Radiant energy – Invisible radiant energy responsive electric signalling – With or including a luminophor
Reexamination Certificate
1999-06-02
2001-12-25
Ham, Seungsook (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
With or including a luminophor
C250S363010, C250S368000, C250S369000
Reexamination Certificate
active
06333502
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a radiation detector and a radiation measurement system, which utilize a scintillator. More specifically, the invention relates to a radiation detector and a radiation measurement system, which can be applied in a high-temperature environment or in a temperature changing environment.
2. Description of the Related Art
Conventionally, there is known a radiation detector utilizing a scintillator for emitting a scintillation light in response to an incoming radiation. Examples of such conventional radiation detectors are shown in
FIGS. 9 and 10
.
First, the radiation detector shown in
FIG. 9
comprises a scintillator
1
for emitting a scintillation light in response to an incoming radiation, a light guide (a main light guide)
4
optically connected to the scintillator
1
via an optical coupling material
3
, and a wavelength shift fiber
5
passing through the light guide
4
(see “Optical Waveguide Scintillator” disclosed in Japanese Patent Laid-Open No. 6-258446).
The light guide
4
is surrounded by reflecting surfaces for inwardly reflecting the incoming scintillation light, except for a plane of incidence (a plane connected by the optical coupling material
3
), on which the scintillation light emitted from the scintillator
1
is incident. The scintillation light entering the light guide
4
is stochastically incident on the wavelength shift fiber
5
by the function of the reflecting surfaces in a process where the light guide
4
is filled with the scintillation light.
The wavelength shift fiber
5
is designed to absorb the incoming scintillation light to re-emit light of a longer wavelength (fluorescent pulses) simultaneously from both end portions thereof.
The light emitted from both end portions of the wavelength shift fiber
5
are guided by light guiding fibers
6
A and
6
B to signal processing parts
7
A and
7
B, each of which comprises a photodetector and so forth, to be converted into electric pulses therein.
In such a radiation detector, electronic circuit parts, such as the signal processing parts
7
A and
7
B, can be arranged apart from the scintillator
1
.
The radiation detector shown in
FIG. 10
comprises a scintillator
1
, and a signal processing part
17
, which comprises a photodetector and so forth and which is directly connected to the scintillator
1
via an optical coupling material
3
. In this radiation detector, since a scintillation light emitted from the scintillator
1
is directly incident on the signal processing part
17
, the loss of the scintillation light is small, so that it is possible to obtain high radiation counting sensitivity.
In the case of the radiation detector shown in
FIG. 10
, the detector itself includes electronic circuit parts in the signal processing part
17
. On the other hand, the radiation detector shown in
FIG. 9
has the advantage of heat resistance since it is not required to provide any electronic circuits in the vicinity of the detector itself (the upper limit to the heat resisting temperatures of typical electronic circuits is about 50° C.).
In the radiation detectors described above, there is the following problem. That is, although there are some of scintillators
1
having a heat resisting temperature of about 200° C., the wavelength shift fiber
5
of component parts has only a heat resisting temperature of 70~80° C. since it is made of a plastic material, such as a polystyrene or a methacrylic resin. At present, there are no alternative parts having a higher heat resisting temperature, so that there is a problem in that conventional radiation detectors can not be used in an environment of a temperature exceeding 70~80° C.
In addition, when the radiation detector is provided in a temperature changing environment, it is difficult to hold the radiation measurement accuracy in accordance with such a temperature change. Particularly in the radiation detector shown in
FIG. 10
, the scintillator
1
is substantially integrated with the signal processing part
17
, and the difference in heat conduction in component parts and the difference in the influence of temperature are intricately intertwisted. Therefore, it is not easy to carry out a temperature correction in the measurement of radiation since it is required to provide temperature compensating circuit means for controlling a high voltage applied to the photodetector by means of a thermistor, or an optical pulser for drift monitoring.
SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to eliminate the aforementioned problems and to provide a radiation detector capable of detecting radiation in an environment of a higher temperature than the heat resisting temperature of a wavelength shift fiber, and a radiation measurement system capable of accurately measuring radiation in a temperature changing environment with a simple construction.
In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, a radiation detector comprises: a scintillator for emitting a scintillation light in response to an incoming radiation; a main light guide surrounded by a plane of incidence for allowing the scintillation light emitted from the scintillator to be incident thereon, and reflecting surfaces for inwardly reflecting the scintillation light entering the plane of incidence; a wavelength shift fiber passing through the main light guide, the wavelength shift fiber absorbing the scintillation light entering the main light guide to re-emit the absorbed scintillation light from both ends thereof; and an auxiliary light guide, provided between the scintillator and the plane of incidence of the main light guide, for guiding the scintillation light to the plane of incidence of the main light guide, wherein the scintillator and the auxiliary light guide are made of a material having a higher heat resisting temperature than that of the wavelength shift fiber.
According to this radiation detector, the scintillator can be exposed to an environment of a higher temperature than the heat resisting temperature of the wavelength shift fiber while the wavelength shift fiber is arranged in an environment of a temperature lower than or equal to the heat resisting temperature thereof. Therefore, it is possible to detect radiation in an environment of a higher temperature than the heat resisting temperature of the wavelength shift fiber without the need of any special cooling means.
The auxiliary light guide may comprise a liquid, through which the scintillation light is permeable, and a tube which is filled with the liquid and which is capable of inwardly total reflecting or specular reflecting the scintillation light. Thus, the scintillation light entering the auxiliary light guide from the scintillator is guided to the plane of incidence of the main light guide by the inwardly total reflecting or specular reflecting function in the tube of the auxiliary light guide.
Alternatively, the auxiliary light guide may comprise a tube capable of inwardly specular reflecting the scintillation light. Thus, the scintillation light entering the auxiliary light guide from the scintillator is guided to the plane of incidence of the main light guide by the inwardly specular reflecting function in the tube constituting the auxiliary light guide.
Moreover, the radiation detector may further comprise a light source for emitting a light of a particular wavelength, wherein one or both of the main light guide and the auxiliary light guide are made of a material capable of obtaining a photo-bleaching effect due to irradiation with the light of the particular wavelength, and the light emitted from the light source are able to be incident on one or both of the main light guide and the auxiliary light guide. Thus, the light having a particular wavelength emitted from the light source are incident on one or both of the main light guide and the auxiliary light guide, so that it is possible to suppress or restore the increase of li
Maekawa Tatsuyuki
Sumita Akio
Foley & Lardner
Ham Seungsook
Kabushiki Kaisha Toshiba
Lee Shun
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