I. INTRODUCTION Page For the past several years the Health and Safety Laboratory has been conducting a detailed investigation of the properties of the external radiation environment. Previous reports have described the development of field gamma spectrometric technigues utilizing high pressure ionization chambers and a 5" x 3" NaI(Tl} detector." These technigues allow reasonably precise and accurate estimates to be made of total open field gamma dose rates from each of the important individual components of the natural and fallout gamma radiation field. The results of eae tae 35 tee ee . 36 cee es 37 a number of field studies utilizing these technigues have we ewes 38 also been reported. * ROUND The development of these techniques has made possible more detailed investigations of various aspects of the external radiation environment such as the variation of natural dose rates with time, geographical differences in wee ee 44 /hr) 963 - fallout distribution, cosmic ray ionization variation with Le eae 45 altitude, and B-ray ionization effects. In attempting to investigate these problems we have found it necessary to improve our instrumentation by acquiring new more sensitive NaI(Tl) ivity cee eee 47 sin at anaes ytes...46 One ayeerr 2 LANE Po Lcate -ermine »pe yands detectors with much better resolution and stability than the 5" x 3" detector which our initial system utilized. Section II of this report describes these new detectors and discusses the laboratory calibration and calculations undertaken to allow total and component dose rates to be inferred from their response. This improved instrumentation was used to study the external radiation field in more detail under a wide range of geographical conditions and radiation levels during an extended survey trip undertaken in August and September of 1965. Section III of this report describes the many different investigations carried out during the course of this trip. Using our spectrometric techniques in conjunction with high pressure ionization chamber readings over both land and on lakes at various altitudes, we were able to infer the variation of cosmic ray ionization intensity with altitude. Our spectrometric techniques were extended to the determination of 13’cs concentrations in soil at a number of sites throughout the United States. ee ee These data