Radiation instrumentation yields a signal when radiation interacts with a sensitive material. Radiation consists of energetic uncharged or charged particles generated from radioactive decay, manmade sources, or cosmic ray interactions in the atmosphere. The sensitive material may be solid, liquid, or gas. The signal is generated as the charge produced by the radiation interaction, either directly or indirectly, is collected. The sensors may also record location, time and/or energy of the radiation interaction.
Capabilities of radiation instrumentation systems
A sensor may be designed to detect radiation, which means that the signal from a radiation source is significantly higher than that of the background radiation and/or instrument noise. Some sensing systems are capable of localizing a radiation source. Furthermore, some radiation instruments are capable of imaging radiation sources. Additionally, some sensors are able to identify the type a particular radiation source. Moreover, some sensing systems are able to characterize, or determine more detailed characteristics, of a source and/or the environment surrounding the source.
Radiation instrumentation is used in a host of applications, ranging from big science to industry. Considering big science, radiation instruments were the enabler of the recent effort at CERN to discover the Higgs Boson– the particle thought to give mass to matter. In this case, the radiation instruments were very large and complex. Additionally, radiation instruments are used on space stations, to sense emissions from distant galaxies, to explore particular planets (e.g., Mars rover), or to sense radiation dose in space for our protection. Radiation instruments used at neutron science centers enable a host of new materials discovery and development. Radiation instruments are also used in medical imaging systems. For example, the instruments used in Position Emission Tomography systems enable doctors to determine whether or not cancer has spread throughout the body. In radiation therapy, radiation instruments are used to verify that that radiation dose is appropriately delivered to patients so that the cancer is killed and normal tissues are spared. Radiation instruments are also used in security at airports and border crossings to look for contraband. Furthermore, they are used in nuclear facilities and for nuclear weapon treaty verification purposes. Radiation instruments find a place in all areas of nuclear and plasma science and engineering. In nuclear reactors, radiation instruments are used to monitor reactor power. In nuclear fusion research, radiation instruments are used to help understand how well the reaction is being sustained. Radiation instruments are also used for a host of industrial processes, including drilling for oil, as well as steel and cast iron manufacturing.
UTK’s Rad IDEAS group
Our group mainly designs instrumentation for sensing of uncharged particles, including gamma rays and neutrons— both slow and fast. We have also designed detectors for alpha sensing and cosmic ray muon sensing.
Many of our projects are concerned with the neutron and gamma emissions that emanate from special nuclear materials, including uranium and plutonium. These particles are emitted as a result of spontaneous nuclear decay, the result of fission chain reactions, and/or due to stimulation from energetic neutron or photon sources. The intensity of these radiations decreases as one over the distance between the source and the sensor squared. Thus, the source radiation intensity is often comparable to that of the radiation background when the detector is located at a standoff distance some tens of meters away from the source. Furthermore, shielding decreases radiation intensity in an exponential manner as thickness of the material increases.
Concerning detector types, our focus is on solid radiation scintillators, or materials that light up when radiation strikes them, especially those used in radiation imaging systems. We also do some work with semiconductor and gaseous detectors. Many of the detector systems that we work with are position-sensitive, meaning that the interaction location of the radiation interaction is measured.
Our group is involved with pioneering work all the way from new radiation detection materials discovery to the design of new methods and algorithms used to interpret the data generated by proof-of-concept systems.
Our main application space is nuclear non-proliferation technology, or technology aimed at stopping the spread of nuclear weapons and nuclear materials, but our interest in the science itself continues to push us into new application areas.
Radiation instrument functions, capabilities and performance
When radiation interacts in an instrument, those interactions are recorded in some form. Some minimum set of recorded events is necessary to make any decision using the instrument, e.g., confirm that a radiation source is detected. Sometimes the radiation instrument simply counts radiation. In other cases, a particular property of the radiation, e.g., its energy, is binned. The resulting histogram is called a spectrum, e.g., an energy spectrum. An instrument that examines any particular radiation property is said to be spectroscopic, or to perform spectroscopy. Thus, two functions of radiation instruments are radiation counting and radiation spectroscopy.
The performance of a radiation instrument is measured according to its intended capabilities, which may include one or more of the following: detect, localize, image, identify, characterize. One property which is often important is detector efficiency. Larger sensors tend to be more efficient, meaning that the source radiation is more likely to interact in the detector. Certain material properties can also increase efficiency. For example, denser materials are more efficient for detecting gamma rays compared with lighter materials. The opposite tends to be true for fast neutrons.
A second performance property that may be of interest, depending upon the intended capability of a radiation instrument, is called resolution. Resolution is the ability to resolve a particular property of the interacting radiation, which could include its energy (energy resolution), interaction location in the instrument (position or spatial resolution), time of interaction in the instrument (timing resolution), or the related angle from which the source radiation originated (angular resolution). For example, in a high energy resolution instrument, two distinct, closely spaced energies are more readily resolved than in a moderate or low energy resolution instrument.
Imaging radiation may be performed in a variety of ways. An image formed by measuring some fraction of radiation, e.g., x-rays, that pass through an imaged object is called transmission radiography. A more detailed image of the object may be reconstructed if there is more than one view of the object taken from one than one angle of observation. A common example of this is x-ray computed tomography, also called a CT scan. If one desires to image a source of radiation rather than an object, the source itself can be imaged through recording some fraction of it that passes through a pinhole collimator onto a position-sensitive radiation detector. As the source moves, the projection of the source onto the detector moves as well. A common example of this is single-photon emission computed tomography, or SPECT. Although we are mainly familiar with imaging x-rays, gamma rays or neutron radiations may be imaged via very similar means.