HabaNERO: A new experimental tool for the study of ($\alpha,xn$) reaction rates in the weak r-process

Recent sensitivity studies have proposed $(\alpha,$x$n)$ reactions are the main production mechanism of $Z$=38-47 abundances in early nucleosynthesis, so called the weak r-process, with the condition of $(n,\gamma)-(\gamma,n)$ equilibrium and temperatures between 3.5 and 5.5~GK. While the uncertainty of $(\alpha,xn)$ reaction rates was critical to change the production yield of elements, they are relatively large due to little experimental data existed for $(\alpha,xn)$ cross sections involved in the nucleosynthesis calculation. We have developed the HabaNERO neutron detector to study $(\alpha,$x$n)$ compound reactions of neutron-rich nuclei near $Z$=26-40 region including $^{75}$Ga$(\alpha,$x$n)$. The HabaNERO is a neutron long counter system which consists of $^{3}$He and BF$_{3}$ gas-filled proportional tubes in the polyethylene matrix optimized to obtain a high average neutron detection efficiency as constant as possible in the wide neutron energy range ($E_n = 0.1$-$19.5$~MeV) that corresponds to the neutron energies of interest. Details of the detector design and its commissioning result will be presented.