  The HGND (High Granular Neutron Detector) is developed for the BM@N (Baryonic
Matter at Nuclotron) experiment on the extracted beam of the Nuclotron at JINR,
Dubna. The HGND will be used to measure the azimuthal flow of neutrons produced
with energies ranging from 300 to 4000 MeV in heavy-ion collisions at beam
energies of 2--4 AGeV. The azimuthal flow of charged particles will be measured
using the BM@N magnet spectrometer. The data on the azimuthal flow of neutrons
will shed light on the study of the high-density Equation of State (EoS) of
isospin-symmetric nuclear matter, which is crucial for studying astrophysical
phenomena such as neutron stars and their mergers. The HGND has a highly
granular structure with approximately 2000 plastic scintillation detectors
(cells), each measuring 4$\times$4$\times$2.5 cm$^3$. These detectors are
arranged in 16 layers, with 121 detectors in each layer, and are subdivided by
copper absorber plates with a thickness of 3 cm. The light from each cell is
detected with SiPM (Silicon Photomultiplier) with an active area of 6$\times$6
mm$^2$. Developed multi-channel TDC board based on the Kintex FPGA chip with a
bin width of 100 ps will be used to perform precise timestamp and amplitude
measurement using Time-over-Threshold (ToT) method. Good spatial resolution due
to the high granularity together with a cell's time resolution of 100-150 ps
ensures neutron reconstruction with good energy resolution. The design of the
detector as well as the results from test measurements and simulations have
been presented.
