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Dose Calculation |  |
About NORM |  |
Regulations in Japan | |
In-depth Data | |
Glossary | |
Information for specialists | |
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| Glossary | ||||||
Radioactivity |
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| The term "radioactivity" has the following two meanings:
i) Character in which an atomic nucleus spontaneously decays and discharges radiation such as alpha-rays, beta-rays, and gamma-rays. ii) Number of times for an atomic nucleus decays per given unit of time. The unit for radioactivity is Bq (Becquerel: number of decay times per 1 second). Radiation type and emission rate differ among the type of radionuclide. |
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Radioactivity concentration (activity concentration) |
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| Radioactivity concentration (activity concentration) refers to the amount of radioactivity per unit volume and unit mass in materials that include radionuclides. The units for radioactivity include Bq/g and Bq/l. | ||||||||||||||||||||||||||||||||||||||||||
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U-238 series nuclides |
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| Through eight processes of alpha-decay and six processes of
beta-decay, U-238 (Uranium 238) alters to Pb-206 (lead 206), which is a
steady nuclide. The nuclides decaying from U-238 to Pb-206 are called the
U-238 series nuclides. <Decay chain> U-238, Th-234, Pa-234m, U-234, Th-230, Ra-226, Rn-222, Po-218, Pb-214, Bi-214, Po-214, Pb-210, Bi-210, Po-210, and steady nuclide Pb-206. Natural rocks and soil in normal condition include the U-238 series nuclides that vary among locations and materials. The radioactivity concentration of the U-238 series nuclides (except for the steady nuclide Pb-206) in natural rocks and soil in normal conditions maintain nearly the same concentration throughout the decay process. For example, if Ra-226 has a value of 1 Bq/g in concentration, U-238, Th-234, Pa-234m, U-234, Th-230, Rn-222, Po-218, Pb-214, Bi-214, Po-214, Pb-210, Bi-210, and Po-210 would also have the value of 1 Bq/g. |
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Th-232 series nuclides |
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| Through six processes of alpha-decay and four processes of
beta-decay, Th-232 (Thorium 232) alters to Pb-208 (lead 208), which is
a steady nuclide. The nuclides decaying from the Th-232 to Pb-208 are called
Th-232 series nuclides. <Decay chain> Th-232, Ra-228, Ac-228, Th-228, Ra-224, Rn-220, Po-216, Pb-212, Bi-212, Tl-208, Po-212, and steady nuclide Pb-208. Natural rocks and soil in normal conditions include the Th-232 series nuclides that vary among locations and materials. The radioactivity concentration of the Th-232 series nuclides (except for the steady nuclide Pb-208) in natural rocks and soil in normal conditions maintain nearly the same concentration throughout the decay process. For example, if Ac-228 has a value of 1 Bq/g in concentration, Th-232, Ra-228, Th-228, Ra-224, Rn-220, Po-216, Pb-212, Bi-212, Tl-208, and Po-212 would also have the value of 1 Bq/g. |
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K-40 |
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| K-40 is a type of naturally occurring radionuclide. Natural rocks and soil in normal condition include K-40 that varies among locations and materials. | ||||||||||||||||||||||||||||||||||||||||||
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Effective dose |
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| Effective dose is a value assigned to evaluate whole-body health effects in a case of exposure to radiation, and it is exclusively employed for purposes of radiation protection. Effective dose is obtained by summing the weighted equivalent doses (the equivalent doses multiplied by the tissue weighting factor) in all tissues and organs of the human body. The unit for effective dose is sievert (Sv). The effective dose was formerly known as effective dose equivalent. | ||||||||||||||||||||||||||||||||||||||||||
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Equivalent dose |
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| Equivalent dose is obtained by multiplying the absorbed dose in the tissue or organ by the radiation weighting factor. The unit for the equivalent dose is sievert (Sv). | ||||||||||||||||||||||||||||||||||||||||||
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Naturally Occurring Radioactive Material (NORM) Naturally Occurring Radionuclide |
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| <General explanation> "Nuclide" means type of atomic nucleus; a nuclide that releases radiation is a radionuclide. Radionuclides are classified as "artificial" (artificial radionuclides) and "natural origin" (naturally occurring radionuclide). Naturally occurring radionuclides can be subdivided to "those that were carried from space during the period of Earth formation" and "those naturally generated by the effect of cosmic rays." A material that includes artificially generated radionuclides is called "artificial radioactive material." A material that includes a significant amount of naturally occurring radionuclides is called Naturally Occurring Radioactive Material (NORM). <Technical explanation> According to the 2007 IAEA Safety Glossary for nuclear safety and radiation protection published by the International Atomic Energy Agency (IAEA), a NORM is defined as "a radioactive material containing no significant amounts of radionuclides other than naturally occurring radionuclides", and a radioactive material is defined as "a material designated by national law or by a regulatory body as being subject to regulatory control because of its radioactivity." That is, NORM can be defined as "a material that does not include significant amount of radionuclides other than naturally occurring nuclides, and is subject to regulation because of its radioactivity." According to the definition in Japan, only a material exceeding the radioactivity concentration and the amount subject to the regulation in the Nuclear Reactor Regulation Law is classified as NORM. In reality, however, a material that contains levels lower than radioactivity concentration and the amount subject to the regulation in the Nuclear Reactor Regulation Law could be called a NORM if its radioactive concentration is relatively higher than that in common rocks and soil. Thus, defining a NORM on the basis of the radioactive concentration or amount is difficult, and no clear definition exists. |
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IAEA Critical Value |
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The IAEA Safety Guide RS-G-1.7, "Application of the Concepts
of Exclusion, Exemption and Clearance", state that standards for exemption
from international protection standards have been suggested. In this database,
these standards are termed as the IAEA Critical Value. It is suggested
that radiation protection contral is not necessary if the radioactivity
concentration value of naturally occurring radionuclides included in a
material is below the IAEA Criteria shown in the following table. Moreover,
it is also suggested that radiation exposure to workers will not exceed
1 mSv/year upon regular handling of a NORM with a radioactive concentration
in listed in IAEA RS-G-1.7.
Of common materials, nuclides that could exceed the IAEA Critical Value are mainly the U-238 series, Th-232 series, and K-40. Rb-87, Sm-147, and Lu-176 are not likely to be included in common materials at levels exceeding the IAEA Critical Value. Unless handling nearly pure materials (such as, lumps of Rb, Sm, and Lu), extreme caution is not required. |
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Radiation effects |
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There are two major types of radiation effects: somatic effects
and hereditary effects. Somatic effects are classified into acute effects,
which include hair loss and sterility, and late effects, which include
cataracts and cancer. Hereditary effects include metabolic problems, and
chondrodystrophy, which have been reported through animal testing. From
the perspective of protection against radiation, radiation effects are
classified as deterministic effects and stochastic effects. The type of deterministic effect depends on the level of exposure, as shown on the left-hand side of the graph below. The deterministic effects include hair loss, sterility, and cataracts. Exposure to radiation below the threshold does not affect the human body. When hadling a NORM, humans are not exposed to radiation exceeding the threshold. The stochastic effects are such that they increase with the amount of exposure, as shown on the right-hand side of the graph below. Therefore, stochastic effects do not have a threshold and include cancer and hereditary disorders. According to epidemologic research on the victims of radiation caused by atomic bombs in Hiroshima and Nagasaki, it is clear that the radiation dose and the mortality from cancer are in proportion to the dose in case exceeding approximately 100 mSv while it is not clear about the dose blow 100 mSv. Moreover, it is not perceived that hereditary disorders have been increased among total survivers in Hiroshima and Nagasaki. In Japan, the dose limit for occupations is 20 mSv/year, while that for the general public is 1 mSv/year.
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Methods of radiation protection |
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The types of radiation exposure are classified as external
and internal exposures. External exposure originates outside the body.
This type of exposure includes that from cosmic rays or radiation released
from the ground. Internal exposure refers to radiation released from radionuclides
that have been previously absorbed by the body. When materials containing
artificial and natural radionuclides are handled, protection measures against
internal and external exposure should be implemented.  <Protection methods for preventing external exposure> The following three protection methods are suggested for preventing external exposure: maintaining a safe distance from the material, reducing work hours, and blocking the radiation. (Three principles of protection: distance, time, and blocking)
 <Protection methods for preventing internal exposure> The following three protection methods are suggested for preventing internal exposure: preventing inhalation, preventing ingestion, and preventing exposure through the skin or wounds.
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