Abstract: A radon detector employs an electrically charged pressed, porous metal filter that allows radon gas diffusion, while blocking ambient light, so that it readily traps both attached and unattached Po-214 and Po-218 ions, that may be present in gas passing through the filter, the filter being charged positively relative to an unbiased PN junction of a photodiode detector within a detection chamber. As a consequence, radon daughter products are prevented from corrupting the radon measurement. Since no voltage differential is applied across its PN junction, the photodiode detector operates in a photovoltaic mode, which avoids the problem of Schottky noise, producing low amplitude current pulses, which are amplified, passband filtered, and thresholded to provide well-defined pulses that are counted over a given measurement interval and converted to radon concentration in terms of picocuries per liter.

Abstract: A radon gas detector comprises a housing having an air inlet port leading to an interior, a radiation detection (e.g. alpha particle measurement) chamber and an air exhaust port leading from the interior chamber to the exterior of the housing. The chamber is closed to the entry of ambient light by a pair of light-obstructing baffles that respectively couple the air inlet and air exhaust ports to the interior chamber. Coupled with the air inlet port is a first removable, electrically conductive mesh filter. Coupled with the air exhaust port is a second, fixed electrically conductive mesh filter. Since each mesh filter is electrically conductive, it readily traps radon daughter products before they can enter into the interior chamber. Also, because of its mesh configuration, each filter readily permits substantial air flow. To measure radon concentration in the air being circulated through detector, a radiation (e.g.

Abstract: The Camera Setting Calculator for Underwater Color Photography is a manual, mechanical calculator to be used in determining the aperture setting (f-number) of a camera and consisting of two circular sheets of data pivoted to rotate over each other. Rotation of the top piece inputs the given data and displays the appropriate f-number.