Decay-Resolved Charge Changes from Radioactive Decays in Levitated Microparticles

TL;DR

This study demonstrates a novel method to detect and analyze individual radioactive decay events by monitoring charge changes in a levitated microsphere, correlating them with scintillation signals to identify decay types and emitted particles.

Contribution

It introduces a new technique for event-by-event detection of radioactive decays through charge measurement in levitated particles, enabling detailed decay analysis at the single-decay level.

Findings

Resolved charge changes with millisecond timing precision.

Correlated charge events with scintillation signals to identify decay types.

Detected low-energy electrons emitted by radon decay products.

Abstract

We measure event-by-event discrete changes in the net electric charge of an optically levitated silica microsphere arising from individual radioactive decays within the sphere, in coincidence with energy depositions in a nearby scintillation detector. The net charge of the levitated sphere is continuously monitored by measuring its driven response to an oscillating electric field, allowing individual charge-change events to be resolved on millisecond timescales with precision below an elementary charge. Simultaneously, $\alpha$ and $\beta$ particles emitted during decays of implanted $^{212}$Pb and its daughters are detected using a scintillator read out with an array of silicon photomultipliers. By correlating reconstructed charge-change times with the scintillator response, we can directly attribute abrupt changes in the sphere's net charge to individual nuclear decays, and identify differences in the distribution of charges ejected for $\alpha$ and $\beta$ decays. These results establish a new approach for studying low energy charged particles emitted by radioactive decays at the single-decay level, and identify showers of radiogenically produced low-energy electrons emitted by $\alpha$-decaying radon daughters implanted near solid surfaces.