JP3273554B2 - Radiation sensitive material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to nuclear chemical research such as measurement of the distribution and concentration of elements (nuclides) such as fissile nuclides and α-particle emitting nuclides, neutron dose measurement, measurement of spontaneous fission constant, and measurement of fission reaction area. It also relates to radiation-sensitive materials for fixed track detectors used in cosmic ray observation, elementary particle research, quantification of uranium and radon concentrations in the environment, and neutron radiography.

[0002]

2. Description of the Related Art There is a method of using an insulating material such as lithium fluoride, mica, and glass to detect tracks of charged particles. This means that as charged particles pass through the interior of an insulating solid, they damage the material along its path (called tracks) and etch the damaged area with a suitable solution. By the speculative truck,
That is, this is a method of generating an etch pit, and is called a track method.

[0003] In recent years, organic plastics have emerged as a substitute for these inorganic materials.
In the case of this organic plastic, the binding of molecules is broken by the passage of charged particles, and the active plastics become active centers for etching.
It is believed that the etch pits appear because the molecular fragments are rapidly dissolved by the etchant. Such organic plastics have much higher detection sensitivity than inorganic materials.

Until now, materials such as cellulosic plastics, polyesters, and polycarbonate have been used as organic plastics. However, the polymer of diethylene glycol bisallyl carbonate discovered by Cartwright et al. It was found that the sensitivity was significantly higher than that of organic plastics. This diethylene glycol bisallyl carbonate polymer is not a solid track detector,
It was originally developed as an optical material for use in spectacle lenses, optical lenses, and the like. However, due to its high sensitivity and good surface condition after etching, monitoring of environmental radon concentration, observation of cosmic ray heavy particles,
It is widely used for neutron radiography and high energy nuclear reaction research.

[0005]

The polymer of diethylene glycol bisallyl carbonate has a high sensitivity to charged particles and a good surface condition after etching, but this material also has limitations. That is, particles with high energy and small charge cannot be detected. For example, high energy (relativistic velocity) lithium, beryllium,
Particles such as boron cannot be detected with this material. Current,
In the polymer of diethylene glycol bisallyl carbonate, it is possible to detect a proton track of 16 MeV or a relativistic rate of boron ⁵⁺ ion, but a material exceeding this has not been found yet.

[0006] If materials capable of detecting these charged particles are obtained, new information on the origin of cosmic rays and propagation in galaxies may be obtained. In addition, such a radiation-sensitive material for a solid-state track detector with high sensitivity is expected to further expand the application range in the field of radiation measurement.

Therefore, in order to obtain such a radiation-sensitive material for a solid-state track detector with high sensitivity, the conversion of diethylene glycol bisallyl carbonate is performed by a method such as purifying monomers, optimizing polymerization conditions, or using additives. Methods of improving the quality or increasing the sensitivity by immersing the detection material in some liquid before etching (presoaking method) have been performed. In addition, Fujii et al. Have attempted to obtain a solid track detector with high sensitivity by changing the ratio of allyl groups to carbonate groups in diethylene glycol bisallyl carbonate. However, at present, satisfactory results have not been obtained with the detection materials obtained by these attempts.

It is therefore an object of the present invention to create a radiation sensitive material for solid state track detectors which has a higher sensitivity than currently used diethylene glycol bisallyl carbonate polymers.

[0009]

SUMMARY OF THE INVENTION Diethylene glycol bisallyl carbonate has relatively high sensitivity to charged particles. Therefore, the present inventors have considered a copolymer system in which a second component is introduced into diethylene glycol bisallyl carbonate as a method for further extracting this property. When systematically examining various second components, it was found that N-
It was found that the copolymer into which isopropylacrylamide was introduced exhibited the highest sensitivity.

In the present invention, it has been found that the copolymer composition of diethylene glycol bisallyl carbonate and N-isopropylacrylamide can provide high sensitivity if the copolymer contains 90% by weight or more of diethylene glycol bisallyl carbonate. However, the copolymer composition exhibiting the highest sensitivity includes 97% by weight of diethylene glycol bisallyl carbonate and 3% by weight of N
A copolymer having a composition ratio of -isopropylacrylamide.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The reason for the increase in the sensitivity of the copolymer obtained according to the present invention was presumed as follows. That is, diethylene glycol bisallyl carbonate and N
The most vulnerable part when charged particles enter the copolymer of isopropylacrylamide is a carbonate bond. On the other hand, the allyl group in diethylene glycol bisallyl carbonate forms a vinyl chain by polymerization to have a stable structure. Further, in the case of N-isopropylacrylamide, similarly, a stable structure is formed by polymerization, and it is hardly damaged. Therefore, in the case of the copolymer of the present invention, the damaged portion is not increased by N-isopropylacrylamide in the copolymer, but the damaged carbonate bond is effectively dissolved in the etching process, resulting in high sensitivity. Thought that was obtained.

A substance that has exerted its effective action is N-isopropylacrylamide. Polymers of N-isopropylacrylamide are known as temperature-sensitive materials. The temperature-sensitive material is a material having such a property that when the temperature of the external environment is changed, the size of the material is changed in response to the change. That is, when the temperature of the N-isopropylacrylamide polymer is changed from low to high in the presence of water, or vice versa, the volume of the polymer changes in response to a certain temperature. In the polymer of N-isopropylacrylamide, the temperature at the boundary is 32 ° C., and below this temperature, the polymer of N-isopropylacrylamide absorbs water and swells, but the temperature rises to 32 ° C. or more. When it comes out, the water that has been absorbed is exhaled and contracts. It shows so-called low-temperature swelling / high-temperature shrinkage behavior.

Therefore, in the etching process for producing etch pits, the temperature is raised (generally 70 ° C. or lower), so that N-isopropylacrylamide in the copolymer tends to shrink due to the shrinkage behavior. is there. Therefore, it was considered that the damaged carbonate bond in diethylene glycol bisallyl carbonate was expanded and the etching agent was easily penetrated therein, and as a result, the sensitivity was increased.

The molding of the radiation-sensitive material for the solid track detector of the present invention can be performed by a radical polymerization method. Generally, a polymer molded body used for a solid track detector is plate-shaped. In this case, a cell is prepared by sandwiching a spacer having a certain thickness between two glass plates (in some cases, a stainless steel plate), and a monomer solution containing a polymerization initiator (diethylene glycol bisallyl carbonate of a certain composition and N- (A mixed solution of isopropylacrylamide) and polymerize by heating. The polymerization initiator is not particularly limited, and a general organic peroxide used for radical polymerization can be used, but a peroxydicarbonate-based peroxide is most suitable for smoothly polymerizing an allyl group. Further, there is no limitation on the heating polymerization conditions.

The evaluation of the sensitivity of the radiation-sensitive material for a solid state track detector of the present invention was performed as follows. After irradiating charged particles vertically to the plate-like copolymer having a thickness of 0.5 mm produced by heat polymerization, a track is formed by performing a predetermined time etching process at 70 ° C. and 7N sodium hydroxide aqueous solution,
The sensitivity (S) was obtained from the track diameter (d) and the bulk etching amount (2B) by the following equation. S = Vt / Vb-1 = [1+ (d / 2B) ² ] / [1- (d / 2B) ² ] -1 Here, Vt is a track etching rate, and Vb is a bulk etching rate.

[0016]

Examples 1 to 5 and

Comparative Example 1 Diisopropyl peroxydicarbonate was used as a polymerization initiator at 3% by weight, and N-isopropylacrylamide was 0% by weight (Comparative Example 1), 1% by weight (Example 1), 3% by weight (Example 2). 5% by weight (Example 3),
7% by weight (Example 4) and 10% by weight (Example 5) were mixed with diethylene glycol bisallyl carbonate and cast-polymerized at 70 ° C. for 24 hours.
Thus, a plate-like copolymer having a thickness of 0.5 mm was obtained.

The plate-like copolymer has a viscosity of 5.6 to 20 MeV.
5 of the energies were vertically irradiated. Thereafter, etching was performed with a 7N aqueous sodium hydroxide solution at 70 ° C. for 30 hours to form tracks, and the sensitivity was determined.

FIG. 1 shows the results. FIG. 1 shows the sensitivities of copolymers composed of diethylene glycol bisallyl carbonate and N-isopropylacrylamide having various composition ratios to protons having various energies. From this figure, the effect of the copolymer composition on the track formation sensitivity of protons becomes clear, and at the same time, the relationship between the sensitivity and the energy of protons can be made clear.

As apparent from the figure, it was found that the sensitivity was higher in all copolymers than that of diethylene glycol bisallyl carbonate alone by introducing N-isopropylacrylamide into diethylene glycol bisallyl carbonate. Considering that the bulk etching rate is not different from that of diethylene glycol bisallyl carbonate alone (FIG. 1), it is considered that the track etching rate was increased and the sensitivity was increased in the copolymer. The increase in sensitivity was found to have a peak in the copolymer having a composition ratio of N-isopropylacrylamide in the copolymer of 3% by weight.

FIG. 2 shows micrographs of etch pits for pronto in various energy regions obtained in Comparative Example 1 and Example 2. That is, FIG. 2 shows micrographs of etch pits caused by protons of diethylene glycol bisallyl carbonate homopolymer and copolymer. This figure clearly shows the difference between the etch pits in the homopolymer system and the copolymer system, and it can be said that the sharper the etch pit, the higher the sensitivity of the material to irradiated ions.

As is apparent from the above, etch pits clearly appeared in the copolymer system (Example 2) when compared with diethylene glycol bisallyl carbonate homopolymer system (Comparative Example 1) in the case of 14 MeV or higher. .

[0022]

EXAMPLE 6 97% by weight of diethylene glycol bisallyl carbonate and 3% by weight of N
A low REL region (N ion, C ion, He ion) using a copolymer having a composition ratio of -isopropylacrylamide.
REL in relatively light particle region such as ions and H ions
(Represents the limited energy loss) when charged particles were irradiated. The result is shown in FIG.

In FIG. 3, the sensitivities of the diethylene glycol bisallyl carbonate homopolymer system and the copolymer system are plotted against the limited energy loss (REL). From this figure, the low REL region (N ions, C ions,
The track generation sensitivity for each material in a relatively light particle region such as He ions and H ions) can be seen.

As is clear from this, the REL value is 50
In the region of ⁰ MeVcm ² g ⁻¹ or less, the sensitivity tended to be higher than that of diethylene glycol bisallyl carbonate homopolymer with decreasing REL value. In this copolymer, it was possible to confirm the detection of a 20 MeV proton which greatly exceeded the threshold value of track formation, which was confirmed by the conventional diethylene glycol bisallyl carbonate homopolymer.

[0025]

Example 7 In an ordinary diethylene glycol bisallyl carbonate homopolymer system, 0.01% by weight of an antioxidant is mixed in to increase the sensitivity and prevent the material from changing over time. In the present copolymer, when the composition ratio is 99% by weight of diethylene glycol bisallyl carbonate, 1% by weight of N-isopropylacrylamide and 0.01% by weight of an antioxidant (Naugard 445), the sensitivity is increased. Was.

Further, as a result of optimizing the etching conditions, it was found that etching at 70 ° C. in a 5N aqueous sodium hydroxide solution exhibited its characteristics to the maximum.

FIG. 4 shows the radiation response characteristics of this copolymer in comparison with diethylene glycol bisallyl carbonate homopolymers (HARSLAS (trade name) and USF-3 (trade name)). That is, in FIG. 4, 0.01% by weight of an antioxidant [Naugard
445 (trade name)] under the optimum conditions of etching (70 ° C., 5N aqueous sodium hydroxide solution). For comparison, a diethylene glycol bisallyl carbonate homopolymer system (HARZ)
The sensitivity curves for LAS and USF-3) are also shown.

As is clear from the figure, the copolymer is LE
It can be seen that the sensitivity is significantly higher than that of a homopolymer at a T (line energy imparting) value of 10 KeV / μm or less. In this example, it was confirmed that in this copolymer, tracks of 27 MeV protons and 400 MeV / n Be ions could be clearly recorded.

[0029]

The copolymer of diethylene glycol bisallyl carbonate and N-isopropylacrylamide developed in the present invention has a lower REL region than USF-3 or SR-90, which is said to be currently the most sensitive. It showed even higher sensitivity. Further, by optimizing the etching conditions, the increase in the sensitivity of the copolymer is 27 MeV proton, which greatly exceeds the threshold value of track generation in the case of diethylene glycol bisallyl carbonate homopolymer;
As for heavy ions, it was possible to confirm the detection of 400 MeV / n Be ions.

[Brief description of the drawings]

FIG. 1 is a graph showing the sensitivity of copolymers composed of diethylene glycol bisallyl carbonate and N-isopropylacrylamide having various composition ratios to protons having various energies.

FIG. 2 is a photomicrograph of etch pits caused by protons of a diethylene glycol bisallyl carbonate homopolymer system and a copolymer system.

FIG. 3 is a diagram plotting sensitivity in a homopolymer system of diethylene glycol bisallyl carbonate and a copolymer system with respect to a limited energy loss (REL).

FIG. 4 shows the sensitivity under the optimum conditions of etching (70 ° C., 5N aqueous sodium hydroxide solution) using a copolymer to which 0.01% by weight of an antioxidant (Naugard 445), which can be expected to increase the sensitivity, is added. FIG.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takeshi Suwa 1233 Watanuki-cho, Takasaki City, Gunma Prefecture Inside the Japan Atomic Energy Research Institute Takasaki Research Institute (72) Inventor Koichi Ogura 2-11-1 Shinei, Narashino City, Chiba Prefecture Japan Univ. Inside the Faculty of Production Engineering (72) Inventor Hiroteru Hasegawa 1st character, Sakai-cho, Sakai-gun, Fukui Prefecture 1st place inside Sakai Plant of Fukubi Chemical Industry Co., Ltd. (56) References JP-A-6-18672 (JP, A) JP-A-2-245689 (JP, A) JP-A-1-201186 (JP, A) JP-A-61-120989 (JP, A) JP-A-1-92683 (JP, A) JP-A-5-341525 (JP JP-A-59-130853 (JP, A) JP-A-61-145213 (JP, A) JP-A-10-254133 (JP, A) JP-A-10-36622 (JP, A) 10-511735 (JP, A) (58) Fields studied (Int. Cl. ^7, DB name) G01T 5/10 C08F 220/56 C08F 216/12 G01T 1/02

Claims (1)

(57) [Claims] 1. A radiation-sensitive material for a solid track detector, comprising 90 to 99% by weight of diethylene glycol bisallyl carbonate having the following formula (1) and the following formula (2):
The raw material comprises a copolymer obtained by polymerizing a monomer having 10% to 1% by weight in combination. Embedded image Embedded image