CORRECTION FACTOR FOR DETECTOR (SN: 496) OPERATING AT LOW VOLTAGE ON ISLAND ALICE DOE/ERSP TECH NOTE NO.5.1 DATED: June 1978 AUTHOR: M. Barnes, DRI The voltage correction factor computed using the method outlined in Tech Note 5 was not correct for the data taken in the initial survey of Alice. This is because the magnitude of the inefficiency bias is very unstable near -2000 volts, so that small fluctuations in voltage can produce large changes in the bias. A eomparison of the IMP data from Alice, corrected by the 1.6 factor from Tech Note 5, with the soil data showed that the IMP values were still much too low. Accordingly, the island was resurveyed with the IMP, and additional soil samples were also taken. The TRU to americium ratio was the same for the new soil samples as for the original. The list below shows the 241Am readings at -2000 volts, and at -3000 volts at the eight locations which were surveyed both times. Figure B-5-2 is a plot of the data. The locations marked with (*) were not used in the analysis because they were severely disturbed by blasting between the first and second surveys. A simple mean was used to determine an additional correction factor. The mean of the six numbers was 1.72 with a standard deviation of 0.18. This factor was used to multiply the 241Am data from the low-voltage survey, which had already been corrected by the 1.6 factor, to obtain final adjusted values. Location *0-BL-0 *2-BL-) 4-N-2 8-BL-0 12-8-2 12-S+4 14-$-2 16-8-2 241 am at 241 Am at -2000 V*¥* -3000 V. -3000 V 0.8 3.5 9.0 10.1 16.3 7.8 13.6 19.8 Ratio -2000 V.** 3.1 3.0 17.3 18.0 23.8 14.4 24.4 30.4 3.88 0.86 1.92 1.78 1.46 1.85 1.79 1.54 **Correeted by factor of 1.6 computed in Tech Note 5. 1 30! S 3 = x | > 20- S & < = ~™ x xX eo ° < Xx x 10+ ‘x x 0 A 9 ey 0 10 20 , 214am AT -2000 V (pCi/g) + oH 30 FIGURE B-5-2. PLOT OF 74! am at -3000V vs - 2000 v ( CORRECTEDBY 1.6 FACTOR) DATA FROM ISLAND ALICE B-5-2