Browsing by Subject "Particle accelerator-based neutron source"

Monoenergetic neutron reference fields are used in neutron metrology for the calibration of different neutron detectors, including dose rate meters. The International Standardization Organization ISO has composed guidelines and requirements for the production of narrow energy spread neutron fields using a particle accelerator. The objective of this Thesis was to investigate a target material that could be used to produce a monoenergetic neutron field by irradiating it with protons. A broader energy distribution was deemed satisfactory in regard to the initial phase of the station’s development, as significant modifications to the beamline would be necessary to acquire more precise beam current values and to achieve proton energies closer to the reaction threshold energy. The target material was chosen to be lithium fluoride (LiF) based on a literature review and Monte Carlo simulations. The simulations were executed with the proton energy of 2.5 MeV, which is close to the threshold energy of the 7Li(p, n)7Be reaction, and with the fixed energy 10 MeV of the IBA cyclotron used to conduct the experiment. The simulations were executed with the MCNP6 code, and the results were compared to those obtained from equivalent Geant4 simulations. The simulations suggested two wide peaks around 3 MeV and 0.6 MeV at the proton energy of 10 MeV. The irradiation experiment included two phases, one of which entailed the use of a shadow cone to estimate the number of scattered neutrons in the neutron yield. The maximum neutron fluence of (2.62 ± 0.78)∙109 s-1 was measured at the pop-up probe current of (8.3 ± 0.8) µA. Gamma spectrometry was utilized after the experiment to further evaluate the number of 7Li(p,n)7Be reactions taken place in the target by calculating the number of 7Be nuclei in the LiF plate. Altogether, lithium fluoride exhibits promising characteristics as a target material for accelerator-based monoenergetic neutron production, although its application demands further considerations regarding for instance, the decrement of the proton energy and the aiming and measurement of the proton beam. These results contribute to the future development of a neutron irradiation station at the University of Helsinki.