Gamma and x-ray radiation create both external and internal radiation exposure hazards for personnel due to their intense penetrating power. Gamma-emitting isotopes which you may encounter in the research laboratory include 125I, 51Cr, 59Fe and 86Rb. It is highly unlikely that you will be exposed to neutron radiation, therefore the specifics of neutron interactions with matter will not be addressed here. That is, neutron radiation, under certain conditions, can transform a nonradioactive material into one that is radioactive. Neutrons are the only type of radiation that can do this.
Dense materials have virtually no shielding effect on neutrons.
Neutrons are slightly less penetrating than gammas and x-rays, but are significantly more penetrating than betas and alphas. Neutron radiation is both an external and internal exposure hazard to personnel. The dose is the cumulative effect of radiation actually received by an individual. The unit of measurement of dose is the rem.