An engineer is investigating a suspected leak in a freshwater utility pipe buried 1.2 m beneath a concrete road. They plan to inject a radioactive tracer into the pipe and use a detector at ground level to locate the point of highest activity. The entire measurement process is expected to take approximately 6 hours6\text{ hours}6 hours to complete.
Which of the following isotopes is most suitable for this application?
An α\alphaα emitter with a half-life of 14 hours14\text{ hours}14 hours
A β−\beta^-β− emitter with a half-life of 15 hours15\text{ hours}15 hours
A γ\gammaγ emitter with a half-life of 15 hours15\text{ hours}15 hours
A γ\gammaγ emitter with a half-life of 48 years48\text{ years}48 years