Understand the physical quantity
What is Activity, Atoms and Isotope Mass?
Radiation measurement distinguishes activity, detected count rate, concentration, attenuation, absorbed dose, and equivalent dose. A conversion or screening relationship must preserve which physical quantity was actually entered.
Automate the mole, atom, decay-constant, and activity steps while requiring visitors to supply isotope-specific data from an authoritative source.
The relationship
Keep quantity and basis explicit
Decay constant λ = ln(2)/T½ in seconds; activity A = λN. In mass mode, radioactive atoms N = sample mass × isotope fraction ÷ molar mass × exact Avogadro constant 6.02214076×10²³ mol⁻¹.
See the workflow
What the calculator is doing
1Entered physical quantity2Apply decay, detector, or geometry model3Reported activity, count, or dose quantity
Worked context
Read the output in context
One gram of a pure 100 g/mol isotope with a 10-day half-life contains 6.02214×10²¹ atoms and has activity about 4.831×10¹⁵ Bq.
Interpret with care
Important boundary
Enter the correct isotope molar mass, physical half-life, and isotopic fraction from authoritative data. This does not identify an isotope, model decay products or chemical form, determine dose, or establish handling, transport, release, or waste requirements.
The result does not provide a safety limit, medical interpretation, personal-risk estimate, shielding approval, release decision, treatment plan, or regulatory authorization.
Browse Light & radiation for related physical quantities.
Quick guide
How to use this calculator
- Choose the physical radiation quantity and solve direction before entering measurements. Keep activity, count rate, absorbed dose, equivalent dose, time, distance, material attenuation, and detector efficiency separate.
- Enter isotope, detector, geometry, material, or field data only from an applicable measurement or authoritative record; these pages do not supply generic safety values or hidden presets.
- Use companion outputs to reconcile the arithmetic, then retain every stated boundary. A screening result is not authorization for exposure, handling, shielding, release, transport, treatment, or disposal.
Calculation method
How the activity, atoms and isotope mass calculator works
Automate the mole, atom, decay-constant, and activity steps while requiring visitors to supply isotope-specific data from an authoritative source.
Decay constant λ = ln(2)/T½ in seconds; activity A = λN. In mass mode, radioactive atoms N = sample mass × isotope fraction ÷ molar mass × exact Avogadro constant 6.02214076×10²³ mol⁻¹.
Worked example
Activity, Atoms and Isotope Mass example
One gram of a pure 100 g/mol isotope with a 10-day half-life contains 6.02214×10²¹ atoms and has activity about 4.831×10¹⁵ Bq.
Decay constant λ = ln(2)/T½ in seconds; activity A = λN. In mass mode, radioactive atoms N = sample mass × isotope fraction ÷ molar mass × exact Avogadro constant 6.02214076×10²³ mol⁻¹.
Supported inputs
Precision and limits
Radiation boundary
Enter the correct isotope molar mass, physical half-life, and isotopic fraction from authoritative data. This does not identify an isotope, model decay products or chemical form, determine dose, or establish handling, transport, release, or waste requirements.
Units and precision
Calculations normalize compatible units once, retain working precision, and round only for display. Very small and large nonzero values use scientific notation; displayed precision cannot exceed the entered measurements or source data.
Decision boundary
This calculator does not provide a dose limit, regulatory threshold, medical interpretation, personal-risk estimate, radiation-protection program, or professional approval. Use applicable instruments, current authoritative data, and qualified radiation-protection expertise for consequential decisions.
Privacy
Entered values and results stay in this browser and are not sent to analytics or third parties.
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