The energy dependence of cluster size and its physical processes in the proton measurement with TimePix3 silicon detector

TL;DR

This study examines how the cluster size in TimePix3 silicon detectors varies with proton energy, combining experimental measurements and simulations to understand the underlying physical processes and detector sensitivity.

Contribution

It provides the first detailed analysis of energy-dependent cluster size in TimePix3 detectors using proton measurements and simulations, highlighting the role of transient induced charges.

Findings

Cluster size ranges between 30 and 80 pixels for 1.5-3.3 MeV protons.

Simulations underestimated cluster sizes and showed no energy dependence.

Detector sensitivity to transient charges explains the observed energy dependence.

Abstract

We investigated the energy dependence of the number of triggered pixels, or cluster size, when charged particles are detected using the TimePix3 detector with a silicon sensor. We measured protons in the range of 1.5~3.3 MeV from a Pelletron accelerator at RIKEN using a TimePix3 detector with a 500 um-thick silicon sensor. We determined from the experimental results a cluster size comprised between 30 and 80 pixels. To understand the physical process that produces large cluster images and its energy dependence, we simulated the charge carrier drifts in the sensor, assuming the incidence of a proton in the detector. The cluster sizes estimated in the simulation were smaller than those observed in the experiment, and remained constant across the entire energy range, when thermal diffusion and charge carriers self-repulsion were considered as the factors of the cluster image formation. In addition, we discovered that the size of the cluster image and its energy dependence observed in the experiment could be well explained when considering that the TimePix3 detector is sensitive to the transient induced charges, allowing even pixels that do not collect the charge carriers to trigger. We conclude that the cluster size measurement is a promising method for evaluating the energy deposited by a charged particle in the TimePix3 detector.