Energy Counts Channel Number 0.445 MeV 230 130 0.657 MeV 1200 190 0.687 MeV 170 200 0.715 MeV 220 220 0.760 MeV 230 225 0.820 MeV 60 250 0.884 MeV 500 260 0.937 MeV 190 280 (Values are estimated from graph) The spectrum obtained from the same streak of metal after re-exposure to neutrons for 100 hours and a delay of approximately 2 months before counting. Activation products from gold and copper have decayed away and the gamma-ray spectrum of silver-110m is now observed. In this case the sample is closer to the detector than for the earlier measurement and the measurement takes 100 minutes. Two months later, the scientist repeats the procedure of counting the samples and standards, except that this time the plastic capsules are closer to the detector, each count is for 100 minutes, and the sample changer operates for about a week. A typical spectrum looks like that in the figure on page 39. The scientist can now compute ratios for the three elements in each sample and compare them with the standard, but he decides that a computer could do it faster and with fewer errors. The data collected during the two series of counts are therefore sent to a data processing center where, in a matter of minutes, a computer does the following for each of 50 samples: 1. Finds the 0.411-MeV gamma-ray peak for gold-198. 2. Determines the total counts in the peak. 3. Repeats the process for the corresponding wire standard. 4. Corrects the total count for the wire for the small amount of radioactive decay that occurred in the few minutes between the sample count and the standard count. 5. Computes the ratio: [total count for sample/total count for standard (corrected)] 6. Repeats all the above for the 0.511-MeV gamma ray for copper-64 and (in the longer counts) for the 0.658-MeV gamma ray for silver-110. 7. Computes the ratios: [sample to standard (for copper)/sample to standard (for gold)] and [sample to standard (for silver)/sample to standard (for gold)]. 8. Tabulates and prints the ratios found in Step 7. [Illustration: Graph: Number of coins at indicated ratios vs. Copper/gold ratio]