Effectiveness of self-shielding type cyclotrons

Abstract

Cyclotrons of the self-shielding type have recently been employed for use in medical applications. Herein, we investigated the shielding power of five types of self-shields by measuring neutron flux from inside to outside the self-shield. Measurements were performed for five types of self-shields through the activation of Au foils, TLD, and the dosimeter with CR-39 as track detector. During the production of 18 F, the thermal neutron flux near the target box was found to be 10 7 cm -2 •s -1 . The neutron flux in the cyclotron vault was 10 1-2 cm -2 •s -1 . The use of self-shielding type cyclotrons reduced neutron flux, which became five orders of magnitude lower than the initial flux. Samples collected from the cyclotron vault material showed no residual activity. We concluded that the induced radioactivity of the material surrounding the self-shield, as a result of activation by neutrons from the cyclotron, is negligible. These results are important to implement proper radiation control of materials surrounding the cyclotron and for the decommissioning of the facility.

ESTIMATION OF THERMAL & EPITHERMAL NEUTRON FLUX AND GAMMA DOSE DISTRIBUTION IN A MEDICAL CYCLOTRON FACILITY FOR RADIATION PROTECTION PURPOSES USING GOLD FOILS AND GATE 9

“…The reaction equation is described as: H2 18 O + p → H2 18 F + n (1) In the light of recent developments in facilities housing medical cyclotrons, there have been efforts to characterize neutron flux and energy. The spatial neutron distribution in the vicinity of the cyclotron room has been modeled through Monte Carlo codes and studied experimentally by applying different methods such as gold foil activation (as neutron monitors) and imaging plates [5]- [10]. One of the essential factors in the characterization process is the induced activity of vault materials caused by neutron activation inside the cyclotron vault.…”