Cyclotron-produced neutrons measurements using chlorine activation

Abstract Certain proton reactions emit fast neutrons, and this study examines the feasibility of measuring the neutrons emitted from a typical medical 18 MeV proton cyclotron using prompt gamma neutron activation on chlorine. This neutron detection method, employed by previous studies, has been deemed successful and highly promising. The measurement system includes a gamma radiation scintillator, for example NaI(Tl), with a spectrometry setup facing a convertor that contains a chlorine solution or compounds thereof. In its natural state, elemental chlorine is a chemically unstable gas, making its use as a convertor challenging. Therefore, chlorine is usually dissolved in solutions. Such solutions are diluted with water and contain hydrogen atoms that interact intensively with the neutrons and may interrupt their detection. Accordingly, in this study, a 25.5 L container of KCl powder was placed in front of a NaI(Tl) (7.62 cm diameter by 7.62 cm length) spectrometer near a cyclotron facility. The gamma radiation spectroscopy allowed the identification of the chlorine INS gamma line at 788 keV, alongside the K-40 gamma peak. In addition, it was possible to detect the fast neutrons using a total-counting mode, when the INS counts appear above the K-40 counting level. The chlorine INS peak in the KCl convertor was detected simultaneously during the cyclotron operations and provided a direct indication of neutron exposure around the cyclotron. We conclude that using KCl as a converter, with a NaI(Tl) gamma rays counter, is successful in detecting cyclotron-produced neutron emissions.