Those syringe shields protect the users from the high energy gamma emitting nuclides such as iodine 131 (360 Kev), fluorine 18, oxygen 15, carbon 11 (511 Kev).
Those virtually unbreakable tungsten shield (6mm minimum thickness) are inside lined with PTFE plastic tube (1mm thick), to reduce the gamma radiation and avoids errant Bermsstrahlung.
