Study of new substrate THGEMs with low neutron scattering and low radioactivity

Abstract

New types of Thick Gaseous Electron Multipliers (THGEMs) made of PCB-type substrates, including Ceramic, Kapton, PTFE, and in addition to FR-4, were developed for applications requiring low neutron absorption, scattering, and low natural radioactivity, such as the THGEM-based neutron detector, and the THGEM-based gaseous multiplier (GPM). Using Geant4 simulation, the result of the total neutron absorption and scattering ratio of bare substrate is Kapton(high) > FR-4 > Ceramic > PTFE (low). The Ceramic and PTFE substrates have lower ratios about 0.707% and 0.635% per layer(0.2 mm thick) respectively. The gamma-induced electron background is the reverse, Ceramic > PTFE > FR-4 > Kapton, from 1.5% to 0.7% at 1.0 MeV, which induces highest electron background in the range of 0∼7 MeV. The natural radioactivity background was measured for these types of substrate samples. The Ceramic substrate has lower radioactivity, 232 Th = 8.8 ± 0.9 Bq/kg, 238 U = 6.3 ± 0.9 Bq/kg, and 40 K is too low to be detected. Some THGEM samples were produced by these four types of substrates in the same shape: 0.2-mm thickness, 0.2-mm hole diameter, 0.6-mm pitch, and 70-µm rim. The performances of these new substrate THGEMs are promising. The effective gain is at the 10 4 level and the gain was stable during more than 100 hours continuous test. The energy resolution @ Ar+IsoB = 97:3 is at the level of 20% to 27%. These new substrate THGEMs are available in 200×200 mm 2 size and even larger, some of them are applied to neutron flux monitor detector and gaseous photomultipliers (GPM).

Developing cold-resistant high-adhesive electronic substrate for WIMPs detectors at CDEX*

“…In this pilot study, we started from the polytetrafluoroethylene (PTFE) as the base substrate because of its remarkably low radioactivity, which has motivated its widespread employment in rare-event experiments. [25][26][27] In order to improve the bonding between the dielectric and conduction layers, a combination of MEVVA and FCVA techniques using Ni + and Cu 2+ ion beams were applied to modify surface properties of the PTFE before electroplating. The intermediate and final products were characterized using scanning electron microscope (SEM) for surficial morphology, broadband dielectric impedance spectrometer for conductivity, and 90 • peel strength tester for adhesivity.…”

Development and study of an imaging detector based on high-position resolution THGEM

“…The study of THGEMs in China is active in recent years, and many progresses had been made, such as mini-rim copper-clad THGEMs [5], Au-coated THGEMs [6], new substrate THGEMs [7] and thinner THGEMs [8]. THGEMs are going to be used in many projects such as DHCAL and neutron detector in China [9].…”