Radon gas measurement apparatus having alpha particle-detecting photovoltaic photodiode surrounded by porous pressed metal daughter filter electrically charged as PO-218 ion accelerator
First Claim
1. A device for detecting the presence of radon in a monitored gas comprising:
- an electrically conductive filter enclosure comprised of an electrically conductive material that is physically configured to allow radon-containing gas to pass therethrough, while preventing the entry of light and radon daughter products into an interior portion of said electrically conductive filter enclosure;
an alpha particle detector element supported within said interior portion of said electrically conductive filter enclosure, said alpha particle detector being operative to generate electrical signals in response to the incidence thereon of alpha particles emitted from daughter products into which said radon-containing gas that has entered into said interior portion of said electrically conductive filter enclosure has decayed;
a signal processing circuit coupled to process said electrical signals generated by said alpha particle detector element and to produce an output signal representative of the presence of radon gas; and
wherein said electrically conductive filter enclosure is positively charged, establishing an electric field between said electrically conductive filter enclosure and said alpha particle detector element, thereby causing radon daughter products present within said electrically conductive filter enclosure to be directed upon said alpha particle detector element.
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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.
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Citations
27 Claims
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1. A device for detecting the presence of radon in a monitored gas comprising:
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an electrically conductive filter enclosure comprised of an electrically conductive material that is physically configured to allow radon-containing gas to pass therethrough, while preventing the entry of light and radon daughter products into an interior portion of said electrically conductive filter enclosure; an alpha particle detector element supported within said interior portion of said electrically conductive filter enclosure, said alpha particle detector being operative to generate electrical signals in response to the incidence thereon of alpha particles emitted from daughter products into which said radon-containing gas that has entered into said interior portion of said electrically conductive filter enclosure has decayed; a signal processing circuit coupled to process said electrical signals generated by said alpha particle detector element and to produce an output signal representative of the presence of radon gas; and wherein said electrically conductive filter enclosure is positively charged, establishing an electric field between said electrically conductive filter enclosure and said alpha particle detector element, thereby causing radon daughter products present within said electrically conductive filter enclosure to be directed upon said alpha particle detector element. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A device for detecting radon gas comprising:
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a filter enclosure physically configured to allow radon gas to pass therethrough while preventing the entry of light and attached and unattached radon daughter products into an interior portion of said filter enclosure; an alpha particle detector element supported within said interior portion of said filter enclosure, said alpha particle detector comprising a PN junction diode across anode and cathode electrodes of which no differential voltage is applied, so that said PN junction diode operates in a photovoltaic mode, producing electrical signals in response to impingement of alpha particles thereon; and a signal processing circuit coupled to receive said electrical signals generated by said PN junction diode and producing an output signal representative of the presence of radon gas in accordance with said electrical signals. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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Specification