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Description
A neutron source based on the 18 MeV cyclotron is designed for thermal neutron imagine. A groove is usually designed at the thermal neutron exit to improve the thermal neutron flux. To further improve the thermal neutron flux and decrease the gamma in the neutron beam, some cerium sticks are placed in the neutron port. Because the thermal neutron reaction cross-section in cerium is smaller than this in the moderator, and the gamma reaction cross-section in cerium is larger than this in the moderator. Neutrons tend to propagate preferentially along the cerium sticks, thereby enhancing the collimation of the emitted thermal neutron beam. Simultaneously, the gamma in the thermal neutron beam is effectively reduced.
A thermal neutron exit is designed as a circle with the 10 cm-diameter, incorporating cerium sticks with a radius of 0.2 mm spaced at 1 cm intervals. By simulation, when the cerium sticks placed in the exit, the thermal neutron flux at 10 meters from the source increased from 5.12×10-11 n/cm2/proton to 5.81×10-11 n/cm2/proton, while the gamma flux decreased from 8.03×10-11 n/cm2/proton to 6.99×10-11 n/cm2/proton .
