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.

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