FPGA-based position reconstruction method for neutron beam flux spatial distribution measurement in BNCT

Abstract

A new measurement method for the spatial distribution of neutron beam flux in boron neutron capture therapy (BNCT) is being developed based on the two-dimensional Micromegas detector. To address the issue of long processing times in traditional offline position reconstruction methods, this paper proposes a field programmable gate array based online position reconstruction method utilizing the micro-time projection chamber principle. This method encapsulates key technical aspects: a self-adaptive serial link technique built upon the dynamical adjustment of the delay chain length, fast sorting, a coordinate-matching technique based on the mapping between signal timestamps and random access memory (RAM) addresses, and a precise start point-merging technique utilizing a circular combined RAM. The performance test of the self-adaptive serial link shows that the bit error rate of the link is better than 10⁻¹² at a confidence level of 99%, ensuring reliable data transmission. The experiment utilizing the readout electronics and Micromegas detector shows a spatial resolution of approximately 1.4 mm, surpassing the current method’s resolution level of 5 mm. The beam experiment confirms that the readout electronics system can obtain the flux spatial distribution of neutron beams online, thus validating the feasibility of the position reconstruction method. The online position reconstruction method avoids traditional methods, such as bubble sorting and traversal searching, simplifies the design of the logic firmware, and reduces the time complexity from O(n²) to O(n). This study contributes to the advancement in measuring neutron beam flux for BNCT.