wszystkiego najlepszego z okazji urodzin: short quotes to live by

Saturday, November 19, 2011

short quotes to live by

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In a fixed mass of radioactive material, the number of becquerels changes with time. Therefore, a sample radioactive decay rate is stated with a timestamp for short-lived isotopes, sometimes after adjustment to some specific date of interest (in the past or in the future). For example, one might quote a ten-day adjusted figure, that is, the amount of radioactivity that will still be present ten days in the future. This can de-emphasize short-lived isotopes.[citation needed] The average human body has 4400 becquerels from decaying potassium-40, which is a naturally-occurring isotope of potassium.

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SI uses the becquerel rather than the second for the unit of activity measure to avoid dangerous mistakes: a measurement in becquerels is proportional to activity, and thus a more dangerous source of radiation gives a higher reading. A measurement in seconds is inversely proportional.

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As any SI unit, Bq can be prefixed; commonly used multiples are kBq (kilobecquerel, 103 Bq), MBq (megabecquerel, 106 Bq), GBq (gigabecquerel, 109 Bq), TBq (terabecquerel, 1012 Bq), and PBq (petabecquerel, 1015 Bq). For practical application, 1 Bq is a small unit; therefore, the prefixes are common. For example, natural potassium (40K) in a typical human body produces 4,000 disintegrations per second, 4 kBq of activity. The nuclear explosion in Hiroshima (14 kt or 59 TJ) is estimated to have produced 8×1024 Bq (8 YBq, 8 yottabecquerel).