For the direct measurement of the 13C(α,n)16O reaction inside its astrophysical Gamow Peak (150 keV < Ecm < 230 keV), the LUNA collaboration designed a neutron detector array with high efficiency and low intrinsic background. The detector is based on 18 3He counters arranged in two concentric rings embedded in a moderator polyethylene block. The detector characterization, performed in two steps between the Hungarian Institute for Nuclear Research Atomki (Debrecen) and LNGS, is described in the paper recently published in NIMA. 

The paper full-text can be found here.