Shielding radioactivity

Resuspend the crude RNA pellet in 25 pL of Buffer I. Use a Geiger counter to check that all of the labeled RNA has dissolved in solution by pulling up all the liquid into a pipet tip and comparing the counts in the tip with the counts remaining in the tube. Store in an appropriately shielded radioactive safety container at -80°C. 

Radioactivity is often thought of as a terrible side effect of nuclear weapons and X-rays, but when properly shielded, radioactive elements have a variety of uses. The actinide series of elements are used as power supplies for pacemakers, nuclear satellites, and submarines. Americium-241 is used in home smoke detectors to control the conductivity of air that changes when smoke is present. 

Persons handling radioactive waste containers should wear protective equipment, including gloves and disposable coveralls if required by local procedures, and should transfer wastes in an area with proper ventilation and shielding. Radioactive waste containers should be checked for leakage and sur-... 

Lead-loaded plastics containing up to 90 wt % lead are used in x-ray protection as aprons and temporary shields in medical and industrial appHcations. Leaded glass is used to attenuate radiation where viewing the ongoing process is requited. Steel-jacketed containers fihed with lead or special lead containers are used to transfer, ship, and store fuel rods, radioactive sources, and nuclear waste. Lead is generahy used where space is limited. 

Nuclear utiUties have sharply reduced the volume of low level radioactive waste over the years. In addition to treating wastes, utiUties avoid contamination of bulk material by limiting the contact with radioactive materials. Decontamination of used equipment and materials is also carried out. For example, lead used for shielding can be successfully decontaminated and recycled using an abrasive mixture of low pressure air, water, and alumina. 

Low level waste with its generally smaller radioactivity level can be stored in suitable containers in buildings. Protective shielding and handling equipment are required. 

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. 

The principal ha2ards of plutonium ate those posed by its radioactivity, nuclear critical potential, and chemical reactivity ia the metallic state. Pu is primarily an a-emitter. Thus, protection of a worker from its radiation is simple and usually no shielding is requited unless very large (kilogram) quantities are handled or unless other isotopes are present. 

The radioactive isotopes available for use as precursors for radioactive tracer manufacturing include barium [ C]-carbonate [1882-53-7], tritium gas, p2p] phosphoric acid or pP]-phosphoric acid [15364-02-0], p S]-sulfuric acid [13770-01 -9], and sodium [ I]-iodide [24359-64-6]. It is from these chemical forms that the corresponding radioactive tracer chemicals are synthesized. [ C]-Carbon dioxide, [ C]-benzene, and [ C]-methyl iodide require vacuum-line handling in weU-ventilated fume hoods. Tritium gas, pH]-methyl iodide, sodium borotritide, and [ I]-iodine, which are the most difficult forms of these isotopes to contain, must be handled in specialized closed systems. Sodium p S]-sulfate and sodium [ I]-iodide must be handled similarly in closed systems to avoid the Uberation of volatile p S]-sulfur oxides and [ I]-iodine. Adequate shielding must be provided when handling P P]-phosphoric acid to minimize exposure to external radiation. 

Some spent fuel is also stored at two off-site storage faciHties, one in Illinois and one in upper New York State (which no longer accepts waste). The water in these holding pools acts as a shield preventing release of radioactivity. At some plants, waste is beginning to be stored dry in heavily shielded,... 

The NRC has developed special procedures for the handling, transportation, and storage of nuclear fuel because radioactivity can be a health hazard if not properly shielded. Spent fuel is typically transported by rail or tmck in heavily shielded (Type B), sealed, thick metal shipping containers designed to withstand possible accidents, such as derailments or coHisions, which may occur during transport. The NRC certifies that each shipping container meets federal requirements. The U.S. Department of Transportation sets the rules for transportation. 

The radioactive isotope Cs is important commercially in process control instmments and for sewage sludge sterilisation. The isotope has along half-life — 30 yi )i however, it must be weU-shielded because of the high biological hasard. 

In NAA the sample is made radioactive by subjecting it to a high dose (days) of thermal neutrons in a reactor. The process is effective for about two-thirds of the elements in the periodic table. The sample is then removed in a lead-shielded container. The radioisotopes formed decay by B emission, y-ray emission, or X-ray emission. The y-ray or X-ray energies are measured by EDS (see Chapter 3) in spe-... 

The philosophy of public health protection used by the AEC and pursued ever since, is the use of multiple independent barriers, each a significant shield for the public. The last barrier involves the removal of people from the area over which the radioactive plume is expected to pass, interdiction of food supplies and the use of prophylaxis to reduce the iodine dose. Blood... 

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. 

A radioactive source was transferred from one container to another by remote operation in a shielded cell. A radiation detector, interlocked with the cell door, prevented anyone from opening the cell door when radiation could be detected inside it. To make sure the interlock was working, an operator tried to open the cell door, by remote control, during a transfer. He found he could open it. He then found that the closing mechanism would not work. Fortunately he had not opened the door very far. 

In addition to the 4 stable isotopes sulfur has at least 9 radioactive isotopes, the one with the longest half-life being which decays by activity (Kmax 0.167 MeV, 87.5 d). can be prepared by Cl(n,p), S(n,> ) or S(d,p) and is commercially available as SeicmcQt H2S, SOCb and KSCN. The radiation has a similar energy to that of C ( mav 0.155 MeV) and similar counting techniques can be used (p. 276). The maximum range is 300 min in air and 0.28 mm in water, and effective shielding is provided by a perspex screen 3-10 mm thick. The preparation of many - S-containii compounds has been... 

The nuclear reactor also must be shielded against the emission of radioactive material to the external environment. Suitable radiation controls include both thermal and biological shielding systems. Radiation from alpha particles (a rays) and beta particles ((3 rays) has little penetrating power, but gamma rays have deep penetration properties. Neutron radiation is, however, the primary area of risk. Typically, extremely thick concrete walls are used as a neutron absorber, but lead-lined concrete and special concretes are also used. 

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