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# Half-life

per minute
 Half-life: s (second)min (minute)h (hour) d (day)a (year) Lifetime: Already % decayed: Still % available: After already % decayed After still % available k (1. order) s-1 k (1. order) min-1

The results have been rounded to significant digits.

This calculator supports calculations concerning the exponential decrease of concentrations as they happen in the radioactive decay and in 1. order chemical reactions. The half-life is the time until the concentration has decreased by 50 %. Within the lifetime the concentration is reduced to 1/e. In addition the duration of decreases of arbitrary amounts as well as 1. order reaction rates are calculated.

Usage: At first, choose a unit of time from the drop-down-menu at the end of the first line (second, minute, hour, day, or year) that will be used for all times shown.
Then type a time, a percentage, or a rate constant into one of the light red input fields. After a mouse click on any free space of the window or on the "calculate" button the other values are calculated.
Move the mouse over a unit or click on it to read its full name. The percentages and times in the grey fields are not calculated, however, the values may be changed any time.
When you change the time unit by the drop-down-menu after a calculation, all times will be calculated in the new unit assuming the same half-life. The rate constants are always displayed as s-1 and min-1.

Example: 60Co has a half-life of 5.2714 years. After which time 99 % of a certain amount of the isotope has decayed ? At first, choose the time unit "a (year)" from the drop-down-menu in the first line. Then type "99" into the corresponding grey field. Finally, you have to type the value of the half-life. After a mouse click on any free space of the window or on the "calculate" button you may read the result: after 35.022 years 99 % of the cobalt isotope have decayed.

Remarks:
- Large and small numbers are written exponentially. As example 2.3e5 = 2.3⋅105 = 230000 or 4.5e-5 = 4.5⋅10-5 = 0.000045.
- There is no warranty for the conversion. Cactus2000 is not responsible for damage of any kind caused by wrong results.
- Please send an email if you have suggestions or if you would like to see more conversions to be included.

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