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FULLER'S EARTH · ATTAPULGITE CLAY · ACTIVATED BAUXITE
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ANALYTICAL CHEMISTRY
REPORT greatly simplified the collection of samples of the range of rock types to be studied. Experimental
Procedure
The detector was positioned above the sample and a count of the background radiation, mainly due to n a t u r a l radioactivity, was performed. The spectrum observed was obtained using a 400 channel pulse height analyzer. A background count was also t a k e n using a single channel analyzer calibrated to store counts resulting from gamma rays with energies greater t h a n 4.5 MeV. This energy range included the 6.13 and 7.12 MeV peaks of 1 0 N produced by fast neutron activation of l e O . The system was then rotated to place the generator in position above the sample, and a 5-minute irradiation was carried out. When the irradiation was complete, the system was turned around and after a delay time of 20 seconds, a 15-second count was t a k e n on the single channel analyzer. Owing to excessive analyzer " d e a d " time immediately after irradiation, the counts using the 400 channel analyzer were delayed until the analyzer " d e a d " time had decreased to approximately 3 0 % . Counts for 1 minute periods were then t a k e n in succession to measure the decay of 2.3 minute half life 28 A1, derived from 28 Si. T h e counting period was then increased to two minutes, at 5 minute intervals, during the remaining lifetime of the 9.5 minute half life 2 7 Mg, derived from 27 A1. Counts of 5 minutes duration were then continued at ten to fifteen minute intervals for an additional one hour. Results of Rock Analysis
Figure 2 shows typical spectra obtained with the " t u r n a r o u n d " system from an irradiated block of gabbro, a t waiting times of ten minutes and forty-six minutes after the end of irradiation. T h e presence of the shorter lived isotopes, 28A1 and 27 Mg, which produce full energy peaks a t 1.78 and 1.01 MeV are clearly seen in Spectrum 1, whereas the full energy peaks a t 1.37 and 0.84 MeV, from the longer lived isotopes 2 4 Na and 5(i Mn, are visible in Spectrum 2 after the shorter lived products have decayed. Spectra
