John K Dempsey

US Patent:

7312439, Dec 25, 2007

Filed:

Aug 17, 2004

Appl. No.:

10/919526

Inventors:

Payasada Kotrappa - Frederick MD, US
Lorin R. Stieff - Kensington MD, US
John C. Dempsey - Frederick MD, US

Assignee:

Rad Elec Inc. - Frederick MD

International Classification:

G01V 5/00

US Classification:

250255, 250DIG 2

Abstract:

A new type of radon progeny monitor called an electret radon progeny integrating sampling unit (E-RPISU) using an electret ion chamber to measure radon progeny concentration. A conventional 1 LPM particulate air sampling system is used to collect the radon progeny on a roughly 3. 5 cmfilter that is mounted on a side of an electret ion chamber such that the collected progeny are exposed to the inside of the chamber. Alpha radiation emitted by the progeny collected on the filter ionizes the air in the approximately 220 ml chamber. Ions of opposite polarity collect on the surface of the electret of suitable thickness and reduce its surface voltage. A specially built surface voltmeter is used to measure the electret voltage before and after sampling. The electret voltage drop that occurs during the sampling period is proportional to the time integrated progeny concentration. A similar unit with a screen in the place of filter is used to measure unattached progeny concentration.

US Patent:

51045540, Apr 14, 1992

Filed:

Dec 14, 1990

Appl. No.:

7/627760

Inventors:

John C. Dempsey - Frederick MD

Assignee:

Aqua-Rid, Inc. - Southampton PA

International Classification:

C02F 174

US Classification:

210747

Abstract:

Substantially the last traces of radon are removed from typical well water at subterranean temperatures prior to significant pressurization of the water by displacement of the radon by a stream of compressed air, such radon mixing with the air vented from the system. Other objectionable gases in well water are removed concurrently with radon.

US Patent:

51265672, Jun 30, 1992

Filed:

Mar 19, 1991

Appl. No.:

7/670781

Inventors:

John C. Dempsey - Frederick MD
Lorin R. Stieff - Kensington MD

Assignee:

Rad Elec, Inc. - Frederick MD

International Classification:

G01T 114

US Classification:

2503361

Abstract:

A small enclosed ion chamber with an electrostatically charged electret attached to the inner chamber wall. Filtered holes in the chamber permits radon in the ambient air in the chamber to enter or exit by diffusion. Positive or negative ions (depending on the polarity of the electret charge) formed in the chamber air by the passing of gamma radiation or X-rays move to and collect on the electret surface by virtue of its electrostatic attraction to ions of opposite polarity. These ions neutralize the ions of opposite polarity on the electret and cause a measurable reduction in its surface voltage which reduction is proportional to the dose of gamma and/or X-ray incidence on the chamber. The reduction of the electret surface voltage is used to calculate the dose of gamma or X-ray radiation incident upon the chamber during a known exposure period. In one embodiment, a sealed radioactive-gas-tight flexible-wall container, such as a bag, surrounds the chamber to prevent any ambient radon from entering the ion chamber.

US Patent:

50085409, Apr 16, 1991

Filed:

Jul 31, 1989

Appl. No.:

7/387497

Inventors:

John C. Dempsey - Frederick MD

Assignee:

Rad Elec Inc. - Frederick MD

International Classification:

G01T 114

US Classification:

2503361

Abstract:

A small enclosed ion chamber with an electrostatically charged electret attached to the inner chamber wall. Positive or negative ions (depending on the polarity of the electret charge) formed in the chamber air by the passing of gamma radiation or X-rays move to and collect on the electret surface by virtue of its electrostatic attraction to ions of opposite polarity. These ions neutralize the ions of opposite polarity on the electret and cause a measurable reduction in its surface voltage which reduction is proportional to the dose of gamma and/or X-ray incidence on the chamber. The reduction of the electret surface voltage is used to calculate the dose of gamma or X-ray radiation incident upon the chamber during a known exposure period. In the preferred embodiment, filtered holes in the chamber permit radon to diffuse out of the ion chamber. A sealed outer container containing an absorbent such as activated charcoal surrounds the inner ion chamber to remove any radon captured within the container and to prevent any ambient radon from entering the ion chamber.