A worker breathes in dust containing a long-lived alpha emitter. The dust remains in the lungs. A second worker is briefly exposed to an external sealed source but receives no radioactive material. Which statement explains why leaving the area ends the second worker's exposure but not the first worker's?
The first worker carries emitting nuclei next to tissue; the second leaves the source behind.
The first worker stores alpha particles in tissue; the second loses stored gamma rays.
The first worker's skin becomes more penetrating; the second worker's skin absorbs the source.
The first worker's nuclei stop decaying in tissue; the second worker's nuclei decay immediately.