JPS6033075A - Plastic scintillator - Google Patents

Abstract

PURPOSE:To volatilize speedily an internal residual monomer, and to shorten considerably a keeping period after manufacture and to improve a responding speed by boring holes which communicate with the outside in the internal core part of a plastic scintillator formed into a block in a desired shape. CONSTITUTION:For example, four communication holes 16 which communication with the outside are bored in the inner center part at the circumference of the center of the main columnar body 15a of the plastic scintillator 15 used as a radiation thickness measurement type from the bottom surface in parallel to the axial line of the main body 15a. In another method, one large-diameter hole 16 or horizontal hole 16 is formed in the center part. It takes conventionally about one year to remove the residual monomer after the injection and polymerization of plastic, to shorter a period about two months; and the product is required to left as it is for stabilization for a long period because a decrease in light output due to the residual monomer is slow, but the period is shortened considerably to obtain the scintillator having quick response.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a plastic scintillator used for radiation detection.

[Technical background of the invention and its problems]

FIG. 1 is a block diagram of a radiation thickness meter measurement system using a plastic scintillator.

Radiation (3) emitted from a radiation source (2) within a radiation source container (1) passes through a plate-shaped object to be measured (4) and enters a plastic scintillator (5). When radiation (3) is incident, the plastic scintillator (5) emits light, which is converted into an electric current and amplified by a photomultiplier tube (6). This current is converted into voltage by the preamplifier (signal processing unit (8)
Enter. The signal processing section (8) performs various calculations to determine the thickness of the object to be measured (4), and outputs the difference from the set value from the program controller (10), that is, a deviation signal, to the recorder (9) and program controller a0. do.

By the way, the production of plastic scintillators takes about 14
Polystyrene (or polyvinyl toluene) is produced by polymerizing a styrene compound (or vinyl toluene compound) in a liquid at 0° C. At this time, unpolymerized styrene (or vinyl toluene) is generated. This is called residual monomer. This residual monomer causes a drawback that the decay time of light that occurs when radiation is incident is long, that is, the response is slow.

The residual monomer gradually evaporates (2), but the plastic scintillator used as a detector in a radiation thickness meter requires a large volume to reduce statistical noise, which is an important error factor for accuracy, and is quite large. In this case, it takes a long time to remove the residual monomer from the center of the plastic enticillator.

A conventional plastic scintillator is shown in FIG. The plastic scintillator (5) has a solid cylindrical body (
The top surface of 5a) is shaped like a light pipe (5b) that forms a connecting part to the photomultiplier tube, and the residual monomer in the center of the main body (5; l) is slow to volatilize. Therefore, it could not be used unless it was left for a long period of time (for example, about one year) after manufacture. The plastic scintillator (5) when a plastic scintillator with no residual monomer removed is used in the radiation thickness meter shown in Figure 1.
) is shown in FIG. 3, where the vertical axis shows time and the horizontal axis shows the optical output of the plastic scintillator. The straight line (4) shown in the figure indicates the optical output of the plastic scintillator (5) when the object to be measured (4) in Figure 1 is not inserted into the path of the radiation (3) from the radiation source (2). ,
Since radiation that is not attenuated by the object to be measured (4) enters, the optical output is large. When the object to be measured is inserted at point B in the figure, the radiation incident on the plastic scintillator is attenuated by the object to be measured, so the optical output of the plastic scintillator should immediately decrease, but the residual monomer causes attenuation of the light emission. Because the time is long (the curve shown in the second figure (C)
) shows a response in which the optical output gradually decreases and settles down to the optical output corresponding to the incidence of attenuated radiation. That is, due to the residual monomer, time 1. It can be seen that there is a response delay time from t2 to t2.

[Purpose of the invention]

An object of the present invention is to provide a plastic scintillator in which the period required for removal of residual monomer is significantly shortened.

[Summary of the invention]

The present invention provides a method of accelerating the volatilization of residual monomer by drilling at least one communication hole communicating with the outside air in the inner core of a plastic scintillator having a desired shape. Achieved the purpose of the term.

[Embodiments of the invention]

Below are drawings of embodiments of the present invention? Refer to and explain.

A plastic scintillator according to an embodiment of the present invention is shown in FIG. A plastic scintillator according to an embodiment of the present invention (■
5) has a cylindrical main body (15a) with a light pipe (15b) protruding from the upper surface thereof, which forms a connection part to a photoelectron J-angle multiplier, and the light pipe (15b) is located at the center of the main body (15a). .

The plastic scintillator according to the embodiment of the present invention having the above structure (1) is determined by the fact that a communicating hole (Ifi) is formed, and the residual monomer in that part is not only contained and removed, but also when there is no communicating hole. In contrast to the case where the residual monomer 67 could only be volatilized from the outer surface of the main body (15a), it is now possible to volatilize also to the communication hole (IGI), and the residual monomer can be removed in a short period of time. , the time required to remove the residual monomer is 1/6 or less compared to conventional products with similar shapes and dimensions.

Therefore, while conventionally it was necessary to leave the product in a cold environment for about one year after manufacture to use it as a detector of a radiation thickness meter, it can now be used for less than two months, which is a great practical advantage. FIG. 5 shows the radiation thickness f? of the plastic scintillator (15) according to the present invention after being aged for about two months after manufacture. This figure shows the vertical characteristic of the optical output of the plastic scintillator θ5) when used at point 1, where the optical output when there is no object to be measured rapidly increases by 1 from point B where the object to be measured is inserted. However, it shows that the optical output settles down to the level corresponding to when the radiation is attenuated by the object to be measured.
It can be seen that the response delay time from time t to time t2 is extremely short, and the residual monomer is completely removed.

Note that the present invention is not limited to the embodiment shown in FIG. 4, and can be implemented with modifications as described below.

(a) The shape is not limited to a cylinder, but may be various shapes as shown in FIGS. 6(a) to 6(g), and the light pipe (15b) may or may not be included. Furthermore, don't underestimate the size of the space.

(b) The communicating hole 〇〇 may be a single large-diameter hole as shown in Figure 7 (a) instead of multiple small-diameter holes as shown in Figure 4. Further, the communication hole (16) is not limited to the vertical direction, but may be formed horizontally as shown in FIG. 7(b).

Furthermore, the continuous free holes (1G) may be made from the bottom or the top. Also, if it is more than ka, it may be penetrating.

〔Effect of the invention〕

As described above in detail 1-1, according to the present invention, in order to promote the volatilization of the residual monomer generated during the manufacturing of the plastic scintillator and contained inside, a communication hole is formed to communicate the inner core of the plastic scintillator with the outside. This not only removes the residual monomer from that area, but also allows it to volatilize into the communication hole, whereas in the case where there was no communication hole, the monomer could only volatilize on the outer surface of the positive blank scintillator. Therefore, the residual monomer will be completely removed in a short period of time. As a result, the time required for cutting out residual monomer with similar shapes and dimensions is shortened to 1/6 or less compared to conventional products. Therefore, until a response speed that can be used as a detector such as a radiation thickness meter is obtained (=, conventional products had to be kept in a dry environment for about a year after manufacture, but with simple additional work, it takes about 20 days
It can be used in less than a month, and has great practical advantages. Furthermore, since the shape of the plastic scintillator as a whole does not change, there is an advantage that the container, holder, etc. can be used as is.

[Brief explanation of drawings]

Fig. 1 is a block doctor 1 showing a radiation thickness H1 measuring system using a plastic scintillator, Fig. 2 is a perspective view showing an example of a conventional plastic scintillator, and Fig. 3 is a perspective view showing an example of a conventional plastic scintillator.
Figure 4 is a graph showing the rise characteristics of the optical output of the Plus Boonck scintillator when a plastic scintillator with no residual monomer removed is used in the radiation thickness meter shown in Figure 1. A perspective view showing a scintillator, and Fig. 5 shows the rise characteristics of the optical output of the plastic scintillator when the plastic scintillator of Fig. 4 is used with the radiation thickness i+ of Fig. 1 after being heated for about two months after manufacture. Graphs, FIGS. 6(a) to 6(gl are perspective views showing different shapes of plastic scintillators that can be implemented according to the present invention, FIGS. 7(a) and (b)
) are close-up views showing different new types of plastic scintillators of the present invention. 15...Plastic scintillator 15a/Thu closed 15b~...Light pipe 16...
・ノ21巳i,nr Hole substitution Yof ``Filled soil Inoue - Male 1st Figure 2 Figure 3 Figure 4 Figure 5 (OL) (i CC> (d) Figure 7

Claims (1)

[Claims] A plastic scintillator that is formed into a block having a desired shape and emits light upon incidence of radiation, characterized in that the inner core of the plastic scintillator is provided with at least one communication hole that communicates with the outside air.