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Indigenous approach to nuclear track studies in academics
Radiation Measurements 44 (2009) 1036–1039
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Indigenous approach to nuclear track studies in academics T. Tsuruta a, b, *, S. Hohara a, Y. Nakanishi b, H. Shimba c a
Atomic Energy Research Institute, Kinki University, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan Interdisciplinary Graduate School of Science and Engineering, Kinki University, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan c Faculty of Science and Engineering, Kinki University, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 October 2008 Accepted 20 October 2009
In a study aimed at introduction of the nuclear tracks in solids into high school education, several experimental methods were developed and proposed. From the experiments of the basic course, students will be able to learn various characteristics of a-particles such as straight-line motion, short range in material, formation of the track, etc. From the experiments of the advanced course, the students will be able to learn various characteristics of neutrons such as (n,a) reaction, recoil reaction, neutron fluence, the relationship between neutron energy and cross section, etc. It is an advantage of the solid state track detector that the trails of invisible radiation can be observed as clearly visible tracks. The tracks must arouse student’s interest in radiation. It is expected that more complete education of radiation in school cultivate people’s better understanding of this field. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: School education Radiation Nuclear tracks Boron doped CR-39 plate Pure CR-39 plate
1. Introduction Japanese people know that numerous survivors of two atomic bombs in Hiroshima and Nagasaki were tormented with the late effects of radiation. They remember that the test of the hydrogen bomb in South Pacific Ocean caused radiation hazards to the Japanese fishermen and the radioactive contamination to the tuna which was Japanese favorite food. They realized the scale of Chernobyl accident from radioactive materials widely diffused in the atmosphere. They still have a vivid memory of the criticality accident which broke out in their country in 1999. Because of the historical background, Japanese people are sensitive to radiation. A lot of people have morbid fear of radiation. They oppose the introduction of food irradiation. Some people seriously worry about a slight radiation for diagnosis. What should we do in order to erase morbid fear of radiation? In order to erase the ‘‘radiophobia’’, the education of radiation must be effective, especially for coming generation. Until now people were frequently taught fearfulness of radiation. However they did not have the occasion to learn intrinsic nature of radiation or the relationship of radiation dose and effects. The difficulty in learning radiation arises from the fact that the radiation is invisible. In general, people are frightened at
* Corresponding author. Atomic Energy Research Institute, Kinki University, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan. Fax: þ81 6 6721 3743. E-mail address: [email protected] (T. Tsuruta). 1350-4487/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2009.10.071
invisible objects. It is difficult for people to realize the existence of the radiation. However, the nuclear tracks indicate visually that the radiation exists really. Therefore, the experiments of the nuclear tracks in solids promote understanding of radiation. It is more effective to introduce the experiments of the track into high school education. We would like to show several experiments which can be put into practice in classrooms at the high school.
2. Basic course 2.1. Materials and methods Fig. 1 shows lantern mantles and welding rods. These materials can be utilized for alpha sources because they are impregnated with thorium. From the analysis of gamma-ray spectrum, it was found that the lantern mantles contain thorium ore and welding rods contain pure thorium. These materials can be used freely in school, because they exist outside of framework of the radiological regulation. The threads of lantern mantle were twisted into a string. Fig. 2 shows that the string or the welding rod is put on a pure CR-39 resin plate. A part of the plate was covered with one or two sheets of wrapping film to investigate the shielding effect of the film for alpha particles. About one week of irradiation time is necessary to obtain sufficient density of the alpha tracks. Therefore it is desirable that two school hours with an interval of a week are allotted for the
T. Tsuruta et al. / Radiation Measurements 44 (2009) 1036–1039
1037
Fig. 1. Alpha sources used in these experiments.
Fig. 2. Set up showing CR-39 plates exposed to alpha sources.
experiment. After irradiation, the plates were etched with the aqueous solution of 30%KOH at 90 C for 8, 15 or 30 min. After etching, the plates were rinsed in running water and dried in air. 2.2. Results
easy to handle because the detector and converter are incorporated. Molecular structure of ortho-carborane is shown in Fig. 6. The plate was irradiated with thermal neutrons in the Research Reactor of Kinki University at the fluence of about 109 (cm2). The pure CR-39 resin plate is a good track detector for fast neutrons. The plates was covered with a polyethylene sheet and
When we hold the etched plates to the light, we can observe a white line on the plate with the naked eye. As shown in Fig. 3, there is difference of shade between the bare part and the part covered with one or two sheets of film during irradiation. From this phenomenon students can learn a nature of alpha particles which lose their energy in very short ranges and damage the material. Fig. 4 shows the etch-pits originating in alpha tracks on CR-39 plate which was directly contacted with the welding rod. A series of three photographs arranged horizontally represents the transition of the same area of a plate at successive stages of etching. Therefore it is observed that the each etch-pit grows in size and changes the shape with etching time. In Fig. 5, a comparison of etch-pits on bare and film covered parts of the plate is made. A large number of various shape of etchpits are observed on the part which was irradiated without the film. On the other hand, a small number of round etch-pits are observed on the part which was wrapped in the film during irradiation. 3. Advanced course 3.1. Materials and methods The CR-39 resin plate doped with a boron compound: orthocarborane is a good track detector for thermal neutrons. The plate is
Fig. 3. White line on the etched plate which was irradiated using a thread of lantern mantle. Etching conditions and time: 30% KOH, 90 C, 15 m.
1038
T. Tsuruta et al. / Radiation Measurements 44 (2009) 1036–1039
Fig. 4. Growth of etch-pits on CR-39 plate with etching time. Etching conditions: 30% KOH, 90 C.
Fig. 5. Comparison of etch-pits on bare and covered part of CR-39 plate exposed to alpha source (welding rod). Etching conditions and time: 30% KOH, 90 C, 15 m.
irradiated with several MeV fast neutrons using an (a,n) neutron source at the fluence of about 109 (cm2). 3.2. Results
we can practice the whole process of the experiment in the classroom, because there is no need to use the radiation sources which are legally controlled. In the case of the advanced course, on the other hand, the process of the neutron irradiation must be done under the cooperation of the facility possessing neutron source.
Fig. 7 shows the etch-pits originating in 10B(n,a)7Li reactions in the ortho-carborane doped CR-39 plate. It was found that the optimum concentration of ortho-carborane in the plate was 0.5%. When the etching was made on an appropriate condition and time, the sensitivity of the plate was about 4 104 etch-pits/neutron for thermal neutrons (Tsuruta and Juto, 1984). Fig. 8 shows the etch-pits originating in recoil reactions in the pure CR-39 plate or the polyethylene sheet as a radiator. From not only in the case of Fig. 7 but also in the case of Fig. 8, it is observed that the etch-pits grow in size and number with the etching time. Increasing of the number of etch-pits is explained from the fact that there are latent tracks in the plate, which is dissoluble in the etching solution. When the etching was made on an appropriate condition and time, the sensitivity of the plate contacted with polyethylene radiator was about 5 104 etch-pits/neutron for several MeV neutrons (Tsuruta et al., 1992). 4. Discussion The CR-39 plate is ideal for the observation of nuclear tracks because it has a good optical quality to identify the tracks as very clear etch-pits on a smooth surface. In the case of the basic course,
Fig. 6. Molecular structure of ortho-carborane.
T. Tsuruta et al. / Radiation Measurements 44 (2009) 1036–1039
1039
Fig. 7. Growth of etch-pits by thermal neutron on CR-39 plate doped with ortho-carborane with etching time. Etching conditions: 30% KOH, 90 C.
Fig. 8. Growth of etch-pits with etching time on the fast neutron irradiated pure CR-39 plate. Etching conditions: 30% KOH, 90 C.
In our institute, a training in radiation and nuclear reactor is given to high school teachers several times a year. In the training, the teachers learn not only above-mentioned experimental method but also behavior of radiation in matter and applications of radiation. When teachers give the additional lecture about the principle of the track formation and the utilization of the solid state track detector for detection of radon, neutron dosimetry, fission track dating etc., the students will be excited their curiosity about radiation. The observation of nuclear tracks in school education seems to be effective to spread the knowledge of radiation. When people obtain basic knowledge of radiation, the radiophobia will disappear. Their impartial understanding of radiation is important to public acceptance of the practical use of radiation and atomic energy.
Acknowledgments We would like to express our thanks to Mr. K. Kobayashi of Yamamoto Kogaku Co., Ltd. and Mr. O. Murata of O. Y. Techno Co. Ltd. for their assistance in the preparation of the pure and the boron doped CR-39 resin plates.
References Tsuruta, T., Juto, N., 1984. Neutron dosimetry with boron-doped CR-39 plastic. J. Nucl. Sci. Technol. 21, 871–876. Tsuruta, T., Niwa, T., Fukumoto, Y., 1992. Experimental study of CR-39 etched track detector for fast neutron dosimetry. J. Nucl. Sci. Technol. 29, 1108–1115.
Contents lists available at ScienceDirect
Radiation Measurements journal homepage: www.elsevier.com/locate/radmeas
Indigenous approach to nuclear track studies in academics T. Tsuruta a, b, *, S. Hohara a, Y. Nakanishi b, H. Shimba c a
Atomic Energy Research Institute, Kinki University, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan Interdisciplinary Graduate School of Science and Engineering, Kinki University, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan c Faculty of Science and Engineering, Kinki University, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 October 2008 Accepted 20 October 2009
In a study aimed at introduction of the nuclear tracks in solids into high school education, several experimental methods were developed and proposed. From the experiments of the basic course, students will be able to learn various characteristics of a-particles such as straight-line motion, short range in material, formation of the track, etc. From the experiments of the advanced course, the students will be able to learn various characteristics of neutrons such as (n,a) reaction, recoil reaction, neutron fluence, the relationship between neutron energy and cross section, etc. It is an advantage of the solid state track detector that the trails of invisible radiation can be observed as clearly visible tracks. The tracks must arouse student’s interest in radiation. It is expected that more complete education of radiation in school cultivate people’s better understanding of this field. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: School education Radiation Nuclear tracks Boron doped CR-39 plate Pure CR-39 plate
1. Introduction Japanese people know that numerous survivors of two atomic bombs in Hiroshima and Nagasaki were tormented with the late effects of radiation. They remember that the test of the hydrogen bomb in South Pacific Ocean caused radiation hazards to the Japanese fishermen and the radioactive contamination to the tuna which was Japanese favorite food. They realized the scale of Chernobyl accident from radioactive materials widely diffused in the atmosphere. They still have a vivid memory of the criticality accident which broke out in their country in 1999. Because of the historical background, Japanese people are sensitive to radiation. A lot of people have morbid fear of radiation. They oppose the introduction of food irradiation. Some people seriously worry about a slight radiation for diagnosis. What should we do in order to erase morbid fear of radiation? In order to erase the ‘‘radiophobia’’, the education of radiation must be effective, especially for coming generation. Until now people were frequently taught fearfulness of radiation. However they did not have the occasion to learn intrinsic nature of radiation or the relationship of radiation dose and effects. The difficulty in learning radiation arises from the fact that the radiation is invisible. In general, people are frightened at
* Corresponding author. Atomic Energy Research Institute, Kinki University, Kowakae, Higashi-Osaka, Osaka 577-8502, Japan. Fax: þ81 6 6721 3743. E-mail address: [email protected] (T. Tsuruta). 1350-4487/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.radmeas.2009.10.071
invisible objects. It is difficult for people to realize the existence of the radiation. However, the nuclear tracks indicate visually that the radiation exists really. Therefore, the experiments of the nuclear tracks in solids promote understanding of radiation. It is more effective to introduce the experiments of the track into high school education. We would like to show several experiments which can be put into practice in classrooms at the high school.
2. Basic course 2.1. Materials and methods Fig. 1 shows lantern mantles and welding rods. These materials can be utilized for alpha sources because they are impregnated with thorium. From the analysis of gamma-ray spectrum, it was found that the lantern mantles contain thorium ore and welding rods contain pure thorium. These materials can be used freely in school, because they exist outside of framework of the radiological regulation. The threads of lantern mantle were twisted into a string. Fig. 2 shows that the string or the welding rod is put on a pure CR-39 resin plate. A part of the plate was covered with one or two sheets of wrapping film to investigate the shielding effect of the film for alpha particles. About one week of irradiation time is necessary to obtain sufficient density of the alpha tracks. Therefore it is desirable that two school hours with an interval of a week are allotted for the
T. Tsuruta et al. / Radiation Measurements 44 (2009) 1036–1039
1037
Fig. 1. Alpha sources used in these experiments.
Fig. 2. Set up showing CR-39 plates exposed to alpha sources.
experiment. After irradiation, the plates were etched with the aqueous solution of 30%KOH at 90 C for 8, 15 or 30 min. After etching, the plates were rinsed in running water and dried in air. 2.2. Results
easy to handle because the detector and converter are incorporated. Molecular structure of ortho-carborane is shown in Fig. 6. The plate was irradiated with thermal neutrons in the Research Reactor of Kinki University at the fluence of about 109 (cm2). The pure CR-39 resin plate is a good track detector for fast neutrons. The plates was covered with a polyethylene sheet and
When we hold the etched plates to the light, we can observe a white line on the plate with the naked eye. As shown in Fig. 3, there is difference of shade between the bare part and the part covered with one or two sheets of film during irradiation. From this phenomenon students can learn a nature of alpha particles which lose their energy in very short ranges and damage the material. Fig. 4 shows the etch-pits originating in alpha tracks on CR-39 plate which was directly contacted with the welding rod. A series of three photographs arranged horizontally represents the transition of the same area of a plate at successive stages of etching. Therefore it is observed that the each etch-pit grows in size and changes the shape with etching time. In Fig. 5, a comparison of etch-pits on bare and film covered parts of the plate is made. A large number of various shape of etchpits are observed on the part which was irradiated without the film. On the other hand, a small number of round etch-pits are observed on the part which was wrapped in the film during irradiation. 3. Advanced course 3.1. Materials and methods The CR-39 resin plate doped with a boron compound: orthocarborane is a good track detector for thermal neutrons. The plate is
Fig. 3. White line on the etched plate which was irradiated using a thread of lantern mantle. Etching conditions and time: 30% KOH, 90 C, 15 m.
1038
T. Tsuruta et al. / Radiation Measurements 44 (2009) 1036–1039
Fig. 4. Growth of etch-pits on CR-39 plate with etching time. Etching conditions: 30% KOH, 90 C.
Fig. 5. Comparison of etch-pits on bare and covered part of CR-39 plate exposed to alpha source (welding rod). Etching conditions and time: 30% KOH, 90 C, 15 m.
irradiated with several MeV fast neutrons using an (a,n) neutron source at the fluence of about 109 (cm2). 3.2. Results
we can practice the whole process of the experiment in the classroom, because there is no need to use the radiation sources which are legally controlled. In the case of the advanced course, on the other hand, the process of the neutron irradiation must be done under the cooperation of the facility possessing neutron source.
Fig. 7 shows the etch-pits originating in 10B(n,a)7Li reactions in the ortho-carborane doped CR-39 plate. It was found that the optimum concentration of ortho-carborane in the plate was 0.5%. When the etching was made on an appropriate condition and time, the sensitivity of the plate was about 4 104 etch-pits/neutron for thermal neutrons (Tsuruta and Juto, 1984). Fig. 8 shows the etch-pits originating in recoil reactions in the pure CR-39 plate or the polyethylene sheet as a radiator. From not only in the case of Fig. 7 but also in the case of Fig. 8, it is observed that the etch-pits grow in size and number with the etching time. Increasing of the number of etch-pits is explained from the fact that there are latent tracks in the plate, which is dissoluble in the etching solution. When the etching was made on an appropriate condition and time, the sensitivity of the plate contacted with polyethylene radiator was about 5 104 etch-pits/neutron for several MeV neutrons (Tsuruta et al., 1992). 4. Discussion The CR-39 plate is ideal for the observation of nuclear tracks because it has a good optical quality to identify the tracks as very clear etch-pits on a smooth surface. In the case of the basic course,
Fig. 6. Molecular structure of ortho-carborane.
T. Tsuruta et al. / Radiation Measurements 44 (2009) 1036–1039
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Fig. 7. Growth of etch-pits by thermal neutron on CR-39 plate doped with ortho-carborane with etching time. Etching conditions: 30% KOH, 90 C.
Fig. 8. Growth of etch-pits with etching time on the fast neutron irradiated pure CR-39 plate. Etching conditions: 30% KOH, 90 C.
In our institute, a training in radiation and nuclear reactor is given to high school teachers several times a year. In the training, the teachers learn not only above-mentioned experimental method but also behavior of radiation in matter and applications of radiation. When teachers give the additional lecture about the principle of the track formation and the utilization of the solid state track detector for detection of radon, neutron dosimetry, fission track dating etc., the students will be excited their curiosity about radiation. The observation of nuclear tracks in school education seems to be effective to spread the knowledge of radiation. When people obtain basic knowledge of radiation, the radiophobia will disappear. Their impartial understanding of radiation is important to public acceptance of the practical use of radiation and atomic energy.
Acknowledgments We would like to express our thanks to Mr. K. Kobayashi of Yamamoto Kogaku Co., Ltd. and Mr. O. Murata of O. Y. Techno Co. Ltd. for their assistance in the preparation of the pure and the boron doped CR-39 resin plates.
References Tsuruta, T., Juto, N., 1984. Neutron dosimetry with boron-doped CR-39 plastic. J. Nucl. Sci. Technol. 21, 871–876. Tsuruta, T., Niwa, T., Fukumoto, Y., 1992. Experimental study of CR-39 etched track detector for fast neutron dosimetry. J. Nucl. Sci. Technol. 29, 1108–1115.