Computer chips and other solid state devices rely on carefully controlled

Computer chips and other solid state devices rely on

This preview shows page 55 - 61 out of 64 pages.

Computer chips and other solid-state devices rely on carefully controlled distributions of electrons and holes in semiconductor materials. Production of ions by ionizing radiation can cause catastrophic failure of electronic devices. The single event effect results when a single ionizing particle can produce large numbers of ions. Electronics in satellites are packaged in “hardened” materials to protect against cosmic rays.
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56 Methods of Detecting Radiation To assess radiation doses, the type and amount of radiation must be measured. The first measurements used a zinc sulfide phosphor, which produced tiny flashes of light when struck by radiation and the light flashes were counted manually. A scintillation counter uses a fluorescent screen to detect radiation, but the resulting photon strikes a phosphor that releases an electron instead of light flashes. A photomultiplier tube amplifies the electronic signal, producing a current pulse registered electronically.
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57 Methods of Detecting Radiation In a Geiger-Mueller tube, radiation passes through a thin window into a gas-filled tube, producing ions in the gas. The resulting ions are attracted to oppositely charged electrodes, producing a pulse of electric current.
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58 Methods of Detecting Radiation A film-badge dosimeter monitors the radiation exposure for people who work with radioactive isotopes. Radiation darkens photographic plates. The darkened badge and a record of exposure provides a warning mechanism if safety levels are exceeded. All measurement methods must take background radiation into account when making measurements. Cosmic rays and natural radioactive isotopes in soil, air, and water are sources of background radiation. Background radiation must be subtracted from measurements of radioactive sources.
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59 Measuring Radiation Dose The interplay between ionizing power and penetrating power results in a number of different ways to express radiation dose. The quality factor , Q , is used to calculate the equivalent dose and is also known as the relative biological effectiveness ( RBE ). The value of Q varies from a value of one for high-energy photons to about 20 for alpha particles. Various scales of exposure and dose
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60 Modern Medical Imaging Methods Modern imaging methods include the use of radioisotopes to obtain images of specific organs and elaborate techniques such as positron emission tomography ( PET ). During an X-ray, X-ray radiation passes through the body and a photographic image is produced based on the amount of radiation absorbed. Bone absorbs X-rays more strongly than organs or other tissues, and is an excellent orthopedic diagnostic tool.
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