Radiation exposure indicator device

#This invention relates to a radiation exposure indicator and in particular to a device having one or more components capable of changing color in response to exposure to radiation.

#Radiation emitting technologies such as electrons in an electron beam sanitation systems and/or X-rays from security inspection systems can be used as mechanisms to counter terrorism. Examples of such applications are electron beam and gamma irradiation can be used to sterilize and protect against biological pathogens in transported packages. In addition, X-ray imaging technology permits a scan inside of transported materials to look for bombs, weapons and smuggled materials. While these technologies provide a deterrent for acts of terrorism, there is often no practical mechanism in place to verify whether individual packages have been exposed to these radiation-based technologies. Packages and luggage composed of typical materials (cardboard, paper and ink, plastics, metal) that are subjected to electron beam sterilization or x-ray inspection often do not demonstrate any obvious changes after exposure and it is difficult for a recipient or inspector to determine if a package was indeed exposed to the radiation-based security system. Conversely, there is potential for products that are sensitive to elevated levels of radiation (e.g. photographic films, electronics, seeds etc.) to be damaged unknowingly from radiation-based security systems.

#The use of dosimeters to determine a specific absorbed dose of ionizing radiation to persons or host to which it is attached is established. There are many types of dosimeters that can be affixed or mounted on a package, however such known dosimeters for indicating exposure to ionizing radiation systems have various limitations.

#The invention is directed towards the use of radiation sensitive glass compositions which provide a directly visually observable color change upon exposure to radiation, which glass compositions have been spun or similarly otherwise formed into glass fibers (glass wool). Various radiation sensitive glass compositions are known in the art which may be used in accordance with the present invention, such as those described in U.S. Pat. Nos. 2,770,922, 2,782,319, 3,899,679 and 4,494,003, as well as in 3,208,860, 4,001,019, 4,407,966, and 5,256,601, the disclosures of which are incorporated by reference herein. For the purposes of the invention, a “color change” is intended to cover visually observable changes in color densities as well as changes in color hues.

#In accordance with a particular embodiment of the invention, the radiation sensitive glass composition may comprise a manganese doped glass, such as described, e.g., in U.S. Pat. No. 4,494,003 referenced above. Upon exposure to radiation, such doped glass exhibits a directly observable color change from colorless (clear) to purple (dark) as the result of Mn+2 being oxidized by radiation events to Mn+3. Manganese concentrations of from about 1×10−9 to about 25 wt percent (i.e., in the parts per billion to parts per hundred range) will generally be effective for providing some level of color change for some level of radiation, and the actual color change upon exposure to radiation will be dependent on the concentration of manganese, the energy of the incoming radiation and the absorbed dose of the dosimeter. The broad range of manganese concentration applicable to glass fiber dosimeters of the invention enables the sensitivity to be adjusted for a greater variety of applications, and the concentration of manganese can be adjusted to indicate a specific threshold to provide a “yes/no” visual color change for a specific electron beam/ionizing radiation source and dose. Glass fibers doped with manganese at a concentration of from about 1×10−9 to 1×10−3 wt percent, for example may be particularly useful for monitoring exposure to electron beam systems, while concentrations of from about 0.5 to 25 wt percent may be particularly useful for monitoring exposure to X-ray Security Inspection systems.

#In accordance with a second particular embodiment of the invention, the radiation sensitive glass composition may comprise glass doped with parts per billion (ppb) through parts per hundred (pph) concentrations of silver halide, such as silver chloride, silver bromide, silver iodide, or mixtures thereof, such as described in the various photochromic glass patent references cited above, including, e.g., U.S. Pat. No. 3,208,860. A glass dosimeter containing silver chloride, e.g., will change from clear (colorless) to dark (blacken) when exposed to radiation from radiation-based security systems, as silver halide compositions are sensitive to various forms of radiation. The change of color in response to radiation in silver halide doped glass can be explained as chemical oxidation-reduction reactions. Glass comprising silicates are often transparent to visible light. Where silver halide (AgX) crystals are added during the manufacturing of the glass while it is in the molten state, the crystals become uniformly embedded in the glass as it solidifies. In a manner similar to how silver halide is developed into an image in photographic film, silver halide in the glass undergoes oxidation and reduction by interaction with photons/light as described below. 1