechanical strength and thermal shock resistance are much better than that of single crystal. Meanwhile, the transparency, luminescence, infrared and ultraviolet optical properties of the material are comparable to those of the original single crystal, and the machinability is also improved significantly, which breaks the large scale at that time This achievement has won the second prize of science and technology progress award of the Ministry of building materials industry. The Nai: TL crystal has been successfully used in the security inspection and large-scale security gate of the 2008 Olympic Games. The products are also widely used in the fields of oil logging, gamma ray camera, isotope therapy and industrial CT. At present, Nai: TL crystals of various specifications can be produced according to the user's use and drawing requirements to meet the requirements of high temperature and seismic resistance.
During the 11th Five Year Plan and the 12th Five Year Plan period, CSI: TL crystal, developed in cooperation with Shanghai Silicate Research Institute of Chinese Academy of Sciences, broke the foreign technology monopoly.
In recent years, with the support of the national key R & D program, the Institute has developed new scintillation crystals and components such as LaBr3: CE and GAGG: CE, focusing on the national major scientific projects and the development trend of the industry and market. LaBr3: Ce crystal has the advantages of high light output, high energy resolution and short decay time. It is the best scintillation crystal known at present. It has a broad application market in space physics, nuclear medicine imaging, environmental detection and other fields. The LaBr3: Ce Scintillation detector is used in the gamma ray spectrometer of the "Chang'e-2" satellite launched by China. Compared with the "Chang'e-1" scintillation detector, the energy resolution is more than twice. In addition, LaBr3: Ce crystal is considered to be the preferred scintillation crystal for time-of-flight positron emission tomography (TOF-PET) due to its high light output and extremely short decay time. GAGG: Ce Scintillation Crystal has the advantages of high light output (the highest known oxide crystal), high energy resolution, short decay time, and no deliquescence. It has potential application market in nuclear medicine imaging, high energy physics and other fields. At present, it has broken through the key technologies of crystal growth and component preparation of LaBr3: CE and GAGG: CE with a diameter of 2 inches, applied for 4 invention patents and formulated 1 industry standard.
Scintillation crystal has greatly expanded the vision of human beings, and will also shine more colorful light for people's better life.