Underground Muography at Buda Castle

Abstract

The Buda Castle project is the largest underground muography project of the Wigner Research Centre
for Physics (RCP) and one of the major ones worldwide. The project has been running for more than
four years, and we have about two more years until completion. The research area is the southern part
of the hill of Buda Castle, Budapest, where the present castle and the partly buried ruins of the ancient
buildings are located. The goal is to find every unknown underground void (caves and tunnels) with a
characteristic extent larger than 2 × 2 × 2 m3, as well as to find the zones with significantly lower density
than the surrounding base rock (backfilled cellars, tunnels, rock debris zones, etc.). During the project we
investigate the whole area which can be reached from the presently known underground facilities. Most
of these facilities are at an ideal depth, about 50 m below the surface, and the corridor system available for
measurements is dense enough to populate an appropriate measurement grid to make even 3D inversion
for the uppermost 30 m of almost the entire castle area. Thanks to the wide range of detectors developed
and built by the Wigner RCP, we can measure with good resolution and efficiency even from places that
are difficult to reach. This paper will introduce the project and the first results obtained by 3D triangulation
based on several dozens of already completed measurement points.