Distribution Characteristics of Yttrium in Large-Aperture Barium Fluoride Crystals

Barium fluoride ($\text{BaF}_{2}$) crystal, with its unique ultrafast scintillation component with subnanosecond decay time, is very promising for timing and high-speed imaging applications. Yttrium (Y) doping can effectively suppress the slow scintillation component with about 600 ns decay time and increase the fast/slow component ratio (F/S) of light output (LO), attracting great attention in recent studies. However, Yttrium's segregation behavior causes axial inhomogeneity in long Ydoped$\text{BaF}_{2}\left(\text{BaF}_{2}: \mathrm{Y}\right)$crystals with small apertures, leading to significant Y concentration difference between the seed and tail ends. This difference affects long crystal's scintillation properties and thus limits their applications in high energy physics. We grew a$10 \text{at} \% \text{BaF}_{2}: \mathrm{Y}$ingot with 4 -inch in diameter and 3 -inch in length. Slices cut with 4 -inch diameter and several series of samples along the radial direction were obtained from the ingot. The yttrium distribution and segregation behavior in large-aperture crystal ingot was investigated by the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Optical transmittance (OT), F/S, and the light response uniformity (LRU), etc., were systematically investigated on selected samples. Compared to previous studies on long$\text{BaF}_{2}: \mathrm{Y}$crystals along axial direction, Y shows a more even distribution along radial direction in large-aperture$\text{BaF}_{2}: \mathrm{Y}$crystals. Quantitative mapping via LA-ICP-MS confirmed radial Y homogeneity with a standard deviation of less than 0.6 % across the 4 inch aperture. The uniform radial distribution of Y observed in the large-aperture ingot offers a possible avenue for improving the performance of$\text{BaF}_{2}: \mathrm{Y}$crystals.