Alpha contamination assay, dosimetry and spectrometry using charge coupled devices

Abstract

The potential of using charge coupled devices (CCDs) to perform in-situ spectroscopy of alpha contamination has been investigated. The literature describing previous research shows that alpha particles give a distinctive readout from CCDs when compared with other types of radiation. TRIM (Transport of Ions in Matter) simulations have been performed to identify optimum features of CCDs for detecting alpha particles. It has been shown that thinner gate structures (i.e. less than 2 μm thickness) are preferable for low-energy alpha particles. For high-energy particles a sensitive region of at least 56 μm is required for maximum charge collection. More than 90% of the ionization has been shown to occur in the sensitive region for a wide range of alpha particle energies using typical CCD specifications and 78% useful ionization occurred for a thick structure at an energy of 2.232 MeV. An experimental investigation into the response of CCDs to alpha particles is described focused on the relationship between the size of the pixel clusters, the corresponding extent of blooming and the incident alpha particle energy.