Open grid pulsed ion chamber operating in the linear ion collection region
First Claim
1. A device for detecting airborne alpha radiation in real time, said device includingan ion pulse collecting chamber comprising a probe, and an open grid surrounding said probe,electrometer means connected between the probe and said grid, said electrometer means having a power gain of approximately 109 or more, and including pulse shaping means, andcounter means for counting the number of pulses detected by said ion pulse collecting chamber.
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Accused Products
Abstract
A detector for airborne alpha radiation includes a ion pulse collecting chamber connected to a phase shifted, 100% negative feedback electrometer circuit. The ion pulse chamber includes a probe surrounded by an 80% open grid, with the spacing between the probe and the grid providing no greater than about 50 ms transit time before collection and having a capacitance of less than 1 pf. The field strength between the probe and the grid is less than 10 V/cm. The ion pulse chamber is contained within a vented cabinet. If it is desired to count only radon, a negative potential with respect to the grid may be applied to the cabinet to collect positively charged free ions. Alternatively, the cabinet wall can be made positive with respect to the grid to create a potential-well at or near the grid to provide an enhanced daughter detection mode. If the cabinet wall and the grid are the same potential, both radon and daughter alpha radiation are detected.
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Citations
12 Claims
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1. A device for detecting airborne alpha radiation in real time, said device including
an ion pulse collecting chamber comprising a probe, and an open grid surrounding said probe, electrometer means connected between the probe and said grid, said electrometer means having a power gain of approximately 109 or more, and including pulse shaping means, and counter means for counting the number of pulses detected by said ion pulse collecting chamber.
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9. A device for detecting airborne alpha radiation in real time, said device including
an ion pulse collecting chamber comprising a probe, and an open grid surrounding said probe, said grid being 80% open, the spacing between the probe and the grid providing no greater than a 50 msec transit time before collection, and having a capacitance of less than 1 pf, electrometer means connected between the probe and said grid, said electrometer means having nearly 100% negative feedback and a power gain of approximately 109 or more, and counter means connected to said electrometer means for counting the number of pulses detected by said ion pulse collecting chamber.
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10. A device for detecting airborne alpha radiation in real time, said device including
an ion pulse collecting chamber comprising a probe, and an open grid surrounding said probe, said grid being 80% open, the spacing between the probe and the grid providing no greater than a 50 msec transit time before collection of ions created within said chamber, and having a capacitance of less than 1 pf, electrometer means connected between the probe and said grid, said electrometer means including an FET having a low capacitance input and an output, feedback circuit means connected between the input and output of said FET for providing a negative feedback voltage to said input of nearly 100%, and phase shift circuit means in said feedback circuit means for delaying momentarily the application of said feedback voltage, thereby to allow the output of said FET to have a momentary power gain of sufficient magnitude and pulse width to drive an external counter circuit, and counter means connected to said electrometer means for counting the number of pulses detected by said ion pulse collecting chamber.
Specification