1. Jun 6, 2006

### jimmy_neutron

I have 3 questions dealing with radioactivity:
Q1. Which particle, alpha or beta, is least massive?
A1. well alpha particles are emitted as 4,2 Helium nuclei and beta particles are emitted as either electrons or positrons. So would the beta particles be least massive?

Q2: Do all alpha, beta particles, and gamma rays carry energy? Do they all carry momentum?
A2: In alpha emission, most of the kinetic energy is carried away by the alpha particle, so it has energy. what about momentum? I am unsure of Beta particles and Gamma rays

Q3:In an experiment, you will use cardboard, copper foil, aluminum plate and lead sheet to block β particles. If you had equal thicknesses of each substance, which would be most effective blocker? Which would be the least effective blocker?
A3:I know that beta particles can penetrate a few millimeters of aluminum, but i dont know which material would be the most effective blocker.

2. Jun 6, 2006

### Hootenanny

Staff Emeritus
That is correct.

You are right, Alpha particles have momentum. As for beta particles, what is the definition of momentum? Do beta particles have mass?

As for photons this is an interesting case, it can be shown that although a photon is mass-less it has a momentum given by;

$$p = \frac{h}{\lambda}$$

If you like, I can show you the full derivation using relativistic mechanics.

I'm not a radiation specialist, but the best materials for stopping beta radiation are those with high nucleon numbers (lead etc). However, when beta particles interact near to heavier nuclei a process occurs which leads to the production of a type of x-ray known as bremsstrahlung radiation. This radiation is far more difficult to shield (because they are x-rays), therefore, in real world applications plastics are usually used made from elements with lower nucleon numbers. However, if you goal is purely to stop the beta radiation in the smallest distance possible and you are not concernd with any secondary radiation, lead would be your choice.

Last edited: Jun 6, 2006
3. Jun 6, 2006

### jimmy_neutron

thank you for your help, you clarified everything for me!

4. Jun 6, 2006

### Hootenanny

Staff Emeritus
My pleasure