Radioactive Half Life
Calculator
Results
- Amount remaining (g)
- 25
- Amount decayed (g)
- 75
- Decay constant (per year)
- 0.00012
- Half-lives elapsed
- 2
Chemistry results
| Amount remaining (g) | 25 |
| Amount decayed (g) | 75 |
| Decay constant (per year) | 0.00012 |
| Half-lives elapsed | 2 |
formula-map diagram
- Amount remaining (g)
- 25
- Amount decayed (g)
- 75
- Decay constant (per year)
- 0.00012
- Half-lives elapsed
- 2
Formula breakdown
Formula
N = N₀ × (½)^(t ÷ t½)= 25
Note
Simplified model: these results assume ideal behaviour (ideal gases, dilute solutions, complete reactions) and standard textbook constants. Real laboratory values vary with temperature, pressure, purity and activity coefficients. Do not rely on this for safety-critical or analytical work.
More in Chemistry
See all →Frequently asked questions
What does half-life mean in radioactive decay?+
Half-life is the time required for exactly half of a radioactive sample's atoms to decay into a different, typically more stable, element or isotope. It's a fixed, statistically predictable property of each specific isotope, unaffected by external conditions like temperature or pressure.
What is the formula used to calculate remaining quantity after a given time?+
The remaining amount is N = N0 x (1/2)^(t/T), where N0 is the initial quantity, t is the elapsed time, and T is the half-life. This exponential decay formula applies regardless of the units used, as long as t and T use the same time unit.
Why doesn't a substance's half-life change over time?+
Radioactive decay is a random process at the level of individual atoms, but with a huge number of atoms in any real sample, the fraction decaying per unit time is statistically constant, so the half-life stays the same throughout the decay process, unlike a linear countdown.
How is half-life used in radiometric dating, like carbon-14 dating?+
By measuring how much of a known radioactive isotope remains in a sample compared to the original amount (or a stable reference isotope), and knowing the isotope's fixed half-life, scientists can calculate how much time has elapsed since the material stopped exchanging that isotope with its environment.
Does a radioactive sample ever reach zero?+
Mathematically, the exponential decay formula approaches but never mathematically reaches exactly zero, since each half-life only removes half of what remains. In practice, after roughly 7-10 half-lives, the remaining quantity becomes negligible or undetectable.