JP2001161795A - Method of electron ray irradiation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To economically increase the efficiency of electron ray irradiation by equalizing doses at center portion and an outer peripheral portion within a plane in the direction of depth of the electron ray irradiation, thus achieving uniform sterilization and processing, and eliminating the need for a large investment. SOLUTION: Sterilization processing using electron ray irradiation carried out while an irradiation assisting material tailored to have approximately the same specific gravity as the subject of irradiation is disposed around the subject of irradiation while in close contact therewith and the subject of irradiation is irradiated with electron rays.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of irradiating an electron beam when sterilizing or processing by irradiating an electron beam with an electron beam accelerator.

[0002]

2. Description of the Related Art Conventionally, sterilization of medical instruments and processing of polymer materials have been performed by irradiating radiation. In particular, since the electron beam has a higher dose rate compared to γ-ray irradiation, the irradiation time can be shortened, and there is little deterioration due to oxidation of the irradiated object. In recent years, it has been widely applied to commercial irradiation, in which products such as injection needles packed in cardboard boxes are conveyed by a conveyer and irradiated with an electron beam by an electron beam accelerator arranged in the middle. .

[0003]

However, in the electron beam irradiation, when an object having a large density and a finite size is irradiated with the electron beam, compared with the dose on the surface of the object, the irradiation depth direction is larger. Shows a tendency that the absorbed dose gradually increases, reaches a peak, and then gradually attenuates.

Further, as the penetration depth of the electron beam becomes deeper, a phenomenon occurs in which the absorbed dose at the peripheral portion of the irradiation object decreases as compared with the dose at the center of the irradiation object. This is because the irradiated electron beam is scattered by the irradiated object and leaks to the outside where the density is smaller than that of the irradiated object. This is because the dose at the peripheral portion decreases.

[0005] If the absorbed dose inside the object to be irradiated is not uniform, there is a concern that the material may be deteriorated due to excessive irradiation in the part where the dose is high, so that it is necessary for sterilization and processing in commercial electron beam irradiation. It is necessary to ensure that the required minimum dose is applied and that the dose is as uniform as possible.

In the commercial electron beam irradiation step, in order to make the dose distribution inside the object to be irradiated uniform, a method such as double-sided irradiation in which the object to be irradiated is turned upside down after the electron beam irradiation and electron beam irradiation is performed again. Although this method can flatten the dose distribution in the direction of electron beam irradiation depth, it is unavoidable that the dose distribution in a plane at a certain depth perpendicular to the electron beam becomes non-uniform. At the periphery of the irradiation object, the dose is reduced due to the leakage of the electron beam as compared with the center of the irradiation object.

In view of the above-mentioned situation, the present inventor has conducted intensive studies to deal with this situation. As a result, the irradiation depth of the electron beam is reduced by placing an irradiation auxiliary material around the object to be irradiated. They have found that the dose in the central part and the peripheral part in a plane having a direction can be made uniform.

According to the present invention, based on such knowledge, an auxiliary material for irradiation is arranged around an object to be irradiated, and the dose in the central portion and the outer peripheral portion in a certain plane in the depth direction of the electron beam irradiation is achieved, An object of the present invention is to improve the efficiency of electron beam irradiation economically without requiring a large investment.

[0009]

That is, a feature of the present invention that meets the above-mentioned object is that, in sterilization or processing by electron beam irradiation, irradiation of an electron beam is performed by irradiating an irradiation auxiliary material around an object to be irradiated. In the way. Here, the auxiliary material for irradiation is not particularly limited in material, but a foamed synthetic resin material such as foamed polyethylene or foamed polystyrene is usually used.

A second aspect of the present invention is an embodiment of the first aspect of the present invention, wherein an object to be irradiated is a plastic material product packed in cardboard, and an irradiation object made of a foamed synthetic resin material is provided therearound. It is characterized in that an auxiliary material is arranged so as to be in intimate contact with it and is irradiated with an electron beam.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described more specifically.

In the electron beam irradiation method of the present invention, in the sterilization or processing by electron beam irradiation as described above, an irradiation auxiliary material is placed around an object to be irradiated, and irradiation is performed within a certain plane in the electron beam irradiation depth direction. Is characterized in that the doses in the central part and the outer peripheral part are uniform.

The electron beam transmission thickness is a thickness at which the absorbed dose in a substance starts increasing from the surface toward the inside, then decreases and then becomes equal to the surface dose again. The 10 MeV electron beam transmission thickness is about 4 cm, and the 5 MeV electron beam transmission thickness is about 2 cm.

When the thickness of the irradiation object is less than the electron beam transmission thickness, the irradiation of the electron beam can be performed from one side or both sides of the irradiation object. Further, when the thickness of the object to be irradiated has a thickness of 1 to 2 times the electron beam transmission thickness, electron beam irradiation can be performed from both surfaces of the object to be irradiated. And
At the time of such irradiation, an auxiliary material for irradiation is placed in close contact with the object to be irradiated, and electron beam irradiation is performed. The material of the irradiation auxiliary material is not particularly limited, but it is preferable to select a material having the same density as that of the irradiation object. Those which can be used repeatedly as long as they are not particularly damaged are preferable. For example, synthetic resin materials such as expanded polyethylene and expanded polystyrene are used. At this time, it is preferable to adjust and use the specific gravity as much as possible with the irradiation object. Also,
It is preferable that the size of the irradiation auxiliary material is appropriately selected in consideration of the leakage of the electron beam from the outer peripheral portion to the outside, the workability, and the like.

[0015]

Embodiments of the present invention will be described below. The present invention is, of course, not limited to the following embodiments.

Example: A plastic material packed in a cardboard box was used as an object to be irradiated. The apparent specific gravity of the irradiation object is about 0.1, and the size of the box is 40 cm × 40 cm.
× 40 cm. CTA dosimeters were installed at equal intervals along the diagonal lines of the upper and lower surfaces of the irradiation object, and the absorbed dose was calculated from the measured absorbance of the CTA dosimeter after electron beam irradiation. In addition, foamed polyethylene adjusted to have a specific gravity of about 0.1 was used as an auxiliary material for irradiation, and was disposed so as to be in close contact with an object to be irradiated. The thickness of the foamed polyethylene was 5 cm or 10 cm. Electron beam irradiation conditions were an acceleration voltage of 10 MeV, a current of 5 mA, a beam scan width of 1 m, and a conveyor conveyance speed of 5 m / min. The electron beam was scanned from the upper scanning horn to the lower beam catcher in a direction perpendicular to the conveyor conveyance direction. The object to be irradiated was conveyed on a conveyor provided between the scanning horn and the beam catcher, and was irradiated with an electron beam during the conveyance.

FIG. 1 shows the results of dose measurement after electron beam irradiation in the embodiment, and shows the dose distribution on the upper and lower surfaces of the object to be irradiated. As shown in FIG. 1, a substantially uniform dose distribution is obtained on the upper surface of the irradiation object. In addition, on the lower surface of the irradiation object, the difference in dose between the center and the periphery of the irradiation object is small, and when the thickness of the auxiliary material for irradiation is as thick as 10 cm, there is almost no decrease in the dose at the periphery of the irradiation object. You can see that.

Comparative Example: The irradiation object was the same as that of the embodiment, and electron beam irradiation was performed under the same conditions as those of the embodiment except that no auxiliary material for irradiation was used. FIG. 2 shows a dose measurement result after electron beam irradiation in the comparative example, and shows a dose distribution on the upper and lower surfaces of the irradiation target. As shown in FIG. 2, a relatively uniform dose distribution is obtained on the upper surface of the irradiation object.
On the lower surface of the irradiation object, the dose at the peripheral portion is lower than that at the center of the irradiation object, and it can be seen that the dose is reduced to about 60 to 70%.

As described above, according to the present invention, by irradiating with the irradiation auxiliary material placed around the irradiation object,
It can be seen that the dose at the center and the outer periphery in a certain plane in the depth direction of electron beam irradiation can be made uniform as compared with the case where the irradiation auxiliary material is not used. Further, the electron beam irradiation method of the present invention is a simple method, does not require a large facility or the like, and is economical because the irradiation auxiliary material can be used repeatedly.

[0020]

As described above, the present invention relates to a method of irradiating an electron beam by irradiating an electron beam with an auxiliary material for irradiation placed around an object to be irradiated. It is possible to equalize the dose at the central part and the outer peripheral part in the plane.
There is no concern about a decrease in dose due to electron beam leakage at the periphery, and the dose required for sterilization and processing is reliably applied to ensure uniformity of sterilization and processing, resulting in economical and efficient sterilization and processing.
It has the effect of processing. Moreover, according to the irradiation method of the present invention, it is simple and does not require a large capital investment, and has an extremely economical effect.

[Brief description of the drawings]

FIG. 1 shows a thickness of 5 cm or 10 c on an outer peripheral portion of an irradiation object.
m is a graph showing the results of measurement of the dose distribution on the upper and lower surfaces of the irradiation object in the case of the present invention in which the irradiation auxiliary material of m is arranged in close contact with each other, along the diagonal line of each surface, and the horizontal axis is the outer periphery of the irradiation object , The distance from one end (cm), and the vertical axis indicates the absorbed dose (kGy) by electron beam irradiation.

FIG. 2 is a graph showing the results of measurement of the dose distribution on the upper and lower surfaces of the object to be irradiated when the object to be irradiated alone is irradiated along the diagonal line of each surface. The distance from one end (cm) and the vertical axis are the absorbed dose (kGy) by electron beam irradiation.

Claims (2)

[Claims] 1. A method for irradiating an electron beam, wherein in irradiation or sterilization by electron beam irradiation, irradiation is carried out with an irradiation auxiliary material placed around an object to be irradiated. 2. The object according to claim 1, wherein the object to be irradiated is a plastic material product packed in a corrugated cardboard, and an irradiation auxiliary material made of a foamed synthetic resin material is arranged so as to be in close contact therewith and irradiated with an electron beam. Electron beam irradiation method.