Alpha Particles, Beta Particles and Gamma Rays

Alpha Decay

The composition of an alpha particle is the same as a helium-4 nucleus.
- It is the combination of two protons and two neutrons, which is very stable.
- It has a nucleon number of 4 and a proton number of +2.
- Alpha particles can be represented by the symbols:

The radioactive decay equation is a balanced nuclear equation which shows a radionuclide and its decay products.
It is in the form of:
- parent nucleus -> daughter nucleus + alpha particle

As an example, the decay of radium-226 results in the emission of an alpha particle:

Alpha particles have considerable kinetic energy.
- However, they have limited penetration of matter (penetrating power).
- This is because they transfer significant amounts of energy in collisions with other atoms/molecules.
The collisions transfer the energy needed to ionize a large number of atoms/molecules in the material through which the alpha particles are passing.
- After most of their energy has been transferred, the alpha particles are effectively absorbed as tiny amounts of helium.

In an unstable nucleus it is possible for an uncharged neutron to be converted into a positive proton and a negative electron.
This also involves the creation of another particle called an antineutrino.

The emitted electron is called the beta-negative particle.
When beta-negative, or beta-minus, decay occurs, the number of nucleons in a nucleus remain the same, but the number of protons increases by one, so that a new element is formed.
This can be represented in a radioactive decay equation of the general form:

Antineutrinos (and neutrinos) are very small particles with no charge, which travel at speeds close to the speed of light, so they are very penetrating and very difficult to detect.
An antineutrino is an antiparticle, which is a particle with the exact opposite physical properties of another.
- It is the antiparticle of a neutrino.
- Antimatter is matter consisting of antiparticles such as neutrinos.
- When a particle and its antiparticle interact they annihilate each other, and all their mass is converted into electromagnetic energy.

In a similar process to beta-negative decay, called beta-positive or beta-plus decay, a proton in a nucleus can be converted into a neutron and a positively charged electron, called a positron (another example of antimatter), which is then ejected from the atom, after which it is called the beta-positive particle and is represented by the symbol of:

Beta-minus decay is radioactive decay resulting in the emission of an electron and an antineutrino.
A neutron is converted into a proton and an electron.

In beta-plus decay there is radioactive decay resulting in the emission of a positron and a neutrino.
A proton is converted into a neutron.
In both decays the nucleon number stays the same but the number of protons changes.

The alpha particles from these decays always have discrete amounts of kinetic energy.
- However, the beta particles were found to have a continuous range of kinetic energies.
  - This would mean that mass/energy wasn't being conserved.

The answer is that some other particles must be produced as well.
This leads to the description of the neutrino and antineutrino.
- The energy of the neutrino/antineutrino varies as they are emitted in random directions.
- This is what allows a range of energies while maintaining mass/energy conservation.

Gamma rays are high-frequency electromagnetic radiation (photons) released from unstable nuclei.
A typical wavelength is about 10^-12m.
- This corresponds tot he energy of about 1MeV (using E = hc/λ).
Gamma rays are usually emitted after an unstable nucleus has emitted an alpha or beta particle.
Gamma rays are represented by the symbol γ, gamma.

Gamma radiation is electromagnetic radiation emitted from some radionuclides and it has an extremely short wavelength.

Alpha particle radiation is the least penetrative, while gamma radiation is very penetrative.

Alpha and beta radiation will be emitted in random directions from their sources, but they can be formed into narrow beams by passing the radiation through slits.
- This process is called collimation.
Because a beam off alpha particles, or beta particles, is a flow of charge, they will be deflected if they pass across an electric or magnetic field.
Gamma rays carry no charge and are thus unaffected.

A radioactive decay does not always produce a stable daughter nuclide.
- If the daughter nuclide is unstable, it will also decay.
- In some cases, there is a series of decays, called a decay series, that does not end until a stable nuclide is reached.

Sources