Radiant energy – Invisible radiation responsive nonelectric signalling – Optical change type
Reexamination Certificate
1999-06-17
2001-05-15
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiation responsive nonelectric signalling
Optical change type
C250S473100, C250S484300, C250S484400
Reexamination Certificate
active
06232610
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a dosimeter and dosimeter system employed in an irradiation process, and more particularly to a dosimeter and related system which simplifies the handling and analyzing of dosimeters.
BACKGROUND OF THE INVENTION
Irradiation systems are used for irradiating articles, such as food stuffs, food utensils, medical devices, consumer goods, cosmetics, and waste products and their containers. The irradiation process employs high energy electromagnetic radiation, generated from radiation sources such as bremstralung x-ray beams, high energy electron beams, gamma rays, and microwaves, for the purpose of sterilizing such articles.
It is known to irradiate articles by utilizing a system that includes a radiation source and may include a conveyor for transporting the articles into and out of the radiation process field. Mounted on the article(s)or located in proximity to the article(s) being irradiated may be a number of dosimeters which are employed to measure the radiation doses or a dose related to the dose(s) which the article(s) has received from the radiation source.
The dosimeter may also comprise an individual piece of radiochromic film enclosed in an environmental container to protect the film from exposure to various environmental factors, such as ultraviolet radiation. Radiochromic films have the characteristic of changing color in a proportionate amount to the radiation absorbed. After the irradiation process is complete, the pieces of radiochromic film may be measured using a device which measures the change in transmissivity, absorption or reflectance of the film, which is indicative of the radiation dosage received.
SUMMARY OF THE INVENTION
The inventors have recognized that certain difficulties exist with handling and analyzing dosimeters employing radiochromic films. In particular, due to the small size of the pieces of radiochromic film employed, they may be difficult to handle. Also, exposure of the radiochromic film to foreign substances such as skin oil may adversely affect the performance of the film. Further, it is common for the radiochromic film pieces to be cut from larger sections of film. Because variations and aberrations may exist at different locations on these pieces, there may be differences in the performance of the individual dosimeters. These differences may include prior exposure of the sheets or individual dosimeters to radiation sources prior to the irradiation process, as well as differences in thicknesses of the film which relate to the rate of change of color of the dosimeter during exposure to radiation.
Described herein is a dosimeter and dosimeter analyzing system. The dosimeter may include a pre-cut piece of radiochromic film and at least one layer of supporting material to which the piece of radiochromic film may be affixed. The layer(s) may be constructed of materials such as paper with a known stiffness, or cardboard or non-woven spun synthetic fibers such as Tyvek™, a trademark of DuPont. Incorporated into one layer of the supporting layer may be an aperture through which the piece of radiochromic film may be viewable. The film may be attached to the first layer such that it adheres to the portions of the layer in proximity to the aperture. The combination of supporting material and film comprise a dosimeter card.
In one aspect of the invention, a second layer may be attached on the opposite side of the film from the first layer. This attachment is made such that the second layer is in contact with both the film and first layer. Based on the type of analysis performed, the second layer may or may not include an aperture.
The dosimeter card described above may be analyzed in a number of different modes with a variety of different instruments. According to one mode, The dosimeter card may be placed in a measuring instrument, such as a laser or scanner, and a light source may be employed to shine light on the film which is then reflected back to a sensing element. The sensing element may measure the intensity of the reflected light a/k/a the absorptive characteristics of the film. Based on this measurement, a radiation dosage for the device may be determined.
In another aspect of the invention, an additional aperture may be incorporated into the second layer of the dosimeter card. Because of the translucent nature of the film, when the dosimeter is placed in a measuring device such as a spectrophotometer, light may be transmitted through the film, and a sensing element on the opposite side of the dosimeter card from the light source may then measure the amount of light which passes through the film. Based on this measurement, the amount of radiation absorbed by the film may be determined.
In addition to the spectrophotometer, a number of other measuring devices may be employed to analyze the film. One instrument is a color or grayscale scanner of the type regularly employed with personal computers. A reflective scan may be performed of the radiochromic film in the dosimeter card, and once the color of the film has been identified, this may be compared against a value stored in a table in a computer memory. Another device which may be employed is a laser scanner. Laser light may be directed at the film and based on an analysis of the reflected light a radiation dosage for the film may be determined.
In yet another aspect of the invention, a unique marking may be included on the dosimeter card. The marking may act as identification for a data file which contains information about the piece of film in the dosimeter card. During the manufacture of the dosimeter cards, it may be advantageous to know in advance information about the radiochromic film. Such pieces of information may include the lot number for the roll, sheet or batch of film from which the piece was cut, the sheet number, and the portion of the sheet from which the piece of film was cut. This information may be relevant when used in conjunction with the analysis of the radiochromic film. For example, measurements of thickness may be taken for the sheets of film at various locations. Also, information may be acquired as to the exposure level of a sheet prior to the cutting out of dosimeter film pieces. At any point in the process, once the identification number for the dosimeter is known, this information may be accessed and used to generate a more accurate dosage reading.
In another aspect of the invention, the marking on the dosimeter card may be a scannable bar code. Prior to any analysis being performed of the dosimeter, the bar code can be scanned, and the scanned information may be used to access information about the dosimeter card. This stored information may be used during the analysis performed by the measuring instruments to provide a more accurate or more complete measure of the dose of radiation received by the film.
In yet another aspect of the invention, the material employed as the first and/or second layers in the dosimeter cards may be used as a calibration tool for the sensing devices. If the reflectance characteristics of the material are known, this may be used as a reference point during analysis of the dosimeter card. This may be especially advantageous in the situations where a scanner or laser device is employed.
The dosimeter system described herein may include a scanning device for directing light at the film in the dosimeter card, and either through a reflectance or transmissive analysis, measuring the amount of light absorbed by the film. The scanning device may be connected to a processing apparatus such as a personal computer which includes a central processing unit and a memory. The connection may be a direct electrical connection, or it may be established over a data network such as the Internet. The processing apparatus may include a processing module directed towards analyzing information gathered from the scanning device. Preloaded in the memory may be entries for each of the dosimeter cards employed during the irradiation process. Information stored in each entry may include specific data abo
Kruger Steve
Pageau Gary M.
Gex Corporation
Hannaher Constantine
Israel Andrew
Marsh & Fischmann & Breyfogle LLP
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