JPH102966A - Measuring apparatus for distribution of radiation intensity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a measuring apparatus by which the attenuation of light in a scintillation fiber and a fluorescent fiber is suppressed and whose sensitivity is enhanced by a method wherein a plurality of scintillators are connected respectively in parallel with an optical fiber, for transmission, whose transmission loss is small. SOLUTION: A plurality of scintillators 1 are connected respectively in parallel with an optical transmission fiber 2 whose transmission loss is small, and the attenuation of radiation detection light is suppressed. Then, a scintillation position is decided on the basis of the arrival time difference of scintillation light between both ends of the fiber 2, and the distribution of a radiation is found on the basis of a light- emitting frequency in every position. At this time, a signal on one side out of both ends of the fiber 2 is delayed by a delay circuit 7, a signal, on the other side, which is not delayed is used as a starting signal, and the signal which is delayed is used as a stop signal. By using the starting signal and the stop signal, the arrival time difference is fetched as an amplitude signal by a time-to-pulse height converter 8. A time difference signal is converted by an A/D converter 9 so as to be integrated by an analyzer 10, and a dose rate in every measuring position is computed by a computing device 11 so as to be displayed on a display device 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation intensity distribution measuring device, and more particularly, to a radiation intensity distribution measuring device for measuring radiation intensity distribution by optically transmitting radiation detection light using an optical fiber.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open Nos. 5-249247 and 6-258446 disclose examples of a radiation distribution measuring device for measuring a radiation distribution by transmitting scintillation light through an optical fiber. The former is a configuration in which a scintillation fiber and a transmission optical fiber are connected in series, and the latter is a configuration in which a plurality of scintillators are connected in series along the transmission optical fiber, and a fluorescent fiber is used in a portion where scintillation light is incident. belongs to. In both methods, the scintillation position is determined from the difference in arrival time of scintillation light at both ends of a fiber in which scintillators are connected in series, and the radiation intensity distribution is determined from the light emission frequency at each position.

[0003]

In the conventional system, all the radiation detecting units are connected in series. FIG. 2 shows an example of the configuration of a conventional radiation distribution measuring device. Light detection is performed at both ends of an optical fiber in which a radiation detector is connected in series, and a time-to-amplitude converter (hereinafter, referred to as T) is used.
(Abbreviation of AC) is used to analyze the difference in arrival time of scintillation light. The scintillation position was determined from the difference in the scintillation light arrival time at both ends of the fiber, and the radiation intensity distribution was determined from the emission frequency at each position.

[0004] In the conventional method, the radiation detection light passes through a scintillation fiber or a fluorescent fiber from the light emission position to the end of the fiber, and reaches the photoelectric conversion element. The scintillation fiber and the fluorescent fiber have larger transmission loss than the transmission optical fiber. Therefore,
Since the radiation detection signal is attenuated, the detection sensitivity is reduced.
There was a defect that the / N ratio deteriorated.

An object of the present invention is to measure a radiation distribution by transmitting scintillation light through an optical fiber, and to suppress the attenuation of light in the scintillation fiber and the fluorescent fiber, thereby providing a more sensitive radiation intensity distribution measuring apparatus. It is an object of the present invention to provide a device capable of constructing.

[0006]

Means for Solving the Problems A first invention of the present invention is:
By connecting a plurality of scintillators in parallel with an optical transmission fiber having a small transmission loss of radiation detection light, attenuation of radiation detection light is suppressed, and a scintillation position is determined from a difference in arrival time of scintillation light at both ends of the fiber. The radiation intensity distribution is obtained from the light emission frequency at the time.

According to a second aspect of the present invention, when a scintillator is connected in parallel to an optical transmission fiber having a small transmission loss,
A radiation intensity distribution measuring device characterized in that the light intensity distribution measuring device is connected so that the light passes through the optical path from the connection part to the connection part in all possible paths.

The scintillation fiber emits scintillation light having a wavelength specific to the scintillator isotropically by interaction with the irradiated radiation. Of the scintillation light, light having a solid angle within the critical angle of the fiber reaches the end of the scintillation fiber. The scintillation fiber is connected at both ends to an optical transmission fiber, and a transmission optical fiber is connected in parallel with the scintillation fiber. At this time, the connection is made so that light is not transmitted from the transmission optical fiber connected in parallel to the scintillation fiber and vice versa.

[0009] Scintillation fiber light is connected in parallel to the optical transmission fiber for each site where the radiation intensity is measured. The scintillation light is transmitted toward both ends of the optical fiber. Another scintillation fiber is connected between both ends. The scintillation light branches and transmits through the scintillation fiber and the transmission optical fiber connected in parallel with the scintillation fiber according to the optical connection characteristics, and merges again. Since the transmission loss of the optical transmission fiber is smaller than that of the scintillation fiber, the transmission loss of light is suppressed as compared with the case where there is no transmission optical fiber connected in parallel. For this reason, the radiation detection light can reach the photoelectric conversion elements at both ends with a larger number of photons, and the signal can be easily separated from noise. Further, it is easier to make the optical fiber longer. At this time, if the optical path lengths of the respective paths are equal, the pulses of the scintillation light are transmitted without being spread, and are thus more effective.

Since the radiation detection light is transmitted through the fiber to the photoelectric conversion elements at both ends of the fiber, the arrival time at the photoelectric conversion element is proportional to the optical path length from the light emitting position to the photoelectric conversion element. Assuming that the total length of the optical fiber is L, the distance from one end of the fiber to the light emission position is X, and the speed of light in the optical fiber is Cc, the time from the arrival time of the radiation detection light to the end at the starting point of X to the other end The arrival time difference T obtained by subtracting the arrival time of the radiation detection light is T = (2X−L) / Cc.
This arrival time difference is converted into a voltage using a TAC, and the distribution of the voltage is measured with a multi-channel analyzer, whereby the intensity distribution of the radiation can be measured.

As described above, the radiation intensity distribution can be measured by connecting a plurality of scintillators in parallel with a fiber having a small transmission loss and measuring the arrival time difference of the radiation detection light to both ends of the optical fiber.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described with reference to embodiments. FIG. 1 shows an example of a radiation intensity distribution meter to which the present invention is applied. In this example, a case where a scintillation fiber is used as the radiation detection unit will be described.

The same number of scintillation fibers 1 as the number of measurement points are connected to a transmission optical fiber 2 using an optical distributor.

FIG. 3 shows an example of the structure of an optical distributor used in the present invention. Optical fibers 17, 18, 19
Is connected, the light incident on the optical fiber 17 from the right side reaches the left end of the optical fiber 18 and the left end of the optical fiber 19. Light incident from the left end of the optical fiber 18 reaches the right end of the optical fiber 17 but does not reach the left end of the optical fiber 19. The light incident from the left end of the optical fiber 19 reaches the right end of the optical fiber 17,
8 does not reach the left end.

Optical fibers are connected using the optical distributor shown in FIG. 3 so that light from the scintillation fiber 1 is not transmitted to the transmission optical fiber 2 in a portion connected in parallel with the optical fiber. The connection portion and the scintillation fiber 1 are shielded from light so that external light does not enter the device from the connection portion of the optical fiber 2 and the scintillation fiber 1.

When radiation enters the scintillation fiber 1, scintillation light is emitted. The scintillation light is transmitted through the transmission optical fiber 2 and reaches both ends of the transmission optical fiber 2. Optical fiber for transmission 2
The scintillation light is measured by the optoelectronic conversion elements 4 at both ends. The photoelectric conversion element 4 outputs a current proportional to the intensity of the incident light, but since the current is weak, the preamplifier 5 and the amplifier 6 amplify the signal. One signal at both ends is delayed by the delay circuit 7, and the other signal not delayed is used as a start signal, and the delayed signal is used as a stop time. Using the start and stop signals, the time-to-peak converter (TA)
C) At 8 the arrival time difference is extracted as an amplitude signal. The analog / digital converter 9 converts the time difference signal into a digital signal, and the multi-channel analyzer 10 integrates the signals for a certain period of time. Then, the arithmetic unit 11 calculates the dose rate at each measurement position, and the display unit 12 To be displayed.

In the conventional radiation intensity distribution measuring device, the scintillator is connected in series, so that the light transmission loss is large. However, according to the present invention, a highly sensitive radiation intensity distribution measuring device which suppresses the light transmission loss is provided. Can be configured.

FIG. 4 shows a modification in which a plurality of scintillators are optically coupled via a fluorescent fiber having a core to which a wavelength shifter is added when optically coupled. Since the diameter of the scintillation fiber is small, the radiation detection sensitivity is low.
In particular, when measuring a low dose rate part, a long scintillation fiber is used to increase the volume of the scintillator, so that light transmission loss increases. In this embodiment, since the scintillator is connected to the transmission optical fiber via the fluorescent fiber, the shape of the scintillator can be changed in any manner. Therefore, there is an advantage that the measured dose rate range can be freely adjusted by changing the shape of the scintillator.

[0019]

According to the present invention, a scintillator is connected in parallel with a fiber having a small transmission loss in a radiation intensity distribution measuring apparatus for measuring radiation intensity distribution by optically transmitting radiation detection light using an optical fiber. Accordingly, it is possible to configure a radiation intensity distribution measuring device that suppresses light transmission loss, is highly sensitive, and can easily make the optical fiber longer. Therefore, the radiation intensity distribution measurement can be made more sensitive and longer distance.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram of a conventional radiation intensity distribution measuring device.

FIG. 3 is an explanatory diagram of the operation of the optical distributor.

FIG. 4 is a block diagram of another embodiment of the present invention.

[Explanation of symbols]

1. Scintillation fiber, 2. Optical transmission fiber,
3 ... branched optical transmission fiber, 4 ... photoelectron conversion element, 5
... preamplifier, 6 ... amplifier, 7 ... delay circuit, 8 ... time wave height converter, 9 ... analog / digital converter, 10 ... multi-channel analyzer, 11 ... arithmetic unit, 12 ... display device.

Claims (3)

[Claims] An apparatus for optically coupling a plurality of scintillators to an optical fiber and detecting light at both ends of the optical fiber, wherein each of the scintillators is connected in parallel with a transmission optical fiber having a small light transmission loss. Characteristic radiation intensity distribution measuring device. 2. An apparatus for connecting a plurality of scintillators in parallel with an optical fiber and detecting light at both ends of the optical fiber, wherein the two optical paths connected in parallel have the same optical path length. 1. A radiation intensity distribution measuring device. 3. The radiation intensity distribution measuring apparatus according to claim 1, wherein the scintillation light is wavelength-converted and then transmitted optically.