A sealed source is removed from a room. A detector is then used close to a worker's sleeve. Each reading lasts one minute.
| Measurement | Count |
|---|---|
| Background away from the sleeve | 24 |
| Near the sleeve before cleaning | 420 |
| Near the sleeve after cleaning | 28 |
| Near the cloth used for cleaning | 390 |
Which explanation best accounts for all the readings?
Radiation stored in the sleeve was transferred into the cleaning cloth.
Cleaning increased the background radiation close to the cleaning cloth.
Radioactive material was transferred from the sleeve to the cleaning cloth.
Cleaning shortened the half-life of radioactive nuclei inside the sleeve.