...
Shielding
https://www.mcmaster.com/9143K25-9143K287/ (2''x2''x6'' → 3.1 kg; 2*2*6*(2.54 cm)^3 * (density of steel))
Radiation length: Fe 1.757 cm, Pb 0.5612 cm
https://pdg.lbl.gov/2017/AtomicNuclearProperties/HTML/lead_Pb.html
https://pdg.lbl.gov/2020/AtomicNuclearProperties/HTML/iron_Fe.html