Enter Alpha Decay Values
Example Data Table
| Parent Isotope | Z | A | Daughter Z | Daughter A | Decay Type |
|---|---|---|---|---|---|
| Uranium-238 | 92 | 238 | 90 | 234 | Alpha emission |
| Radium-226 | 88 | 226 | 86 | 222 | Alpha emission |
| Polonium-210 | 84 | 210 | 82 | 206 | Alpha emission |
Formula Used
Alpha decay lowers the atomic number by 2 and mass number by 4.
Zdaughter = Zparent - 2
Adaughter = Aparent - 4
The Q value estimates released energy from mass difference.
Q = [Mparent - (Mdaughter + Malpha)] × 931.49410242 MeV
The alpha particle receives most released energy.
Ealpha = Q × Adaughter / Aparent
The daughter nucleus receives recoil energy.
Erecoil = Q × 4 / Aparent
Radioactive decay follows exponential reduction.
λ = ln(2) / half-life
N = N0 × e^(-λt)
Activity = λN
How to Use This Calculator
Enter the parent atomic number and mass number first.
Add the parent, daughter, and alpha particle masses in atomic mass units.
Enter the half-life and elapsed time using the same time unit.
Add the initial number of atoms.
Select the activity unit you want to display.
Press the calculate button.
The result appears above the form and below the header.
Use the CSV or PDF button to save the calculated report.
Alpha Decay Calculator Guide
What Alpha Decay Means
Alpha decay is a nuclear process. A heavy nucleus emits an alpha particle. That particle contains two protons and two neutrons. It is the same as a helium nucleus. The parent nucleus becomes a lighter daughter nucleus. The atomic number drops by two. The mass number drops by four.
Why the Calculator Is Useful
This calculator helps with advanced alpha decay work. It does more than show the daughter isotope. It also estimates the mass defect and released energy. The released energy is called the Q value. A positive Q value means energy is available from the decay. The calculator also splits energy between the alpha particle and the recoiling daughter nucleus.
Mass and Energy Results
Nuclear mass changes are very small. Yet they release measurable energy. The calculator converts atomic mass units into mega electron volts. It uses the standard conversion factor of 931.49410242 MeV per atomic mass unit. The alpha particle receives most of the kinetic energy because it is lighter than the daughter nucleus. The daughter nucleus moves backward with lower recoil energy.
Decay Constant and Activity
Half-life describes how fast a sample decays. The decay constant is found from the natural logarithm of two divided by half-life. Remaining atoms are then calculated with the exponential decay equation. Activity is the number of decays per time unit. It depends on both decay constant and remaining atoms.
Best Input Practice
Use accurate isotope masses for better results. Keep half-life and elapsed time in the same unit. Do not mix seconds with years unless you convert first. For learning, use known alpha emitters such as uranium, radium, or polonium. For research, verify masses from trusted nuclear data tables.
FAQs
1. What is alpha decay?
Alpha decay is radioactive decay where a nucleus emits an alpha particle. The daughter nucleus has two fewer protons and four fewer nucleons.
2. What does the Q value mean?
The Q value is the energy released by the decay. It comes from the mass difference between parent and decay products.
3. Why does atomic number decrease by two?
An alpha particle contains two protons. When it leaves the nucleus, the parent loses two protons, so atomic number decreases by two.
4. Why does mass number decrease by four?
An alpha particle contains two protons and two neutrons. These four nucleons leave the parent nucleus, reducing the mass number by four.
5. What mass unit should I use?
Use atomic mass units for parent, daughter, and alpha particle masses. Consistent mass units are required for correct Q value results.
6. Can the Q value be negative?
Yes. A negative Q value means the entered masses do not represent an energetically allowed spontaneous decay under this calculation.
7. Why must half-life and elapsed time match?
The exponential decay formula needs matching time units. If half-life is in years, elapsed time should also be in years.
8. What is activity in this calculator?
Activity is the decay rate of the remaining sample. It equals the decay constant multiplied by the number of remaining atoms.