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5.4.4 Radiological Hazards

Radiological hazards can be divided into three general forms: alpha, beta, and gamma radiation, which are emitted by radio- isotopes that may occur as an aerosol, be carried on particulate matter, or occur in a gaseous state. Alpha particles, consisting of two neutrons and two protons, are the least penetrating and the most ionizing form of radiation. They are emitted from the nu- cleus of radioactive atoms and transfer their energy at very short distances. Alpha particles are readily shielded by paper or skin and are most dangerous when inhaled and deposited in the respira- tory tract. Beta particles are negatively charged particles emitted from the nucleus of radioactive atoms. Beta particles are more penetrating than alpha particles, presenting an internal exposure hazard. They can penetrate the skin and cause burns. If they con- tact a high density material, they may generate x-rays also known as “Bremmstrahlung radiation.” Gamma particles are emitted from the nucleus of an atom during radioactive decay. Gamma ra- diation can cause ionization in materials and biological damage to human tissues, presenting an external radiation hazard.

There are three primary scenarios in which radioactive materials could be dispersed by a terrorist: use of conventional explosives or other means to spread radioactive materials (a dirty bomb), attack on a fixed nuclear facility, and use of a nuclear weapon. In any of these events, filtration and air cleaning devices would be ineffec-

tive at stopping the radiation itself; however, they would be useful in collecting the material from which the radiation is emitted. Micrometer-sized aerosols from a radiological event are effectively removed from air streams by HEPA filters. This collection could prevent distribution throughout a building; however, decontami- nation of the HVAC system would be required.

Answer 1

Radioactive elements can be used by some anti-social elements and these can cause harm to a human body. By these elements hazards occur in three general forms as alpha, beta and gamma that are emitted by radioisotopes from the nucleus of radioactive atoms and their state may be aerosol. Briefly, Alpha particles having 2 neutrons and 2 protons have the least penetrating and moisturizing form of radiation. It only can transmit energy in a short-range and it is dangerous to the respiratory tract. While Beta is more penetrating which have negatively charged particles. It can cause internal exposure hazard and can burn skin. Beta can generate Bremmstrahlung radiation while in contact with high-density material. Gamma can ionize materials and can damage human tissues, it is an external radiation hazard. So, various air filter devices can't easily detect these so high-efficiency particulate air filters are placed there. In a building Heating, ventilation, and air conditioning (HVAC) systems required to prevent these radiological hazards.