Development of a Thin CVD Diamond Detector as a Transmission-Type Alpha Particle Counter at McMaster University Biological Microbeam Facility

Abstract

Microbeams have been applied in radiobiology research for decades. The goal is to irradiate single cellular and subcellular targets with individual charged particles. This study describes the simulation and fabrication of a super-thin single crystalline chemical vapor deposited diamond membrane, intended to act as a radiation detector and a vacuum window at the McMaster University biological microbeam facility. The ultimate goal is to deliver very accurate and controlled doses to cellular targets through single-particle alpha irradiation. To study the options of the material and detectors, Monte Carlo simulations were employed to simulate the energy loss and beam broadening through different materials and component con gurations, including vacuum window, air gap, and petri dish. A transmission-type detector based on a super-thin diamond membrane was selected because of the minimal energy loss and beam broadening. Two diamond detectors (250 um and 50 um thick) were fabricated for initial alpha source tests following plasma etching, cleaning, sputtering, and electrical connection. Promising signals proved the feasibility of diamond as an alpha counter, and the spectra were collected. However, the diamond detector could not maintain the counting rate in the stability experiments, and the counting efficiency is not consistent with Monte Carlo simulations for this alpha source test geometry.