Modification of Lead Tungstate Crystal by Ion Diffusion Method

As a new type of scintillation crystal, lead tungstate crystal (PbWO4) has been used by European Center for Nuclear Research (CERN) for its high density (8.28g/cm³), short radiation length (0.87cm) and Moliler radius (2.12cm), fast scintillation attenuation time (t < 50ns), strong radiation damage resistance and low cost. The precise electromagnetic calorimeter (ECAL) of the Large Hadron Collider (LHC).

PbWO4 scintillation crystal has many advantages, but each crystal is not perfect, has its own defects, PWO is no exception, the low light yield of PWO crystal (LY) limits its application in other fields outside the high-energy field, how to improve the LY of PWO crystal to broaden its application fields, especially in PET and other medical imaging fields. Application is a problem that needs to be solved urgently.

In order to improve the light yield of PWO crystal, some scholars have adopted ion diffusion method to modify lead tungstate crystal. This method includes the following steps:

1)Using 99.999% PbO powder and 99.999% WO₃ powder as raw materials, lead tungstate crystals were grown by crucible descent method or pull-down method according to the molar ratio of n (PbO):n (WO₃)=1:1.

2)Lead tungstate crystals were precisely oriented, cut and ground into lead tungstate wafers with thickness of 2-5mm by X-ray orientator. After cleaning, pure lead tungstate crystals were obtained.

3)Put the sample of pure lead tungstate crystal into a crucible filled with metal oxide powder, wrap the sample of pure lead tungstate crystal tightly by metal oxide powder, then put the crucible into a muffle furnace, raise the temperature to 800-1000 ℃, keep it for 12-36 hours, then diffuse to the room temperature, and get the modified tungsten. Lead acid crystals. The modified lead tungstate crystal can be cleaned and polished to test the scintillation properties.

Compared with the existing technology, the advantages of ion diffusion method are as follows: the introduction of metal ions into lead tungstate crystal improves the scintillation performance of tungstate crystal and obtains high quality modified lead tungstate crystal; moreover, the equipment and process are simple, which greatly reduces energy consumption and time, and improves efficiency.

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