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| natural radioactivity | |||
| natural activity | |||
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| natural radioactivity; natural radioactivity Radiation stemming mainly from uranium, present in small amounts in many rocks, soils, building material, etc. | |||
| natürliche Radioaktivität: 4 phrases in 3 subjects |
| Electronics | 2 |
| Geophysics | 1 |
| Research and development | 1 |