The gamma-ray spectrum obtained after activation of a sample of silicon having “unusual” electrical properties. While most of the spectrum is identical with that obtained from the ordinary material, there is an interesting difference. Using the equation given on page 12, the approximate known values for half-life, sample weight, neutron flux, and periods of irradiation and decay after irradiation, and an estimated value for the number of arsenic-76 atoms measured by the gamma-ray spectrometer, you calculate that the arsenic content of the sample is approximately 44 parts per million (ppm). (See appendix.) With this information as a starting point, you are now ready to proceed with further research on the properties of your semiconductor, e.g., if you double the concentration of arsenic, how will that affect its properties? In a Hospital _The Problem_ You are a physician treating a patient who, because of a severe calcium deficiency, has been suffering from osteoporosis (a softening of the bones). You think you are on the right track with your treatment, but you would like to be sure in order to know whether you should continue the treatment or try something else. You would have your answer if you knew that the calcium content of his skeleton had stopped decreasing. How can you determine the amount of calcium in a living human being? _The Solution_ You know that the usual techniques for determining calcium in the bones are not very useful. They are either too inaccurate to show that your patient’s calcium loss has been stopped or can only be used to measure the calcium content of the bones in his extremities. The latter is not satisfactory because these few bones may not be representative of the rest of his skeleton. Recently, however, there have been reports of neutron activation analysis of whole persons, in which the calcium content of their bones has been measured with unusually good reliability. This has been accomplished by scientists and doctors working at the University of Washington School of Medicine in Seattle.