Effect of Air-scattered Beta Particles on Instrument and Dosimeter Response

Air-scattered beta particles are responsible for many of the inaccuracies encountered when readings are obtained with many types of beta survey instruments and personnel dosimeters. The ratio of beta particles scattered at various angles to beta's coming directly from the source increases as the distance from the source increases. This ratio, at a given distance from the source, is also a function of the beta energy, becoming larger for lower-energy beta sources. Changes in this ratio cause the response of beta instruments to have an apparent change in the directional response. These air-scattered beta particles are also responsible, in many cases, for a part of the apparent decrease in the efficiency of beta survey instruments when detecting low-energy beta sources. Air-scattered beta's also cause personnel dosimeters, which are not properly designed to detect them, to have responses that are low. We give experimental results to confirms the above effects. Design changes to survey instruments and dosimeters are suggested that would eliminate the errors created by the failure of the instruments to detect these air-scattered beta particles.