Study of the neutron field in the vicinity of an unshielded PET cyclotron

Abstract

The neutron field in the proximity of an unshielded PET cyclotron was investigated during 18F radioisotope production with an 18 MeV proton beam. Thermoluminescent detector (TLD) models TLD600 and TLD700 as well as Bonner moderating spheres were irradiated at different positions inside the vault room where the cyclotron is located to determine the thermal neutron flux, neutron spectrum and dose equivalent. Furthermore, from a combination of measurements and Monte Carlo simulations the neutron source intensity at the target was estimated. The resulting intensity is in good agreement with the IAEA recommendations. Neutron doses derived from the measured spectra were found to vary between 7 and 320 mSv per 1 microA h of proton-integrated current. Finally, gamma doses were determined from TLD700 readings and amounted to around 10% of the neutron doses.

Source term calculation and validation for 18F-production with a cyclotron for medical applications at HZDR

“…We attribute the difference to additional neutron-producing reaction channels opening at 18 MeV proton energy, as suggested in [21]. It should be noted however that measurements of the neutron yield rate reported in [22] and [23] give results which are close to the value of 1.115×10 10 n/s for 1 µA §.…”

Distribution of residual long-lived radioactivity in the inner concrete walls of a compact medical cyclotron vault room

“…Thermal neutrons contribute to the activation of the concrete (Table 3). According to previous studies that evaluated the neutron energy in the cyclotron vault room, the neutron energy generated by the nuclear reaction with the target is a continuous spectrum with a peak at 1 MeV, and the thermal neutron component is small [17][18][19]. In the vicinity of the target, fast neutrons are the main component at the surface of the concrete.…”

Characterization of epitaxial 4H-SiC for photon detectors

“…For a preliminary evaluation of the detector hardness to fast neutrons a set of detectors was exposed to combined neutron and gamma radiation induced by 18 O(p, n) 18 F nuclear reaction. In the experiment 40 µA of 18 MeV protons were utilized to bombard an H 18 2 O target producing 4.7×10 11 s −1 neutrons with a mean energy of 2.5 MeV [24]. Taking into account the position of the detectors, the integral number of neutrons impacting on the area unit was estimated to be ∼ (3±1)×10 12 cm −2 .…”