Radioactive Decay


Initial activity (No)
Decay time (t)
Time units s m h
d y
Final activity (N)  *
Timed Decay

t = -(T½/0.693) * ln(N/No)
Initial activity (No)
Final activity (N)
Decay time (t)  *

Timed Solid Disposal

t = -(T½/0.693) * ln(D.L./(No/m))
Initial activity (No) MBq
mass (m) kg
Decay time (t)  *

Regulated Quantities
(Based on Canadian Regulations)

Exemption Quantity2 Activity Concentration (Bq/g) Activity (Bq)    
ALI estimate (MBq/yr)3          
Wipes (Bq/cm2)3 Controlled Area Public Area    
Disposal Limits3 Solid (MBq/kg)* Liquid (MBq/yr)** Gaseous (kBq/m3)

* - Field at surface of container must also be < 0.25 mR/h (2.5 µSv/h).
** - Aqueous disposal only.
NOTE: some of these values may vary from your licence conditions. If in doubt, always refer to your licence or contact your radiation safety officer to confirm their relevance to your situation.

Unit Converter
Find the difference between two dates
Add or subtract days to a date
Activity 1 kBqMBqµCimCi
Activity 2 kBqMBqµCimCi

Date 1
Date 2
Date 1
Date 2


  1. Chang, J.: Table of Nuclides, KAERI(Korea Atomic Energy Research Institute).
    Available at: Retrieved 23-Aug-02.
  2. Canadian Nuclear Safety Commission; Nuclear Substances and Radiation Devices Regulations (SOR/2000-207), Schedule 1 - Exemption Quantities
    Available at: Retrieved 25-Mar-14.
  3. Canadian Nuclear Safety Commission; Consolidated Use of Nuclear Substances (C-222), Appendix C - Quick Reference: Regulatory Quantities for Typical Radionuclides