{"id":7917,"date":"2025-04-27T13:12:38","date_gmt":"2025-04-27T04:12:38","guid":{"rendered":"https:\/\/www.envraddb.go.jp\/entesttest\/?page_id=7917"},"modified":"2026-05-27T16:54:13","modified_gmt":"2026-05-27T07:54:13","slug":"carbon","status":"publish","type":"page","link":"https:\/\/www.envraddb.go.jp\/en\/special\/tec-info\/carbon\/","title":{"rendered":"Carbon 14 \uff0814<\/span>C\uff09"},"content":{"rendered":"
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Overview<\/h2>\r\n <\/div>\r\n
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What is 14<\/span>C?*1, *2, *3<\/span><\/h3>\r\n <\/div>\r\n
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\r\n Carbon-14 (14<\/span>C) is a radioactive isotope of carbon and a \"pure \u03b2-<\/span> emitting\r\n nuclide,\" meaning it emits \u03b2 rays\r\n due to \u03b2 decay but does not emit \u03b3 rays. It has a half-life of 5,700 years.
\r\n The primary sources of 14<\/span>C are:
\r\n 1. Interactions between cosmic rays and nitrogen atoms,
\r\n 2. Atmospheric nuclear tests,
\r\n 3. Activation reactions involving nitrogen, etc., in nuclear reactors.
\r\n Regarding source 3, 14<\/span>C is released during the reprocessing of spent nuclear fuel. Cosmic rays\r\n produce\r\n approximately 1.4 PBq (PETA = 1015<\/span>) of 14<\/span>C annually, and the global inventory of\r\n 14<\/span>C is estimated to be\r\n around 8,500 PBq. The majority resides in the oceans, with approximately 140 PBq present in the\r\n atmosphere.
\r\n During the 1950s and 1960s, frequent atmospheric nuclear tests released about 350 PBq of 14<\/span>C\r\n into the\r\n atmosphere. This significant supply caused a rapid increase in the specific radioactivity of\r\n 14<\/span>C in\r\n atmospheric carbon dioxide, peaking at 1.5 to 2 times the pre-nuclear testing levels by the mid-1960s.
\r\n Since then, the cessation of atmospheric nuclear tests and the release of \"dead carbon\" (carbon devoid of\r\n 14<\/span>C) from fossil fuel combustion (the Suess effect) have led to a decline in the specific\r\n radioactivity of\r\n 14<\/span>C in the atmosphere. In comparison, global emissions of 14<\/span>C from reprocessing\r\n plants are estimated to be\r\n about 2 PBq, which is negligible relative to the releases from atmospheric nuclear tests.\r\n <\/p>\r\n\r\n <\/div>\r\n\r\n <\/div>\r\n

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14<\/span>C Analysis objective*4, *5<\/span><\/h3>\r\n <\/div>\r\n
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14<\/span>C is measured to estimate and evaluate radiation doses received\r\n by residents living near reprocessing facilities during routine monitoring. 14<\/span>C is widely\r\n utilized across various research fields. In environmental research, it serves as a natural tracer to\r\n identify the sources and understand the dynamics of various substances of both natural and human sources. In\r\n the field of archaeology, carbon dioxide is used for dating because plants and animals absorb carbon dioxide\r\n during photosynthesis and the food chain, and its levels decrease after their death.\r\n <\/p>\r\n <\/div>\r\n\r\n <\/div>\r\n\r\n

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Main methods of analysis for 14<\/span>C<\/h3>\r\n <\/div>\r\n
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Benzene synthesis method<\/h4>\r\n <\/div>\r\n
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The benzene synthesis method involves pretreatment with a vacuum line,\r\n followed by measurement with a liquid scintillation counter. This method enables high-accuracy analysis\r\n and is suitable for environmental radiation monitoring.
\r\n Detectable level: 0.002 Bq\/gC (1.7 g of carbon, counting efficiency 75 %, BG count rate 0.3 cpm,\r\n measurement time 500 min).\r\n <\/p>\r\n <\/div>\r\n <\/div>\r\n

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Carbon dioxide absorption method<\/h4>\r\n <\/div>\r\n
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\r\n The carbon dioxide absorption method involves pretreatment with commercially available instruments and\r\n measurement with a liquid scintillation counter. It offers a simple analysis method (including\r\n screening) for environmental radiation monitoring.
\r\n Detectable level: 0.02 Bq\/gC (1.0 g of carbon, counting efficiency 55 %, BG count rate 11 cpm, and a\r\n measurement time of 500 minutes).\r\n <\/p>\r\n <\/div>\r\n <\/div>\r\n

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Accelerator mass spectrometry (AMS)<\/h4>\r\n <\/div>\r\n
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Accelerator Mass Spectrometry (AMS) is primarily employed by research\r\n institutions for the analysis of environmental samples for research purposes.
\r\n This method involves preparing measurement samples through chemical treatment tailored to the sample,\r\n followed by the use of an accelerator to measure the target mass number. At present, it provides the\r\n highest sensitivity for the quantification of carbon-14 (C-14). However, because the measurement system\r\n is extremely large and expensive, its general use has not become widespread, and the number of\r\n analytical institutions capable of performing such measurements remains limited. Despite these\r\n limitations, C-14 analysis using AMS is applied in a wide range of fields beyond environmental\r\n monitoring, including age determination and other research applications.\r\n
\r\n Detectable level: 0.0002 Bq\/gC (converted from 14<\/span>C\/12<\/span>C =\r\n 1.0x10-15<\/span>; measurement sample amount is about 1 mg).\r\n <\/p>\r\n <\/div>\r\n <\/div>\r\n\r\n\r\n\r\n <\/div>\r\n <\/div>\r\n\r\n <\/section>\r\n\r\n

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Analytical flow (benzene synthesis method)<\/h2>\r\n <\/div>\r\n
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Organism sample<\/p>\r\n <\/div>\r\n

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Freeze dryer<\/p>\r\n