Comparison of neutron fluxes in an 18-MeV unshielded cyclotron room and a 16.5-MeV self-shielded cyclotron room

Abstract

Some medical compact cyclotrons have self-shielding to reduce neutron fluxes. Thermal neutron fluxes in an 18-MeV unshielded cyclotron room and in a 16.5-MeV self-shielded cyclotron room were evaluated. In addition, the radioactivities in concrete and metals due to thermal neutrons in the cyclotron rooms for 30 years were calculated of operation such that the sum of the ratio of the nuclide concentration to the nuclide clearance level was equal to 1. The thermal neutron flux from the unshielded cyclotron was approximately 10(2) cm(-2) s(-1), whereas that from the self-shielded cyclotron was approximately 10(2) cm(-2) s(-1). The thermal neutron fluxes for concrete, stainless steel, vessel steel, and aluminum that reached their clearance levels were 9.80 × 10(4), 2.17 × 10(3), 1.87 × 10(4), and 2.41 × 10(5) cm(-2) s(-1), respectively. The specific activities in the cyclotron room were found to be sufficiently below the clearance level when the self-shield was employed.

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

“…Fujibuchi et al. divided 14 pieces of peripheral equipment into stainless steel, vessel steel, and aluminum and found 60 Co, 54 Mn, and 22 Na derived from these metals using calculation . The C/M of cyclotron components tended to be smaller due to the lower calculated radioactivity concentrations.…”

“…Positron emitters for PET radiopharmaceuticals are usually generated by nuclear reactions between accelerated protons or deuterons and specific targets. A large number of neutrons generated at the target and deflector of the cyclotron during this process is widely distributed in the room harboring an unshielded cyclotron . Thus, not only the cyclotron itself and peripheral equipment but also all the concrete walls of the room become irradiated and radioactivated by neutrons.…”

“…Some studies have identified radioactivated materials among cyclotron components after operation . Various radionuclides have been determined and radioactivity concentrations have been measured in irradiated Havar ® target foil to control the quality of [ 18 F]FDG that is injected into patients, and to reduce and manage amounts of radiation to which cyclotron operators are exposed .…”

“…A large number of neutrons generated at the target and deflector of the cyclotron during this process is widely distributed in the room harboring an unshielded cyclotron. 3 Thus, not only the cyclotron itself and peripheral equipment but also all the concrete walls of the room become irradiated and radioactivated by neutrons. The identification of radionuclides and their amounts of these radioactivated materials or radioactivated wastes are required when the PET facilities are decommissioned.…”

“…Some studies have identified radioactivated materials among cyclotron components after operation. 3,[11][12][13][14][15][16] Various radionuclides have been determined and radioactivity concentrations have been measured in irradiated Havar â target foil to control the quality of [ 18 F]FDG that is injected into patients, and to reduce and manage amounts of radiation to which cyclotron operators are exposed. [13][14][15] Radionuclides and their radioactivity concentrations in cyclotron components such as the deflector, dee, and target have been calculated 11 and measured.…”