Radiopurity of Micromegas readout planes

TL;DR

This paper presents the first measurement of the radiopurity of Micromegas readout planes, demonstrating their suitability for low-background particle physics experiments and highlighting potential for further improvements.

Contribution

It provides the first radiopurity measurements of Micromegas planes using germanium spectrometry, showing they meet stringent low-background requirements.

Findings

Micromegas readouts have radiopurity below 30 microBq/cm2 for Th and U chains.

Measured radiopurity levels are comparable to the cleanest detector components.

Radiopurity can be improved with dedicated manufacturing controls.

Abstract

Micromesh Gas Amplification Structures (Micromegas) are being used in an increasing number of Particle Physics applications since their conception fourteen years ago. More recently, they are being used or considered as readout of Time Projection Chambers (TPCs) in the field of Rare Event searches (dealing with dark matter, axions or double beta decay). In these experiments, the radiopurity of the detector components and surrounding materials is measured and finely controlled in order to keep the experimental background as low as possible. In the present paper, the first measurement of the radiopurity of Micromegas planes obtained by high purity germanium spectrometry in the low background facilities of the Canfranc Underground Laboratory (LSC) is presented. The obtained results prove that Micromegas readouts of the microbulk type are currently manufactured with radiopurity levels below 30 microBq/cm2 for Th and U chains and ~60 microBq/cm2 for 40K, already comparable to the cleanest detector components of the most stringent low background experiments at present. Taking into account that the studied readouts were manufactured without any specific control of the radiopurity, it should be possible to improve these levels after dedicated development.