You're slightly off! While beta radiation can penetrate paper, it doesn't necessarily stop at metal. Here's a breakdown:

Beta Radiation:

* What it is: Beta radiation consists of high-energy electrons or positrons emitted from the nucleus of an atom during radioactive decay.

* Penetration Power: Beta radiation has a higher penetration power than alpha radiation, but less than gamma radiation. It can penetrate a few millimeters of aluminum or plastic, but is stopped by a few centimeters of a dense material like lead.

Why paper "stops" beta radiation:

* Density: Paper has a lower density than metals, so beta particles have a greater chance of colliding with atoms within the paper and losing their energy.

* Thickness: Even though paper is relatively thin, it can be enough to stop most beta particles, especially those with lower energies.

Why metal doesn't always stop beta radiation:

* Density: While metals are denser than paper, beta particles can penetrate thin sheets of metal.

* Type of metal: The thickness and atomic number of the metal determine how much radiation it can absorb. Heavier metals (like lead) are more effective at stopping beta radiation than lighter metals (like aluminum).

In summary:

Beta radiation can be stopped by paper due to its lower density and the fact that paper can be thick enough to slow down most beta particles. However, metal isn't a universal barrier. While some metals can stop beta radiation, the type and thickness of the metal determine its effectiveness.