7.1 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. Radiation exposure can be reduced by minimizing the time of exposure. Practice runs without the 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 because of the time required to perform a given task, then other means of reducing exposure should be utilized. Distance is a simple, inexpensive, and very effective method 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 a very effective method for reducing exposure, but it may be more expensive. Shielding material selection is dependant on the type and energy of the radiation used. Only authorized personal are allowed to operate RPMs.