Simulation study of energy resolution with changing pixel size for radon monitor based on Topmetal- $${II}^-$$ II - TPC

Abstract

In this paper, we study how pixel size influences energy resolution for a proposed pixelated detector-a high sensitivity, low cost, and real-time radon monitor based on a Topmetal-II − time projection chamber (TPC). This monitor was designed to improve spatial resolution for detecting radon alpha particles using Topmetal-II − sensors assembled by a 0.35 µm CMOS integrated circuit process. Owing to concerns that small pixel size might have the side effect of worsening energy resolution due to lower signal-to-noise ratio, a Geant4-based simulation was used to investigate the dependence of energy resolution on pixel sizes ranging from 60 µm to 600 µm. A non-monotonic trend in this region shows the combined effect of pixel size and threshold on pixels, analyzed by introducing an empirical expression. Pixel noise contributes 50 keV full-width at half-maximum energy resolution for 400 µm pixel size at 1 ∼ 4 σ threshold that is comparable to the energy resolution caused by energy fluctuations in the TPC ionization process (∼ 20 keV). The total energy resolution after combining both factors is estimated to be 54 keV for a pixel size of 400 µm at 1 ∼ 4 σ threshold. The analysis presented in this paper would help choosing suitable pixel size for future pixelated detectors.

Advances in nuclear detection and readout techniques

“…The Topmetal series pixel sensor [162,163] can also collect charge from the sursroundisng media through the exposed part of its topmost metal layer. Figure 37 shows a photo of the Topmetal-II- [164] bonded to a PCB base with gold bonding wire. Both sensors are promising candidates for future TPC applications.…”

Performance study of a directional fast neutron detection system based on TPC and plastic scintillation detectors

“…σ δ p can be calculated using equations (A.2), (A.6), and (A.15). Some parameters used in the calculation are from [16] and listed in table 1. The pad size is a crucial design parameter related to both the angular resolution and the detection efficiency.…”

“…If k zx and k yx are fitted using the Least Squares Method, their uncertainties are deduced as [16]:…”

“…where w is the width of the readout pad of the TPC and n is the number of readout pad rows in the event. If the y and z position of the pad rows are calculated using the COG method, σ y and σ z are the position resolution of the TPC and are calculated as [16,21]:…”

“…As shown in figure 31, σ y 0 arises mainly from the deviation of y reconstructed by the COG method at small diffusion width [21]. N eff can be calculated as [16,21]:…”