Activation Reduction Method for a Concrete Wall in a Cyclotron Vault

Abstract

Background:The concrete walls inside the vaults of cyclotron facilities are activated by neutrons emitted by the targets during radioisotope production. Reducing the amount of radioactive waste created in such facilities is very important in case they are decommissioned. Thus, we proposed a strategy of reducing the neutron activation of the concrete walls in cyclotrons during operation. Materials and Methods:A polyethylene plate and B-doped Al sheet (30 wt% of B and 2.5 mm in thickness) were placed in front of the wall in the cyclotron room of a radioisotope production facility for pharmaceutical use. The target was Xe gas, and a Cu block was utilized for proton dumping. The irradiation time, proton energy, and beam current were 8 hours, 30 MeV, and 125 μA, respectively. To determine a suitable thickness for the polyethylene plate set in front of the B-doped Al sheet, the neutron-reducing effects achieved by inserting such sheets at several depths within polyethylene plate stacks were evaluated. The neutron fluence was monitored using an activation detector and 20-g on de Au foil samples with and without 0.5-mm-thick Cd foil. Each Au foil sample was pasted onto the center of a polyethylene plate and B-doped Al sheet, and the absolute activity of one Au foil sample was measured as a standard using a Ge detector. The resulting relative activities were obtained by calculating the ratio of the photostimulated luminescence of each foil sample to that of the standard Au foil.Results and Discussion: When the combination of a 4-cm-thick polyethylene plate and Bdoped Al sheet was employed, the thermal neutron rate was reduced by 78%. Conclusion:The combination of a 4-cm-thick polyethylene plate and B-doped Al sheet effectively reduced the neutron activation of the investigated concrete wall.

Pre‐discard estimation of radioactivated materials in positron emission tomography cyclotron systems and concrete walls of a cyclotron vault

“…The production of radioactivated materials is not inhibited when using an unshielded cyclotron. A method using an additional shield has been proposed to reduce the amount of radioactivated materials . Kumagai et al.…”

“…Kumagai et al. reported that a polyethylene plate combined with boron‐doped aluminum effectively shielded neutrons and resulted in the reduced concrete radioactivation …”

“…A method using an additional shield has been proposed to reduce the amount of radioactivated materials. 26 Kumagai et al reported that a polyethylene plate combined with boron-doped aluminum effectively shielded neutrons and resulted in the reduced concrete radioactivation. 26 Our study has some limitations.…”

“…26 Kumagai et al reported that a polyethylene plate combined with boron-doped aluminum effectively shielded neutrons and resulted in the reduced concrete radioactivation. 26 Our study has some limitations. We did not decommission our facility and demolish the cyclotron.…”

The Radioactivity Estimation of the Irradiated 13 Mev Cyclotron’s Concrete Shield

“…The other researchers have examined the activation of concrete in the nuclear reactors [7] and accelerators [8]. However, materials of concrete may differ depending on their sand, cement, and aggregate.…”