This project belongs to the field of new materials, the discipline of artificial lens materials.
Inorganic scintillators are a type of optically functional materials that can convert high-energy particles or ray energy incident on them into optical pulses. Bismuth germanate (Bi4Ge3O12, BGO) is an inorganic scintillator with excellent comprehensive properties. However, the preparation technology of ultra-large size BGO crystals has not made substantial breakthroughs, which seriously limits its wide application in medical imaging, security inspection, environmental monitoring and cutting-edge science. The existence of dark matter has been confirmed by a large number of observation data, but it has never been directly observed. Uncovering the mystery of dark matter will be another major scientific breakthrough after relativity and quantum mechanics. The international competition for dark matter detection is extremely fierce. In order to seize the global commanding heights, my country successfully launched the "Wukong" Dark Matter Particle Detection Satellite (DAMPE) at the end of 2015. This satellite has the widest energy range and the best energy resolution for human on-orbit observation. Space detector, its scientific detection indicators have reached the international leading level. The core detection component of DAMPE is a 14-layer BGO scintillation crystal with a total of 308 pieces, a size of 25mm×25mm×600mm, and a total weight of nearly 59% of its payload. These ultra-large size BGO crystals are the direct medium that interacts with high-energy cosmic rays and possible annihilation products of dark matter. They are the "center of gravity" of DAMPE's mass, the "center" of structure and the "core" of the detection component for the realization of scientific goals. They are the super "retina" of "Golden Eyes".
Prior to the project, only the Czochralski method could mass-produce BGO crystals with a length of 450 mm. Breakthroughs in key preparation and low-cost mass production technologies for crystals with a net length of 600mm were one of the basic prerequisites for the development of DAMPE. According to the urgent needs of DAMPE, the project carried out research on the development and application of large size BGO crystals, and achieved a series of innovative results. The main technical inventions are summarized as follows:
(1) Invented a descent method growth device for ultra-long and wide-plate BGO crystals. By adding an auxiliary heating system, a four-temperature-zone growth device was built; through the linkage control of the main and auxiliary heating, technical problems such as solid-liquid interface imbalance, quality deterioration and cracking were solved. Through the original design of the "L"-shaped upper insulation brick, a furnace with an ultra-wide horizontal uniform temperature zone width is built; through the adjustable furnace cap and movable guide rail design, the furnace can be flexibly adjusted horizontally and vertically.
(2) Invented the multi-crucible descent growth technology for ultra-long BGO crystals. The ultra-long crystal descent method growth equipment is adopted, and the main and auxiliary heating systems are linked to stabilize the solid-liquid interface in the temperature gradient region and suppress the difference between mechanical descent and the movement rate of the solid-liquid interface; the "secondary crystallization" and "accelerated growth" are adopted. The method significantly weakens the erosion of platinum crucibles; achieves low-cost and efficient mass production of 22 ultra-long BGO crystals in a single furnace.
(3) Invented the bridgman growth technology for wide-plate BGO crystals. Using wide-plate crystal descent growth equipment, creatively using strip crystals as seed crystals, and using ultra-wide platinum and down-lead crucible production, low-cost wide-plate BGO crystals are achieved through equipment, temperature field and process optimization. Efficient preparation.
This project breaks through the key preparation technologies of ultra-long and wide-plate-shaped BGO crystals, achieves low-cost and efficient mass production of 600mm net length BGO crystals, and creates a BGO crystal length (up to 945mm) and monomer area (up to 610mm×280mm) world record, greatly enhancing my country's international position in the field of BGO crystals and even scintillation crystal technology.
The project was authorized for 2 invention patents, applied for 1 invention patent, published 2 academic papers, and established 1 corporate standard. The project developed 650 600mm net-length BGO crystals and successfully applied them to my country's DAMPE satellite, achieving an output value of 25.9 million yuan. It has helped my country achieve milestone breakthroughs in dark matter detection research and achieved good economic and social benefits. The overall project has reached the international leading level.