Congratulations to Bill Chuirazzi for defending his Doctoral Dissertation "Combinatorial Optimization of Scintillator Screens for Digital Neutron Imaging"
Bill Chuirazzi, PhD Candidate, Nuclear Engineering
Dr. Lei R. Cao, Advisor (OSU)
Dr. Aaron Craft (INL)
Dr. Marat Khafizov (OSU)
Dr. Vaibhav Sinha (OSU)
Dr. Richard Vasques (OSU)
Neutron radiography, a nondestructive method for imaging the internal condition of samples by measuring the neutron transmission through a sample. It provides contrast between certain sample materials in a complementary manner to other imaging techniques, such as X-rays radiography. Neutron radiography has been used for a wide variety of applications such as studying cultural heritage objects, fuel cells, nuclear fuels, and quality control of industrial products.
Digital neutron imaging techniques have become more commonplace, opening the possibility to perform digital neutron tomography. Specialty applications, such as imaging highly radioactive fuels or using fast neutrons to image large or dense objects, are emerging in the field of digital neutron imaging. However, digital neutron imaging has several challenges that must be addressed to provide optimum performance. The scintillator screen, which produces a visible image under neutron exposure, must be improved to deliver images with higher spatial resolution in a shorter acquisition time. 6LiF scintillator screens are currently the industry standard, but more study is needed to explore if other scintillator screen compositions can deliver improved performance in some applications.
This work advances the state-of-the-art of digital neutron imaging by providing a combinatorial study on borated scintillator screens for thermal and epithermal neutron imaging applications. Converter material, scintillator thickness, scintillator particle size, converter-to-scintillator mix ratio, and substrate material are all parameters studied to determine their impact on digital image quality. High-resolution scintillator screens are also tested, and their underlying theory is explained. Boron-based scintillator screens were shown to have an increased neutron detection efficiency of 33% in a cold neutron beam when compared to 6LiF screens. The same screens exhibited a 10% improvement in detection efficiency of epithermal neutrons.
Fast neutron imagers are also investigated as part of this effort. Plastic scintillator packaging and dopants are varied to determine which produce the best images. This study also focuses on distinguishing between a fast neutron signal and signals produced by gamma-rays.
Finally, a new method for digitally imaging highly radioactive nuclear fuel is developed. Novel scintillator screens were characterized and optimized for this application. This digital transfer method neutron imaging is used to produce radiographs on fuel with a dose rate of 884 R/hr. Neutron tomography was also performed on irradiated nuclear fuel using a traditional method.