Dr. Patrick Saull

Ionizing Radiation Standards, National Research Council
1200 Montreal Road
Ottawa, ON K1A 0R6
613-993-2715 Ext 240
patrick [dot] saullatnrc-cnrc [dot] gc [dot] ca

Research Summary

The National Research Council's primary standard for beta-ray absorbed dose to skin [1-2] is based on measurements with an extrapolation chamber, a thin-window parallel-plate ionization chamber with variable plate separation. The standard is currrently undergoing a number of upgrades, chiefly to improve automation and readout. Traditionally, Bragg-Gray cavity theory has been applied to convert ion chamber measurements to dose rate, but Spencer-Attix theory offers an intriguing alternative worthy of further study using Monte-Carlo simulations.

Compton-gamma imaging [3-6] is a tool for imaging gamma fields in the 0.3 to 3 MeV range. Together with NRCan we have just completed a 262-channel Compton imager using state-of-the-art silicon photomultipliers supplemented with conventional PMTs. This instrument must be characterized for different gamma energies and angles, and its imaging algorithm extended to handle distrubuted sources. Primarily used for locating sources in 2D at large distance (counter terrorism, gamma-ray astronomy), the Compton approach has potential medical-physics applications worth exploring in 3D and at short distances.

Several upgrades to our neutron program [7] are underway. Sealed neutron sources are characterized by their neutron emission rate, typically in the 1e6 n/s range. We are reviving our primary standard for neutron emission rate, the manganese bath method, which entails the immersion of the neutron source in a large bath of MnSO4 solution to capture the emitted neutrons, and a subsequent measurement of the induced activity (Mn-56). As an alternative to sealed neutron sources, we will shortly take possession of a neutron generator requiring commissioning, characterization, and Monte-Carlo simulation. Neutron imaging and prompt-gamma activation analysis are two potential projects associated with this program.

A student working in any of these areas will develop skills in 1) radiation detection (beta and gamma spectroscopy, ionization chambers, proportional counters, Geiger counters, scintillators, germanium detectors, solid-state devices); 2) Monte-Carlo simulation (GEANT4, EGSnrc++, MCNP, or FLUKA); 3) hardware control via software (RS-232, GPIB, USB, TCP/UDP, or VME); 4) theory and data analysis (usually C/C++, usually using the ROOT package, and always on Linux); and 5) sports (lunch-time ball hockey, soccer, and volleyball).

Selected Publications

1. T.P.Selvam, P.R.B.Saull, D.W.O.Rogers, "Monte Carlo modeling of the response of NRC's 90Sr/90Y primary beta standard", Med Phys. 32 (2005) 3084.
2. R.Behrens et al, "International comparison EUROMET.RI(I)-S2 of extrapolation chamber measurements of the absorbed dose rate in tissue for beta radiation (EUROMET project No 739)", Metrologia 44 (2007) 06003.
3. P.R.B.Saull, L.E.Sinclair, H.C.J.Seywerd, D.S.Hanna, P.J.Boyle and A.M.L.MacLeod, "First demonstration of a Compton gamma imager based on silicon photomultipliers",   Nucl. Instrum. Meth. A 679 (2012) 89.
4. L.E.Sinclair, D.S.Hanna, A.M.L.MacLeod, P.R.B.Saull, "Simulations of a scintillator Compton gamma imager for safety and security", IEEE Trans. Nucl. Sci. 56, 1262-1268, 2009.
5. P.R.B.Saull, L.E.Sinclair, H.C.J.Seywerd, P.J.Boyle, A.M.L.MacLeod and D.S.Hanna, "A two-pixel Compton imager", Proc. SPIE, Vol. 7665, 76651E, 2010.
6. A. MacLeod, P.Boyle, D.Hanna, P.Saull, H.Seywerd, L.Sinclair, "All-scintillator Compton gamma imager", Phys. Canada 65 (2009) 136.
7. J.P.Archambault and P.R.B.Saull, "A fully automated, liquid-moderated neutron spectrometer system", IEEE Nuclear Science Symposium, Knoxville, TN, October 2010.
8. L.E.Sinclair, H.C.J.Seywerd, R.Fortin, J.M.Carson, P.R.B.Saull et al., "Aerial Measurement of Radioxenon Concentration off the West Coast of Vancouver Island following the Fukushima Reactor Accident", J. Environ. Radioact. 102 (2011) 1018.
9. C.Ross, R.Galea, P.Saull, W.Davidson, P.Brown, D.Brown, J.Harvey et al., "Using the 100-Mo Photoneutron Reaction to Meet Canada's Requirement for 99m-Tc",  Phys. Canada 66 (2010) 19.