Figure 1:

3D representation of treatment head geometry used for testing in the CK-1 vault. The materials of collimator shielding are polyethylene (green), lead (dark-grey), tungsten(light-grey). Source images produced in Flair (Vlachoudis 2009). The single layer design, approximately 350 kg, stems from information documented in NCRP report 79 (NCRP 1984). The multilayered treatment head shielding design, approximately 390 kg, utilizes the same shielding methodology as reported by Rosenstrom et al (Rosenstrom et al. 2023).