Devices detecting emitted gamma-rays

For years, doctors have used a variety of devices, such as X-ray imaging, to get a view inside a person s body. Nuclear reactions have enabled them to get a much more detailed view of the body. For example, doctors can take a close look at a person s heart by using a thallium stress test. The person is given an intravenous injection of thallium-201, which acts chemically like calcium and collects in the heart muscle. As the thallium-201 decays, low-energy gamma rays are emitted and are detected by a special camera that produces images, such as the one shown in Figure 19. 

Rutherford and his students used a screen coated with zinc sulfide to detect the arrival of alpha particles by the pinpoint scintillations of light they produce. That simple device has been developed into the modern scintillation counter. Instead of a ZnS screen, the modern scintillation counter uses a crystal of sodium iodide, in which a small fraction of the Na ions have been replaced by thallium (TH) ions. The crystal emits a pulse of light when it absorbs a beta particle or a gamma ray, and a photomultiplier tube detects and counts the light pulses. 

The transuranium elements have a number of commercial uses. Plutonium-238 emits only alpha radiation, which is easily stopped by shielding. The isotope has been used as a power source for space sateUites, navigation buoys, and heart pacemakers. Americium-241 is both an alpha-ray and a gamma-ray emitter. The gamma rays are used in devices that measure the thickness of matmals such as metal sheets. Americium-241 is also used in home smoke detectors, in which the alpha radiation ionizes the air in a chamb within the detector and renders it electrically conducting. Smoke reduces the conductivity of the air, and this reduced conductivity is detected by an alarm drcuiL... 

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