An LNGS Mobile Neutron Detector (ALMOND): Mapping Ambient Neutron Background of Gran Sasso National Laboratory

In deep underground laboratories, environmental neutrons, which are produced at the cavern walls, introduce a source of background to rare event searches. The flux and spectrum of the ambient neutrons vary considerably with time and location. Precise knowledge of this background is necessary to devise shielding and veto mechanisms, thereby improving the sensitivity of the neutron-susceptible underground experiments. ALMOND, currently in operation, is a low-flux mobile neutron spectrometer developed for the LNGS underground laboratory to measure the ambient neutron background of the entire facility. In this paper, an overview of the design, construction and calibration of ALMOND is given. Furthermore, the result of the first underground neutron measurement is shown along with an outlook for future measurements and analyses.