One mistake many lay people
make is confusing radiation
with radioactive material
Radiation is emitted from radioactive material, as a result of the atomic decay of the nuclei of the unstable isotopes that make up such materials. Radiation usually consists of one or more of the following, in approximate order of increasing energy:
The distinction between "radiation" and "radioactive" is an important one. For example, it is not possible to have a spill of radiation, nor is it possible to become radioactive through exposure to most forms of radiation, with the notable exception of neutron radiation, which is unique in its ability to "activate" other nuclei.
It is correct to state that radiation is a noun and radioactive is an adjective, but the correct term for a spill of radioactive material is a radioactive spill.
Think of it this way, if one is fond of analogies: radiation is is to radioactive material as stench is to shit. In other words, you cannot "spill stench", but you can spill shit. There is no such thing as a radiation spill.
It is important to note, however, that the phrase radiation leak is indeed a legitimate usage. A radiation leak occurs when there is a gap or hole in the shielding of a radioactive source. However, there is a world of difference between a radiation leak and a radioactive spill.
One is reminded at this point that most nuclear radiation is not, in fact, particulate in nature. Most forms of radiation exhibit wave/particle duality - that is to say, they exhibit simultaneously both the properties of waves and the properties of particles.
To provide yet another analogy, think of this: Can you have a light spill? No. Can you have a spill of light? No. This is the key distinction. It is possible to have a spill of light-emitting, or luminescent, material, but no reasonable person talks in terms of spilling the actual photons of light themselves. Why? Because one cannot "contain" light, any more than one can contain radiation. The proper verb for this situation is block, shield, or attenuate. Of course, it is quite acceptable to speak of a "light leak", and many camera afficianados do so on a daily basis.
As a point of fact, in the event of a radioactive spill, it is only the spilt mass of radioactive material that is of concern. Of course, in the process of cleanup, radiation levels will be measured and duly noted, but the overriding concern is that the physical amount of material spilled is fully and accurately quantified and accounted for. In fact, most of the radiation measurements made at the scene of a spill are strictly for the purpose of empirically determining the amount and nature of the spilt radioactive material, while determining the radiation levels at the scene is a more peripheral concern.