Sadly that graphic representation was somewhat misleading:
Radiation does not consist of radioactive elements themselves.
(as one source of radiation) Radioactive decay of these elements is the splitting off of a high energy particle causing the molecule to drop down the elemental chart a few spaces or just losing a neutron, generally the element becomes more stable, sometimes it will continue to decay (depending on the number of neutrons in relation to the current atomic weight).
Anyhow, radiation from atgomic decay comes in 3 forms:
alpha (energetic, possitively charged helium),
Beta (energetic electrons),
Gamma (high energy photons).
Penetration goes up in this row (size goes down, as well as lack of charge allows gamma to penetrate material without interacting much), energy goes up though.
alpha is not very dangerous, it can virtually be blocked by a piece of cardboard or several metres of air, but will severely affect your skin when exposed. Beta travels further through air and material and thus requires more shielding, this radiation will damage underlying tissues as well.
gamma radiation will travel, it has no charge and has masses of energy for a photon, several metres of lead will shield, but minimum exposure is the key. Cosmic radiation is mostly gamma and it will mostly pass through your body as if it was not there, occasionally hitting a molecule head on and causing havoc.
The alegory can be used to represent the types of radiation. a beachball for alpha, a football for beta and a medium steel bearing for gamma: imparted speed and inertia will represent potential energy of the particles while size (and inertia) will represent penetration.
(a better model would put small immovable objects in the path of the balls, causing the bigger balls to be deviated more often)
Disclaimer: this overview of radiationtypes is from memory only, small factual errors may occur.