The radioactive by-products contained in an entire series of target foil, [ 18 O]H 2 O and synthesis apparatus were identified and quantified. From the perspective of waste management, 60 Co induced in Havar foil should be taken into consideration. Because the exempt activity of 60 Co in BSS is 0.1 MBq, the used Havar foil should be managed more than for 20 years. The radionuclides in the [ 18 F]-FDG synthesis apparatus are negligible. Equivalent doses at skin and to tissues were estimated assuming a point source at a distance of 30 cm in air. The annual equivalent doses at skin and equivalent dose at deep tissues of such an operating staff will be 56 and 8.3 mSv, respectively, as two times the remove of the target foil and five hundreds times the synthesis of the [ 18 F]-FDG. When proper radiation protection is provided, the exposure from the cyclotron management and the [ 18 F]-FDG synthesis process will not cause meaningful radiological risk to the operating staff. The activity concentration of 3 H, 180 kBqÁcm À3 , detected in the target water, is 3,000 times the legal limit of effluent for 3 H. The operators should take care of the treatment of the target water when they make a distillation for reuse and a disposal.

The number of positron emission tomography (PET) examinations has greatly increased world-wide. Since positron emission nuclides for the PET examinations have short half-lives, they are mainly produced using on-site cyclotrons. During the production of the nuclides, significant quantities of neutrons are generated from the cyclotrons. Neutrons have potential to activate the materials around the cyclotrons and cause exposure to the staff. To investigate quantities and distribution of the thermal neutrons, thermal neutron fluxes were measured around a PET cyclotron in a laboratory associating with a hospital. The cyclotron accelerates protons up to 18 MeV, and the mean particle current is 20 μA. The neutron fluxes were measured during both 18F production and C production. Gold foils and thermoluminescent dosimeter (TLD) badges were used to measure the neutron fluxes. The neutron fluxes in the target box averaged 9.3 × 10(6) cm(-2) s(-1) and 1.7 × 10(6) cm(-2) s(-1) during 18F and 11C production, respectively. Those in the cyclotron room averaged 4.1 × 10(5) cm(-2) s(-1) and 1.2 × 10(5) cm(-2) s(-1), respectively. Those outside the concrete wall shielding were estimated as being equal to or less than ∼3 cm s, which corresponded to 0.1 μSv h(-1) in effective dose. The neutron fluxes outside the concrete shielding were confirmed to be quite low compared to the legal limit.

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The radioactive by-products contained in an entire series of target foil, [18 O]H 2 O and synthesis apparatus were identified and quantified. From the perspective of waste management, 60 Co induced in Havar foil should be taken into consideration. Because the exempt activity of 60 Co in BSS is 0.1 MBq, the used Havar foil should be managed more than for 20 years. The radionuclides in the [18 F]-FDG synthesis apparatus are negligible. Equivalent doses at skin and to tissues were estimated assuming a point source at a distance of 30 cm in air. The annual equivalent doses at skin and equivalent dose at deep tissues of such an operating staff will be 56 and 8.3 mSv, respectively, as two times the remove of the target foil and five hundreds times the synthesis of the [18 F]-FDG. When proper radiation protection is provided, the exposure from the cyclotron management and the [18 F]-FDG synthesis process will not cause meaningful radiological risk to the operating staff. The activity concentration of 3 H, 180 kBqÁcm À3 , detected in the target water, is 3,000 times the legal limit of effluent for 3 H. The operators should take care of the treatment of the target water when they make a distillation for reuse and a disposal.

Short-lived radionuclides for positron emission tomography (PET) examinations in medicine are produced mainly using on site small cyclotrons. The operation of the cyclotron generates a significant quantity of neutrons, which will activate the cyclotron and surrounding materials. A new technique is proposed to estimate the neutron fluxes in the cyclotron rooms, in which small bolts in the cyclotron rooms were used as surrogates for neutron detectors. The measurements were carried out at four PET cyclotrons. The induced radioactivity of the bolts was analyzed by gamma-ray spectroscopy and elemental analysis. A gold foil activation method was applied to compare the results. The neutron fluxes in the PET cyclotron rooms were in the range of 105∼106 cm−2 s−1 during 18F production. In the brass bolts, 69mZn, 65Zn, 64Cu, 58Co, and 60Co were detected. In the iron bolts, 56Mn, 54Mn, 59Fe, 60Co, 69mZn, and 65Zn were detected. In the stainless steel bolts, 58Co, 60Co, 56Mn, 54Mn, and 59Fe were detected. Neutron fluxes estimated from the activities of 56Mn agreed well with those by the Au foil method. The feasibility of estimating the neutron fluxes in cyclotron rooms by means of radioactive analysis of bolts in the rooms was proven.