Neutron activation
Neutron activation analysis can be done in situ. For example, aluminium (Al-27) can be activated by capturing relatively low-energy neutrons to produce the isotope Al-28, which decays with a half-life of 2.3 minutes with a decay energy of 4.642 MeV. This activated isotope is used in oil drilling to determine the clay content (clay is generally an alumino-silicate) of the underground area under exploration.