Radioactivity inhalation

Radon decays radioactively into a series of decay products, or Rn daughters (RnD), which are themselves radioactive. Inhalation and subsequent deposition in the respiratory tract of these RnD constitutes a radiation hazard, due to the irradiation of the respiratory tract tissue by decay of deposited RnD. 

Fig. 5 [86] shows an example of the mean unit spray content for drug and radioactivity for several study days using this labeled powder. Each bar of the graph represents a mean standard deviation of 10 unit doses. While the CV of the daily measurements for both dmg and radioactivity must be within specified limits, it should be understood that the mean daily level of radioactivity in the formulation or nominal dose of radioactivity varies as a function of the level of the specific activity available from the generator on the day of the study. This variability in the amount of radioactivity affects only the absolute dose of radioactivity inhaled and not the measured deposition distribution. Deposition results should be normalized to account for these differences, even for the small, day-to-day variability in the supply of radioactivity. 

The radioactivity inhaled by an exposed person during the passage of the contaminated cloud. 

Care must be taken in handling radon, as with other radioactive materials. The main hazard is from inhalation of the element and its solid daughters which are collected on dust in the air. Good ventilation should be provided where radium, thorium, or actinium is stored to prevent build-up of the element. Radon build-up is a health consideration in uranium mines. Recently radon build-up in homes has been a concern. Many deaths from lung cancer are caused by radon exposure. In the U.S. it is recommended that remedial action be taken if the air in homes exceeds 4 pCi/1. 

One feature of reprocessing plants which poses potential risks of a different nature from those ia a power plant is the need to handle highly radioactive and fissionable material ia Hquid form. This is necessary to carry out the chemical separations process. The Hquid materials and the equipment with which it comes ia contact need to be surrounded by 1.5—1.8-m thick high density concrete shielding and enclosures to protect the workers both from direct radiation exposure and from inhalation of airborne radioisotopes. Rigid controls must also be provided to assure that an iaadvertent criticahty does not occur. 

Poison A gas explosives-A/B, organic peroxide, flammable solid, materials dangerous when wet, chlorine, flourine, anhydrous ammonia, radioactive materials, NFPA 3 4 for any categories including SF>ecial hazards. PCB s fire, DOT inhalation hazzird, EPA extremely hazardous substances, and cryogenics. 

The radiation dose from being in or near a "cloud" of aiibome radioactivity can be calculated if the radionuclide concentration in the cloud is known. While radioactive noble gases may be inhaled, they are not retained in the body, hence, most of their dose contribution is by cloud radiation. 

Ground radiation is from deposited radioactive particles. The deposition rate from a radioactive cloud without rain (dry deposition) is so low that the ground radiation dose is about the same as the inhalation dose. A heavy rain, however, may wash out enough particles from the plume to make ground radiation the dominant contributor to the total dose in a limited area. Rain will also attenuate radiation by leaching the radioactivity to be shielded by the soil and by moving it to streams for further removal. 

The previous chapter described the consequences of a nuclear reactor accident. Chemical process accidents are more varied and do not usually have the energy to melt thick pressure vessels and concrete basemats. The consequences of a chemical process accident that releases a toxic plume, like Bhopal did, are calculated similarly to calculating the dose from inhalation from a radioactive plume but usually calculating chemical process accidents differ from nuclear accidents for which explosions do not occur. 

Although government officials attempted to educate the public and military personnel about atomic civil defense, in retrospect these efforts seem hopelessly naive if not intentionally misleading. Army training films advised soldiers to keep their mouths closed while obser"ving atomic test blasts in order to not inhale radioactive flying dirt. Civil defense films used a friendly animated turtle to teach schoolchildren to duck and cover during a nuclear attack—that is, duck under their desks and cover their heads. Such measures, of course, would have offered pitiful protection to those in the blast zone. 

Plutonium has a much shorter half-life than uranium (24.000 years for Pu-239 6,500 years for Pu-240). Plutonium is most toxic if it is inhaled. The radioactive decay that plutonium undergoes (alpha decay) is of little external consequence, since the alpha particles are blocked by human skin and travel only a few inches. If inhaled, however, the soft tissue of the lungs will suffer an internal dose of radiation. Particles may also enter the blood stream and irradiate other parts of the body. The safest way to handle plutonium is in its plutonium dioxide (PuOj) form because PuOj is virtually insoluble inside the human body, gi eatly reducing the risk of internal contamination. 

Information on the excretion of americium after dermal exposure in humans or animals is extremely limited. Some qualitative information is available from an accidental exposure in which a worker received facial wounds from projectile debris and nitric acid during an explosion of a vessel containing 241 Am (McMurray 1983). The subject also inhaled 241Am released to the air as dust and nitric acid aerosols, which was evident from external chest measurements of internal radioactivity thus, excretion estimates reflect combined inhalation, dermal, and wound penetration exposures (Palmer et al. 1983). Measurements of cumulative fecal and urinary excretion of241 Am during the first years after the accident, and periodic measurements made from day 10 to 11 years post accident indicated a fecal urine excretion ratio of approximately 0.2-0.3, although the ratio was approximately 1 on day 3 post accident (Breitenstein and... 

The ICRP (1994b, 1995) developed a Human Respiratory Tract Model for Radiological Protection, which contains respiratory tract deposition and clearance compartmental models for inhalation exposure that may be applied to particulate aerosols of americium compounds. The ICRP (1986, 1989) has a biokinetic model for human oral exposure that applies to americium. The National Council on Radiation Protection and Measurement (NCRP) has also developed a respiratory tract model for inhaled radionuclides (NCRP 1997). At this time, the NCRP recommends the use of the ICRP model for calculating exposures for radiation workers and the general public. Readers interested in this topic are referred to NCRP Report No. 125 Deposition, Retention and Dosimetry of Inhaled Radioactive Substances (NCRP 1997). In the appendix to the report, NCRP provides the animal testing clearance data and equations fitting the data that supported the development of the human mode for americium. 

LaFuma J, Nenot JC, Morin M, et al. 1974. Respiratory carcinogenesis in rats after inhalation of radioactive aerosols of actinides and lanthanides in various physicochemical forms. In Karbe E, Park JF, eds. Experimental lung cancer Carcinogenesis and bioassays, international symposium. New York Springer, 443-453. 

NCRP. 1997. Deposition, retention and dosimetry of inhaled radioactive substances. National Council on Radiation Protection and Measures. Bethesda, MD. Report No. 125. http //www.ncrp.com. 

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