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Berlin Environmental Atlas

01.09 Radioactivity in Soils (Cesium-134 and Cesium-137)

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The effects on health caused by ionizing radiation are of particular interest. These complex interrelations are still not completely clear today. In simplified form, the interrelations can be described as follows: radioactive decay transforms instable nuclides into stable isotopes by either emitting particles (electrons, positrons, neutrons) and/or electromagnetic radiation (photons). The energy of radiation is of great importance for dangers to health. After the emission of particles, new nuclides are often formed, which can also decay.

The activity of a radioactive substance is measured in Becquerel (Bq) units. It expresses the number of nuclear disintegrations per second. 1 Bq signifies one disintegration per second. Half-life is the time required for the decay process to reduce activity by one-half. Half-life thus quantifies the time-period of higher activity and accumulation of that element in the environment. Activity is not the only physical factor that must be known in order to judge the effects of ionizing radiation (load charge transmission) on the human body. The fundamental danger of ionizing radiation is that changes in the cells can cause cancer or genetic damage. In order to judge these dangers in individual cases, other physical qualities must be taken into consideration. The effective equivalent dose, measured in Sievert (Sv), has a special significance. The Sievert attempts, by means of conversion factors, to quantitatively express the different biological effects of different kinds of radiation on individual organs of the human body - and in respect to their differing susceptibility to radiation. This is used as a basis in radiation protection regulations for determining limit values, assuming the average foodstuff consumption habits of a healthy adult. The determination of limit values also differentiates between persons exposed to radiation in their professions, and the general population.

Development of Contamination by Man-made Radioactivity

Investigations have deepened knowledge of the global spread and distribution of radionuclides in various areas of the biosphere ever since nuclear weapons tests began releasing man-made radionuclides into the atmosphere.

A measurement series to determine average radioactive contamination in the air in Berlin was conducted for many years. Average man-made radiation values amount to less than 10% of natural levels (5-7 Bq/m³) even in periods of high contamination. Peak values for individual days, such as those reached after the reactor accident in Chernobyl, however, can be considerably above these values (cf. Fig. 4). Figure 2 shows a clear link between airborne contamination and atmospheric nuclear tests. Values in Berlin are to be interpreted as delayed effects, appearing in Berlin about one year after the nuclear tests. The length of time nuclides remained in higher levels of the atmosphere is an important factor. There were particularly high contamination levels 1963, caused by the nuclear weapon tests of 1961/62, when high-yield hydrogen bombs were detonated in the atmosphere.

Radioactivity measured in the 70's was due to tests by China and France, carried out in spite of the test ban. There was a drop-off to a very low level in the 80's. The level of man-made radiation in 1963 was a thousand times greater than from 1982 to 1985. Contamination values were driven up again only with the Chernobyl incident in 1986. Within a few days, a single event caused contamination levels over a large portion of Europe that are comparable only to the effects of the nuclear tests of 1961/62. Washout by rain and settling (sedimentation) led to a reduction of airborne contamination to " pre-Chernobyl-levels" by 1986.

Figure 2
Fig. 2: Average Daily Rates of Man-made Radioactivity in the Air at Dahlem Measuring Station (remaining Beta activity) (FU Berlin 1992)

[Statistical base of Figure 2 is also available as Excel-File (MS-Excel is required).]

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