- Development of Personnel Dosimeters
- Radon Gas
- Environmental Radiation Measurements
- Internal Radiation Dose Assessment
Development of Personnel Dosimeters
Radiation dosimeters are issued to workers in any environment in which occupational exposure to radiation is likely. Dosimeters typically consist of film, thermoluminescent dosimeters (TLD), or optically stimulated luminescent (OSL) materials. All of these materials integrate or store a signal representing total radiation dose received over their deployment time. They are analyzed following completion of the measurement period in the laboratory using a variety of methods. Dosimeters are often specifically designed and calibrated for special characteristics of the particular workplace and types of radiation expected to be encountered. Often, dosimeters are employed in the environments themselves, including the outdoor surroundings, in order to monitor external radiation (such as sky-shine or radiation delivered when an accelerator is turned on) or radionuclides traveling through the environment.
Equipment in the laboratory includes a planchet and hot-gas capable laboratory TLD reader capable of reading chips, cards, and powders, material, a selection of TLD materials, and phantoms for performing uniform calibration irradiations.
Research of interest to member of the Radiological Health Engineering Laboratory includes:
- Timed Dosimetry: The development of thermoluminescent detectors (TLD) and optically stimulated luminescent (OSL) dosimeters capable of determining the temporal characteristics of radiation exposures during the radiation integrating period. These projects would allow for very inexpensive field deployment of non-electronic dosimeters to perform measurements as a function of time.
- Ultra-sensitive Bulk Dosimetry: The development of large sheets of TLD and OSL dosimeters for a variety of applications in which spatial information or high radiation sensitivity is needed
- Dosimetry Measurements: Provision of precise dose measurements to medical, dental, physics, or environmental researchers using TLD or OSL systems. Adjustments are made to protocols to ideally suit the given application for optimum results.
Uranium is found in relative abundance throughout the earth’s crust. The most common uranium isotope, U-238, decays through a series of other radionuclides to Rn-222. Because radon is a gas, Rn-222 may then move through the environment and concentrate in locations of lower pressure, such as in homes. The decay products of radon pose a health-hazard, namely the increased probability of lung cancer.
The laboratory has the capability of making measurement of both Rn 222 and its radioactive progeny. Available equipment in the laboratory includes a shielded cave and NaI detectors for measurements of Rn 222 absorbed in charcoal, working-level meters, electrets, and other devices and measurement systems.
Individuals in the laboratory have had interests in comparative measurements, localization of geographical hot-spots of radon gas, variations of radon gas concentrations under different circumstances, and the mitigation of unusual radon gas containing structures.
Environmental Radiation Measurements
Radiation found in the environment includes naturally-occurring radionuclides (remaining from the Earth’s creation), cosmogenic radiation, the products of nuclear weapons testing, and other human-produced forms of radiation. Measurements of small amounts of radionuclides in the environment, in which radionuclides are identified and distinguished from normal background, are desirable under a variety of circumstances. Environmental radiation measurements are needed for verification of the regulatory compliance of operating nuclear facilities, decontamination or decommissioning activities, evaluation of nuclear terrorist events, and the study of radionuclide migration such as may occur near waste disposal or contaminated facilities.
The laboratory has the capability of identifying and quantifying tiny amounts of radionuclides in samples of soil, water, and air (filters) collected from the environment. In addition, radionuclide quantification is possible at the location of the radionuclides or in large objects brought into the laboratory using in situ gamma ray spectroscopy.
Available equipment includes an alpha spectroscopy system (Ametek Octete-Plus), several high purity germanium (HPGe) spectroscopic detectors, large NaI detectors, ethernet-ready high-performance multi-channel buffer (Ametek 919E), an electrical cooling system for attaining LN2 temperatures (Ametek X-cooler), a portable 16k channel analyzer (Ametek DigiDart), and various Nuclear Instrument Modules (NIMs). Two graded, low-background shields are available for low level counting and spectroscopy. A selection of phantoms and radionuclide standards are available for calibrating equipment.
Research of interest to laboratory members includes:
- In Situ Gamma-Ray Spectroscopic Tomography: Special collimators are employed with in situ gamma-ray spectroscopic analysis equipment to grant it positional capability. Algorithms similar to those used in medical tomography are then used to unfold depth information. Design of the collimators and algorithms may be varied to enable depth-sensitive measurements for a variety of radionuclides for different applications, particularly those in decommissioning and decontamination, and for response to radiation terrorist events.
- Applied Environmental Measurements: Interest exists in improving the accuracy and precision in the identification and quantitation of alpha, beta, x-ray and gamma-ray emitting radionuclides. Protocols and methods may be adapted to support specific research studies of background and human-produced radiation.
Internal Radiation Dose Assessment
Radionuclides enter the bodies of individual as a result of nuclear medicine diagnostic scans, radiotherapeutic administration, routine nuclear workplace activities, or other non-planned incidents. The estimation of doses to individuals due to these internally deposited radionuclides is particularly complex. In nuclear medicine and radiotherapy, the amount of radionuclide given to the patient is known, as is often the distribution throughout the patients’ bodies as function of time. For other circumstances, the actual amount of radionuclide entering the person’s body is unknown, and must be inferred through a series of bioassays (e.g. external photon measurements or urinalysis). Radiation dose is assessed based upon this information combined with information about radiation absorption by the body.
Individuals associated with the laboratory have performed significant prior work in the area of internal radiation dose assessment. This work has included both medical and occupational radionuclide intakes. Current interests in the laboratory include dose assessment for transuranics in nuclear power environments, implementation of the new ICRP 66 models, verification of alpha dose estimations, and evaluation of mixed inhalation and ingestion doses.