Theoretical simulation and experimental study of the polycapillary neutron focusing lens

To analyze the influence of neutron wavelengths and lens geometric parameters on the focusing performance of a polycapillary neutron focusing lens, the simulation model of the lens was established and the neutron beam transmission in the lens was simulated by the ray tracing method using MATLAB software. Moreover, the focusing performance of the lens was tested by using a polychromatic neutron beam in the wavelength range of 0.1~1.18 nm at China Spallation Neutron Source. The simulated focal spot size of 562 μm and the measured value of 549 μm are very consistent, which verifies the correctness of the simulation model and program. According to the data analysis of the measured focal spot, the applicable range of the lens is 0.2~1.18 nm. In this range, the focal spot size is positively correlated with the neutron wavelength, and the gain increases first and then decreases. In addition, the relationship between the focusing performance of the lens and the channel diameter was simulated. The results show that reducing the inner diameter of the microchannels is beneficial to obtain small focal spots with high gain when the inner diameter to outer diameter ratio is 0.8.