Methods for measuring radiation dose

Abstract

This invention provides a method for measuring radiation dose that can be easily measured using readily available materials. [Solution] Using cellulose fibers or a structure made of cellulose fibers, radiation is irradiated onto the dosimeter material, thermogravimetric measurements are performed on the dosimeter material after radiation irradiation, the thermogravimetric rate of the dosimeter material is determined from the results of the thermogravimetric measurements, and the radiation dose corresponding to the thermogravimetric rate at any temperature within the range of 200°C to 300°C is obtained based on the correlation between the thermogravimetric rate and the radiation dose. As shown by arrows A and B in Figure 2, the electron beam irradiation energy (Dose) is estimated from the differential thermogravimetric first derivative rate (DTG).

Description

Technical Field

[0001] The present invention relates to a method for measuring the radiation dose to a cellulose-based material.

Background Art

[0002] Radiation irradiation is used for crosslinking, modification, curing, sterilization, and other surface treatments of irradiated objects such as organic materials, foods, medical products, clothing, etc., for example, films, sheets, fibers, etc. In such treatments, since the dose of electron beam affects the resulting effects, it is very important to determine the dose. As an industrial dosimeter used during radiation irradiation, a film-like polymer is used as the dosimeter. Examples of such dosimeters include cellulose triacetate (CTA) film, radiochromic film, and blue cellophane. As a prior art, Patent Document 1 proposes obtaining the absorbed dose by irradiating a cellulose triacetate (CTA) film with radiation to be measured and measuring a quantity related to the chemical change of the film caused by the irradiation. That is, the method using this CTA film utilizes the fact that the change in absorbance near a wavelength of 280 nm before and after radiation irradiation is proportional to the absorbed dose, measures the change in absorbance near a wavelength of 280 nm, and determines the radiation dose.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the cellulose triacetate (CTA) film described in Patent Document 1 has a problem that it is a special film and is not easily available.

[0005] To solve the aforementioned conventional problems, the present invention provides a method for measuring radiation dose that can easily measure the dose using readily available materials. [Means for solving the problem]

[0006] One embodiment of the present invention is a method for measuring radiation dose, Irradiating a dosimeter with radiation, Perform thermogravimetric measurements on the dosimeter material after radiation irradiation. From the results of the thermogravimetric measurement, determine the thermogravimetric rate of the dosimeter material. This includes obtaining a radiation dose corresponding to the thermogravimetric loss rate at any temperature within the range of 200°C to 300°C, based on the correlation between the thermogravimetric loss rate and the radiation dose. The present invention relates to a method for measuring radiation dose, wherein the dosimeter material is a cellulosic fiber or a structure made of cellulosic fibers. [Effects of the Invention]

[0007] The present invention provides a method for measuring radiation dose that is readily available and allows for easy measurement of dose by using cellulosic fibers or structures made of cellulosic fibers as the dosimeter material. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a graph showing the thermogravimetric loss behavior when an electron beam is irradiated onto cellulose fiber paper according to Example 1 of the present invention. [Figure 2] Figure 2 is a graph (calibration curve) showing the correlation between the thermogravimetric loss rate at 280°C and the absorbed dose obtained from a CTA dosimeter in Example 1 of the present invention. [Figure 3] Figure 3 is a graph (calibration curve) showing the thermogravimetric loss behavior when gamma rays are irradiated onto cellulose fiber paper according to Example 2 of the present invention. [Figure 4] Figure 4 is a graph showing the correlation between the thermogravimetric loss rate at 280°C and the absorbed dose obtained from a CTA dosimeter in Example 2 of the present invention. [Figure 5] Figure 5 is a graph showing the thermogravimetric loss behavior when an electron beam is irradiated onto a cotton sheet according to Example 3 of the present invention. [Figure 6] Figure 6 is a graph (calibration curve) showing the correlation between the thermogravimetric loss rate at 290°C and the absorbed dose obtained from a CTA dosimeter in Example 3 of the present invention. [Modes for carrying out the invention]

[0009] The present invention relates to a method for measuring the radiation dose of a cellulose-based material. First, a dosimeter material is irradiated with radiation. After irradiation, thermogravimetric analysis is performed on the dosimeter material, and the rate of thermogravimetric loss of the dosimeter material is determined from the results of the thermogravimetric analysis. Then, based on the correlation between the rate of thermogravimetric loss and the radiation dose, the radiation dose corresponding to the rate of thermogravimetric loss at any temperature within the range of 200°C to 300°C can be obtained. The dosimeter material is a cellulose-based fiber or a structure made of cellulose-based fibers. This allows for easy measurement of radiation dose using readily available materials.

[0010] Thermogravimetric analysis is preferably performed using a thermogravimetric differential thermal analyzer (TG-DTA). A TG continuously measures the weight change of a sample while heating it at a constant rate. Meanwhile, a DTA measures the change in the temperature difference between a sample and a reference substance when both are heated together. By combining and simultaneously measuring with both TG and DTA instruments, the thermal changes of the sample can be estimated.

[0011] Radiation includes electron beams, alpha rays, beta rays, neutron beams, proton beams, particle beams, meson beams, gamma rays, and X-rays, but electron beams or gamma rays are preferred. Electron beams are used for crosslinking, modification, hardening, sterilization, and other surface treatments of irradiated materials such as organic materials, food, medical supplies, and clothing, including films, sheets, and fibers, and are practically useful.

[0012] The cellulose-based fiber is preferably a fiber derived from pulp or cotton, more preferably paper or non-woven fabric. These are easily available materials.

[0013] In the present invention, a calibration curve can be created from the thermogravimetric weight loss rate and the radiation dose, and the radiation dose can be estimated from the calibration curve. Specifically, it will be described in the following examples.

Examples

[0014] Hereinafter, it will be described using examples. Note that the present invention is not construed as being limited to the following examples. (Example 1) Kimwipe S-20 (2×2 cm, about 8 mg) manufactured by Nippon Paper Crecia Co., Ltd., which is easily available as paper of cellulose-based fiber, was vacuum dried overnight. After vacuum drying, it was put into a vacuum pack together with a CTA dosimeter, degassed and sealed, and irradiated with an electron beam (acceleration voltage: 250 keV) so that the irradiation dose was 0 to 120 kGy at 1 pass of 10 kGy. After irradiating with the electron beam, the irradiated Kimwipe was measured for thermogravimetric weight loss rate absorption dose dependence at 250 to 300 °C of the Kimwipe by using a differential thermal thermogravimetric simultaneous measurement device "NEXTA-STA200" manufactured by Hitachi High-Tech Corporation in a nitrogen atmosphere (400 mL / min) at a heating rate of 40 o C / min up to 300 °C.

[0015] Fig. 1 shows the thermogravimetric weight loss behavior of the Kimwipe at 250 to 300 °C when irradiated with an electron beam of 0 to 120 kGy. In Fig. 1, the vertical axis is the differential thermogravimetric first derivative rate (DTG), and the horizontal axis is the temperature. It was confirmed that at 250 to 300 °C, as the dose increased, the thermogravimetric weight loss rate increased. Cellulose is a degradable polymer with respect to radiation, and it is considered that the thermogravimetric weight loss rate of the Kimwipe was improved by the decrease in the molecular weight of cellulose due to the irradiation with the electron beam.

[0016] Figure 2 shows the correlation between the thermal weight loss rate at 280 °C and the absorbed dose determined by the CTA dosimeter. In Figure 2, the horizontal axis represents the differential thermogravimetric primary differential rate (DTG), and the electronic beam irradiation energy dose (Dose). A quadratic function correlation was confirmed for the absorbed dose and the thermal weight loss rate. This suggests that it is possible to measure the irradiation dose at the measurement location by measuring the thermal weight loss rate of the cellulose-based material. The sample required for thermogravimetric analysis is very small, only a few mg, and can be measured stably. The dose distribution of electron beam irradiation can be measured with high spatial resolution.

[0017] The dose D of the CTA dosimeter is represented by the following formula (Equation 1).

Equation

Equation

[0018] Next, the influence when changing the electron beam dose per pass was investigated. Table 1 shows the CTA measured values and the values calculated from the above formula (Equation 2) (using Kimwipe).

Table 1

[0019] As shown in Table 1, the measurements obtained using cellulose fiber paper (Kimwipes) were close to the actual measurements obtained with a CTA dosimeter.

[0020] (Example 2) The procedure was carried out in the same manner as in Example 1, except that the irradiation beam was replaced with gamma rays. Figure 3 shows the thermogravimetric loss behavior of Kimwipes at 250-300°C after irradiation with gamma rays ranging from 2.5 to 20 kGy. Figure 4 shows the correlation between the thermogravimetric loss rate at 280°C and the absorbed dose obtained from a CTA dosimeter. The following equation (Equation 3) can be derived from Figure 4.

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[0021] (Example 3) The procedure was the same as in Example 1, except that a cotton sheet was used instead of Kimwipes. The cotton sheet was cut with scissors, and 0.2 g was vacuum-dried overnight. After vacuum drying, it was placed in a vacuum pack, degassed and sealed, and irradiated with an electron beam (acceleration voltage: 250 keV) so that the irradiation dose was 10-120 kGy in one pass of 10 kGy. After electron beam irradiation, the irradiated cotton sheet sample was heated in a nitrogen atmosphere (400 mL / min) at a heating rate of 40 o The absorbed dose dependence of the thermogravimetric loss rate of cotton sheet samples at 250-300°C was evaluated by heating from 50°C to 300°C at a rate of C / min and performing thermogravimetric measurements. Figure 5 shows the thermogravimetric loss behavior of a cotton sheet sample at 250-300°C after irradiation with an electron beam of 0-120 kGy. Figure 6 shows the correlation between the thermogravimetric loss rate at 290°C and the absorbed dose obtained from a CTA dosimeter. The following equation (Equation 4) can be derived from Figure 6.

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[0022] The radiation dose measurement method of the present invention is useful for organic materials, food, medical equipment, clothing, films, sheets, fibers, crosslinking, modification, curing, sterilization, disinfection, and other surface treatments.

Claims

1. This is a method for measuring radiation dose. Irradiating a dosimeter with radiation, Perform thermogravimetric measurements on the dosimeter material after radiation irradiation. From the results of the thermogravimetric measurement, determine the thermogravimetric rate of the dosimeter material. This includes obtaining a radiation dose corresponding to the thermogravimetric loss rate at any temperature within the range of 200°C to 300°C, based on the correlation between the thermogravimetric loss rate and the radiation dose. A method for measuring radiation dose, wherein the dosimeter material is a cellulosic fiber or a structure made of cellulosic fibers.

2. A method for measuring radiation dose according to claim 1, comprising creating a calibration curve from the thermal weight loss rate and the radiation dose, and estimating the radiation dose from the calibration curve.

3. The method for measuring radiation dose according to claim 1 or 2, wherein the thermogravimetric measurement is performed using a thermogravimetric differential thermal analyzer (TG-DTA).

4. The method for measuring radiation dose according to claim 1 or 2, wherein the radiation is an electron beam or a gamma ray.

5. The method for measuring radiation dose according to claim 1 or 2, wherein the cellulose fiber is a fiber derived from pulp or cotton.

6. The method for measuring radiation dose according to claim 1 or 2, wherein the cellulose fiber is paper or nonwoven fabric.

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