Hi, I was reading about PWR control system and I saw that control rods are stainless steel tubes encapsulating a Hafnium absorber material , it has Excellent mechanical properties and exceptional corrosion-resistance properties allow its use in the harsh environment of a pressurized water reactors and The German research reactor FRM II uses hafnium as a neutron absorber. so the question is if I'm designing a nuclear reactor based on what I should choose the control rods' material ? and as a Hafnium absorber why its better than Gadolinium [Gd] as control rods while Gd has much higher absorption cross section..? is Hf used as pure or in some composition ? and what's the Hf interactions with neutron?