Abstract: A proportional-type detector for the detection of low levels of radioactivity, such as alpha and beta particles generated by radioactive materials. In the preferred embodiment, this detector has a pancake-shaped cavity with a disk-shaped base and a cylindrical wall, with at least one anode member traversing the cavity. This anode member is maintained at an elevated potential so as to multiply and collect electrons formed within a counting gas within the cavity as a result of interaction between the radioactivity and a counter gas cavity. A perforated grid member, in one embodiment being a spiral coil, is substantially concentric with the anode member to provided a uniform electric field around the anode member. In the preferred embodiment, spacing between turns of the spiral grid is equal to or less than twice the radial distance between the anode member and the inside diameter of the grid.

Abstract: A method and apparatus for correcting for the ballistic deficit effect that occurs when determining the spectra of radioactive substances with an ionizing radiation detector. Two pulses derived from each output pulse of the detector, each having different peaking times but both containing effects of the ballistic deficit, are compared to produce an error signal related to the difference of the peak heights of these two pulses. A part (or all) of the error signal is added to one of the pulses to produce a corrected amplitude pulse. In order to effectively compare the two pulses, each is separately stretched at its peak height. The corrected amplitude pulse is reformed for better handling by multichannel analyzer analog-to-digital converters, with a plurality of these reformed corrected amplitude pulses then being analyzed by the multichannel analyzer to achieve a nuclear spectra for which the ballistic deficit has been corrected.

Abstract: An intimate mixture of americium-241 and iodine-129 provides an energy spectrum that reliably simulates the spectrum of iodine-125 in a well-type detector. As such, it may be used as a long-lived standard to calibrate instruments such as well scintillation spectrometers in which measurements are to be made involving iodine-125.