It has been alleged that the radiation used in radioactive tracers and neutron well logging are not that penetrating.
Neutrons ARE penetrating but can be less damaging than say energetic, massive, and charged alpha particles.
Less massive, charged beta particles, unless very high energy, tend to be stopped with far less shielding.
Fertile natural isotopes can dramatically increase neutron well logging risks of chemical and radiation poisoning.
Radioisotopes are most harmful when inhaled or ingested and concentrated, like 131- and 125-Iodide in the thyroid.
Others concentrate in bone marrow and target stem cells.