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INTRODUCTION

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Radiation exposure may either be accidental or intentional. The year 2015 marked the 70th anniversary of the bombing of Hiroshima and Nagasaki, with nearly 200,000 acute deaths and untold numbers with chronic disability. Accidental exposures can occur during transport, storage, or working with radioactive materials or with errors in dosing radiotherapy. Most civilian incidents involve industrial exposures from sealed radiation sources.1 The Fukushima Daiichi nuclear disaster resulted in about 1000 disaster-related deaths; however as of this writing, no deaths were related to radiation exposure.2

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The largest reported accidental exposure took place in Goiania, Brazil in 1987. An "orphaned" cesium-137 radiosource was left in place at an abandoned radiotherapy institute. Individuals looking for scrap metal removed the source and dismantled it. They proceeded to sell it to a junk dealer, who observed the material glowing in the dark. Due to this unique characteristic, he distributed it to family and friends, who quickly became ill with acute radiation syndrome. At the conclusion of this event, there were 112,000 individuals evaluated for exposures, 249 who were contaminated, 20 who required hospital admissions, and four who died.3,4

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A famous case of malicious intentional exposure involved Alexander Litvinenko, a former KGB agent who had defected to England. In 2006, after a meeting with former co-workers, he suffered a protracted gastrointestinal illness with associated leukopenia. On the day of his death, elevated levels of polonium-210 were identified, confirming his death from radiation exposure. Investigations into his murder revealed that there are had been rehearsals in multiple areas of England leading to contamination.5 The public health response that followed found that there were 1693 local and international individuals who were potentially exposed during such rehearsals.6,7

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Radiologic dispersal devices, or "dirty bombs," combine radioactive materials with conventional explosives in attempts to disperse "hot material" over an unsuspecting population. The intended use of these devices is to generate some injuries, but the true goal is to generate massive panic and hysteria, overwhelm local resources, affect the local economy, and lead to prolonged clean-up efforts.4

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FUNDAMENTALS OF RADIATION PHYSICS

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Radiation energy includes the entire electromagnetic spectrum: from low-energy, long-wavelength, and low-frequency nonionizing radiation, such as radio waves and microwaves, to high-energy, short-wavelength, and high-frequency forms of ionizing radiation. Ionizing radiation has enough energy to remove an electron from an atom and generate charged particles. Sources of ionizing radiation are: alpha particles, beta particles, neutrons, and sole energy waves that include x-rays and gamma rays.8

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Alpha and beta particles and positrons are charged particles that directly interact with electrons of the atom. Neutrons are not charged, and they lead to expulsion of other particles after interactions with the atomic nuclei, so neutrons indirectly generate charged atoms. Gamma and x-rays are electromagnetic waves that destabilize the atomic nucleus and lead to the ...

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