http://www.researchonline.mq.edu.au/vital/access/services/Feed ${session.getAttribute("locale")} 5 http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:22439 For the commissioning process of the OPAL nuclear reactor of the Australian Nuclear Science and Technology Organization (ANSTO), the thermal neutron flux is measured through the activity measurement of an activated Au wire, Au-Al (0.112% of Au) alloy wire and Au foil. The absolute activities of ¹⁹⁸Au in the form of Au wire, Al-Au wire and Au foil were determined using the conventional 4πβ - γ coincidence-counting method. Monte Carlo simulation technique was employed to simulate the complicated absorption and attenuation processes of electrons and gamma photon interactions with the surrounding materials. The Monte Carlo calculated probabilities of escape beta particles, internal conversion electrons and photon-interaction generated photoelectrons and Compton electrons were used to determine the correction term of the coincidence equation. The corrections for the Au wire (length: 8.000 mm, radius: 0.064 mm), Al-Au wire (length: 7.690 mm, radius: 0.255 mm) and Au foil (thickness: 0.025 mm, radius: 3.000 mm) were found to be 5.2%±0.1%, 2.6%±0.1% and 4.2%±0.2% respectively. The study demonstrates that the Monte Carlo calculation for the correction term of the coincidence equation can be applied to the absolute activity determination of radionuclides with well-defined source geometries with an uncertainty of better than 1%. 2012-10-30T18:45:00.815Z ]]> http://www.researchonline.mq.edu.au/vital/access/manager/Repository/mq:6516 In this paper we formulate a new approach to medical image reconstruction from projections in emission tomography. This approach conceptually differs from the traditional methods such as filtered backprojection, maximum likelihood or maximum penalized likelihood. Similar to the Richardson-Lucy algorithm ([1], [2]), our method develops directly from the Bayes formula with the final result being an iterative algorithm, for which the maximum likelihood expectation-maximization of [3] (or [4]) is a special case. Although there are different ways to enforce smoothness in the reconstructions using this method, in this paper we opt to focus only on the way which smoothes the camera bin measurements before reconstruction. In fact, this method can be explicated as maximizing a special penalized log-likelihood function. Its theoretical properties are also analyzed in the paper. 2010-01-27T22:16:52.127Z ]]>