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Radio isotope decay

Purpose of this page

This page is designed to calculate how much radio activity is remaining after a specific number of days. To calculate the current activity enter the compounds original activity, the elapsed time in days since the activity date and the compounds half life press the calculate button.

Original activity  
Days elapsed since activity date  
Compounds half life  

The rate of radioactive decay is given by:
t is the time in days since the stated activity (A0),
h is the half life of the isotope in days.

Selected values for commonly used isotopes

Isotope Half life (days) Energy maximum
Energy average
Distance in air
35S 87 beta 0.167 0.049 32cm
32P 14.29 beta 1.710 0.695 730cm
33P 25.3 beta 0.249 0.077 56cm
3H 4492.575 beta 0.0186 0.0057 1cm
14C 2092882.5 beta 0.156 0.049 30cm

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