JPH11326526A - Radiation measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate inside noises occurred in a measuring chamber in a device for measuring a radiation from a radioactive example mixed with a liquid scintillator. SOLUTION: A detection part 10 is provided with sample detectors 26, 28, cosmic rays detectors 20, 22, 24, and inside background detectors 30, 32. Cosmic rays and a detection pulse corresponding to an inside background out of the detection pulses detected by the sample detectors are eliminated, thereby performing a radiation detection with high precision. A light shielding film 34 is provided between the sample detector and the inside background detector.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radiation measuring apparatus, and more particularly, to an apparatus for mixing a radioactive sample with a liquid scintillator and detecting the light emission of the sample by a photomultiplier tube.

[0002]

2. Description of the Related Art An apparatus for measuring a radioactive sample is known as a radiation measuring apparatus. In such an apparatus, a liquid scintillator is mixed with a radioactive sample in a vial,
Light emitted by the liquid scintillator upon receiving radiation is detected by a photomultiplier tube. In order to achieve high-precision measurement by removing the background as much as possible, a coincidence circuit, a detector for removing cosmic rays, and the like are used.

[0003]

However, the background also occurs in other than cosmic rays. For example, when radiation from a radioactive sample directly irradiates the glass surfaces of two opposing photomultiplier tubes or cosmic rays, luminescence occurs there, but this is detected by the photomultiplier tube. Further, although the glass and the electrodes of the photomultiplier contain, for example, a small amount of ⁴⁰ K, the radiation emitted therefrom may be similarly detected as the background. Further, there is a possibility that radiation from a radioactive substance floating in the measurement chamber may be detected. In such a background, cosmic rays can be excluded because they are detected by a dedicated background detector,
Background caused by the inside of the measurement chamber cannot be completely excluded. In particular, when simultaneous counting is performed by a pair of photomultiplier tubes, the background can be reduced, but those that simultaneously enter both photomultiplier tubes are detected as signals.
This is sometimes called crosstalk.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to effectively eliminate noise, particularly crosstalk, generated in a measurement room in real time.

[0005]

In order to achieve the above-mentioned object, the present invention provides a sample detecting apparatus which is provided near a radioactive sample in a measuring chamber for accommodating the radioactive sample and detects radiation from the radioactive sample. A first background detector provided around the measurement chamber for detecting cosmic rays, and a second background detector provided in the measurement room for detecting internal noise generated in the measurement chamber. A background detector, a light-shielding body that shields light between at least the radioactive sample and the second background detector, and the sample based on a detection result of the first and second background detectors. And a signal processing circuit for removing a background from a detection result of the detector.

Further, the present invention provides a plurality of sample detectors provided near a radioactive sample in a measurement chamber for accommodating the radioactive sample, the detectors detecting radiation from the radioactive sample, and a plurality of sample detectors. A first coincidence circuit for outputting a first coincidence pulse when the detection pulses are simultaneously inputted, and a first background detector provided around the measurement chamber for detecting cosmic rays And a plurality of second background detectors provided in the measurement chamber for detecting internal noise generated in the measurement chamber, and detection pulses from the plurality of second background detectors are simultaneously input. A second coincidence circuit that outputs a second coincidence pulse in the case of a light-shielding member that shields light between at least the radioactive sample and the plurality of second background detectors. Out of the first coincidence counting pulses, excluding those input simultaneously with the second coincidence counting pulse or the detection pulse of the first background detector, and removing the pulse from which the background has been removed. And an inverse coincidence circuit for outputting.

According to the above configuration, cosmic rays are detected by the first background detector, and internal noise in the measurement room is detected by the second background detector.
Then, both background components are removed from the signal from the sample detector. Therefore, there is an advantage that radiation can be detected with high accuracy by reducing internal noise such as crosstalk.

[0008] Preferably, the plurality of second background detectors are provided in substantially the same arrangement as the arrangement of the plurality of sample detectors. According to this configuration, it is possible to measure the internal noise under substantially the same conditions as the sample detector, and to specify the internal noise component detected by the sample detector.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a preferred embodiment of the radiation measuring apparatus according to the present invention, and FIG. 1 is an explanatory view showing the entire configuration.

The radiation measuring apparatus of this embodiment is roughly divided into a detecting section 10 and a signal processing section 12. First, the detection unit 10 will be described.

The detection unit 10 has a sample detector, a cosmic ray detector, and an internal background detector. A vial 16 containing a radioactive sample 18 is arranged in the measurement chamber 14. Here, a liquid scintillator is mixed into the vial 16 together with the radioactive sample 18. The liquid scintillator emits light due to the radiation generated in the radioactive sample. The emitted light is emitted from the photomultiplier tube 2 that constitutes the sample detector.
Detected at 6,28. In the present embodiment, the sample detector is constituted by the two photomultiplier tubes 26 and 28, but may be constituted by three or more photomultiplier tubes. The photomultiplier tubes 26 and 28 are provided near and on both sides of the vial 16.

The measuring chamber 14 is surrounded by a cosmic ray detector. The cosmic ray detector is specifically composed of a solid scintillator 20 having a box shape or a hemispherical shape, and photomultiplier tubes 22 and 24 for detecting light emission generated in the solid scintillator 20. is there. Of course, the light emission generated in the solid scintillator 20 may be detected by three or more photomultiplier tubes. When the cosmic ray 100 reaches the solid scintillator 20, light emission occurs there, which is detected by one of the photomultiplier tubes 22, 24.

Although the above-described configuration has been adopted in the conventional apparatus, in the present embodiment, an internal background detector is particularly provided. The internal background detector includes a pair of photomultiplier tubes 30 and 32 in the present embodiment. Of course, three or more photomultiplier tubes may be used. In this embodiment, the photomultiplier tubes in the internal background detector are arranged in the same arrangement pattern as the arrangement pattern of the photomultiplier tubes in the sample detector. Therefore,
The arrangement of the photomultiplier tubes in the sample detector and the arrangement of the photomultiplier tubes in the internal background detector are parallel, and each detector can detect radiation under the same conditions. However, a light-shielding film 34 is provided between the sample detector and the internal background detector, and the light-shielding film 34 prevents light generated at each detector from reaching the counterpart detector. Have been.

Therefore, since the internal background detector is provided, for example, if light emission occurs in the glass of the photomultiplier, such internal noise is detected in the sample detector, but the same as that of the internal noise detector. Under such a condition, such an internal noise is also detected by the internal background detector, so that such an internal background can be effectively removed as described later.

In the configuration example shown in FIG. 1, the light-shielding film 34 is provided only between the sample detector and the internal background detector. However, the light-shielding film 34 is provided so as to individually surround any of the detectors. It may be provided.

Although the cosmic ray detector has a box shape or a hemispherical shape in the present embodiment, it is needless to say that the cosmic ray detector can be constructed so as to cover the entire measurement room.

In the coincidence circuit 36, respective output pulses from two photomultiplier tubes 26 and 28 constituting the sample detector are inputted, and when these output pulses are inputted simultaneously, a coincidence pulse is outputted. ing. On the other hand, also in the coincidence circuit 38, output pulses from two photomultiplier tubes 30 and 32 constituting an internal background detector are input, and when those output pulses are input simultaneously, the coincidence counting is performed. The circuit 38 outputs a simultaneous pulse.

In the reverse coincidence circuit 40, the coincidence circuit 3
6, the coincidence counting circuit 38
Those that are input at the same timing as the input timing of the simultaneous pulse output from are excluded. That is, the pulse corresponding to the internal background has been removed.

The detection pulses output from the two photomultiplier tubes 22 and 24 constituting the cosmic ray detector are output from an OR circuit 42.
Alternatively, it is detected by the coincidence circuit and input to the inverse coincidence circuit 44. The inverse coincidence circuit 44 excludes, from among the pulses output from the inverse coincidence circuit 40, pulses input simultaneously with the pulse output from the OR circuit 42. As a result, detection pulses corresponding to cosmic rays are eliminated.

Accordingly, a pulse from which both of the detection pulses corresponding to the cosmic rays as the internal background and the external background have been removed is output from the inverse coincidence circuit 44. Calculation of radiation dose and the like is performed based on the appropriate pulse. The calculation result is displayed on the display 48.

According to the above embodiment, since internal noises other than cosmic rays, especially crosstalk, can be eliminated, there is an advantage that radiation measurement with high accuracy can be performed. For example, the internal background occupies as much as 30% of the background, and such noise components can be removed to measure the true radiation from the radioactive sample.

[0023]

As described above, according to the present invention,
Noise generated in the measurement room, particularly crosstalk, can be effectively eliminated in real time. Therefore, there is an advantage that highly accurate radiation measurement can be performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a radiation measuring apparatus according to the present invention.

[Explanation of symbols]

10 detection unit, 12 signal processing unit, 14 measurement room, 16
Vials, 18 radioactive samples, 20, 22, 24 cosmic ray detectors (first background detector), 26,
28 sample detector, 30, 32 internal background detector (second background detector), 34 light shielding film, 36, 38 coincidence circuit, 40, 44 reverse coincidence circuit.

Claims (3)

[Claims] 1. A sample detector provided near a radioactive sample in a measurement chamber for containing a radioactive sample for detecting radiation from the radioactive sample, and provided around the measurement chamber to detect cosmic rays. A first background detector, a second background detector provided in the measurement chamber, for detecting internal noise generated in the measurement chamber, at least the radioactive sample and the second background A light-shielding body that blocks light between the ground detector and a signal processing circuit that excludes a background from a detection result of the sample detector based on a detection result of the first and second background detectors; A radiation measurement device comprising: 2. A plurality of sample detectors provided near a radioactive sample in a measurement chamber for accommodating a radioactive sample, for detecting radiation from the radioactive sample; and detecting pulses from the plurality of sample detectors. A first coincidence circuit that outputs a first coincidence pulse when they are input simultaneously; a first background detector provided around the measurement chamber for detecting cosmic rays; A plurality of second background detectors provided in the room, for detecting internal noise generated in the measurement room; and a plurality of second background detectors when detection pulses from the plurality of second background detectors are simultaneously input. A second coincidence circuit that outputs two coincidence pulses; a light shield that shields light between at least the radioactive sample and the plurality of second background detectors; Out of the simultaneous counting pulses excluding those input simultaneously with the second simultaneous counting pulse or the detection pulse of the first background detector, and outputting a pulse from which the background has been removed. A radiation measuring device, comprising: a counting circuit; 3. The radiation measurement apparatus according to claim 2, wherein the plurality of second background detectors are provided in substantially the same arrangement as the arrangement of the plurality of sample detectors. apparatus.