are being compared with radiochemical analysis of soil sample from these sites. Measurements were made at selected sites exhibiting unusually high cr low radioactivity levels in order to study the response of our instrumentaticn under such conditions as well as to compare with simultaneous measurements by other investigators using different types of instrumentation. The influence of beta radiation on various instruments was studied by comparing the dose rate inferred from our high pressure ionization chamber and spectrometer to the dose rates measured simultaneously with thin-walled plastic chambers. Measurements were also made at particular Sites where the natural and fallout gamma dose rates were of interest for related studies such as measurements in western Nebraska for correlation with neo-natal death rate and birth weight. In addition to these particular studies, a number of sites visited on past trips were resurveyed to determine the changes if any in the natural and fallout gamma dose rates. The complete dose rate results inferred for all measurement sites are tabulated. The consistency cf the various measurements was used to indicate the accuracy and precision of our techniques. The comparison of simultaneous data obtained from the new 4" x 4" Nai(T1l) detector and from the old 5" x 3" detector was used to verify the laboratory calibration of the 4" x 4" detector. Most of the studies undertaken on this survey trip are part of our continuing investigation of external radiation prebiems. More detailed investigations of the 6-ray ionization at various levels above the ground and the variation of natural y dose rates with time are discussed in Section IV of this report along with our plans for the future. Also discussed in Section IV is the present state of our continuing program of high pressure ionization chamber development. Our newest ionization chamber is described and the theoretical and experimental determination of its response to gamma rays and cosmic rays is discussed in detail. Although most of the studies described in this report are yet to be completed the discussions and data presented indicate the scope of our investigations as well as the value of gamma-spectrometric and ionization chamber techniques for studying the external radiation environment.