A Sensor Employing an Array of Silicon Photomultipliers for Detection of keV Ions in Time-of-Flight Mass Spectrometry

TL;DR

A new sensor using silicon photomultipliers improves ion detection in mass spectrometry with better speed and throughput.

Contribution

A prototype scintillation detector with SiPM arrays and FastIC ASIC achieves high ion throughput and time resolution.

Findings

The system can process ion rates above 10⁹ cm⁻² s⁻¹ with a dead time of ~20 ns per channel.

Time resolutions of 3.3±0.1 ns and 2.5±0.2 ns were achieved for m/z 196 and 18 ions, respectively.

Mass resolution of ~1000 for m/z < 200 was limited by ion arrival time spread.

Abstract

Pixellated scintillation detectors have the potential to overcome several limitations of conventional microchannel-plate-based detectors employed in time-of-flight mass spectrometry (ToF-MS), such as extending detector lifetime, reducing vacuum requirements, or increasing the ion throughput. We have developed a prototype comprising a fast organic scintillator (Exalite 404) coupled to an array of 16 silicon photomultipliers (SiPMs), with read-out electronics based on the FastIC application-specific integrated circuit (ASIC). Each SiPM signal processed by FastIC is fed into its own time-to-digital converter (TDC). The dead time of a single channel can be as short as ∼20 ns. As a result, our system have the potential to process ion rates above 109 cm−2 s−1. We have evaluated the performance of our prototype using a velocity-map imaging ToF-MS instrument, recording the time-of-flight mass spectra of C3H6 and CF3I samples. We achieved time resolutions of (3.3±0.1) and (2.5±0.2) ns FWHM for ions of mass-to-charge ratio (m/z) values of 196 and 18, respectively. This corresponds to a mass resolution of ∼1000 for m/z<200, which we found to be dominated by the spread in ion arrival times.

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