milliroentgen. MINSY. Mare [stand Naval Ship Yard, California. MPE. Maximum Permissible Exposure (rule dose). That exposure to ionizing radiation that 1s established by authorities as the maximum over certain periods without resulting in undue risk to human health. MPL. Maximum Permissible Limit. That amourt of radioactive material in air, water, foodstuffs, etc. tnat is established by authorities as the maximum that would not create undue risk to human health. mR;mr. MSTS. Abbreviation for milliroentgen. Military Sea Transportation Service, (Navy). mushroom cap. Hares anteemma aM One-tnousandth of a roentgen. Top of the cloud formed from the fireball of a nuclear detonation. M/V. Motor vessel. MWB. Motor whale boat. NAS. Naval Air Station. NAU. Naval Administrative Unit, Sandia Base, New Mexico. NavMed. Naval Medical School, Bethesda, Maryland. NBS. National Bureau of Standards. NCO. Noncommissioned officer. NCRP, National Committee on Radiation Protection and Measurements. mittee on Radiation Protection. NEL. Before 1956 simply the National Com- Naval Electronics Laboratory. neutron. A neutral elementary particle (i.e., with neutral electrical charge) of approximately unit mass j.e., the mass of a proton) that is present in all atomic nuclei, except those of ordinary (light) nydrogen. Neutrons are required to initiate the fission process, and large numbers of neutrons are produced by both fission and fusion reactions in nuclear explosions. neutron flux. The through 1 cme NM&DSO. NPG. intensity of neutron radiation. in 1 second. It is expressed as the number of neutrons passing Navy Medical and Dental Supply Office, Brooklyn Navy Yard, New York. Nevada Proving Ground, now the Nevada Test Site (NTS). NRDL. Naval Radiological Defense Laboratory. NRL. Naval Research Laboratory. NRSTI. Naval Receiving Station, Treasure Island, California. NSCTI. Naval Schools Command, Treasure Island, California. NTPR. Nuclear Test Personnel Review. NTS. Nevada Test Site. NUCCS. Naval Unit, Chemical Corps School, Ft. McClellan, Alabama. nuclear cloud. See radioactive cloud. nuclear device (or weapon or bomb). Any device in which the explosian results from the energy released by reactions involving atomic nuclei, either fission or fusion, or both. Thus, the A- (or atomic) bomb and the H- (or hydrogen) bomb are both nuclear weapans. It would be equally true to cal] them atomic weapons, Since the energy of atomic nuclei is involved in each case. However, it has become more or less customary, although it is not strictly accurate, to refer to weapons in which all the energy results from fission as A-bombs. [In order to make a distinction, those weapons in which part of the 479