We are constantly exposed to ionizing radiation in both the natural and the modern technological environment. This section describes the sources of ionizing radiation used in the research and teaching environment.
Radiochemicals
The evolution of medical research and patient care over the last fifty years was made possible in large part by the use of radioactive atoms to label molecules. This technology provides a simple method by which a chemical compound can be marked, observed, and measured as it is processed by a simple cell culture or a human being. There are applications throughout the life, physical, and engineering sciences.
The quantity of a naturally occurring analyte can be measured with isotope dilution analysis. Similar technologies permit the study of, for example, solubility constants of slightly soluble salts. Environmental samples can be analyzed using radiometric titration or by measuring naturally occurring radiotracers.
Sealed Sources
Many devices use sealed radioactive sources because they provide a convenient, inexpensive source of ionizing radiation. Sealed radioactive sources are often made by encapsulating the salt or metal of a radionuclide in a welded metal container whose size typically ranges from smaller than a pencil lead to the size of a golf ball. The encapsulation ensures that there will be no radioactive contamination of the laboratory. Alpha “sealed” sources have an open window construction with the source material bonded to the surface of a silver foil mounted in the recess of the plastic disc. Sealed source applications range from low activity alpha sources that are used in home smoke detectors through high activity, self‐shielded irradiators that permit the study of dose effects.
X‐ray Machines
Any electronic device that has fast‐moving electrons is a potential source of ionizing radiation. One is the diagnostic x‐ray machine. First used in 1896, it permitted non‐invasive imaging of internal human structures. Today, in the US alone, diagnostic radiology accounts for two‐thirds of our dose from man‐made sources.
X‐ray Diffraction and X‐ray Fluorescence
Because their wavelength is comparable to the lattice separation in crystals, x‐ray diffraction units can be used to study the arrangement of atoms in crystals. X‐ray fluorescence permits the chemical analysis of a sample because each element has a unique fluorescent spectrum whose intensity is proportional to that element’s concentration in the sample. Both techniques require narrow, intense x‐ray beams.
High energy X‐ray machines and particle accelerators
High energy x‐ray machines, operating in the 4 MV to 25 MV energy range, are used to treat many illnesses, and very‐high‐energy particle accelerators are used by physicists to understand the internal structure of the elementary particles.
Electron Microscopes
Although they are electronic devices, electron microscopes do not normally present a radiation hazard due to their engineering design and operating parameters. Microscopists who use uranyl acetate (UA) when examining biological specimens should observe hazardous chemical precautions. Any lab worker that actively handles the bulk vial to prepare stock UA solutions must be licensed under a Controlled Radiation Authorization (CRA) because of the toxic and radiological hazards posed by UA inhalation. This does not include workers using only the dilute UA solution to prepare samples or slides. Working with the dilute solution itself does not require staff to be on a CRA or to receive radiological training. Health Physics should be contacted for guidance regarding CRA review and disposal.
Cabinet X‐ray machines
Cabinet x‐ray machines are enclosed, self‐shielded, interlocked irradiation chambers. The machine can only operate when the chamber door is securely closed. The exposure rates at every location on the exterior meets the rate specified for uncontrolled areas.
