What is Ionizing Radiation?
Ionizing radiation are particles that cause the electrons in matter to become excited in energy, resulting in the breaking of chemical bonds. Ionizing radiation can also interact with nuclei, which can result in its transmutation to other isotopes/elements. The general types of ionizing radiation include charged particles (electrons and heavy charged particles), energetic photons (X-rays and gamma-rays), and neutrons. Ionizing radiation comes from a variety of sources. They can be natural (e.g., potassium-40, carbon-14, uranium, and cosmic rays) or man-made (e.g., plutonium, iodine-127, and many others). Naturally occuring radiation is all around us and varies from location to location on the planet. Man-made sources of ionizing radiation are used in a variety of applications (i.e., medical, industrial, and security applications).
How Do We Detect Radiation?
Most commonly, there are three different types of radiation detectors; gaseous, scintillating, and semiconducting. Each have their advantages and disadvantages, and their attributes range from sensitivity to certain types of radiation, energy resolution, timing capability, spatial resolution, dynamic range, and radiation hardness. The specific attributes that a detection system requires is specific to the application, and great care in system design and implementation is required. A complete discussion of radiation instrumentation cannot be easily summarized on a single webpage, but several excellent references are available. One such reference specific to nuclear security and nonproliferation is the Passive Nondestructive Assay Manual - PANDA.
Why is Radiation Important?
Radiation detection is an integral and essential aspect of many fields of study. Whenever ionizing radiation is used, suitable detectors, electronics, and algorithms are required. The purpose and method of radiation detection and data processing is highly dependent on the field. In nuclear security, the source may be undeclared, and focus is given on its detection, identification, and/or characterization. In the field, rapid detection is important for economical concerns, and development of both detection systems and processing algorithms is ongoing. In physics, the measurement of ionizing radiation comes from a controlled system, used to further our understanding of the nature of matter. The radiation detection system and associated data processing is designed around the experiment. The likely best known application of radiation detection in nuclear physics is at the Large Hadron Collider. One of the experimental stations, the Compact Muon Soleniod (CMS), uses thousands of semiconductor and scintillator detectors to track secondary charged particles created from the collision of protons at an energy of 13 TeV in 25 nanosecond intervals.
A more common use of large detector arrays in the scientific community are those at neutron scattering facilities, such as the Spallation Neutron Source (SNS), where thousands of neutron detectors are used to study new materials, chemical processes, and biological samples. One excellent example is the use of the High Flux Isotope Reactor at Oak Ridge National Laboratory, just down the road from the University of Tennessee, where manufacturing challenges in the development of the pretzel M&M were overcome using neutron imaging. In addition to these applications, other common uses of radiation detection technologies include electron detectors in scanning electron microscopes (SEM), quantification of radiation fields for human safety (health physics), medical treatments and imaging (from dentistry to CT scans), nuclear nonproliferation (monitoring of radioactive materials to ensure that material is not lost or diverted to persons or organizations seeking to use it illicitly), and the measurement of radiation for industrial applications (e.g., weld checking and oil well logging).