Enhanced suppression of background in capture reaction measurements with LAMBDA-II in ground laboratories

The precise determination of cross sections for key nuclear reactions within the Gamow window is crucial for advancing the study of stellar evolution and nucleosynthesis. However, extremely low reaction yields combined with the cosmic-ray-induced background make these measurements highly challenging, particularly for capture reactions. This work demonstrates the second configuration of the Large-scale Modular BGO Detection Array (LAMBDA-II) designed to capture reaction measurements, and introduces a method for suppressing γ-ray detection background in ground laboratories. By employing active and passive shielding, the background of LAMBDA-II was significantly reduced by approximately two orders of magnitude, reaching 8.1 × 10−3 and 1.0 × 10−3 keV−1h−1 in the 6–11 and 11–20 MeV energy ranges, respectively. When combined with a mA-scale intensity beam, this reduced background enables the investigation of several capture reactions of astrophysical interest in ground laboratories.