Innovative Radioactive Technique Sheds Light on GEM Detector Performance in High-Radiation Environments

Gas Electron Multiplier (GEM) detectors, introduced by Prof. Fabio Sauli in 1997, have become essential tracking devices in high-energy physics experiments.

Researchers at the Bose Institute in India have pioneered a novel technique using a radioactive source to simplify the study of radiation effects on Gas Electron Multiplier (GEM) detectors—critical components in nuclear and particle physics experiments. This breakthrough is expected to significantly enhance the understanding of the charging-up phenomenon, a key factor influencing detector performance in high-radiation settings.

GEM Detectors: A Cornerstone of High-Energy Physics

Gas Electron Multiplier (GEM) detectors, introduced by Prof. Fabio Sauli in 1997, have become essential tracking devices in high-energy physics experiments. These detectors utilize a thin, perforated Kapton foil with a high electric field to amplify the signals produced by ionizing radiation. The amplified signals enable precise detection of particles such as muons, making GEM detectors invaluable in experiments requiring high spatial resolution and sensitivity.

Constructed from a 50 μm thick Kapton foil, clad with 5 μm of copper on both sides, GEM detectors are not only instrumental in fundamental physics but are also strong candidates for medical diagnostic applications due to their excellent position resolution. However, the inclusion of Kapton, a radiation-resistant polyimide film with superb insulating properties, introduces sensitivity to radiation-induced effects, particularly the charging-up of the dielectric medium.

Understanding the Charging-Up Effect

During operation, ionizing radiation deposits energy into the detector, initiating electron avalanche formation. This process leads to charge accumulation on the Kapton foil, which subsequently enhances the electric field within the GEM holes—the primary sites for electron multiplication. The increased electric field boosts the detector’s gain and efficiency. Over time, a dynamic equilibrium is established, stabilizing the gain and ensuring consistent detector performance.

This charging-up phenomenon is of particular interest as India has been entrusted with the complete construction of GEM chambers for the upcoming Compressed Baryonic Matter (CBM) experiment at the Facility for Antiproton and Ion Research (FAIR) in Germany. These detectors will operate in extremely high-radiation environments, making it crucial to thoroughly understand and mitigate the charging-up effects to ensure reliable performance.

Breakthrough Study by Bose Institute Researchers

Dr. Saikat Biswas and his PhD student, Dr. Sayak Chatterjee, along with their collaborators from the Department of Physical Sciences at the Bose Institute—an autonomous institution under the Department of Science and Technology (DST), Government of India—conducted an in-depth investigation into the charging-up effect on Kapton foils and its subsequent impact on GEM detector performance.

The team developed a specialized experimental setup to study the charging-up effect in triple GEM detectors by analyzing gain variations over time. Their findings revealed that as either the detector gain (the ratio of primary charges to the charges detected by the readout board) or the irradiation rate increased, the charging-up time decreased significantly. This behavior was attributed to higher particle densities, which facilitated quicker charge equilibrium within the GEM holes.

Implications for High-Radiation Experiments

The insights gained from this study are invaluable for predicting behavioral changes in GEM detectors when exposed to external radiation. These findings will inform the design and operational parameters of GEM chambers in high-radiation environments like the CBM experiment at FAIR, ensuring optimal performance and reliability.

Moreover, the implications of this research extend beyond the CBM experiment. The results are relevant to other high-rate experiments where GEM detectors are utilized, highlighting the broader significance of this work in the field of high-energy physics and beyond.

Future Directions

Building on their success, the researchers plan to extend their investigations to explore the impact of GEM foil geometry on the charging-up effect. Additionally, they aim to study the behavioral changes of GEM detectors under various types of irradiation, extending beyond the capabilities of current laboratory setups.

The studies, published in the Journal of Instrumentation and Nuclear Instruments and Methods in Physics Research Section A, mark crucial milestones in the indigenous development of gaseous detectors. These advancements position India at the forefront of detector technology, contributing significantly to global high-energy physics research.