Radiant energy – Invisible radiant energy responsive electric signalling
Reexamination Certificate
2001-08-24
2003-09-23
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
C250S363020
Reexamination Certificate
active
06624415
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for measuring radioactivity, radioactivity concentration and radioactivity surface density. More particularly, the present invention relates to a radioactivity measuring method for measuring radioactivity by obtaining a conversion factor without using an actual calibration radiation source and a measuring apparatus for carrying out this method and a measuring method and a measuring apparatus for measuring radioactivity concentration and a method and an apparatus for measuring radioactivity surface density based on the radioactivity measured by the former method and apparatus.
DESCRIPTION OF THE RELATED ART
In order to obtain the radioactivity concentration or the radioactivity surface density of a measurement subject such as demolition wastes and the like of nuclear facilities, the radioactivity of the measurement subject must be first obtained. In a conventional radioactivity measurement method, a conversion factor for calculating the radioactivity from a counting rate obtained from a count of a radioactivity detector is acquired by comparison with a conversion factor obtained by separately preparing a calibration radiation source whose radioactivity is already known and actually performing measurement.
Further, although the radioactivity of the surface of the measurement subject must be first measured in order to measure the radioactivity surface density of the measurement subject, it is general to use a &bgr; ray having the weaker penetrability than that of a &ggr; ray in order to measure the radioactivity of the surface. That is, when the &ggr; ray having the stronger penetrability than that of the ⊖ ray is a target of measurement, it is difficult to determine whether the measured &ggr; ray is emitted from the surface of the measurement subject or emitted from the inside, and hence the &ggr; ray is inappropriate for measurement of the radioactivity of the surface of the measurement subject. Therefore, the radioactivity of the surface of the measurement subject with the &bgr; ray as a measurement target is measured by using a portable type radioactivity detector called a survey meter specified in JIS (Japanese Industrial Standards) Z 4329 “Portable radioactive surface contamination meter” or an article carrying out monitor specified in JIS Z 4337 “Installed articles surface contamination monitoring assemblies for beta emitters”.
However, in the method for measuring the surface radioactivity for obtaining the radioactivity surface density mentioned above, since the surface radioactivity is measured by measuring the &bgr; ray by using the survey meter, the survey meter can not be inserted into a narrow tube when the measurement subject is, for example, a metal narrow tube. Accordingly, measurement of the radioactivity of the inner peripheral surface of the narrow tube is difficult.
Furthermore, in the radioactivity measurement method with the &ggr; ray having the stronger penetrability than that of the &bgr; ray being a target of measurement, a conversion factor for calculating the radioactivity is obtained by comparison with the conversion factor acquired by performing actual measurement by using a calibration radiation source. Therefore, in order to accurately obtain the radioactivity of the measurement subject, an optimum calibration radiation source must be produced in accordance with a shape or a dimension of the measurement subject, and this method is not appropriate for the radioactivity measurement of the measurement subjects having different shapes or dimensions. For example, in case of measuring the radioactivity of demolition wastes and the like of nuclear facilities, it is difficult to produce each optimum calibration radiation source for each waste in nature because wastes having various shapes and dimensions are mixed. Thus, this method is hardly applied to the radioactivity measurement of the demolition wastes generated in volume.
It is an object of the present invention to provide a method and an apparatus for measuring the radioactivity, a method and an apparatus for measuring the radioactivity concentration, and a method and an apparatus for measuring the radioactivity surface density, which do not require an actual calibration radiation source, respectively. Further, it is another object of the present invention to provide a method and an apparatus for measuring the radioactivity surface density capable of obtaining the radioactivity surface density by utilizing a &ggr; ray having the stronger penetrability than that of a &bgr; ray.
SUMMARY OF THE INVENTION
To achieve this aim, according to the present invention, there is provided a method for measuring the radioactivity comprising: a virtual modeling step for arranging virtual three-dimensional models of a measurement subject and a radiation detector in a virtual three-dimensional space with the same positional relationship as an actual geometric positional relationship; a conversion factor setting step for associating the number of times of gene ration of a virtual radiation ray emitted from the virtual three-dimensional model of the measurement subject with the number of times of incidence of the virtual radiation ray upon the virtual three-dimensional model of the radiation detector and obtaining a conversion factor; an actual counting rate calculating step for calculating a counting rate by actually counting the number of times of incidence of the radiation rays emitted from the measurement subject upon the radiation detector; and a radioactivity calculating step for calculating the radioactivity of the measurement subject from the counting rate and the conversion factor.
Here, the interaction of the radiation ray and a substance is generated with a given probability, and the conversion factor can be obtained by recreating this phenomenon in the pseudo-manner even if actual measurement using the actual calibration radiation source is not used. That is, the conversion factor can be obtained by virtually recreating the three-dimensional shapes and position relationship of the measurement subject and the radiation detector and associating the number of times of generation of the virtual radiation ray emitted from the virtual three-dimensional model of the measurement subject with the number of times of incidence of the virtual radiation ray upon the virtual three-dimensional model of the radiation detector based on the recreation. Further, the actual radioactivity of the measurement subject can be calculated by the obtained conversion factor and the count by the actual radiation detector.
In case of this radioactivity measurement method, it is preferable that the conversion factor setting step includes: a virtual count calculating step for randomly generating a virtual radiation ray from the virtual three-dimensional model of the measurement subject by utilizing the Monte Carlo calculational technique, and for counting the number of times of incidence of the virtual radiation ray upon the virtual three-dimensional model of the radiation detector to obtain a virtual count; and a conversion factor calculating step for obtaining a conversion factor from the number of times of generation of the virtual radiation ray and the virtual count.
By utilizing the Monte Carlo calculational technique, the three-dimensional shapes and positional relationship of the measurement subject and the radiation detector can be virtually recreated, and it is possible to simulate how the virtual radiation ray randomly generated from the virtual three-dimensional model of the measurement subject enters on the virtual three-dimensional model of the radiation detector.
In this case, since a generation rate of the virtual radiation ray from the virtual three-dimensional model of the measurement subject corresponds to the radioactivity of that virtual three-dimensional model, the conversion factor can be obtained from the number of times of generation of the virtual radiation ray and the count in the virtual three-dimensional model of the radiatio
Hattori Takatoshi
Ichiji Takeshi
Central Research Institute of Electric Power Industry
Hannaher Constantine
Moran Timothy J.
Notaro & Michalos P.C.
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