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Certain materials, when exposed to ionizing radiation, can be stimulated to emit a measurable signal that may be used to estimate the received radiation dose. Certain of these materials may be incorporated into a dosimeter that is worn or carried by an individual to measure the individual's exposure. A thermoluminescent dosimeter (TLD) is an example. To be effective in monitoring radiation exposure, the TLD must be worn or carried by the individual during periods of possible radiation exposure. For medical/industrial applications of ionizing radiation, dosimeters are used to assess the quality of the treatment or process.
Dosimetry systems and techniques exist that exploit radiation-induced signals emanating from biological materials. In some of these techniques, the signals may be measured in vivo. Examples of such techniques include electron paramagnetic resonance (EPR) dosimetry, which may be used to measure signals in teeth, fingernails, toenails, bone and hair. These techniques hold out the promise for screening (i.e., as part of a triage effort), at a point-of-care facility, large populations groups that may have been exposed to ionizing radiation.
The figure below is a block diagram of an alternate EPR dosimetry system. The EPR dosimetry system 700 includes dosimeter reader 710, which in turn includes power supply 711, EPR electronics 713, user interface 715, processor 717, and measurement unit 719. The measurement unit 719 may include a resonator (not shown) that contacts one or more teeth of patient 730. The measurement unit 719 includes a magnet coil section 718 which provides the required magnetic field to induce an EPR signal.
Also shown in this figure is a reference source 720, which is used to confirm proper operation of the system 710.
In operation, the EPR system 710 may be field deployed to perform triage operations following a large-scale radiation event. This figure illustrates one possible configuration of an EPR measurement unit 719. In this configuration the patient's head may be surrounded by, or merely adjacent a set of magnet coils that induce the magnetic field necessary to generate an EPR signal.
The reference source 720 is used to perform an initial check of the system 710 and may thereafter be used to periodically confirm proper operation of the system 710. The reference source 720 may have a form dictated by the system 710.
Prior to shipment to the operator of system 710, the reference source 720 may be irradiated. For example, a certified laboratory may irradiate the reference source 720 using a Co-60 source. After such irradiation, and prior to shipment, the reference source 720 may be tested in the laboratory to verify that it provides the desired EPR signal.

Patent Abstract: 

An electron paramagnetic resonance device includes a crystalline, emission-sensitive mass and a housing containing the device. The mass includes structurally incorporated carbonate content in a range of about 3% by weight to about 10% by weight of the mass, one or more structurally incorporated non-calcium metallic cations, and one or more structurally incorporated phosphate anions. When irradiated with a known source, the EPR device may function as a reference. When unirradiated, the EPR may function as a dosimeter. As a dosimeter, the EPR device may be used as a personal dosimeter or as a monitor for inanimate objects being subjected to radiation sources. The EPR dosimeter may be used for both gamma radiation and neutron radiation measurements.


EPR dosimetry is based on the following: (1) ionizing radiation generates unpaired electrons (e.g., free radicals) in proportion to the absorbed dose; (2) EPR dosimetry can selectively and sensitively detect and determine the number of unpaired electrons; and (3) the unpaired electrons can persist in some tissues, such as teeth and nails, with enough stability so as to be measured by EPR dosimetry weeks to years after radiation exposure.


Laurence Chow, Shozo Takagl, Marc Frederic Desrosiers

Patent Number: 
Technology Type(s): 
Ionizing Radiation, Manufacturing and Materials
Internal Laboratory Ref #: 
Patent Issue Date: 
January 8, 2020
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