238 LOWDER, BECK, AND CONDON factor.’ Note that this dose-rate estimate agrees closely with the pres- sure-chamber prediction in almost all cases. The column labeled “1” under the “Fallout gamma” heading gives the sums of the ®Zr—®*Nb, 106Rh, and *’Cs dose rates as estimated from the spectrum absorption peaks. The column labeled “2” gives the differences between the best value of the total gamma doSe rate and the sum of the natural-gamma dose-rate components. The agreement of these two fallout estimates over this wide range of natural, fallout, and cosmic dose-rate levels is typical of almost all our data. These results imply that the fallout emitters considered in our analyses do contribute the bulk of the fallout dose rate and also indicate the general validity of our component doserate estimates. The North Conway, N. H., measurements show that our estimates are reproducible within the limits imposed by actual time variations in the natural-gamma-radiation field due to such causes as natural fallout, soil-moisture changes, and ?”*Rn migration. Further evidence of the accuracy of our natural-component dose- rate estimates is provided in Figs. 3 and 4. Figure 3 shows mean soil concentrations of ‘°K obtained by spectrometric analysis of soil sam- ples carried out at several laboratories plotted against the HASL doserate estimates. The curve is the theoretical conversion from percent potassium to dose rate, assuming uniform soil distribution. The soil concentrations are given in terms of percent of potassium per gram of dry soil, whereas our dose-rate estimates are for in situ material. Thus, since most soils contain some moisture, the points should be expected to fall slightly above the line on the average, Furthermore, since only one or two soil samples were taken at each site, these de3 T —T T T ° oo ° — 2 x oO x ° Te oe e 2 °o 4 fe} °o 0 0 L 1 | | 2 3 | 4 — 5 pR/ HR Fig. 3——Potassium soil content determined by soil-sample analysis vs. HASL “K dose-rate estimate. , the theoretical conversion from bercent potassium to microroentgens per hour.