RADIATION RE-EDUCATION MATERIALS THE UNIV. OF TOKYO DOC No. 39 (2021)1. Background on Revision of Dose Limit of the Lens of the Eye

and Method of Dose Management 1

2. Let’s Discuss Potential Problems and/or Accidents Relating to Radiation Facilities 5

3. Radiation Effects on the Fetus and Exposure Control for Women 7

4. Conventions and Agreements on Safeguards in Japan and Several Points for Carrying Out Material Accountancy 9

5. Point to Note Regarding Maintainance and Inspection of X-ray Devices 11

Edited by Division for Environment, Health and Safety

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1 Background on Revision of Dose Limit of the Lens of the Eye and Method of Dose Management

1. Current Regulations in JapanThe effective dose and the equivalent dose limits for radiation workers in the

current domestic law are as shown in Table 1, these are based on the ICRP 1990 recommendation.

The equivalent dose for the lens of the eye is an amount that cannot be measured directly, and as a measurable amount to estimate this, ICRP recommend using a 3mm dose equivalent of the dose applied to the external exposure of an individual. In Principle, these measurements are not obligatory on this basis the domestic law adopted, as an appropriate dose calculation method for the lens of the eye, the 1cm dose equivalent or 70μm dose equivalent.

2. New Dose Limit and Overseas SituationThe ICRP issued a “Statement on Tissue Reactions (Seoul Statement)” in April

2011. The Statement indicated that a threshold dose of radiation-induced cataracts is considered to be about 0.5Gy (previously thought to be 8Gy) for both acute and chronic exposures, based on the findings of an epidemiological survey of atomic bomb survivors and Chernobyl accident dissemination workers. Therefore, it is recommended that the equivalent dose limit of the lens of the eye for occupational exposure in the planned exposure situation should “not exceed 20 mSv per year, average over defined periods of 5 years and 50 mSv in any single year”. In addition, the recommendations were incorporated into the IAEA’s “International Basic Safety Standards for Protection (BSS)”, and countries such as EURATOM member countries, Australia and Norway have incorporated new equivalent dose limits for the lens of the eye into their national law.

3. Response to Japan (Discussion on the Radiation Council)The Radiation Council established “The Radiation Protection Study Group for Eye Lens”

at the 135th General Meeting on July 21, 2017 in response to the Seoul Statement, with respect the concept of radiation protection systems internationally agreed by ICRP, IAEA, etc. and from the perspective of incorporating it into domestic law as standard for radiation

Table 1 Effective dose and equivalent dose limits for radiation workers

Dose limit Measuring site Radiation workersEffective dose Body (1) Effective dose limit

•100mSv / 5 years *1

•50mSv/year(2) Women 5mSv/three months(3) Pregnant women

•Internal exposure 1mSv / pregnancy periodEquivalent dose Lens of the eye 150mSv/year

Skin •100mSv / 5 years *2

•50mSv/yearThe surface of abdomen of pregnant women 2mSv/ pregnancy period

*1 Period divided into five years from April 1, 2001*2 Period divided into five years from April 1, 2021

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Table 2 Related laws and regulations concerning the state of radiation protection pertaining to the lens of the eyeMinistries under the jurisdiction

Related Legal name

National Personnel Authority

Rules of the National Personnel Authority

Rules of the National Personnel Authority (Prevention of Radiation Hazard for Staff)

Ministry of Health, Laboure and Welfare

Medical Care Act Enforcement Regulations of the Medical Care ActMethods for measuring doses exposed by radiation practitioners, etc., and methods for calculating effective and equivalent doses

Clinical Laboratory Technician Act

Standards for structural equipment, etc. of a sanitation laboratory with radioactive isotopes for specimen testing prescribed in Article 12, paragraph 1, item 5 of the Enforcement Regulations of the Clinical Laboratory Technician Act

Pharmaceuticals and Machinery Act

Regulations on the Manufacture and Handling of RadiopharmaceuticalsStandards for the quantity of radioactive materials, etc.

Industrial Safety and Health Act

Regulations for the Prevention of Ionization Radiation HazardsLimits and methods prescribed by the Minister of Health, Laboure and Welfare pursuant to the provisions of Article 3, paragraph 3 and Article 8, Article 5 and Article 9, paragraph 2 of the Regulations for the Prevention of Ionization Radiation Hazards

Ministry of Agriculture, Forestry and Fisheries

Veterinary therapy Veterinary Therapy Enforcement RegulationsMatters that specify the method prescribed by the Minis-ter of Agriculture, Forestry and Fisheries pursuant to the provisions of Article 14 of the Veterinary Therapy Enforcement Regulations

Ministry of Economy, Trade and Industry

Mine Safety Act Standards, etc. established by the Minister of Economy, Trade and Industry in accordance with the Mine Safety Act Enforcement Regulations

Ministry of Land, Infrastructure, Transport and Tourism

Seamen Act Seamen Ionization Radiation Hazard Prevention RegulationsLimits and methods specified by the Minister of Land, Infrastructure, Transport and Tourism in accordance with the Seamen Ionization Radiation Hazard Prevention Regulations

Nuclear Regulators Asso-ciation

Radioisotopes, etc. Regulation Act

Ordinance for Enforcement of Radioisotopes, etc. Regulation ActNotification to Specify the Quantities, etc. of Radioisotopes

Nuclear Reactors, etc. Regulation Act

Notification of dose limits based on rules, etc. concerning the business of refining nuclear raw materials and nuclear fuel materialsNotification of necessary matters concerning the security of the reactor facility of the Fukushima Daiichi Nuclear Power Plant of TEPCO Co., Ltd., and the protection of specified nuclear fuel materials

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protection technology.The subcommittee organized the problems associated with the adoption of the new

equivalent dose limit, conducted an arbitrary call for opinions (public comments), and compiled a report “How radiation protection is applied to the lens of the eye” in February 2018.

At the 140th General Meeting held on March 2, 2018, the Radiation Council reported the establishment of a radiation protection subcommittee on the lens of the eye in response to the ICRP’s “Statement on Organizational Response” and compiled the report. Afterwards, the Radiation Council requested the relevant government agencies (Table 2) to take necessary measures with reference to this.

The National Personnel Authority, the Ministry of Health, Labour and Welfare, the Ministry of Agriculture, Forestry and Fisheries, the Ministry of Land, Infrastructure, Transport and Tourism, and the Nuclear Regulators Association, in response to an opinion from the Radiation Council at the 140th General Meeting, consulted on the revision of the rules, etc. at the 147th General Meeting on December 23, 2019 (the Ministry of Economy, Trade and Industry’s consultation occured at the 149th General Meeting on July 17, 2020).

At the 148th General Meeting held on January 24, 2020, the Radiation Council reported that amendments to the rules made the National Personnel Authority, the Ministry of Health, Labour and Welfare, the Ministry of Agriculture, Forestry and Fisheries, the Ministry of Land, Infrastructure, Transport and Tourism, and the Nuclear Regulatory Commission were generally valid.

4. Points Relating to Major AmendmentsIn the medical field where the exposure dose is highest in Japan, we will implement

appropriate protective measures and measurements, and in the decommissioning work of TEPCO’s Fukushima Daiichi Nuclear Power Plant, they will voluntarily adopt management standards and start management, so it is possible to incorporate new lens equivalent dose limits in Japan. Therefore, a new lens equivalent dose limit will be adapted that it does not exceed 20 mSv per year, average over defined periods of 5 years and 50 mSv in any single year. To match the treatment of the starting point of “20 mSv per year, average over defined periods of 5 years “ with the management of the current effective dose, the starting year will be 2021.

As operational quantities for calculating the equivalent dose of the lens of the eye, it is possible to measure the equivalent dose of the lens of the eye at a 3 mm dose equivalent as a measurement method for the external exposure of the individual. However, it is also possible to calculate the equivalent dose of the lens of the eye by the measuring the previous 1 cm dose equivalent or 70 μm dose equivalent. Further, for neutrons, the basic measurement remains 1cm dose equivalent.

Authority urges relevant government agencies and businesses to work to optimizing protection, keep in mind that even if the new limits are observed, long period exposure can exceed the threshold dose. Moreover, related academic societies will formulate guidelines to ensure that optimization efforts by business operators in the medical field proceed smoothly, and relevant government agencies will support them.

There is currently little need to change the equivalent dose limit of the lens of the eye for emergency workers. Therefore, while maintaining the current system for the time being, we will closely monitor the latest knowledge and international trends and consider it if necessary.

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5. Transitional Measures at the Ministry of Health, Laboure and WelfareThe Ministry of Health, Labour and Welfare has established its own “Study Group on

Reviewing the Exposure Limit of the Lens of the Eye,” and, from its consideration,added the following transitional measures.

Equivalent dose limit of the lens of the eye for the doctors among radiation workers, whose equivalent dose to the lens of their eyes still exceeds 100 mSv per 5 years, even with shielding and other appropriate radiation protection measures, and who have highly specialized knowledge, skills and experience in the medical treatment they perform and, therefore, cannot easily obtain a successor, shall be 50 mSv per year from April 1, 2021 until 31st of March 2023, and 60 mSv per 3 years and 50 mSv per year from April 2023 until 31st of March 2026.

In response to this transitional measure, the Radiation Council requests the Ministry of Health, Laboure and Welfare to take necessary measures to ensure thorough dose control and grasp the exposure situation during the transitional measure period and to report them properly to the Radiation Council.

Former member of the Radiation CouncilHeadquarters Radiation Management Advisor

Shoji FUTATSUGAWARe-education Theme:

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“It’s really difficult for a person to die from radiation exposure...”These were the words of a professor when I was an undergraduate student about 30

years ago. I still remember how shocked I was because his message was quite different from my (young) impression of “radiation” at the time. As you can imagine, depending on the situation and context, it could have been correct, but it could also have been very misleading or even completely wrong. Now that we have come to think about the existence of radiation and radioactive materials, and their application and safety management from a wide range of perspectives, this sentence can be used as an example to help us understand things from various angles, including the true meaning of the message, the complex social and scientific perspectives represented by the relationship between the sender and the receiver including the scientific perspective.

Regardless of whether radiation exposure is directly linked to death or not, the reality is that radiation-related accidents or problems can cause anxiety and even harm to people inside and/or outside the facility. Once a problem occurs at a facility, many stakeholders may be caught in a very difficult situation, both physically and psychologically. To prevent this from happening, we have developed a safety culture system, rules, and handling behavior based on our long historical experience in the application of radiation since the discovery of X-rays by Dr. Roentgen in 1895. Only a few of these items have been positioned as regulatory items in the legal system, which is exactly where we are now.

I personally believe that the root causes of accidental problems occurring at radiation facilities are not much different from those at other facilities. It is true that the main characteristics of radiation facilities are the slightly stronger administrative constraints on user registration and continuity of registration, the restrictions on the purpose, amount, and location of radiation and radioactive materials that can be used, and the strict prior agreements on how to store and handle materials, including wastes. In this sense, I think that the ideal form of management is to share past cases and experiences of other facilities from the perspective of what kinds of accident problems are likely to occur in the environment and from the use of the facility, and to take the necessary rational measures.

By focusing on the source of radiation, facilities can be classified as RI (Radioisotopes) facilities, accelerator facilities, X-ray facilities, nuclear fuel facilities, and nuclear reactor facilities. All the past accidents handled by the Nuclear Regulation Authority of Japan can be viewed through the website (accidents information: https://www.nsr.go.jp/activity/bousai/trouble/index.html). It is advisable for UTokyo members involved in radiation safety management to check this information at least once a year.

Three years ago, we submitted a brief commentary entitled “Case Studies of Accidents Relating Radiation and Radioactive Materials” to ISOTOPE NEWS magazine (June 2017 issue) (https://www.jrias.or.jp/books/pdf/201706_TRACER_YAMAMOTO_HOKA. (pdf). Although relatively serious cases have been reported in domestic facilities in the following three years, the situation of accidents related to universities and small and medium-sized research facilities that we are familiar with does not seem to have changed significantly.

Typical accident involving radiation workers are (1) loss, theft, or improper disposal of radioactive materials (cases in which the whereabouts of the materials have somehow been lost, or cases in which the materials have been unintentionally and accidentally disposed of), (2) damage to sealed radiation sources or storage containers (cases in which workers are unaware of the fact that they have been damaged for a long time),

2 Let’s Discuss Potential Problems and/or AccidentsRelating Radiation Facilities

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(3) outpouring of materials that should be registered and controlled, and (4) unplanned exposure due to accelerators, irradiation devices, or X-ray devices (accidental intrusion of the body into the irradiation field during irradiation).

In addition to these, from the manager’s point of view, it is important to pay attention to the items checklist during facility inspections, periodic inspections, periodic checks, and on-site inspections. I think the most vexing and potentially “scary” cases are those related to hardware failures due to aging facilities and sources (underground piping and reservoirs, old sources that have been handed down from generation to generation, etc.). I imagine that there are still many cases where the regulations at that time did not set rules on how to deal with such materials and situations, and as a result, the matters that were considered adequately dealt with by the administrators and workers at that time persist in present facilities. There are still many cases (with or without recognition by the successor administrators) where the then members (i.e., the seniors) thought was good, but then it is realized that the case no longer conforms to the current legal system and manner.How it should be handled may require discussion and standardization of responses from a wide perspective, not on an individual basis. From this perspective, if we can have a frank exchange of opinions and positive discussions with not only the safety managers of radiation facilities registered at UTokyo, but also with workers, this will also serve as an opportunity to improve radiation literacy and foster a culture of safety at the university.

The Law Concerning the Prevention of Radiation Hazards due to Radioisotopes, etc., which covers radioisotopes and accelerator facilities, was revised into the Law Concerning the Regulation of Radioisotopes, etc., which came into full effect in September 2019. The law was enacted to “prevent radiation hazards and ensure public safety by regulating the application of radioisotopes and radiation generating devices and the disposal of items contaminated by radioisotopes”. Under the revised law, several new items have been added to the radiation hazard prevention rules that each facility must prepare on its own, and it reads that the law’s goal of “public safety” includes “security”. In addition to careful measures to prevent accidents from occurring, there is now a stronger need for appropriate care and ingenuity in dealing with problems after they are recognized.

Division for Environment, Health and SafetyRadiation Safety Promotion Manager

Professor Takeshi IIMOTORe-education: Application, Regulations and Laws

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3 Radiation Effects on the Fetus and Exposure Control for Women

Proliferating cells are more sensitive to radiation than quiescent cells, and embryos and young organisms are generally susceptible to radiation. The same is true for the human: fetuses and children are more sensitive to radiation than adults. The radiation effects on the development of a fetus of a pregnant worker are of concern. The type and extent of these effects depend on the embryonic development.

About one day after fertilization, the first cleavage occurs, and it becomes a two-cell embryo. Sperm and egg cells are haploid, meaning they carry half the number of chromosomes of somatic cells. The male and female pronuclei don’t fuse. Instead, their membranes dissolve, leaving no barriers between the male and female chromosomes. Their chromosomes can then combine and become part of a single diploid nucleus in the resulting embryo, containing a full chromosome set. On the third day, it becomes morula, an early-stage embryo consisting of 16 cells. The changes occur in the chromatin structure, which is a complex of DNA and protein, and many embryos do not develop normally, and the radiation sensitivity is extremely high.

Further cell division and the formation of a cavity in the ball of cells induce the blastocyst. Two types of cells are produced in the blastocyst: the trophic ectoderm, which will become the placenta, and the inner cell mass, which is the “pluripotent” stem cells that will become the body (the first nine days after fertilization are called the pre-implantation period). After that, the embryo implants on the uterus wall to form the placenta. During the organogenesis, cells differentiate and spatially rearrange and ensure that organs form at specific sites within the organism. Once the organs are formed, the fetus continues to grow until birth (fetal stage).

It is known that the radiation effects on fetal development depend on the stages of irradiation (Table 1). Exposure before the early stages of implantation causes embryo death, and in most cases, the dead embryo is absorbed and is not recognized by the mother. Embryonic death is a deterministic effect, with a threshold value of 0.1 Gy. During

Table 1 Effects of radiation on mammalian embryos and fetuses

Irradiation period Pre-implantation Implantation Organogenesis Fetus

Days after fertilization (human) 0~9 9~14 15~50 50~280

Lethality ＋＋＋ ＋ ＋ －－－Malformation development －－－ －－－ ＋＋＋ ±

Developmental delay (at birth) －－－ ＋ ＋＋＋／＋＋ ＋Growth retardation

(after birth) －－－ ＋ ＋＋＋／＋＋ ＋＋

Infertility －－－ ± －－－ ＋＋Cataracts －－－ －－－ ＋ ＋

Nervous system disorder －－－ －－－ ＋＋＋／＋＋ ＋＋Disorders observed after 1 Gy irradiation in utero studies. The appropriate time of gestation in humans is shown above. Various stages from high frequency (+++) to no occurrence (---) are indicated by + and - symbols.（放射線影響協会「放射線と胎児」）。

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the organogenesis phase, radiation exposure results in a high incidence of cell death and an increased incidence of malformations. In severe cases, death after birth is common, and the brain’s deformities, eyes, and skeleton are frequently observed.

Data on atomic bomb survivors exposed in utero show a dose-dependent increase in the frequency of microcephaly (a small head size) and severe mental retardation. The excess incidence of intellectual disability was pronounced in those exposed during the organogenesis period. An increase in carcinogenesis was seen in those exposed in utero but was less pronounced than irradiated at childhood.

Thus, the current law sets the effective dose (quantity indicating the stochastic effect, which means cancer and hereditary effect) limit for women of childbearing potential at 5 mSv/3 months to avoid the fetus’s exposure to doses above the general public protection standard, even when the pregnancy is unnoticed. Individual monitors for measuring and assessing the radiation dose of female workers are required to be installed in the abdomen. During pregnancy (from the time the employer knows of the pregnancy), the internal exposure must not exceed 1 mSv. The equivalent dose (the absorbed radiation dose in an organ or tissue corrected by a radiation weighting factor assessing the risk of carcinogenesis for each type of radiation) on the abdomen’s surface due to external exposure is limited to no more than 2 mSv during pregnancy.

The ICRP 2007 Recommendation (Pub. 103) sets an effective dose limit of 1 mSv/year for the public. Still, in special circumstances, a higher value of the effective dose may be acceptable in a single year. However, it states that the annual average over a five-year period should not exceed 1 mSv and that dose limits for women should ensure that the additional dose to the embryo/fetus does not exceed 1 mSv for the remainder of the period after the pregnancy. It is also strongly recommended that women who have declared pregnancy or are breastfeeding should not engage in emergency measures involving high doses.

Amendments to the law are currently discussed to respect these recommendations and ensure the safety of the embryo and fetus as public while protecting women’s working environment.

The Graduate School of Frontier SciencesDirector of Radiation Management

Prof. Hiroshi MITANIRe-Education Theme: Human body effects and Regulation

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4 Conventions and Agreements on Safetyguards in Japan and Several Points for Carrying Out Material Accountancy

There are many radioactive substances and their compounds in the world. Although, many of them are regulated by the law “Act on the Regulation of Radioisotopes, etc”, treatment/handling of nuclear fuel materials and its compounds like uranium and thorium especially must be regulated by the law “Act on the Regulation of Nuclear Source Material, Nuclear Fuel Material and Reactors”.

1.Nuclear Materials and SafeguardsIn 1976, Japanese government

concluded “The Treaty on the Non-Prol i feration of Nuclear Weapons (NPT)”. The objective of this treaty is to deter the spread of nuclear weapons and to avoid military use of nuclear material.

Under the NPT treaty, each member coutry is required to conclude a safeguards agreement wi th the International Atomic Energy Agency (IAEA), and to conduct safeguards properly as designated in the agreement. In 1977, Japanese concluded the agreement with IAEA.

Safeguards are to ensure that nuclear materials will not be diverted to nuclear weapons and will only be used for peaceful purposes. Following acceptance of IAEA safeguards, Japanese government has revised relevant domestic laws, such as “The Regulation of Nuclear Source Material, Nuclear Fuel Material and Reactors”, “Regulations Concerning the Use, etc. of International Controlled Material” and so on, thereby strengthening the internal safeguards system.

2.Nuclear Accounting ReportIn order to use nuclear materials, each facility must submit the reports that state the

increase, decrease and the total quantity of nuclear materials in a fixed-term, and these reports are different according to the amount of the inventory. There are 2 types of facilities that can possess nuclear materials. One is J facility that holds more than 300 g of natural and/or depleted uranium (compounds) and/or more than 900 g of thorium (compounds). Another is K facility that holds less than 300 g of uranium or less than 900 g of thorium (compounds) (Figure 1).

For K facilities, it is required to submit the material accounting report twice a year (from January 1 to June 30 and from July 1 to December 31) . The reports must contain information such as the name of the facility, the element of nuclear materials/compounds (natural and/or depleted uranium and/or thorium), and the quantity of received, shipped, and domestically consumed nuclear materials for each element and for each name of the origin of material that has supplied international controlled material. On the other hand,

International Atomic Energy Agency (IAEA)

The Nuclear Regulation Agency

Nuclear Facilities

Inspection

K Facilities J Facilities

Nuclear MaterialsInventry Change

Report

Inventory etc.

More than 300 g of uranium (compounds) More than 900 g of thorium (compounds)

Less than 300 g of uranium (compounds) Less than 900 g of thorium (compounds)

Report

Control Report

Figure 1 The safeguards

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J facility must submit the report of inventory change, inventory and so on whenever such change is carried out, and the report itself is different from that of K facility. All the reports of both K and J facilities are submitted to the IAEA by the government.

All the reports are summarized reports based on the user’s daily record of received, discharged, and consumed nuclear materials in each department. For appropriate reporting, it is recommended that the administrator of the nuclear materials should refer “The Regulation of the Material Accountancy” and/or “The Material Accounting Report”. All the users must record their received, discharged and consumed nuclear material according the rules regulated by each department.

Useful websites are shown below. These websites are for more details of the knowledge of The Treaty on the Non-Proliferation of Nuclear Weapons (NPT), Safeguards and Material Accounting Report.

NRThttps://www.un.org/disarmament/wmd/nuclear/npt/text/

Safeguardshttps://www.iaea.org/topics/safeguards-explained/

Material Accounting Report (in Japanese)https://www.nsr.go.jp/activity/hoshousochi/tetsuduki/tetsuduki06.html

Division for Environment, Health and SafetyRie MIZUNO, Keiji KIMURA and Satori KUKITA

Re-Education Theme: Nuclear materials and related rules

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5 Point to Note Regarding Maintainance and Inspection of X-ray Device

X-ray device managers are required to a periodical inspection whether or not high safety and performance of X-ray devices can be maintained. Points of attention for each inspection item of an X-ray device are described below (see also Figure 1). The following items are common inspection ones in the University of Tokyo, so the X-ray device managers and inspectors need to check them for the periodic inspection.

① The Lock State of Doors for the X-ray DeviceIn the case of closed type X-ray device whose radiation-controlled area is set inside

the device, classified as category A or B types in the University of Tokyo, an inspector of the X-ray device needs to confirm at the time of the periodical inspection (1) whether a safety key of the device is appropriately managed by the device manager, (2) whether the door lock mechanism of the device is released with the key plugged in it, and (3) whether the indicator light will turn on when the X-ray is generated. Even if the X-ray device is the same closed type one, in the case of a category C type device whose radiation-controlled area is extended outside the device, the inspector needs to confirm (1) whether X-ray users recognize that safety lock of the device is released while the device is in use, and (2) whether the manager inform the users about danger of unlock state of the device and its countermeasure. A special note for all closed types of X-ray devices: please be careful about accidents, such as finger pinching etc., when you open and close it.

② Switching On/Off of X-rays, Shutter Opening/Closing, and Warning Device etc.In order to maintain safety of the X-ray device, it is necessary to perform inspections to

lighting state of an indicator lamp of the warning device automatically linked with the X-ray beam shutter opening/closing and the switch of on/off of X-rays. Please check whether the indicator lamp will turn on when the X-ray switch is on and the shutter is opened, and, vice versa: whether the indicator lamp will turn off when the X-ray switch is off and the shutter

② Confirmation of the shutter opening/closing

② Confirmation of the indicator lamp ② Confirmation of X-ray on

② Radiation exposure prevention when the shutter is open

⑥ Filament inspection

③ Posting of signs, etc.

⑤ Inspections of high-voltage power supply and cable.

⑦ Confirmation of fixing device

① Inspection of door lock state

⑦ Emergency broking switch

① Finger pinch accident at the door, etc.

④ Inspections of cooling water, filter, joint of hose, etc.

Cooling water system

Figure 1 Inspection items of a X-ray device

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is closed. Regarding the display when the shutter is opened/closed, the indicator lamp is attached not only to the warning device mounted on the device body case but also to near the shutter inside it. Many of the users who operate the X-ray devices can replace the sample confirming that the indicator lamp turns off (that is, the shutter is closed). Because the radiation exposure accident may occur if this indicator lamp does not light due to the failure, please always confirm the operation of the indicator lamp. Also, we should keep in mind that the shutter often fails due to frequent use, we must perform the periodical inspection without avoiding a safety inspection of the shutter body.

③ Posting of Signs etc.X-ray device manager and inspector need to confirm that the signs mentioned the items

which are specified by the Ministerial Ordinance for Prevention of Hazards from Ionizing Radiation, hereinafter referred to as the Ionizing Radiation Ordinance, are posted on or near the device (Article 14 of the Ionizing Radiation Ordinance).•The setting and indication of radiation-controlled areas (Article 3)

The radiation-controlled area must be set and separated from the outside, and it must be clearly indicated by posting signs. In the cases of the category A and B types devices whose controlled areas are established inside them, a sign showing the controlled areas must be posted on the device’s surface.

•Posting at Radiation Equipment Rooms (Articles 15 and 18)A sign which indicates the “Radiation equipment room” must be posited at the

entrance of the room. When an X-ray device is to be used in a place other than the radiation equipment room, we need check that not only the sign of the radiation-controlled area but also the sign of the restricted area must be clearly indicated.

•Posting of Operations Chief of Work with X-rays (Article 46)In the cases of the category C, D, and E types devices, name of the operations chief

and implementation items must be displayed at the workplace.

The following items need to be checked according to the type of X-ray device.

④ Equipment for Water SectionWe need to inspect around the equipment of water section with special care, because

water leakages lead to earth leakage accidents. Therefore, please confirm whether or not water leaks from the X-ray device and an accompanying circulation cooling water system, and especially around hoses which cooling water flows. Loosening inspections for hose bands at the joint parts between the X-ray device or the circulation cooling water system and the cooling water houses, and between hoses, and a crack inspection of the hose itself are needed. In addition, it is necessary to pay attention to the following points and inspect it regularly regarding the circulating cooling water system.•Cooling water

If you are using the circulation cooling water system, you have to check the cooling water level of the liquid tank, and in the case of the shortage of quantity of the water, you have to replenish the water to the tank after checking for problems of water leakage, etc. The cooling water also needs to be exchanged periodically.

•Filter for cooling waterImpurities in the cooling water are removed by using a filter. Since hydraulic pressure

of the cooling water often does not rise when this filter is clogged by the impurities, you should replace it regularly.

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•Joint of hoseHose bands are often used for joint parts between vinyl hoses and the device.

However, if the hose band is used for a long time, the hose becomes easy to come off from the device because of deterioration of elasticity of the hose, rusting of the hose band, and the thermal expansion effect of water. If you use a metallic hose connecter whose product name is called ‘Amack’ connecter in Japan at the joint part instead of the hose band, the hose become hard to come off compared with the use of the hose band. To eliminate the possibility of the water leakage accident, in the case of the device that has been in use for a long time, we recommend replacing the hose and a use of the metallic hose connecter.

⑤ High-Voltage Generating Part A hot and humid environment causes deterioration of circuits and transformers, which

is not good for X-ray equipment with high-voltage power supply. Therefore, in the case of rainy weather in summer, the X-ray device manager needs to prevent the hot and humid environment by using air conditioning, etc. Also, a dusty environment is also not good for high-voltage power supply because it induces overheating effects due to short circuits in the circuit and obstruction of air convection. The device manager needs to be careful of dust buildup around the X-ray device and especially at the inlet of the cooling fan.

Poor Insulation of high-voltage cables can also cause failure of X-ray device. If the high-voltage cable is not grounded or is not properly attached to the power supply, an arc discharge may occur and damage the X-ray device. In addition, if the grease (insulating layer) applied to the connection part solidifies and deteriorates, it may cause insulation failure. Therefore, the device manager should inspect the high-voltage cable connections and re-grease them regularly.

⑥ Filament InspectionThe filament (X-ray bulb) itself deteriorates due to emission of electrons and may

eventually break. It is recommended that the device manager exchange the filament on a regular basis because the surface of a target will be rough due to excessive electron emission when the filament is broken. By the way, a voltage of 50 to 60 kV is applied to the filament, and a direct current of about 30 to 50 mA is flowing through it. Since it is extremely dangerous to touch this high voltage, you should turn off the power and discharge the high-voltage charge sufficiently before replacing the filament or performing inspection and maintenance of the device.

⑦ Other ItemsA number of X-ray generating devices are equipped with an “emergency blocking

switch”. If an accident occurs, or when a risk of the accident exists, you should immediately stop the device by pressing this switch. Therefore, it is also necessary to check whether this emergency blocking switch actually works.

As is the case with ordinary measuring devices, fixing device is important to prevent accidents. Do not forget to confirm whether the fixing of the X-ray device have been made sufficiently.

Institute of Industrial Science Masao Kamiko Ph.D,

Re-Education Theme: X-ray