Radiation Physics, Interactions, and Units 2. External Radiation Protection External radiation can be reduced by limiting the duration of an exposure period, increasing distance between the external radiation source and the person, and placing a shielding material between the external radiation source and the person. Practice runs without source may help to reduce exposure times when an actual experiment is performed. If limitation of the stay time in the vicinity of an external radiation source is not possible due to the required time to perform a given task, then other means of exposure reduction should be utilized. Distance is a simple, inexpensive, and very effective way of dose reduction.
Alpha radiation requires no shielding.
High Beta radiation can be effectively shielded by low atomic number material such as lucite and plastic. Gamma and x-rays require a high density material such as lead. Shielding can be very effective to reduce exposure but it may be more expensive. Shielding material selection is dependant on the type and energy of radiation. Security of radioactive material All radioactive material under UNR license must always be under the surveillance of the user, or kept locked.