41 removed TABLE 17. — Sample number} fore the: and direction ras used, *_ 1ed, and . 1s samples j -y ashed | re, SN HCI. oh roheey cae 4.0 4.0 15.0 25.5 35.5 45.5 53.5 55.5 55.5 61.0 72.0 80.5 91.5 (101) 101 101 0.059 + 0.007 0.090 + 0.039 0.052 0.058 0.032 0.037 0.030 0.026 0.022 0.037 0.025 0.022 0.030 0.027 0.025 0.024 0.029 0.020 + + + + + + + + + + + + + + + + 0.006 0.006 0.004 0.004 0.004 0.004 0.008 0.005 0.004 0.008 0.004 0.003 0.003 0.004 0.003 0.008 Ratio 210P9/20Ph 1.53 + 0.69 0.027 0.030 0.030 0.0067 0.089 0.041 0.036 + + + + + + + 0.034 0.037 0.023 0.023 0.025 0.023 0.020 0.51 0.52 0.95 0.20 1.382 1.55 1.638 + + + + + + + 0.66 0.64 0.74 0.69 0.85 0.90 0.94 0.006 0.020 0.018 0.017 0.002 0.013 0.006 0.043 + + + + + + + + 0.022 0.020 0.022 0.020 0.020 0.021 0.021 0.021 0.25 0.94 0.60 0.63 0.11 0.52 0.21 2.10 + + + + + + + + 0.87 0.92 0.75 0.76 0.79 0.88 0.73 1.11 Mean 0.0154 + 0.0023 0.85 + 0.61 (8.D.) QO SOUTH hickory and 50% and upwards in the oaks. These large O NORTHEAST errors in the oak data were caused by the low activities in these trees and by the long (1 year) interval be- tween acquisition of the specimens and analysis. rT. 4& SOUTHEAST A ey QO wood are shown on semilogarithmic plots in Figures 34 ; to 37, The 2!°Pb concentrations in hickory (Figure 34) ; are constant in the 20 outer rings or even increase, 0028 presumably because the **°Pb circulates. After this 0041 time the concentration drops off with a 21-year half0023 Ft lite, as shown by the close correspondence of the data 0025 points with the line representing the half-life of the “Pb, That the concentrations are fairly constant within a ring can be seen from the agreement among 4 CENTER Q ° \ = 2l.4yrs 2 The results of the 71°Pb analyses versus age of the re 0.0116 + 0.0025 The fractional errors of the 7!°Pb data range from about 5 to 20% and of the *2°Po from 10 to 20% in the Although Students’ t-test shows the mean ratio of esenta111+ 0.34 (S.D.) in the 74°Po to 7!°Pb concentrations which in hickoryto be significantly greater than 1.00 (P < ily the 0.025), it is still very close to unity. For the white oaks these means of 1.18 + 0.70 and 0.85 + 0.61 for I and Il, respectively, beeause of greater experimental variations, are not significantly different than unity, indicatf ine that the 22°Po follows the *4°Pb in thetree. 0.02 Oo 20 040 60 80 ! 1990 | «120 AGE (YRS) Fic. 34.—Variation of *°Pb specific activity with age of wood in hickory. as do those of the hickory. The fit of the data for White Oak I is poorer, and for White Oak II poorer the cireles representing values within a ring (or set of rings) along one radius of the tree, and the squares and yet, as shown by the upper sets of data points in Figures 36 and 37. The tendencyto level off with age indicates either that 10 to 30% of the 74°Pb cireulates in hark, despite exposure to dust and weather, shows no higher concentration of 2?°Pb than does the adjacent 210Ph is continuously being produced by parent nu- triangles representing values along other radii. The Wood, The curves for the three oak trees are less spectacu- —-4 26Ra, pCi/g dry 0 og centra- 4.0 210Po, pCi/g dry oO n units in each ‘Ings in Te also ; deter- 1-7 1-7 13-17 22-29 33-28 43-48 52-55 53-58 53-58 59-63 70-74 79-82 90-93 100 99-103 99-103 *0Pb, pCi/g dry oO | i ' i : 1-7 Meanage, years oO 2 calcu- roactive ated by hod.) e about °Po the level of Ageof ring, years 9 a 1 onto a r which 2re then growin, ! “dl. The ; 1W N os 33 4s 5s Hs WwW N 7s Ss Os [G38 11S center Ww N 2°Pb, 2°Po anp #@Ra CONCENTRATIONS IN WHITE Oak II i 210Bb (pCi/gm DRY) sarefully iit and less uniform. The black oak data shown in l'izure 35 do not fit the 21-year half-life nearly as well these trees, that the early uptake of this nuclide was greater than the morerecent, or that a “background”of clides, **®Ra or 7°?Rn, present in the wood. Thus, if values of 0.010 and 0.015 pCi/g are substracted from each of the data points for White Oak I and White Oak II, respectively, the points fall more nearly with a