| Stable Nuclei | 1- Elements with fewer protons (near the top of the table) are stable if no. of neutrons = no. of protons
2- As no. of protons increases, more neutrons are needed to keep the nucleus stable
3- Nuclei with too many/few neutrons naturally exist but are stable and decay by emitting radiation |
| ALPHA PARTICLES | 1) Emitted when nucleus has too few neutrons, 2 neutrons + 2 protons emitted (Helium-4 nucleus)
2) Decreases Mass No. by 4 & decreases Atomic No. by 2 |
| BETA PARTICLES | 1) Emitted when nucleus has too many neutrons, a neutron will turn into a proton and emit a fast-moving electron called a Beta (β) particle - this process is known as beta radiation.
2) A beta particle has a relative mass of zero, so its mass number is zero |
| GAMMA PARTICLES | 1) After alpha/beta particle is emitted, the nucleus will be too hot & will lose energy by emitting Gamma rays (rather than infrared radiation or EM waves - which are emitted due to hot gas)
2) Emission: Since energy levels in the nucleus are much higher than those in a gas, the nucleus emits a more energetic EM wave called a gamma ray.
3) Causes no change in no. of particles in the nucleus therefore atomic and mass number remain the same |
| How is Radioactive decay detected? | All types of radioactive decay can be detected by a Geiger-Muller tube, or G-M tube. The radiations ionise the gas inside and the resulting charged particles move across the chamber and get counted as charges rather like an ammeter |
| NEUTRON EMISSION | 1) Occasionally emitted by radioactive decay:
- Naturally: absorption of cosmic rays high up in the atmosphere can result in neutron emission
- Artificially: James Chadwick alpha particle fired at Beryllium resulted in neutrons emitted from that
- Nuclear Fission Reactions: Neutrons released from parent nucleus as it splits
2) Neutron emission causes decrease by 1 in mass no. of nucleus, but no change in atomic no. |
| Half Life | Half-life is the time it takes for half of the unstable nuclei in a sample to decay or for the activity of the sample to halve or for the count rate to halve. Count-rate is the number of decays recorded each second by a detector, such as the Geiger-Muller tube
- This process continues and does not drop to zero completely |
| Nuclear Equations | Nucleus changes into new element by emitting alpha/beta particles. These changes can be described using nuclear equations
NOTE: Gamma is pure energy and will not change the structure of the nucleus in any way |
