Dr. Malcolm Mcewen

Biography

Dr. Malcolm McEwen Adjunct Research Professor

Research Interest

The Ionizing Radiation Standards (IRS) Group at the NRC is part of the Institute for National Measurement Standards – the National Metrological Institute for Canada. The Institute maintains and disseminates standards of measurement – time, length, mass, temperature, etc – to Canadian organisations (e.g. industry, university, government). IRS is responsible for standards of radiation absorbed dose and my work falls into two main categories: Development of calorimetric absorbed-dose standards for electron and photon beam dosimetry. The primary area of focus at present is water calorimetry in clinical photon and electron beams, which in terms of precision, accuracy and experimental constraints is a very challenging measurement problem. For this work we maintain and operate two linear accelerators at the NRC – a 3-40 MeV Vickers research accelerator and a 4-25 MeV Elekta clinical accelerator. A significant amount of investigative work has gone into ensuring that these accelerators can produce the very stable and reproducible radiation beams that are necessary for calorimetry. Experimental and theoretical work on the performance and calibration of secondary dosimeters in megavoltage photon and electron beams - in particular ionization chambers, but also diodes and chemical dosimeters (e.g. alanine, Fricke). Primary devices such as calorimeters are generally restricted to the primary standards laboratory and for measurements “in the field” some kind of secondary dosimeter is required. There are a large number of different systems to choose from and the work we do within IRS in this area includes accurate characterization of new devices, development of new or existing instruments and investigation of the physical underpinnings of dosimetry systems.