INITIAL BULK SHIELDING ASSESSMENT FOR A PET CYCLOTRON

Client:
GE HEALTHCARE (formerly AMERSHAM plc)

Description:
This project determined the bulk biological shielding and neutron activation for a cyclotron vault that is used in the production of radioisotope sources for use in Positron Emission Tomography (PET).

Bulk shielding assessments were performed to determine the thicknesses of ordinary concrete, magnetite concrete, ironshot concrete and dry sand required to ensure that dose rates on the outer surfaces of the shield walls would not exceed 2.5µSv/h during cyclotron operations.

Neutron activation assessments were also performed to determine the time delay required before decommissioning due to the neutron activation of Fe-54 and Fe-58, both of which are present in natural iron. Maximum allowable impurity levels in each of the concrete shield materials and the associated mild steel reinforcement bars to satisfy the current UK clearance levels were also determined.

An indication of the cost of disposing of the concrete and mild steel reinforcement bars as Low Level Waste (LLW) to the National LLW Repository at Drigg was presented.

Scope of service supplied

• Neutron source strength derivation

• Analysis of bulk shielding required to meet dose rate target

• Assessment of the activation of the impurities within the bulk shield

• Assessment of activation of the impurities within the steel reinforcing bars