JPS63169587A - Method for evaluating radiation operation environment - Google Patents

Abstract

PURPOSE:To enable accurate radiation working environment evaluation by finding an area dosage rate as to a triangular unit working area having its vertexes at three spatial dosage rate measurement points, and evaluating radiation working environment according to the area dosage rate. CONSTITUTION:Three points are selected among spatial dosage rate measurement points in a working area to be evaluated and triangular working areas t1-t9 having vertexes at the three measurement points are set. Then, the area S of a unit working area, the area SIGMAS of the whole, and the geometrically mean value are used to calculate an area dosage rate. The radiation working environment is evaluated by using the area dosage rate, so the evaluation is accurately performed.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a radiation work environment evaluation method for evaluating the exposure dose of radiation workers, and particularly relates to an area-weighted average ambient dose rate. (hereinafter referred to as area dose rate).

(Prior Art) Conventionally, radiation work environment measurements for radiation exposure evaluation of radiation workers have been performed using stationary (fixed) monitors such as area monitors, or using portable survey meters such as ionization chambers. The former is measured at about one representative point of the working environment, and the latter is measured at several to several dozen points depending on the size of the working area, the condition of the radiation source, etc.

By the way, these measured values usually vary widely depending on the positional relationship with the radiation source, etc., so the correlation with the exposure dose of radiation workers in the area concerned is based on the arithmetic average value of each measurement point or Evaluation is based on the geometric mean value. Here, it is known that the dose rate distribution within a certain area generally shows a distribution that approximates a lognormal distribution to some extent, and therefore, the geometric mean value is considered to have a relatively better correlation with the exposure dose. ing.

However, when trying to more accurately evaluate the relationship between the radiation work environment and the exposure dose, there are many work environments where the lognormality of the dose rate distribution is not very good. The method of determining #j differs depending on the determiner and is not reproducible.

The problem is that it lacks universality.

Therefore, as a method to more accurately evaluate the relationship between the exposure dose of radiation workers and the radiation work environment, some researchers are using the area dose rate method, which adds information on the spatial undulations (distribution) of measurement points. Proposed.

In this method, when a dose rate distribution as shown in Fig. 12 is obtained, for example, 3*R/h, as shown in Fig. 13,
10aR/h, 30*R/h, 100*
The iso-dose rate line L1. L2. ..., and each iso-dose rate line L1. L2. A divided area A1 surrounded by... A2
．． A3. The area of ... is multiplied by the representative value (for example, the median value) of the category, added, and then divided by the area of the target area to obtain the area dose rate, which is determined by the following formula (1).

ΣS1 However, the representative value of the RI two-section area S6; Area of the section area The present inventors applied the above method in an atomic couplet radiation work environment, and found that the areal dose rate obtained by this method was just a fraction of the measured radiation measurement value. Compare with arithmetic mean value and geometric mean value,
It was confirmed that there was a more accurate correlation with the exposure dose of radiation workers.

(Problem to be Solved by the Invention) By the way, in the conventional method of calculating area dose rate, it is necessary to draw an isodose rate line by interpolating between each measurement value, but in this case, complicated calculation processing is required. It also requires measurements at a large number of measurement points, and measuring the area of the divided areas surrounded by iso-dose rate lines requires a lot of effort, such as measuring the survey drawing with a planimeter (area measuring device). There is a problem in that it requires

The present invention has been made in consideration of these points, and provides a radiation work environment evaluation that allows for accurate calculation of area dose rate and accurate evaluation of the radiation work environment using fewer measurement points and less labor. The purpose is to provide a method.

[Structure of the invention]

(Means for Solving the Problems) The present invention divides a radiation work area having a predetermined number of air dose rate measurement points into a plurality of triangular unit work areas with three air dose rate measurement points as vertices. Then, find the geometric mean value of the air dose rates at the three vertices in each unit work area, multiply this by the area of the unit work area, divide the total value by the overall area to find the area dose rate, and calculate the area dose rate. The feature is that the radiation work environment is evaluated based on the area dose rate.

(Function) In the radiation work environment evaluation method according to the present invention, instead of drawing iso-dose rate lines and calculating the areas of divided areas,
Draw a triangular unit work area with the three measurement points as vertices, calculate its area, and calculate the geometric mean value of each vertex instead of the representative value of the class value of the divided area. The area dose rate is calculated by multiplying the area and dividing the total value by the total area. And since a unit work area can be drawn if there are at least three measurement points,
The area dose rate can be calculated with a small number of measurement points, and the unit work area has a triangular shape, making it easy to calculate the area.
Area dose rate can be calculated with simple calculation process.

(Example) Examples of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a flowchart showing an example of a radiation work environment evaluation method using a computer.

First, a drawing of a work area to be evaluated is input into a computer and displayed on a CRT.

Next, use the keyboard or mouse to enter the coordinates (xl.

Y,) and the dose rate d at each measurement point. This is then repeated for the number of measurement points.

Measurement point coordinates (x,,y,) and dose rate d, +1 When the manual labor is completed, select three points from among the measurement points and form a triangular shape with the three measurement points as vertices, as shown in Figure 2. Unit work area t , t 't , tl 2'
3 4' Draw ts, te, ty, ts, ts,... At this time, each unit work area should not overlap with each other.

Each unit work area ti, t2. t3. t4. ts.

t6. Once the settings of tl, ts, ts, . The geometric mean value A1 is determined by formula (2) shown below.

A -EXb(1/3ΣRn-d,) -- (2) Then, using the area S1 of each unit work area obtained in this way, the entire area ΣS1, and the geometric mean value A1, the following is calculated. Calculate the area dose rate using equation (3).

That is, the geometric mean value A of the three vertices is multiplied by the area of the unit work area to obtain a total value, and this is divided by the total area ΣS to calculate the area dose rate DT.

Note that instead of the geometric mean value A1, other calculation results such as the arithmetic mean value can be used, but since the dose rate distribution relatively follows a log-normal distribution, it is better to use the geometric mean value A1 for better accuracy. .

Table 1 shows a comparison of evaluation results by the method according to the present invention and other methods based on the dose rate distribution shown in FIG. 12.

Table 1 The measured values shown in Figure 12 fit the lognormal distribution very well (risk rate of 5% in the prime distribution test), so in this example, the actual exposure rate and the geometric mean of the dose rate are It can be seen that the method according to the present invention has almost the same accuracy as the area dose rate based on the isodose rate line, which is currently considered to have the highest accuracy. Furthermore, it was confirmed that the variation when changing the selection method of the unit work area was within about ±20%, and that the reproducibility was excellent.

Figures 3 to 11 show other embodiments of the present invention, in which the area dose rate is calculated using a personal computer, and the area dose rate can be displayed in different colors for each class. .

That is, this system is broadly divided into area dose rate calculation software, a data input device, a calculation device, and an output device, and the area dose rate calculation software is configured based on the flowchart shown in FIG. 3. Further, the survey data input operation is performed based on the flowchart shown in FIG. 4, and the procedure for calculating the area dose rate is performed based on the flowchart shown in FIG.

When calculating the area dose rate, first input a building drawing 1 showing the area to be calculated into a personal computer in advance, and convert this building drawing 1 into C shown in Fig. 5.
It is displayed on RT2 as shown in FIG. And on top of that,
The position data of the measurement point 4 and the air dose rate of the Mj fixed point 4 are entered manually from the keyboard 5 using the mouse 3 shown in FIG. 6 or a screen input device such as a light bench (not shown).

Next, each manually measured measurement point is marked on the building drawing 1 as shown in Figure 7, and areas that are not subject to evaluation (for example, areas with interference or areas where people cannot enter) are marked as shown in Figure 8. Triangular unit work areas 6 having the three measurement points 4 as vertices are sequentially selected while avoiding areas (areas where there is no data). At this time, the position of the apex of the unit work area 6 that is being manually operated (for example, CRT
Based on the X, Y coordinates 7) on 2, the unit work area 6
The area S of , and the geometric mean value G1 of the air dose rates at the three apex positions are calculated.

As shown in FIG. 9, once all unit work areas 6 have been selected for the area to be evaluated, the area dose rate M is calculated using equation (4) shown below.

ΣS1 This calculation result is displayed on the CRT 2 shown in FIG. Note that the output device is not limited to the CRT 2, and a color printer or plotter can also be used.

In addition, by dividing the selected unit work area 6, calculating the average dose rate for each divided triangle, and color-coding according to predetermined dose rate classifications based on the results, a dose rate distribution map (Dose Map) is created. can be made.

For example, as shown in FIGS. 10 and 11, in the case of 16 divisions, the four small triangles created by connecting the midpoints of each side of the unit work area 6 are further divided into four equal parts to create a 16 division triangle 8. . The air dose rate at each vertex is calculated based on the geometric mean value of the air dose rates at the vertices of the unit work area 6. For example, the 10th
As shown in the figure, if the air dose rate at the two vertices of the unit work area 6 is 61°G2, then the air dose rate at the apex 0 of the 16-division triangle 8 in the middle is G1-2. l・ 1-2.2・
G1-2.3 is G-(GxG)2 1-2.1 1 1-2.2 ■ G-(GxG)2)...(5)1-2
．． 2 1 2 ■ G - (G

The three vertices of this 16-division triangle 8 are further geometrically averaged, and this value is color-coded by class 9 as shown in FIG.
If displayed on RT2, it becomes a dose rate distribution map.

In this way, the air dose rate at each vertex of the 16-division triangle 8 is
Since it is calculated from the air dose rate at the three vertices of the unit work area 6, the number of measurement points can be significantly reduced.

〔Effect of the invention〕

As explained above, the present invention calculates the area dose rate from a triangular unit work area with three air dose rate measurement points as vertices, and evaluates the radiation work environment based on this area dose rate. Therefore, with fewer ml fixed points and less labor, it is possible to calculate the area dose rate with high accuracy and accurately evaluate the radiation work environment.

[Brief explanation of the drawing]

Fig. 1 is a flowchart showing a method for calculating area dose rate according to an embodiment of the present invention, Fig. 2 is an explanatory diagram showing the state of a triangular unit work area selected by this method, and Fig. 3 is a flowchart showing a method for calculating an area dose rate according to an embodiment of the present invention. A flowchart of a method for calculating an area dose rate showing another embodiment of the invention,
Figure 4 is a flowchart showing the operation of inputting survey data;
The figure is a flowchart showing the procedure for calculating the area dose rate.
7 to 9 are explanatory diagrams sequentially showing display states on a CRT in a step-by-step manner when the method shown in the flow chart shown in FIG. 3 is carried out, Figure 10 is an explanatory diagram showing how to set a 16-division triangle, and Figure 11 is a diagram showing the D drawn using this 16-division triangle.
An explanatory diagram showing the dose map, Figure 12 is a normal survey diagram, and Figure 13 is a dose map drawn by isodose rate lines.
It is an explanatory diagram showing Map. 11・t2・t3・t4・t5・t6・t
7.t8. t9, 6...Unit work area, 4...Measurement point. Applicant's agent Mr. Yu Sato 6th day // Figure

Claims (1)

[Claims] 1. A radiation work area having a predetermined number of air dose rate measurement points is divided into a plurality of triangular unit work areas with three air dose rate measurement points as vertices, and each unit work area is 3 in
Calculate the geometric mean value of the air dose rates at the two vertices, multiply this by the area of the unit work area, divide the total value by the entire area to obtain the area weighted average air dose rate, and calculate the area weighted average air dose rate. A radiation work environment evaluation method characterized by evaluating a radiation work environment based on a radiation rate. 2. The radiation work environment according to claim 1, wherein the evaluation of the radiation work environment is performed by multiplying the area weighted average air dose rate by a predetermined exposure conversion coefficient to determine the radiation exposure dose of the worker. Evaluation method.