Estimation of thermal neutron flux in pet cyclotron rooms by means of radioactive analysis of bolts in the rooms

Abstract 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.