Development of a scCVD diamond detector as a transmission-type alpha particle counter

We present the simulation and fabrication for an ultra-thin single crystalline (sc) chemical vapor deposited (CVD) 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. MCNP 6.1 Monte Carlo was used to simulate the energy loss and beam broadening of different materials and endstation components, including the vacuum window, an air gap, and membrane. Based on the minimal energy loss and beam broadening, an ultra-thin diamond transmission-type detector was selected for further study. A 3 × 3 × 0.3 mm3 optical grade scCVD diamond membrane was thinned with Ar/O2 plasma etching, and the surface roughness was examined by a light microscope. Then the aluminum contacts were made through physical vapor deposition. Promising signals with 241Am alpha source demonstrate the feasibility of diamond as a transmission-type alpha counter.