Cold Neutron Imaging and Efficiency Measurements with a Boron-10 Coated Double-GEM Detector

A ${}^{10}\mathrm{B}$-coated double-GEM neutron detector (BGEM) was developed as a ${}^{3}\mathrm{He}$-free cold-neutron beamline detector using a single $\mathrm{B}_{4}\mathrm{C}$ converter cathode and a 512-channel APV25 orthogonal-strip readout over an active area of $10 \times 10~\mathrm{cm}^{2}$. The detector was tested at the HANARO Bio-REF beamline with a monochromatic $4.5~\mathring{\mathrm{A}}$ beam ($E_{n}=4.03~\mathrm{meV}$). The absolute detection efficiency relative to a ${}^{6}\mathrm{Li}$-based Ce:LiCAF reference detector was $\varepsilon_{\mathrm{BGEM}}=(8.69 \pm 0.20)\%$ (stat.). The pulse-height spectrum was qualitatively consistent with Geant4 energy-deposition simulations, and Cd-mask imaging yielded a Gaussian-equivalent edge-spread width of $\sigma = 555 \oplus 102~\mu\mathrm{m}$. These results establish a cold-neutron beamline benchmark for a single-converter BGEM detector with full-strip APV25 readout.