JP6586616B2 - Standard sample for radioactivity measurement, and method for producing standard sample for radioactivity measurement - Google Patents

Description

  The present invention relates to a standard sample for measuring radioactivity and a method for producing a standard sample for measuring radioactivity.

  Standard samples are used for nondestructive inspection of radioactivity of foods and the like.

  Patent Document 1 describes a simulated food radiation source simulating apples, fish, vegetables, and packed rice. In Patent Document 1, a simulated food radiation source is produced by pulverizing an environmental radioactive material, mixing with an organic or inorganic built-in component, stirring, homogenizing, forming, and the like.

Japanese Patent No. 5337288

  However, in the raw wood for mushroom cultivation, the distribution of radioactive substances is not uniform, and it has been difficult to obtain a highly accurate standard sample by the method as described in Patent Document 1. Therefore, highly reliable non-destructive inspection has not been realized, and it has been necessary to measure the raw wood to be measured into sawdust.

  Most of the radioactive substances contained in the logs for mushroom cultivation are contained in the bark surface and the inner bark, and the amount of radioactive substances contained in the woody part is very small. In order to improve the reliability of standard samples used for radioactivity measurement, it is desirable to bring the form close to the real thing, and stability that can withstand long-term use is required. It was difficult to make a sample.

  The present invention provides a standard sample that can be used for measuring the radioactivity of raw wood used for mushroom cultivation and is excellent in reliability and stability.

According to the present invention,
It is a standard sample used for radioactivity measurement of raw wood used for mushroom cultivation,
A cylindrical core material containing wood,
A covering member covering the core material,
The core material has a radioactive substance-containing region on the side surface part,
A standard sample for radioactivity measurement is provided.

According to the present invention,
A method for producing a standard sample used for measuring radioactivity of raw wood used for mushroom cultivation,
A step of preparing a core material including a wood having a radioactive substance-containing region on a side surface;
Covering the core material with a covering member,
A method for producing a standard sample for radioactivity measurement is provided.

  ADVANTAGE OF THE INVENTION According to this invention, it can use for the radioactivity measurement of the raw wood used for mushroom cultivation, and can provide the standard sample which is excellent in reliability and stability.

It is a figure which shows the standard sample for radioactivity measurement which concerns on 1st this embodiment. It is sectional drawing which shows a cross section perpendicular | vertical to the length direction of the standard sample which concerns on 1st this embodiment. It is a figure for demonstrating the manufacturing method of the standard sample which concerns on 1st Embodiment. (A) is sectional drawing which shows a cross section perpendicular | vertical to the length direction of the standard sample which concerns on 2nd Embodiment, (b) is a cross section perpendicular | vertical to the length direction of the standard sample which concerns on the modification of 2nd Embodiment. FIG. It is a figure for demonstrating the manufacturing method of the standard sample which concerns on 2nd Embodiment. It is sectional drawing which shows a cross section perpendicular | vertical to the length direction of the standard sample which concerns on 3rd Embodiment. It is a figure for demonstrating the manufacturing method of the standard sample which concerns on 3rd Embodiment. It is a figure which shows the relationship between the apparatus conversion factor of Examples 1-3 and the weight of a standard sample. It is a figure which shows the relationship between the apparatus conversion factor of Comparative Examples 1-3, and the weight of a standard sample.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

(First embodiment)
FIG. 1 is a view showing a standard sample 10 for measuring radioactivity according to the first embodiment. Hereinafter, the “standard sample for measuring radioactivity” is simply referred to as “standard sample”. FIG. 2 is a cross-sectional view showing a cross section perpendicular to the length direction of the standard sample 10 according to the present embodiment.
The standard sample 10 is a standard sample used for radioactivity measurement of raw wood used for mushroom cultivation. The standard sample 10 includes a cylindrical core material 20 including wood and a covering member 40 that covers the core material 20. The core material 20 has the radioactive substance containing area | region 220 in a side part. This will be described in detail below.

  The standard sample 10 is used for confirming whether the radiation measuring apparatus is in a state where it can be normally measured and the measurement accuracy. For example, prior to the measurement of a log (mushroom growing log) used for mushroom cultivation to know the amount of radioactivity, the standard sample 10 is measured with a radiation measuring device. Then, it is confirmed whether the radiation measuring apparatus can correctly measure the known radiation dose of the standard sample 10. Then, the reliability of a measurement result is securable by measuring the raw wood for mushroom cultivation. The measurement of the standard sample 10 may be performed once a day, but may be performed every time the raw wood for mushroom cultivation is measured. The standard sample 10 can also be used for calibration of the radiation measuring apparatus and derivation of an equipment conversion coefficient.

  In the measurement of the standard sample 10 and the raw wood, it is preferable to use a background measurement sample that has the same structure as the standard sample 10 and does not contain a radioactive substance. By subtracting the count number obtained by measuring the background measurement sample from the count number obtained by measuring the standard sample 10 or the raw wood, the true count number of the standard sample 10 or the raw wood can be obtained.

  Here, in the standard sample 10, it is important from the viewpoint of reliability that the measurement characteristics such as the expected angle of the measuring instrument, the conditions such as the self-absorption effect, and the blocking effect are made the same as those of the measurement object. Moreover, the stability which can be used for a long time is calculated | required.

  In addition, the kind of mushroom cultivated with the raw material for mushroom cultivation to be measured is not particularly limited, and examples thereof include shiitake mushroom, maitake mushroom, enokitake mushroom, sea cucumber, mushroom, chestnut mushroom, oyster mushroom and the like.

  The raw wood includes raw wood immediately after cutting, raw wood dried for several months after cutting, and raw wood used for mushroom cultivation. The type of raw wood is not particularly limited, and examples thereof include broadleaf trees such as Mizunara, Shii, Sakura, Side, Kunugi, Quercus, Beech, Oyster, Chestnut, and Walnut, and conifers such as Sugi, Larch, and Pinus.

  A plurality of standard samples 10 can be prepared by changing the moisture content, density, dimensions, etc., and can be selected and used in accordance with the mushroom cultivation raw wood to be measured.

  The standard sample 10 has a cylindrical shape. FIG. 2 is a cross-sectional view perpendicular to the longitudinal direction of the standard sample 10, that is, the rotation axis of the cylinder. Note that the shape of the standard sample 10 is not limited to a true cylindrical shape. That is, the bottom surface is not limited to a perfect circle, but may be an ellipse or a rounded shape with irregularities. Further, the axis of the cylinder may be slightly inclined from the normal direction of the bottom surface, or the side surface may be slightly uneven.

  The core material 20 has a radioactive substance-containing region 220 and an inner region 210. The radioactive substance containing region 220 is formed from the side surface of the core material 20 toward the inside. On the other hand, the inner region 210 includes the central axis of the core material 20 and is formed toward the side surface. The radioactive substance containing region 220 has a higher density of radioactive substances than the inner region 210. The boundary between the inner region 210 and the radioactive substance-containing region 220 may be clear. That is, the content density distribution of the radioactive material in the radial direction of the core material 20 may be discontinuous at the boundary between the internal region 210 and the radioactive material-containing region 220. On the other hand, the boundary between the inner region 210 and the radioactive substance-containing region 220 is not necessarily clear. That is, the content density of the radioactive substance may continuously decrease from the side surface of the core material 20 toward the inside.

  From the viewpoint of reliability, the radioactive substance-containing region 220 is preferably formed on the entire side surface of the core material 20. That is, it is preferable that all the side surfaces of the core material 20 are configured by the radioactive substance-containing region 220. However, the structure is not limited to such a structure, and the radioactive substance-containing region 220 may be formed only on a part of the side surface of the core material 20. The radioactive substance-containing region 220 may also be formed on the bottom surface of the core material 20.

  When the core material 20 includes the radioactive substance-containing region 220 on the side surface portion, the core material 20 can be close to the non-uniform distribution of the radioactive substance in the raw wood used for mushroom cultivation, and the reliability can be improved.

The core material 20 includes wood at least partially. In the present embodiment, the core material 20 is a cylindrical wood whose surface is coated with a radioactive material solution. The radioactive substance is a substance to be measured, and is not particularly limited. For example, radioactive cesium ( ¹³⁴ Cs and ¹³⁷ Cs) is used. By using wood as the core material 20, it is possible to easily obtain the standard sample 10 having a moisture content and density close to the moisture content and density of the raw wood to be measured.

  In the standard sample 10, the core material 20 is covered with a covering member 40. The covering member 40 is, for example, a resin film or tube. The material of the covering member 40 is not particularly limited. For example, fiber reinforced plastics (FRP), vinyl chloride resin, acrylic resin, fluorine resin such as polytetrafluoroethylene, silicon resin, urethane resin, epoxy resin, etc. Is mentioned. The covering member 40 may have a single layer structure made of any resin or may be composed of a plurality of layers. By covering the core material 20 with the covering member 40, the moisture content and the content of the radioactive substance can be stabilized, and long-term use becomes possible. From the viewpoint of improving stability, the thickness of the covering member 40 is preferably 0.1 mm or more. On the other hand, from the viewpoint of improving reliability, the thickness of the covering member 40 is preferably 2.0 mm or less, and more preferably 1.0 mm or less.

  The moisture content of the standard sample 10 is preferably 35% or more, and more preferably 38% or more. On the other hand, the moisture content of the standard sample 10 is preferably 45% or less, and more preferably 43% or less. If it does so, especially in the measurement of the raw wood from immediately after logging to one month, reliability will improve.

  On the other hand, the moisture content of the standard sample 10 is preferably 25% or more and 40% or less. In this way, reliability is particularly improved in the measurement of raw wood dried after cutting. Since mushroom cultivation uses logs that have been dried at least once after logging, it is important to adapt to the measurement of such logs. The raw wood that has been dried after felling is subjected to water treatment or the like as necessary, and the radioactivity of the raw wood can be measured after drying to a constant weight at 105 ° C., for example.

  The moisture content is a moisture content on a wet basis and is a value obtained by dividing the weight of moisture contained in the standard sample 10 by the weight of the entire standard sample 10 containing moisture. The moisture content of the standard sample 10 can be obtained by measuring the moisture content of the core material 20 using, for example, an electric resistance moisture meter. In particular, when the internal region 210 is the main volume portion of the standard sample 10, for example, the moisture content measured using an electric resistance moisture meter for the internal region 210 portion can be regarded as the moisture content of the standard sample 10.

The density of the standard sample 10 is preferably 0.5 g / cm ³ or more, and more preferably 0.8 g / cm ³ or more. On the other hand, the density of the standard sample 10 is preferably 1.5 g / cm ³ or less, and more preferably 1.1 g / cm ³ or less. If it does so, especially in the measurement of the raw wood from immediately after logging to one month, reliability will improve.

The density of the standard sample 10 is preferably 0.30 g / cm ³ or more, and more preferably 0.35 g / cm ³ or more. On the other hand, the density of the standard sample 10 is preferably 0.95 g / cm ³ or less, and more preferably 0.80 g / cm ³ or less. In this way, reliability is particularly improved in the measurement of raw wood dried after cutting.

  For example, the standard sample 10 can have a length of 12 cm to 120 cm, a diameter of 6 cm to 18 cm, and a weight of 330 g to 31000 g.

Below, the manufacturing method of the standard sample 10 which concerns on this embodiment is demonstrated.
FIG. 3 is a diagram for explaining a method of manufacturing the standard sample 10 according to this embodiment. The method for manufacturing the standard sample 10 according to the present embodiment includes a step of preparing a core material 20 including a radioactive material-containing region 220 on a side surface portion and including wood, and a step of covering the core material 20 with a covering member 40. .

  In the standard sample 10 according to the present embodiment, the core material 20 is a cylindrical wood whose surface is coated with a radioactive substance solution. In the step of preparing the core material 20, the columnar wood 100 is prepared as shown in FIG. The columnar timber 100 is obtained by processing timber immediately after logging (for example, within two months after logging) into a columnar shape. However, it is not limited to this, and it can prepare using the wood which time passed after felling, the dried wood, the commercially available wood, etc. as needed.

  The type of the columnar timber 100 is not particularly limited. For example, broad-leaved trees such as Mizunara, Shii, Side, Sakura, Kunugi, Quercus, Beech, Oyster, Chestnut, and Walnut, and conifers such as cedar, larch, and red pine can be used. Note that the columnar wood 100 is preferably wood that does not contain a radioactive substance to be measured.

The core material 20 as shown in FIG. 3B can be obtained by applying a radioactive substance solution to the surface of the prepared columnar wood 100. In the columnar wood 100, the region in which the solution permeates and contains the radioactive substance becomes the radioactive substance-containing region 220, and the other region becomes the inner region 210. The radioactive substance is a substance to be measured when measuring the radioactivity of the raw wood for mushroom cultivation, and is, for example, radioactive cesium ( ¹³⁴ Cs and ¹³⁷ Cs). The radioactive substance can be collected, for example, in an area where mushroom cultivation raw wood is grown. The solution of the radioactive substance can be obtained by dissolving the radioactive substance in, for example, water.

  The radioactive substance solution is applied to at least the side surface of the cylindrical wood 100. At this time, it may be applied to only a part of the side surface, but from the viewpoint of improving the reproducibility of measurement, it is preferably applied to the entire side surface, more preferably uniformly applied to the entire side surface. In addition, you may apply | coat the said solution not only to a side surface but to the bottom face part of the columnar timber 100, ie, the mouth part of the columnar timber 100. FIG.

  By adjusting at least one of the concentration of the solution and the coating amount, the amount of radioactivity of the standard sample 10 can be adjusted.

  Next, a step of covering the core material 20 with the covering member 40 is performed. In this process, by applying a liquid resin to the core material 20 and curing it, the core material 20 is covered with the covering member 40 made of resin, and the standard sample 10 can be obtained as shown in FIG. Here, examples of the resin include fluorine resins such as polytetrafluoroethylene, FRP, silicon resin, acrylic resin, urethane resin, and epoxy resin, but are not limited thereto. Instead of applying and curing a liquid resin, for example, a sheet-like resin may be laminated on the core material 20 as the covering member 40, or the core material 20 may be sealed inside the resin tube. . When a resin tube is used as the covering member 40, examples of the material include vinyl chloride resin, acrylic resin, and silicon resin.

  In this step, it is preferable to cover the entire core member 20 with the covering member 40 in order to prevent fluctuations in the moisture content and the amount of radioactivity and to improve the stability of the standard sample. The covering member 40 may have a single layer structure or a multilayer structure made of a plurality of materials. Further, another member may be interposed between the core material 20 and the covering member 40 for the purpose of improving adhesion, or the core material 20 and the covering member 40 may be in direct contact with each other. Further, the core material 20 and the covering member 40 may be bonded together using an adhesive or the like.

Next, the operation and effect of this embodiment will be described.
The standard sample which concerns on this embodiment can be used for the radioactivity measurement of the raw wood used for mushroom cultivation, and is excellent in reliability and stability.

  When the core material 20 includes the radioactive substance-containing region 220 on the side surface portion, the core material 20 can be close to the non-uniform distribution of the radioactive substance in the raw wood used for mushroom cultivation, and the reliability can be improved.

  Further, since the core material 20 is covered with the covering member 40, the moisture content and the content of the radioactive substance can be stabilized, and long-term use is possible.

  Further, by using wood whose surface is coated with a radioactive material solution as the core material 20, the standard sample 10 having a moisture content and density close to the moisture content and density etc. of the raw wood to be measured is easily obtained. be able to.

(Second Embodiment)
The standard sample 10 according to the second embodiment will be described below.
FIG. 4A is a cross-sectional view showing a cross section perpendicular to the length direction of the standard sample 10 according to this embodiment. In the standard sample 10 according to the present embodiment, the core material 20 includes a first member 120 containing wood and a second member 140 that covers the first member 120 and forms the radioactive substance-containing region 220. This is the same as the standard sample 10 according to the first embodiment. This will be described in detail below.

  The core material 20 according to the present embodiment includes a first member 120 and a second member 140, and the first member 120 is columnar wood. As the 1st member 120, the thing similar to the columnar timber 100 which concerns on 1st Embodiment can be used. By doing so, the standard sample 10 which has a moisture content, a density, etc. close | similar to the moisture content, the density, etc. of the raw wood used as a measuring object can be obtained easily.

  The first member 120 may be made of a resin cylinder filled with at least wood powder instead of columnar wood. Examples of the material of the cylinder include vinyl chloride resin, acrylic resin, and silicon resin. The type of wood powder is not particularly limited, but for example, broad-leaved trees such as Mizunara, Shii, Side, Sakura, Kunugi, Quercus, Beech, Oyster, Chestnut, Walnut, etc., conifers such as cedar, larch, red pine, etc. can be used. From the viewpoint of reliability, it is preferably a hardwood. Moreover, the wood powder may be water-containing if necessary. The magnitude | size of wood powder is not specifically limited, A powder form or a chip-like thing can be used. In addition to the wood powder, the cylinder may be filled with other materials such as brown rice.

  By using a resin-made cylinder filled with wood powder as the first member 120, it is easy to adjust the density and moisture content of the standard sample 10, particularly the internal region 210. For example, in the case where raw wood (hodwood) that has been dried for a long period of time (for example, three months or more) after logging is to be measured, such raw wood has a lower density and lower moisture content than the raw wood immediately after logging. Therefore, rather than using the columnar timber 100 using the timber immediately after cutting as the first member 120, the resin cylinder filled with wood powder is used as the first member 120 to adjust the density and moisture content. A highly reliable standard sample 10 can be obtained.

  The core material 20 of the standard sample 10 according to the present embodiment has a second member 140 that covers the first member 120. The second member 140 has a sheet shape and is made of one or more selected from paper, cork, and wood. In the case where the second member 140 is made of wood, the second member 140 may be cut into a sheet from a larger piece of wood, or may be obtained by agglomerating wood powder into a sheet. The second member 140 contains a radioactive substance and constitutes a radioactive substance-containing region 220.

  When the core material 20 includes the first member 120 and the second member 140, the core material 20 can be brought close to the non-uniform distribution of the radioactive substance in the raw wood used for mushroom cultivation, and the reliability can be improved.

The second member 140 only needs to cover at least part of the side surface of the first member 120, but it is preferable to cover the entire first member 120 from the viewpoint of improving reproducibility. Further, not only the side surface but also the bottom surface portion of the cylindrical first member 120 may be further covered.
Note that the first member 120 and the second member 140 may be in direct contact with each other, or an intervening layer may be provided therebetween.

  The concentration of the radioactive substance in the second member 140 is higher than the concentration of the radioactive substance in the first member 120. The second member 140 constitutes the radioactive substance-containing region 220, while the first member 120 constitutes the inner region 210. . Therefore, in the standard sample 10 according to the present embodiment, the boundary between the inner region 210 and the radioactive substance-containing region 220 in the core material 20 is clear.

  FIG. 4B is a cross-sectional view showing a cross section perpendicular to the length direction of the standard sample 10 according to a modification of the present embodiment. In the core material 20 of this modification, a diffusion preventing member 160 is interposed between the first member 120 and the second member 140. Examples of the diffusion preventing member 160 include films of fluorine resin such as vinyl chloride resin, acrylic resin, polytetrafluoroethylene, silicon resin, urethane resin, and epoxy resin. From the viewpoint of improving reliability and stability, the thickness of the diffusion preventing member 160 is preferably 5 μm or more and 15 μm or less. The diffusion preventing member 160 is preferably provided in all regions where the second member 140 covers the first member 120.

  By providing the diffusion preventing member 160 between the first member 120 and the second member 140, it is possible to prevent the radioactive substance in the radioactive substance-containing region 220 from diffusing into the second member 140. . Therefore, changes in the radioactive material and moisture distribution are suppressed over a long period of time, and the stability of the standard sample 10 is improved. The effect of the diffusion preventing member 160 is particularly noticeable when the first member 120 is columnar wood.

Next, a method for manufacturing the standard sample 10 according to this embodiment will be described.
FIG. 5 is a diagram for explaining a method of manufacturing the standard sample 10 according to the present embodiment. In the step of preparing the core material 20, the first member 120 and the second member 140 are prepared as shown in FIG. Next, the first member 120 is covered with the second member 140. The process of covering the core material 20 with the covering member 40 can be performed similarly to the first embodiment.

  When the first member 120 is a columnar wood, the first member 120 is prepared in the same manner as the columnar wood 100 of the first embodiment. On the other hand, when the first member 120 is a resin cylinder filled with wood powder, the first member 120 is prepared by filling the resin cylinder with wood powder and sealing. The moisture content of the wood powder is adjusted as necessary. The second member 140 is prepared by applying a radioactive substance solution to, for example, paper or cork.

  Next, the first member 120 is covered with the second member 140 by winding the second member 140 around the side surface of the first member 120 as shown in FIG. 5B, for example, and the core material 20 as shown in FIG. Get. The first member 120 and the second member 140 may be adhered with an adhesive or may be simply brought into close contact with each other. When the diffusion preventing member 160 is provided, the diffusion preventing member 160 is interposed between the first member 120 and the second member 140 as shown in FIG. As a specific example, the standard sample 10 is first covered with the diffusion preventing member 160 and then covered with the second member 140. Alternatively, the first member 120 may be covered after the diffusion preventing member 160 is attached to the surface of the sheet-like second member 140 that contacts the first member 120.

  Next, the standard sample 10 is obtained as shown in FIG. 5D by performing the process of covering the core material 20 with the covering member 40 in the same manner as the method for manufacturing the standard sample 10 according to the first embodiment.

Next, the operation and effect of this embodiment will be described. In this embodiment, the same operation and effect as in the first embodiment can be obtained.
In addition, when the core material 20 includes the first member 120 and the second member 140, the degree of freedom in selecting the constituent material is improved, and the reliability of the standard sample 10 can be further improved.

(Third embodiment)
The standard sample 10 according to the third embodiment will be described below.
FIG. 6 is a cross-sectional view showing a cross section perpendicular to the length direction of the standard sample 10 according to the present embodiment. In the standard sample 10 according to the present embodiment, the first member 122 is a columnar timber having a plurality of recesses on the side surface, and the second member 142 is embedded in the recesses, except that the second member 142 is embedded. This is the same as the standard sample 10 according to the embodiment. This will be described in detail below.

  The core material 20 according to the present embodiment includes a first member 122 and a second member 142, and the first member 122 is a columnar wood provided with a plurality of concave portions on the side surface.

  As the 1st member 122, what provided the some recessed part in the side surface of the columnar timber similar to the columnar timber 100 which concerns on 1st Embodiment can be used. By doing so, the standard sample 10 which has a moisture content, a density, etc. close | similar to the moisture content, the density, etc. of the raw wood used as a measuring object can be obtained easily. The shape and arrangement of the recesses are not particularly limited, but the recesses are preferably arranged at a substantially constant density over the entire side surface of the first member 122.

  The second member 142 is made of, for example, a piece of wood, cork, paper, or the like. The second member 142 contains a radioactive substance and constitutes a radioactive substance-containing region 220. The second member 142 is embedded in the recess of the first member 122, and the second member 142 covers a part of the first member 122 in this embodiment.

  A diffusion preventing member may be interposed between the first member 122 and the second member 142. The diffusion preventing member can be made of the same material as that of the diffusion preventing member 160 of the second embodiment.

Next, a method for manufacturing the standard sample 10 according to this embodiment will be described.
FIG. 7 is a diagram for explaining a method of manufacturing the standard sample 10 according to this embodiment. In the step of preparing the core material 20, the first member 122 and the second member 142 are prepared as shown in FIG. Next, the second member 142 is fitted into the recess 124 of the first member 122. The process of covering the core material 20 with the covering member 40 can be performed similarly to the first embodiment.

  In the step of preparing the core material 20, the first member 122 is obtained by providing a plurality of recesses 124 using a drill or the like on the side surface of the columnar wood prepared in the same manner as the columnar wood 100 of the first embodiment. On the other hand, for example, a radioactive substance solution is applied to a plurality of pieces of wood shaped to fit into the recesses 124 to obtain the second member 142.

  Next, for example, as shown in FIG. 7B, the second member 142 is embedded in the concave portion 124 of the first member 122, so that a part of the first member 122 is covered with the second member 142 to obtain the core material 20. When providing the diffusion preventing member, for example, the second member 142 is coated with resin or the like and then embedded in the recess 124.

  Next, the standard sample 10 is obtained as shown in FIG. 7C by performing the step of covering the core material 20 with the covering member 40 in the same manner as the method for manufacturing the standard sample 10 according to the first embodiment.

  In this embodiment, the same operations and effects as those in the first embodiment and the second embodiment can be obtained.

  In addition, the standard sample 10 according to the present embodiment can obtain particularly high reliability when the contamination distribution on the surface of the raw wood to be measured is spot-like.

  Further, the distribution of the radioactive substance can be freely adjusted by adjusting the arrangement of the second member 142 and the content of the radioactive substance.

  Next, examples of the present invention will be described.

Example 1
The wood just after felling was processed into a cylindrical shape having a diameter of 120 mm and a length of 900 mm to obtain a cylindrical wood. Next, an aqueous solution of ¹³⁴ Cs and ¹³⁷ Cs was applied to the surface of the columnar wood so that the radioactivity concentration was 15 Bq / kg as the whole standard sample. Thereafter, liquid FRP was applied and cured, so that the entire cylindrical wood was covered with an FRP film having a thickness of 0.2 mm to obtain a standard sample 1. The weight of the obtained standard sample 1 was 11.06 kg, and the density was determined to be 1.1 g / cm ³ . Moreover, when the moisture content of the columnar wood was measured using an electric resistance moisture meter for wood before being covered with the FRP film, it was 40.9%.

On the other hand, a sample 1 for background measurement was prepared in the same manner as the standard sample 1 except that the aqueous solution of ¹³⁴ Cs and ¹³⁷ Cs was not applied. The weight of the background measurement sample 1 was 11 kg, and the water content was 41.5%.

  The standard sample 1 and the background measurement sample 1 are each measured with a radiation measuring instrument, and the value obtained by subtracting the measurement value obtained for the background measurement sample 1 from the measurement value obtained for the standard sample 1 is true. Calculated as a count value. As a result, the true count value was 1.000 cps, and the equipment conversion factor was determined to be 166 Bq / cps from the relationship between the radioactivity concentration and weight of the prepared standard sample 1.

(Example 2)
The wood just after felling was processed into a cylindrical shape having a diameter of 120 mm and a length of 900 mm to obtain a cylindrical wood. Next, the entire columnar wood was covered with a resin film. Thereafter, a paper waste coated with an aqueous solution of ¹³⁴ Cs and ¹³⁷ Cs is wound around the side surface of the cylindrical wood so that the radioactivity concentration becomes 30 Bq / kg as a whole standard sample, and further, a resin film is placed thereon to cover the whole. Covered. Next, liquid FRP was applied and cured, so that the entire cylindrical wood was covered with an FRP film having a thickness of 0.2 mm to obtain a standard sample 2. The weight of the obtained standard sample 2 was 11.03 kg, and the density was determined to be 1.1 g / cm ³ . Moreover, when the moisture content of the columnar wood was measured using an electric resistance moisture meter for wood before being covered with the resin film, it was 40.8%.

  On the other hand, a background measurement sample 2 was prepared in the same manner as the background measurement sample 1 of Example 1. The weight of the background measurement sample 2 was 11 kg, and the water content was 39.8%.

  The standard sample 2 and the background measurement sample 2 are each measured with a radiation measuring instrument, and the value obtained by subtracting the measurement value obtained for the background measurement sample 2 from the measurement value obtained for the standard sample 2 is true. Calculated as a count value. As a result, the true count value was 1.946 cps, and the equipment conversion factor was determined to be 170 Bq / cps from the relationship between the radioactivity concentration and the weight of the produced standard sample 2.

(Example 3)
A standard sample 3 was obtained in the same manner as in Example 2 except that the wood immediately after felling was processed into a cylindrical shape having a diameter of 100 mm and a length of 900 mm. The weight of the obtained standard sample 3 was 7.92 kg, and the density was determined to be 1.1 g / cm ³ . The water content was 41.6%.

  On the other hand, a sample 3 for background measurement was produced in the same manner as the sample 1 for background measurement of Example 1 except that the wood immediately after felling was processed into a cylindrical shape having a diameter of 100 mm and a length of 900 mm. The weight of the background measurement sample 3 was 7.9 kg, and the water content was 42.0%.

  Each of the standard sample 3 and the background measurement sample 3 is measured with a radiation measuring instrument, and a value obtained by subtracting the measurement value obtained for the background measurement sample 3 from the measurement value obtained for the standard sample 3 is true. Calculated as a count value. As a result, the true count value was 1.650 cps, and the device conversion factor was determined to be 144 Bq / cps from the relationship between the radioactivity concentration and weight of the prepared standard sample 3.

(Comparative Example 1)
A transparent vinyl chloride tube having an inner diameter of 130 mm, a length of 900 mm, and a tube wall thickness of 5 mm is sealed with activated carbon, an aqueous solution of ¹³⁴ Cs and ¹³⁷ Cs, and distilled water so that the water content is 40%. Sample 4 was obtained. At this time, the radioactivity concentration was set to 50 Bq / kg for the entire standard sample. The weight of the obtained standard sample 4 was 12.0 kg.

  On the other hand, in a transparent vinyl chloride tube having an inner diameter of 130 mm, a length of 900 mm, and a tube wall thickness of 5 mm, activated carbon and distilled water were added and sealed so that the water content was 40%, whereby a sample 4 for background measurement was obtained. The weight of the sample 4 for background measurement was 12.0 kg.

  Each of the standard sample 4 and the background measurement sample 4 is measured with a radiation measuring device, and the value obtained by subtracting the measurement value obtained for the background measurement sample 4 from the measurement value obtained for the standard sample 4 is true. Calculated as a count value. As a result, the true count value was 4.225 cps, and the equipment conversion factor was determined to be 115 Bq / cps from the relationship between the radioactivity concentration and the weight of the prepared standard sample 4.

(Comparative Example 2)
A standard sample 5 was obtained in the same manner as in Comparative Example 1 except that the weight was 8.6 kg. The density of the obtained standard sample 5 was determined to be 0.85 g / cm ³ .

  On the other hand, Sample 5 for background measurement was produced in the same manner as Comparative Example 1 except that the weight was 8.6 kg.

  Each of the standard sample 5 and the background measurement sample 5 is measured with a radiation measuring instrument, and a value obtained by subtracting the measurement value obtained for the background measurement sample 5 from the measurement value obtained for the standard sample 5 is true. Calculated as a count value. As a result, the true count value was 3.458 cps, and the device conversion factor was determined to be 124 Bq / cps from the relationship between the radioactivity concentration and weight of the prepared standard sample 5.

(Comparative Example 3)
A standard sample 6 was obtained by placing sawdust and an aqueous solution of ¹³⁴ Cs and ¹³⁷ Cs in a transparent acrylic tube having an inner diameter of 100 mm, a length of 900 mm, and a tube thickness of 5 mm so that the water content was 40%. . At this time, the radioactivity concentration was set to 50 Bq / kg for the entire standard sample. The weight of the obtained standard sample 6 was 4.1 kg, and the density was 0.6 g / cm ³ .

On the other hand, a sample 6 for background measurement was obtained in the same manner as the standard sample 6 except that distilled water was used instead of the aqueous solution of ¹³⁴ Cs and ¹³⁷ Cs. The weight of the background measurement sample 6 was 4.1 kg.

  Each of the standard sample 6 and the background measurement sample 6 is measured with a radiation measuring device, and a value obtained by subtracting the measurement value obtained for the background measurement sample 6 from the measurement value obtained for the standard sample 6 is true. Calculated as a count value. As a result, the true count value was 1.344 cps, and the device conversion factor was determined to be 152 Bq / cps from the relationship between the radioactivity concentration and the weight of the produced standard sample 6.

(Measurement of logs and brown rice for shiitake cultivation)
The relationship between the weight of the logs for shiitake cultivation containing ¹³⁴ Cs and ¹³⁷ Cs and the device conversion factor was measured. Specifically, after each non-destructive measurement of each log for shiitake cultivation and obtaining a count number C (cps), the same log for shiitake cultivation was processed into sawdust and the amount of radioactivity B (Bq) was measured. . The device conversion coefficient K (Bq / cps) was obtained from the relationship of K = B / C. The measurement was performed for each log with a moisture content of 40% and 34%. The moisture content was measured using an electric resistance moisture meter.

  Further, the relationship between the weight and the equipment conversion factor was measured for brown rice having a moisture content of 12%. Specifically, brown rice was non-destructively measured to obtain a count, and the device conversion coefficient was obtained in the same manner as the raw wood measurement.

  Table 1 summarizes the measurement results of “Raw wood moisture content 40%”, “Raw wood moisture content 34%”, and “Brown rice moisture content 12%”.

FIG. 8 shows the relationship between the equipment conversion coefficient obtained in Examples 1 to 3 and the weight of the standard sample, and FIG. 9 shows the relationship between the equipment conversion coefficient obtained in Comparative Examples 1 to 3 and the weight of the standard sample. It was. In FIG. 8 and FIG. 9, the result of having measured the log for shiitake cultivation containing ¹³⁴ Cs and ¹³⁷ Cs and the result of measuring brown rice are shown together. In both figures, “Raw wood moisture content 40%” and “Raw wood moisture content 34%” are the measurement results of the above-mentioned raw logs for shiitake cultivation with a moisture content of 40% and a moisture content of 34%, respectively. "It is a measurement result of the brown rice having a moisture content of 12%.

  From the measurement results, it was found that the equipment conversion coefficient was significantly different from “Raw wood moisture content 40%” and “Raw wood moisture content 34%”, and the difference in moisture content affected the equipment conversion coefficient. Therefore, in order to improve the accuracy of the standard sample, it has been found that it is important to bring the moisture content of the standard sample closer to the measurement target log.

  On the other hand, “Rawwood moisture content 34%” and “Brown rice 12%” showed relatively close equipment conversion coefficients, although the moisture content was greatly different. Therefore, it was found that not only the moisture content but also the sample shape, material, and other factors greatly affect the equipment conversion factor.

  The standard samples of Examples 1 to 3 were in good agreement with the measurement characteristics of the raw wood having a moisture content of 40%, and it was confirmed that the reliability as the standard sample was high. Moreover, even if it measured by the method similar to the above after 6 months, the standard sample of Examples 1-3 was maintaining the same precision, and it confirmed that it was excellent in stability.

  On the other hand, in Comparative Examples 1-3, although the moisture content was set to 40%, a characteristic different from that of the raw wood having a moisture content of 40% was shown. Therefore, it turned out that Comparative Examples 1-3 is not reliable as a standard sample of the raw wood for mushroom cultivation.

  Also, for background measurement, the sample for measuring background of the comparative example has a count number that is significantly different from that of the raw wood that does not contain radioactive material, so it was found that it cannot be used for background measurement on the raw wood for mushroom cultivation. .

  As mentioned above, although embodiment of this invention was described with reference to drawings, these are the illustrations of this invention, Various structures other than the above are also employable.

10 Standard Sample 100 Cylindrical Wood 120, 122 First Member 124 Recess 140, 142 Second Member 160 Diffusion Prevention Member 20 Core Material 210 Internal Region 220 Radioactive Substance Containing Region 40 Covering Member

Claims (13)

It is a standard sample used for radioactivity measurement of raw wood used for mushroom cultivation,
A cylindrical core material containing wood,
A covering member covering the core material,
The core material has a radioactive substance-containing region on the side surface part,
Standard sample for radioactivity measurement. In the standard sample for radioactivity measurement according to claim 1,
The core material includes a first member containing wood and a second member that covers the first member and constitutes the radioactive substance-containing region.
Standard sample for radioactivity measurement. In the standard sample for radioactivity measurement according to claim 2,
A diffusion preventing member is interposed between the first member and the second member.
Standard sample for radioactivity measurement. In the standard sample for radioactivity measurement according to claim 2 or 3,
The first member is cylindrical wood;
Standard sample for radioactivity measurement. In the standard sample for radioactivity measurement according to claim 2 or 3,
The first member is formed by filling at least wood powder into a resin cylinder,
Standard sample for radioactivity measurement. In the standard sample for radioactivity measurement according to any one of claims 2 to 5,
The second member has a sheet shape, and is composed of one or more selected from paper, cork, and wood.
Standard sample for radioactivity measurement. In the standard sample for radioactivity measurement according to claim 2,
The first member is a columnar wood provided with a plurality of recesses on a side surface,
The second member is embedded in the recess.
Standard sample for radioactivity measurement. In the standard sample for radioactivity measurement according to claim 1,
The radioactive substance-containing region is soaked with a radioactive substance solution,
Standard sample for radioactivity measurement. In the standard sample for radioactivity measurement according to any one of claims 1 to 8,
The moisture content on a wet basis is 35% or more and 45% or less,
Standard sample for radioactivity measurement. In the standard sample for radioactivity measurement according to any one of claims 1 to 9,
The density is 0.5 g / cm ³ or more and 1.5 g / cm ³ or less,
Standard sample for radioactivity measurement. A method for producing a standard sample used for measuring radioactivity of raw wood used for mushroom cultivation,
A step of preparing a core material including a wood having a radioactive substance-containing region on a side surface;
Covering the core material with a covering member,
A method for producing a standard sample for radioactivity measurement. In the manufacturing method of the standard sample for radioactivity measurement of Claim 11,
In the step of preparing the core material, a first member containing wood is covered with a second member that constitutes the radioactive substance-containing region.
A method for producing a standard sample for radioactivity measurement. In the manufacturing method of the standard sample for radioactivity measurement of Claim 12,
A diffusion preventing member is interposed between the first member and the second member.
A method for producing a standard sample for radioactivity measurement.

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