JPH0333677A - Measuring apparatus for surface dose - Google Patents

Abstract

PURPOSE:To enable highly-precise evaluation of a does from the direction of a source without being affected by a background dose, by determining a difference in the dose between a state wherein a source shielding body is drawn into a main body and a state wherein it is drawn out therefrom. CONSTITUTION:A background shielding body 11 and a source shielding body 12 enclose a radiation detector 13, and the shielding body 12 can be drawn into and out of a main body 14. With a detecting element 10 brought into contact with the surface of an element 15 to be measured, a dose is measure din a state wherein the shielding body 12 is drawn into the main body 14, and it is store din an arithmetic unit 16. Next, the dose is measured in a state wherein the shielding body 12 is drawn out therefrom, and it is sent into the arithmetic unit 16. A dose from the direction of a source is evaluated by using the difference between the two doses. Thereby the dose of the source can be evaluated with high precision irrespective of the magnitude of a background dose.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to a surface dose measurement method for measuring the surface dose of a part to be measured such as specific equipment or piping in an environment where a plurality of radiation sources coexist. Concerning a measuring device.

(Prior Art) When measuring the dose of specific equipment, piping, etc., a surface dose measuring device 1 as shown in the schematic diagram of FIG. 5 is used. This surface dose measuring device 1 consists of a main body 2 and a detection section 3, and the main body 2 and the detection section 3 are connected by a cable 4. The detection unit 3 has a configuration in which a radiation detector 6 is arranged at the center of a hemispherical background shield 5,
This is applied to the surface of the part to be measured 7, such as equipment or piping, and the dose is measured. At this time, if the dose from the radiation source direction of the part to be measured 7 is S, the dose from other directions is B, and the attenuation rate due to the background shield 5 is b, then the measured dose D2 is as follows: Become.

D2 = S + B - b And when evaluating the dose, B - b is sufficiently small (actually, the thickness of the shield is 2 to 3 ann and the lead equivalent is b = 0.2 to 0.
4), this term is ignored and it is regarded as D2αS.

(Problem to be solved by the invention) There is no problem when the dose S from the radiation source is sufficiently large compared to the background dose B, but when B becomes 173 or more of S, the measured dose D2 is more than 10% larger than S. This results in an overestimation of the dose due to the source.

An object of the present invention is to obtain a surface dose measuring device that can accurately evaluate the dose S in the direction of the radiation source, regardless of the magnitude of the background dose B.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, in the present invention, the radiation detector is arranged between the part to be measured and the radiation detector in the first state, and the part to be measured and the radiation detector in the second state. a radiation source shield that is moved or removed from between the radiation detector and the radiation source; It consists of a background shielding body surrounding the shielding body, and a computing unit that calculates the dose from the part to be measured by processing the dose values measured for the two states, the first state and the second state. Provided is a surface dose measuring device characterized by the following.

(Function) For example, the dose Dl measured in the first state, that is, the state in which the source shield is placed, is determined by the attenuation rate by the source shield being a, the dose from the direction of the source being S, and the other values. If the dose from the direction is B and the attenuation rate due to the background shield is b, then D, = S - a + Ilb Also, the dose measured with the source shield removed (second state) D2 becomes 4 D2 = S + B - b, and the dose S from the radiation source is if the attenuation rate a is known,
It can be calculated using the following formula.

(Example) An example of the present invention will be described below with reference to FIGS. 1 to 4.

The detection unit 10 includes a background shield 11, a radiation source shield 12, and a radiation detector 13 surrounded by these shields. The source shield 12 is configured to be retractable into the body 14. The detection unit 10 is applied to the surface of the part to be measured 15 such as piping or equipment, and the radiation source shield 12 is retracted into the main body 14 (second The dose is measured in the state (state) and in the state pulled out from the main body 14 (first state). A computing unit I6 that processes the measured doses D□ and D2 is built into the main body 14.

As shown in FIG. 3, the radiation source shield 12 has a radiation source of 0.5 to 1.3 M e V, which is a typical energy in a nuclear power plant.
Made of iron with little change in linear absorption coefficient (μ=0.
42 to 0.65 (帥-1): average 0.530-1).

As shown in FIG. 4, the thickness of the shielding body 2 is set to be approximately 2 to 30 mm, so that the attenuation rate a changes little due to the energy of the radiation even when the build-up due to the material is taken into account. Here, if the thickness of the shielding body 2 is 2.5 marks, then a =0.5.

The detection unit IO is placed on the surface of the measurement target 15 and the radiation source shield 12
The dose is measured in a state where the device is retracted into the main body 14 (second state). This measured value D2 is stored in the calculator 16.

Next, the source shield I2 is pulled out from inside the main body 14 (
The dose is measured in the first state). This measured value D□ is sent to the computing unit 16, where it is subjected to arithmetic processing with the previous D2, and the dose S from the radiation source is evaluated using the following equation.

S=□d -a 2 (D, -D□) In this example, 2.5 cm thick iron was used as the shield 12, and the dose was measured in two states: with and without the source shield. Since the configuration is such that the source-contributed dose S is evaluated from the above, the source-contributed dose S can be evaluated accurately without being influenced by the magnitude of the background dose B or the energy of γ-rays.

〔Effect of the invention〕

According to the present invention, the dose S from the source direction is evaluated based on the difference in the dose side emplacement due to the presence or absence of a source shield, so the source dose S can be evaluated accurately regardless of the magnitude of the background dose B. can.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the surface dose measuring device according to the present invention, FIGS. 2(a) and 2(b) are block diagrams showing the usage state of the embodiment, and FIG. 3 is a block diagram showing the usage state of the embodiment. FIG. 4 is a graph of the linear absorption coefficient depending on the type of material, FIG. 4 is a graph of the attenuation curve of gamma rays, and FIG. 5 is a configuration diagram of a conventional surface dose measuring device. DESCRIPTION OF SYMBOLS 11... Background shielding body, 12... Radiation source shielding body, 7 13... Radiation detector, 16... Arithmetic unit.

Claims (2)

[Claims] (1) a radiation source shield that is disposed between the part to be measured and the radiation detector in a first state and is moved or removed from between the part to be measured and the radiation detector in a second state; a background shield that is arranged in a direction opposite to the measured part with respect to the radiation detector and surrounds the radiation detector with the radiation source shield in the first state; 1. A surface dose measurement device comprising: a calculation unit that calculates the dose from the part to be measured by processing the dose values measured for the two states; (2) The computing unit sets the dose value measured in the first state to D_1 and the dose value measured in the second state to D_1.
2. The surface dose measuring device according to claim 1, wherein when the attenuation rate by the radiation source shield is a, the dose S from the part to be measured is determined by the following formula: S=D_2-D_1/1-a .