  Beam monitoring and evaluation are very important to boron neutron capture
therapy (BNCT), and a variety of detectors have been developed for these
applications. However, most of the detectors used in BNCT only have a small
detection area, leading to the inconvenience of the full-scale 2-D measurement
of the beam. Based on micromegas technology, we designed a neutron detector
with large detection area and high counting rate. This detector has a detection
area of 288 mm multiples 288 mm and can measure thermal, epithermal, and fast
neutrons with different detector settings. The BNCT experiments demonstrated
that this detector has a very good 2-D imaging performance for the thermal,
epithermal, fast neutron and gamma components, a highest counting rate of 94
kHz/channel, and a good linearity response to the beam power. Additionally, the
flux fraction of each component can be calculated based on the measurement
results. The Am-Be neutron source experiment indicates that this detector has a
spatial resolution of approximately 1.4 mm, meeting the requirements of
applications in BNCT. It is evident that this micromegas-based neutron detector
with a large area and high counting rate capability has great development
prospects in BNCT beam monitoring and evaluation applications.
