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.

Abstract: A detector for airborne alpha radiation includes an 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.