Aging tests of the proportional wire chambers using Ar/CF4/CH4 (74:20:6), Ar/CF4/CH4 (67:30:3), Ar/CF4/CO2 (65:30:5) mixtures for the HERA-B Muon Detector

TL;DR

This study evaluates the aging and stability of various Ar/CF4/CH4 and Ar/CF4/CO2 gas mixtures used in the HERA-B muon detector, focusing on their performance under high radiation to ensure reliable muon detection.

Contribution

The paper provides a comprehensive analysis of aging effects in different gas mixtures for gaseous detectors, highlighting the importance of stability criteria for long-term operation in high-radiation environments.

Findings

Aging rates vary significantly between different irradiation sources.

Certain gas mixtures demonstrate better stability against aging effects.

Laboratory aging results may not directly extrapolate to large-area detectors.

Abstract

The Muon Detector of the HERA-B experiment at DESY is a gaseous detector that provides muon identification in a high-rate hadronic environment. We present our studies on the properties of several fast gases, Ar/CF4/CH4 (74:20:6), Ar/CF4/CH4 (67:30:3) and Ar/CF4/CO2 (65:30:5), which have been found to fulfill muon detection requirements. The severe radiation environment of the HERA-B experiment leads to the maximum charge deposit on a wire, within the muon detector, of 200 mC/cm per year. For operation in such an environment, the main criteria for the choice of gas turned out to be stability against aging. An overview of aging results from laboratory setups and experimental detectors for binary and ternary mixtures of Ar, CH4, CF4 and CO2 is presented and the relevance of the various aging results is discussed. Since it is not clear how to extrapolate aging results from small to large areas of irradiation, the lifetime of aluminum proportional chambers was studied under various conditions. In this paper we provide evidence that aging results depend not only upon the total collected charge. It was found that the aging rate for irradiation with $Fe^{55}$ X-rays and 100 MeV $\alpha$-particles may differ by more than two orders of magnitude.