Developments on muonic X-Ray measurement system for historical-cultural heritage samples in Japan Proton Accelerator Research Complex (J-PARC)

Abstract

Negative muon elemental analysis is a groundbreaking technology that allows for the measurement of elemental compositional distribution in the depth direction of samples, ranging from 100 nm to several centimeters, with a depth resolution on the order of micrometers, eliminating the need for cross-sectional cutting for analysis. Recently, this technique has begun to be applied to historical cultural heritage, providing new insights into Japanese archaeological artifacts. We are developing a negative muon X-ray measurement system for elemental analysis of historical cultural heritage at the KEK Muon Science Laboratory (MSL) in the Japan Proton Accelerator Research Complex (J-PARC). At MSL, machine time is very limited, necessitating rapid measurement of archaeological samples. To achieve this, it is crucial to enhance the detection efficiency of high-purity germanium semiconductor detectors (HP Ge), capable of obtaining energy spectra of negative muon X-rays over a wide energy range with high resolutions. Particularly, at the pulsed muon source in J-PARC, only one photon or less can be detected per pulse. Therefore, the use of multiple Ge detectors is essential to achieve high detection efficiency. To address this, we developed a hemispherical chamber system capable of accommodating as many detectors as possible. By modifying the beam duct and increasing the number of Ge detectors with small crystals (1 cm$^3$) from 4 to 9, we report an approximately five-fold increase in detection efficiency.