The comment on original condition is copied from Tech Note #1 which checks exact., with the operator's log sheet. The open area 241Am assay values may be averaged to give 43.2 pCi/g. Using the equations and open area data of Tech Note #1, BCF is 1.328. The following is an ordered list of BCF for all ten points: 5-5-3 1.328 6-8-2 1.275 5-N-1 1.241 6-N-1 1.172 5-8-2 1.170 T-N-1 1.132 6-8-1 1.117 4-8-3 1.082 7-S-1 1.080 4-N-1 1.053 The comparison of the nine-point and ten-point data mean and standard deviation (as percent of mean) is given below. TEN POINTS Mean 1.165 = 1.17 Standard Deviation ORIGINAL NINE POINTS 1.147 = 1.15 7.8% 6.5% There is no practical difference between the data with or without 5-S-3. Approach by Brush Weight Per Unit Area Because of the high interest in BCF, a direct measure of the amount of brush coverage was made. An experienced IMP operator selected two typical areas of maximum brush density encountered in field operations. Both were on Tilda. One was at approximately 10-S-1, the other at 6-S-1. For both sites an area 9x10 feet wide was stripped of brush, deadwood and vines, and the vegetation placed in plastic bags. An approximate square cut was used so that the total weight of vegetation vertically covering the area was gathered. The samples weighed 126 and 147 pounds each. The average areal density was 1.52 lb/ft? or 0.742 g/em2. A representative sample was dried and the water fraction found to be 0.55. Combining these data and the assumption that the brush was composed of cellulose (CgH905),, the attenuation coefficient at 60 keV was calculated at 0.148.* (This value is not much affected by composition except for large weight fractions of hydrogen. Even if the water content were grossly different, say 10%, the attenuation coefficient would be 0.144. If the material were pure carbon, the attenuation coefficient would be 0.131.) *Mass attenuation coefficient used is: H = 0.326, C = 0.176 and O = 0.191 em2/g (Radiological Health Handbook). B-1-10