1. A portable device with an image capturing capability, comprising: a semiconductor image sensor comprising a plurality of pixels; a visible light obstructer for blocking visible light from impinging on the semiconductor image sensor when in place; and processing circuitry configured for: causing the semiconductor image sensor to be exposed to high-energy photons during a period of interest and while the visible light obstructer is in place; repeatedly sampling the semiconductor image sensor during the period of interest to generate a plurality of images; determining a common noise in the plurality of images, wherein the common noise is determined from noise in two or more images of the plurality of images; generating a composite image comprising a combination of the two or more images of the plurality of images with the common noise removed so the composite image includes image information corresponding to one or more radiated pixels of the plurality of pixels that absorbed at least some energy from one or more of the high-energy photons; processing the composite image to determine pixel groups, each pixel group comprising two or more adjacent radiated pixels; for each pixel group, identifying lines of radiated pixels between two radiated pixels in that pixel group; determining a line ratio as a number of pixel groups with one or more lines relative to a total number of pixel groups; and determining a type of nuclide that generated the high-energy photons responsive to the line ratio.